Hi, guys. I am updating my home studio (got a pre-amp, new mic, new monitors, etc.) and I thought a good hardware addition would be to ad a hardware equalizer. I started looking online for options, but then I remembered I have already done pedals with 3 band EQ, so I figured, "why spend money on this, when you got most of the parts in stock?".
What I have:
[/li]
- Resistors (most of the relevant values)
- Caps (most relevant values; I got polirized in uF, box and film in nF and ceramic for pF)
- Pots (most relevant values, though I would have to see if for each value I have audio curves; but we will cross the bridge when we get to the river!)
- Diods (most relevant ones, though I suspect I may only use them for voltage control)
- OpAmps
- 741 (2)
- LM833 (3)
- JRC4558D (5)
- NE5532 (1)
- NJM13600D (3)
- RC4558P (3)
- RC4559P (3)
- TL071 (3)
- TL072 (1)
- TL074 (2)
- LM386N (2)
- MC1458P
- C4558C (4)
- NE5532P (6)
[/list]
I also got some other IC's (NE556N, PT2399, MCO41100) which I doubt will be relevant to this build, and I got all kinds of transistors (2N3904, 2N3906, 2N4123, 2N4124, 2N4125, 2N4401, 2N4402, 2N5087, 2N5088, 2N5089, and a bunch more) but I doubt I will need them for an EQ as well.
I looked online, and found some options, but I am still not good at predicting how good a circuit will be... Keep in mind this will be used for a MIC, not a guitar, so I need it to be clean. I found this simple option, and I figured I can replace the OpAmp with one I have:
(https://homemade-circuits.com/wp-content/uploads/2013/06/10_band_graphic_equalizer_circuit-1.png)
What do you guys think? Or do you have any good recommendations I can look up?
Use a KA2223. It's a 5-band EQ on a chip.
I kind of want to use the parts I got in stock if at all possible... I live in Panama (Central America) and all electronic parts shops around here are closed (actually, all RETAIL stores are closed), and ordering online becomes very expensive due to shipping overseas...
On the contrary of Mark :icon_redface:, I should propose you BL3812(L)..
From what you have, NE5532P should be excellent choice..
(you can use all of them or use TL072 for IC1/1 & IC1/2..)
Of course, you can use 2N5089 for gyrators with almost the same performance..
P.S.
IMHO, 10 band "graphic" EQ for audio band might be useful but for guitar is should be overkill..
la3600?
https://www.diystompboxes.com/smfforum/index.php?topic=107612.msg978821#msg978821
Quote from: antonis on May 20, 2020, 05:47:39 AM
On the contrary of Mark :icon_redface:, I should propose you BL3812(L)..
From what you have, NE5532P should be excellent choice..
(you can use all of them or use TL072 for IC1/1 & IC1/2..)
Of course, you can use 2N5089 for gyrators with almost the same performance..
P.S.
IMHO, 10 band "graphic" EQ for audio band might be useful but for guitar is should be overkill..
Nothing contrary at all. I just mentioned the first chip of that type I saw in my directory of audio-processing chips. BA3812 is good, too, as is LA3600. I think choice of resonant frequencies will be just as important as chip-choice, if the purpose is to tailor vocals. Most graphic EQs are not designed around any particular purpose, so they try to cover as many possibilities as possible with the number of bands they offer. Many of those bands have absolutely nothing to do with voice. Five of the
right bands may be all you need for voice. And some might argue that 3 bands of parametric or semi-parametric would be enough.
Quote from: Mark Hammer on May 20, 2020, 07:30:57 AM
And some might argue that 3 bands of parametric or semi-parametric would be enough.
I'm one of those "somes".. :icon_smile:
But I totally agree about resonant frequencies "customization" for each particular purpose/use..
(although double/single/half octave spacing for the entire EQ band is definately easier to design/build..)
Quote from: antonis on May 20, 2020, 05:47:39 AM
From what you have, NE5532P should be excellent choice..
(you can use all of them or use TL072 for IC1/1 & IC1/2..)
How about LM833? Is that a good choice for a transparent sound?
Quote from: antonis on May 20, 2020, 05:47:39 AMIMHO, 10 band "graphic" EQ for audio band might be useful but for guitar is should be overkill..
Remember this is not for guitar, but rather my home studio mic... And I am thinking 5 band now, as I may run out of OpAmps... But optimize the frequencies to vocals.
Quote from: Mark Hammer on May 20, 2020, 07:30:57 AM
I think choice of resonant frequencies will be just as important as chip-choice, if the purpose is to tailor vocals. Most graphic EQs are not designed around any particular purpose, so they try to cover as many possibilities as possible with the number of bands they offer. Many of those bands have absolutely nothing to do with voice. Five of the right bands may be all you need for voice. And some might argue that 3 bands of parametric or semi-parametric would be enough.
Quote from: antonis on May 20, 2020, 08:25:21 AM
I totally agree about resonant frequencies "customization" for each particular purpose/use..
(although double/single/half octave spacing for the entire EQ band is definately easier to design/build..)
Which frequencies would you guys recommend?
One more question; the schematic above does not include any of the power side of the circuit, and since I am unschooled in such things, I found [url+https://bestengineeringprojects.com/5-band-audio-equalizer-circuit-using-lm833/]this other schematic[/url], which I really like, but ran into a small snag;
(https://bestengineeringprojects.com/wp-content/uploads/2017/12/5-band-audio-equalizer-1024x893.jpg)
The issue is that (1) I only have 3 LM833N chips, and I need 4 (well, 3.5 really!). So I was thinking using a TL072 for IC1A and IC2A and using the LM833 for the rest (I am not adding one more band because I only got 5 5K pots). I could even use the TL071 instead of the TL072 (for IC2A) and leave that for when I need a dual OpAmp (only got one TL072 left).
Also, the parts list is suggesting the following caps:
C1, C3, C6, C9, C`12, C15, C18, C19 = 10 µF (Electrolytic Capacitors) - NO PROBLEM
C2 = 100 µF (Electrolytic Capacitors) - I THINK I GOT ONE LEFT IN A BREADBOARD PROJECT, BUT SHOULD BE OK
C4. C5, C7, C8, C20 – C23 = 0.1 µF (Ceramic Disc) - NO PROBLEM (JUST HAVE 5 100pF LEFT!)
C10, C11 = 0.047 µF (Electrolytic Capacitors) - ELECTROLITIC? I HAVE CERAMIC, AND THEY ARE NOT LABELED AS POLARIZED, SO I PLAN TO USE CERAMIC
C13, C14, C16, C17 = 0.0022 µF (Electrolytic Capacitors) - AGAIN, ELECTROLITIC? I HAVE 3 CERAMIC LEFT, BUT I COULD FUDGE IT BY USING 2 X 10pF FOR THE LAST ONE.
So, main questions are, you think this will work by replacing one LM833N with a TL072 or TL071? Or having one different OpAmp will affect the sound too much? And will the cap change to ceramic affect too much the transparency of the sound? And, as I stated above, which 5 frequencies would you recommend?
Oh, and one more question; any good circuits you guys can recommend to filter a bit the power supply and have polarity protection (just in case) considering the above circuit is 12V? The ones I have used are typically 9V...
LM383 is an audio amplifier so it can't be directly substituted by a general purpose op-amp..
(it could be done but in the expence of significant circuitry changes..)
Forget the above.. Eye-typo.. :icon_redface:
I'll vote once more for NE5532 but desicion it's up to you.. :icon_wink:
Any good circuit for 9V can also be good for 12V..
(16V rated filter cap should be OK and 25V should be fine..)
I always thought the NE5532 and LM833 were largely interchangeable.
As for "what frequencies would you recommend?", that's probably the best recommendation for a simple semi-parametric (i.e., boost/cut with sweepable frequency). The optimal frequencies will really depend on the voice itself. I'm not trying to be evasive. Rather, it's like asking what EQ would work best for a kick drum, for a cello, for a flute. They all have their particular voices and sensitive ranges. Individual singers are like different instruments. That's why they all have their individual preferences for this mic or that. If it is not possible to know in advance what frequency bands are going to be most relevant for a particular voice, then best to make the bands sweepable, so that you can find the ones most relevant.
The PAiA 4-Band equalizer is probably a suitable unit for you. Though you probably only need the first 3 sections.
https://www.scribd.com/doc/96494162/4-Band-Equalizer-Www-circuitdiagram-net
Quote from: antonis on May 20, 2020, 04:12:10 PM
I'll vote once more for NE5532 but desicion it's up to you.. :icon_wink:
The issue is I only have 1; and I have 3 LM833. I could use it instead of the TL071 I am using in the breadboard...
Quote from: antonis on May 20, 2020, 04:12:10 PM
Any good circuit for 9V can also be good for 12V..
(16V rated filter cap should be OK and 25V should be fine..)
OK, I will find one and use.
Quote from: Mark Hammer on May 20, 2020, 04:47:35 PM
The PAiA 4-Band equalizer is probably a suitable unit for you. Though you probably only need the first 3 sections.
https://www.scribd.com/doc/96494162/4-Band-Equalizer-Www-circuitdiagram-net
Wish I had seen that one before I started breadboarding. Looks interesting. I will finish this one, and if I do not like it, I will certainly give that one a shot.
Quote from: jfrabat on May 20, 2020, 07:43:43 PM
Quote from: antonis on May 20, 2020, 04:12:10 PM
I'll vote once more for NE5532 but desicion it's up to you.. :icon_wink:
The issue is I only have 1;
Quote from: jfrabat on May 19, 2020, 03:58:09 PM
What I have:
NE5532 (1)
NE5532P (6)
My maths suck but I can ensure you that, by adding anything but zero to unity, the last loses its uniqueness.. :icon_wink:
P.S.
Differences between the many versions of NE5532 (other than price..) are unimportant for your task..
(they have to do with lowest guaranteed noise, THD measure, etc..)
http://e2e.ti.com/support/amplifiers/f/14/t/344 (http://e2e.ti.com/support/amplifiers/f/14/t/344)
Quote from: antonis on May 21, 2020, 07:20:21 AM
My maths suck but I can ensure you that, by adding anything but zero to unity, the last loses its uniqueness.. :icon_wink:
Well, yes, but what I mean is that I want something that will not add color to the sound (even if it is adding volume to a frequency). Does that make sense?
Quote from: antonis on May 21, 2020, 07:20:21 AM
P.S.
Differences between the many versions of NE5532 (other than price..) are unimportant for your task..
(they have to do with lowest guaranteed noise, THD measure, etc..)
http://e2e.ti.com/support/amplifiers/f/14/t/344 (http://e2e.ti.com/support/amplifiers/f/14/t/344)
Ah, I checked my list from the original post, but I did not notice I repeated the same OpAmp... Thanks for checking my counting! I guess math is not my strong point either!
By the way, I ran out of 0.1uF caps anyway, so I had to place an order. By the way, anyone got any good replacement alternative to Small Bear? They are out of all the caps I need... and I also need some pots.
Quote from: Mark Hammer on May 20, 2020, 04:47:35 PM
The PAiA 4-Band equalizer is probably a suitable unit for you. Though you probably only need the first 3 sections.
https://www.scribd.com/doc/96494162/4-Band-Equalizer-Www-circuitdiagram-net
Mark (and the rest of you), I started looking more into this EQ, and I like it, but I have a question; looking at the diagram, I cannot figure out what the dotted lines mean.
(https://i.postimg.cc/0NVFx9jS/4-band-equalizer-question.jpg)
From what I can see in the PAiA page for this product (https://www.paia.com/proddetail.asp?prod=9303K), it seems the kit only has 2 pots per channel, but the schematics show 3 (trim pot?).
(https://www.paia.com/prodimages/9303FP-fourbandeq-hi.jpg)
It's intended to show that the two 100k pots are each half of a dual ganged 100k pot.
Just a few things I noticed:
Quote from: jfrabat on May 20, 2020, 03:17:10 PM
1) C2 = 100 µF (Electrolytic Capacitors) - I THINK I GOT ONE LEFT IN A BREADBOARD PROJECT, BUT SHOULD BE OK
2) C4. C5, C7, C8, C20 – C23 = 0.1 µF (Ceramic Disc) - NO PROBLEM (JUST HAVE 5 100pF LEFT!)
3) C10, C11 = 0.047 µF (Electrolytic Capacitors) - ELECTROLITIC? I HAVE CERAMIC, AND THEY ARE NOT LABELED AS POLARIZED, SO I PLAN TO USE CERAMIC
4) C13, C14, C16, C17 = 0.0022 µF (Electrolytic Capacitors) - AGAIN, ELECTROLITIC? I HAVE 3 CERAMIC LEFT, BUT I COULD FUDGE IT BY USING 2 X 10pF FOR THE LAST ONE.
1) it's for power filtering. Probably a 47uF cap would do it, but you can use any bigger value you have.
2) 100pF? You need 0.1uF, which is 100nF, which is 100000pF. Watch for the unit prefixes! And you need 8 caps, not 5.
3) not eletrolytic. You can use ceramic or film caps.
4) again, watch for the unit prefixes! 0.0022uF is the same as 2.2nF which is the same as 2200pF. By using 2x 10pF caps, you'll end up with 20pF, which is 100x smaller than the required value.
Also:
Quote from: jfrabat on May 20, 2020, 03:17:10 PM
I am not adding one more band because I only got 5 5K pots
The schematic calls for 3 4.7K (or 5K) pots and 2 47K (or 50K) pots, not 5 4.7K/5K pots.
I don't know if you're still interested in this exact project, just want to point out the unit prefixes, so you don't use the wrong values on this project (or any other one) and end up with something that doesn't work as expected.
Quote from: Marcos - Munky on May 21, 2020, 02:03:48 PM
I don't know if you're still interested in this exact project, just want to point out the unit prefixes, so you don't use the wrong values on this project (or any other one) and end up with something that doesn't work as expected.
This is much appreciated. I started breadboarding, so I may finish just to try it, but the other schematic (4 band) seems a lot more interesting now... That is the one I am going to build as a final build, as I can tailor the frequencies on the fly, but if this one sounds good, I may end up building both. It's not like I have a bunch of other stuff to do right now anyway!
Quote from: Mark Hammer on May 21, 2020, 01:30:42 PM
It's intended to show that the two 100k pots are each half of a dual ganged 100k pot.
Ah... You learn something every day! Good to know!
If you're aiming to have a good quality and low noise EQ, all those capacitors in the signal path shall be polymer type, not ceramic! Those 10n (0.1uF) in power supply can be ceramic. It is also better to have regulated power supply with linear regulators.
Quote from: jfrabat on May 22, 2020, 12:16:27 AM
Quote from: Mark Hammer on May 21, 2020, 01:30:42 PM
It's intended to show that the two 100k pots are each half of a dual ganged 100k pot.
Ah... You learn something every day! Good to know!
Often, schematics will do us the service of labeling dual-ganged pots in a manner like "VR1a / VR1b" to indicate that the two are halves of a single unit. Not so in this case. I guess they figured the dotted line would implicitly convey that information.
Quote from: rankot on May 22, 2020, 02:53:15 AM
If you're aiming to have a good quality and low noise EQ, all those capacitors in the signal path shall be polymer type, not ceramic! Those 10n (0.1uF) in power supply can be ceramic. It is also better to have regulated power supply with linear regulators.
My idea was to build this one:
(https://i.postimg.cc/2y2SZ2QJ/4-band-equalizer.jpg)
I was planning to use film (brownies) capacitors (except for the electrolytic, of course; those will be Panasonic caps). The only thing is that I was planning to change the 0.0039uF for 0.0033uF, as I do not have 0.0039uF available (not sure how much 0.0006uF will change the frequencies, but it is what I have). I will replace 1N4001 diodes with 1N4004, but that should have no effect. Resistors will all be Metalic +-1% throughout. Neutrik jacks and Alpha pots.
Quote from: jfrabat on May 22, 2020, 09:41:54 AM
I was planning to use film (brownies) capacitors (except for the electrolytic, of course; those will be Panasonic caps). The only thing is that I was planning to change the 0.0039uF for 0.0033uF, as I do not have 0.0039uF available (not sure how much 0.0006uF will change the frequencies, but it is what I have). I will replace 1N4001 diodes with 1N4004, but that should have no effect. Resistors will all be Metalic +-1% throughout. Neutrik jacks and Alpha pots.
That's fine!
Here is what I am thinking:
(https://i.postimg.cc/VsJM5yPq/4-band-equalizer-with-voltage-regulation-and-switches.jpg)
EDIT: I noticed you cannot read anything above. direct image link here (https://postimg.cc/w3d3bGvM).
It is basically the PAiA 9303 4 band equalizer with a power supply regulator circuit added. If I went overboard, or if I am duplicating the protection, please let me know. I also want to have 2 switches, one for power, and another to bypass the circuit (same wiring as a stompswitch, but with a toggle switch), each with an LED indicator (I am thinking blue would look nice!).
I also changed the .0039 caps for 0.0033 (because I have those!). But I was wondering what effect will that have on the frequency. Anyone with time on their hands care to teach me how I do that? I tried reading online, but did not understand...
> 0.0039 caps for 0.0033
Frequency is 1/C.
1kHz becomes 1.18kHz.
Five semi-parametric bands is a little nuts. I mean it is certainly ambitious, and aims high, but the question is whether it accomplishes anything you actually need.
However, if you feel 5 bands is necessary, I recommend including bypass toggles for each section. The idea is that
a) Whatever hiss from sections you don't need to use can be avoided, and
b) You can zero in on one aspect of the frequency response at a time, identify what more may be needed, and then engage another section/band, and perhaps another; the toggle will let you easily compare with and without, without having to fiddle with the knobs. Remember that the bands will overlap to some degree, so what you hear in the end is a joint product of what band A and B are both doing.
Quote from: Mark Hammer on May 22, 2020, 07:19:32 PM
Five semi-parametric bands is a little nuts. I mean it is certainly ambitious, and aims high, but the question is whether it accomplishes anything you actually need.
However, if you feel 5 bands is necessary, I recommend including bypass toggles for each section. The idea is that
a) Whatever hiss from sections you don't need to use can be avoided, and
b) You can zero in on one aspect of the frequency response at a time, identify what more may be needed, and then engage another section/band, and perhaps another; the toggle will let you easily compare with and without, without having to fiddle with the knobs. Remember that the bands will overlap to some degree, so what you hear in the end is a joint product of what band A and B are both doing.
Sorry, you are right! It is actually 4, but I messed up when I stitched all the print screens together (not sure how to save an image out of Eagle another way!) But rest assure, it is only 4 bands... The Hammond 1590Q will fit 4 bands nicely, but 5 would be too crowded! Not to mention I have 4 gray and 4 tan knobs I plan to use; I do not have enough for 5 bands, unless I go to my aluminum knob stash, and I plan to keep those for guitar pedals!
Sorry about that!EDIT: I modified the above image and link to the correct one
Quote from: PRR on May 22, 2020, 06:18:04 PM
> 0.0039 caps for 0.0033
Frequency is 1/C.
1kHz becomes 1.18kHz.
OK, have some patience with me here...
So, we have 4 bands in the original schematic.
(https://i.postimg.cc/2y2SZ2QJ/4-band-equalizer.jpg)
Lets focus on the third one, which is the one I changed the cap value...
That one uses 2 X 0.0039 caps. According to the schematic, that band controls signals from 450Hz to 8.5KHz. The math does not add up... Now here, the caps are kind of both in series and in parallel at the same time. So how do I count C? 0.0078? Then 1/0.0078 = 128Hz, right? If it is counted as 0.0039 then 1/0.0039 would be 256Hz. In neither case is it the frequencies listed on the schematic (I imagine they are not exact, but these are not even close!). So how do I calculate the frequencies I will be able to select in band 3?
I mean, I did use the 1/c to calculate a ratio, and when I use the 0.0033 caps, I get 500Hz-10KHz (well, 490Hz to 9.7KHz really, but who's being exact!), but I do not know how to get to that number with pure math...
> that band controls signals from 450Hz to 8.5KHz.
If it is variable 20:1, why even think about 1.18:1 cap change?
The filter is a Wien Bridge. The formula for F has root(1/(R*R*C*C)) and some pie.
https://en.wikipedia.org/wiki/Wien_bridge
https://en.wikipedia.org/wiki/Wien_bridge_oscillator
When R1=R2=R and C1=C2=C, the frequency of oscillation is given by:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/f8da7c8ff53b1fb61429534cb6a100a0902eb778)
The bridge works for unequal parts but 97% of designs use equal values for sanity. There is a variant with useful values of un-equal but only H-P had the brains to get anywhere on that.
QuoteIf it is variable 20:1, why even think about 1.18:1 cap change?
22:1 to be precise.
10:1 range is a bit more repeatable to adjust.
For high frequency spans like that you will need to use Reverse-audio/Antilog taper pots.
(If you are willing to compromise with back to front frequency scales you can use
audio/log taper pots.)
If you intend to use linear taper pots then it would be wise to reduce the range somewhat.
Perhaps 4:1 or at a squeeze 5:1.
your power supply makes no sense. what are you feeding in, and what are you expecting out?
Quote from: PRR on May 23, 2020, 12:53:44 AM
If it is variable 20:1, why even think about 1.18:1 cap change?
So you mean don't worry about the change? I did not get your meaning...
Quote from: PRR on May 23, 2020, 12:53:44 AM
The filter is a Wien Bridge. The formula for F has root(1/(R*R*C*C)) and some pie.
https://en.wikipedia.org/wiki/Wien_bridge
https://en.wikipedia.org/wiki/Wien_bridge_oscillator
When R1=R2=R and C1=C2=C, the frequency of oscillation is given by:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/f8da7c8ff53b1fb61429534cb6a100a0902eb778)
The bridge works for unequal parts but 97% of designs use equal values for sanity. There is a variant with useful values of un-equal but only H-P had the brains to get anywhere on that.
OK, you lost me again... I tried understanding Wiki, but it just went over my head...
But after toying with Excel, I kind of figured it out (I do not get the EXACT values listed, but I am REALLY close those values!)
Band 1 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.000000047 X 104700) = 32.34Hz
Band 1 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.000000047 X 4700) = 720.48Hz
Band 2 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.00000001 X 104700) = 152.01Hz
Band 2 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.00000001 X 4700) = 3,386.28Hz
Band 3 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 104700) = 389.77Hz
Band 3 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 4700) = 8,672.76Hz
Band 4 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000022 X 104700) = 690.96Hz
Band 4 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000022 X 4700) = 15,392.16Hz
And then, according to the formula, my change would make the bands as follows:
Band 3 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 104700) = 460.64Hz
Band 3 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 4700) = 10,261.44Hz
If that is the case, I am 100% fine with this.
Quote from: Rob Strand on May 23, 2020, 01:20:53 AM
QuoteIf it is variable 20:1, why even think about 1.18:1 cap change?
22:1 to be precise.
In stock form, the range would be (with the above mentioned figures):
32Hz to 720Hz = 22.3:1
152Hz to 3,386Hz = 22.3:1
390Hz to 8,683Hz = 22.3:1
691Hz to 15,392Hz = 22.3:1
Mi change would make band 3 461Hz to 10,261Hz, so 22.3:1
Quote from: Rob Strand on May 23, 2020, 01:20:53 AM
10:1 range is a bit more repeatable to adjust.
If you intend to use linear taper pots then it would be wise to reduce the range somewhat.
Perhaps 4:1 or at a squeeze 5:1.
Well, i am kind of stuck because I only got 100K pots... Sure, I could lower the range by increasing the resistor value in R, but I would lose my high end control if I do (for example, to go to 5:1, and keeping 100K pots, I would need to raise the resistor to 25K, which means the highest frequency would be 2.9KHz; if I go to 10:1, by using a 12K resistor, the highest frequency would be 6KHz. I loose all the "airy" frequencies). And the smallest cap I got (not counting ceramics) is the 0.0022, so changing cap is not the way either.
Quote from: Rob Strand on May 23, 2020, 01:20:53 AM
For high frequency spans like that you will need to use Reverse-audio/Antilog taper pots.
(If you are willing to compromise with back to front frequency scales you can use
audio/log taper pots.)
I have (in dual gang) Audio and Linear pots in 100K. I intended to use linear; why do you recommend reverse logarithmic?
Quote from: duck_arse on May 23, 2020, 10:57:58 AM
your power supply makes no sense. what are you feeding in, and what are you expecting out?
I I was kind of following Rankot's advise... Remember, this is for vocals, not guitars!
Quote from: rankot on May 22, 2020, 02:53:15 AM
It is also better to have regulated power supply with linear regulators.
So I added this in front of the power supply to insure no electrical noises:
(https://www.amb.org/audio/sigma25/sigma25_100_sch.png)
QuoteBand 3 (low end): f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 104700) = 389.77Hz
Band 1 (high end): f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 4700) = 8,672.76Hz
my change would make the bands as follows:
Band 3 (low end): f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 104700) = 389.77Hz
Band 1 (high end): f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 4700) = 8,672.76Hz
It appears that changing 39 to 33 makes
NO change of frequency.
And "Band 1" won't go away.
While I never trust Excel too far, this result is likely user/finger error.
You are asking for a very fancy "transparent" EQ, using only parts under your lock-down bench. Maybe it isn't that easy?
Throw together ONE band. Try it out. Does the opamp really make much difference? Do the pots turn the right way? Can you even hear 39 vs 33?
Quote from: PRR on May 23, 2020, 04:44:56 PM
It appears that changing 39 to 33 makes NO change of frequency.
And "Band 1" won't go away.
While I never trust Excel too far, this result is likely user/finger error.
Ah, yes, finger error. The frequency with 33's is:
Band 3 (low end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 104700) = 460.64Hz
Band 3 (high end):
f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 4700) = 10,261.44Hz
I corrected that and the BAND 1 error in the original post.
Quote from: PRR on May 23, 2020, 04:44:56 PM
You are asking for a very fancy "transparent" EQ, using only parts under your lock-down bench. Maybe it isn't that easy?
Throw together ONE band. Try it out. Does the opamp really make much difference? Do the pots turn the right way? Can you even hear 39 vs 33?
I am going to breadboard it as soon as I clear one breadboard; I have 2 projects on breadboards, so I need some space (one is almost done, so in a week or two I will start). I will not make anything I do not breadboard first!
Quote from: PRR on May 23, 2020, 12:53:44 AM
If it is variable 20:1, why even think about 1.18:1 cap change?
PRR is right. If the band is variable over such a wide range, a small change in capacitor value really isn't important. You can tune it to get it where you need it anyway, so there's no problem. It only makes a tiny different to the very lowest and very highest frequencies you can get, but those aren't likely to be the ones you use most. There are other bands for that. So go for it, and don't worry too much.
Quoteif I go to 10:1, by using a 12K resistor, the highest frequency would be 6KHz. I loose all the "airy" frequencies). And the smallest cap I got (not counting ceramics) is the 0.0022, so changing cap is not the way either.
When you reduce the range you need to place the frequencies so they are all in the region you want. It's OK to use 100k pots. The frequencies are then by changing the caps. On a project of this scale it seems crazy holding back doing the right thing for the price of a few caps. If you don't have the parts on hand you could use two caps in series to create a smaller value.
QuoteI have (in dual gang) Audio and Linear pots in 100K. I intended to use linear; why do you recommend reverse logarithmic?
Professional equipment use reverse-log pots because it spreads the frequencies evenly over the range of the control.
For arguments sake, suppose you have a frequency control range 500Hz to 10kHz.
From the point of view of having the frequency control being naturally centered the pot position 5 (on 0 to 10 pot scale) should be 2.2kHz. That gives even frequency control 2.2 octaves up or down from 2.2kHz and would sound even to the ear.
With a linear pot the center is about 1kHz. The problem now is you have 0.86 octave span (500Hz to 1kHz) over the range of pot settings from 0 to 5 but a 3.5 octave span (1kHz to 10kHz) over pot setting 5 to 10. In use that means the control gets very bunched up on the high frequency side. As you get closer to 10kHz the bunching up gets worse. It's not nice to use and it means every time you set-up the EQ on the high-frequency side it won't quite be the same as last time.
The reverse-log pot evens that out to be much more like the naturally centered case.
Quote from: Rob Strand on May 23, 2020, 07:35:53 PM
[On a project of this scale it seems crazy holding back doing the right thing for the price of a few caps. If you don't have the parts on hand you could use two caps in series to create a smaller value.
Good point...
Quote from: Rob Strand on May 23, 2020, 07:35:53 PM
Professional equipment use reverse-log pots because it spreads the frequencies evenly over the range of the control.
For arguments sake, suppose you have a frequency control range 500Hz to 10kHz.
From the point of view of having the frequency control being naturally centered the pot position 5 (on 0 to 10 pot scale) should be 2.2kHz. That gives even frequency control 2.2 octaves up or down from 2.2kHz and would sound even to the ear.
With a linear pot the center is about 1kHz. The problem now is you have 0.86 octave span (500Hz to 1kHz) over the range of pot settings from 0 to 5 but a 3.5 octave span (1kHz to 10kHz) over pot setting 5 to 10. In use that means the control gets very bunched up on the high frequency side. As you get closer to 10kHz the bunching up gets worse. It's not nice to use and it means every time you set-up the EQ on the high-frequency side it won't quite be the same as last time.
The reverse-log pot evens that out to be much more like the naturally centered case.
Sold on the reverse audio tapered pots.
Where is a good source for dual gang reverse audio pots? I looked in Mouser, but they do not have any. Also, I was thinking about the frequency range... I could go with a 10:1 ratio. I would need to get caps for the base (33nF would be nice), but the rest I have. So if I am going to order the pots, may as well order the caps. I ran the numbers and this is what I could get with the caps I have:
Band C (nF) R1 (min) R2 (max) Lower Freq Highest Freq Band ratio
1 22.0nF 12,000Ω 112,000Ω 65 Hz 603 Hz 9.33:1
2 6.8nF 12,000Ω 112,000Ω 209 Hz 1,950 Hz 9.33:1
3 2.2nF 12,000Ω 112,000Ω 646 Hz 6,029 Hz 9.33:1
4 1.0nF 12,000Ω 112,000Ω 1,421 Hz 13,263 Hz 9.33:1
If I get 33nF, then it looks more like this:
Band C (nF) R1 (min) R2 (max) Lower Freq Highest Freq Band ratio
1 33.0nF 12,000Ω 112,000Ω 43 Hz 402 Hz 9.33:1
2 6.8nF 12,000Ω 112,000Ω 209 Hz 1,950 Hz 9.33:1
3 2.2nF 12,000Ω 112,000Ω 646 Hz 6,029 Hz 9.33:1
4 1.0nF 12,000Ω 112,000Ω 1,421 Hz 13,263 Hz 9.33:1
Although, the only reason to have to go down to 43Hz is to equalize instruments. Vocals do not go below 80Hz, so I could make do just fine with 22nF (or I could use a 22nF and add a 10nF in parallel and call it good).
QuoteWhere is a good source for dual gang reverse audio pots?
I think Small Bear does them. In the past I bought them as spare parts from amp manufacturers, which can be a little expensive. The last parametric I built was for bass and I used linear taper pots with reduced frequency ranges.
QuoteBand C (nF) R1 (min) R2 (max) Lower Freq Highest Freq Band ratio
1 33.0nF 12,000Ω 112,000Ω 43 Hz 402 Hz 9.33:1
2 6.8nF 12,000Ω 112,000Ω 209 Hz 1,950 Hz 9.33:1
3 2.2nF 12,000Ω 112,000Ω 646 Hz 6,029 Hz 9.33:1
4 1.0nF 12,000Ω 112,000Ω 1,421 Hz 13,263 Hz 9.33:1
All that looks OK to me.
C100k dual pots can be bought at Tayda for cheap.
https://www.taydaelectronics.com/100k-ohm-anti-log-dual-taper-potentiometer.html (https://www.taydaelectronics.com/100k-ohm-anti-log-dual-taper-potentiometer.html)
Quote from: rankot on May 24, 2020, 05:56:10 AM
C100k dual pots can be bought at Tayda for cheap.
https://www.taydaelectronics.com/100k-ohm-anti-log-dual-taper-potentiometer.html (https://www.taydaelectronics.com/100k-ohm-anti-log-dual-taper-potentiometer.html)
Wanted the 90* ones, but no one has them, so I ordered those from Tayda. Will start breadboarding soon (will have to wait for the pots, though!)
The other thing I was thinking was decreasing the R values (the fixed ones) in band 4 to get a little higher frequency there. I was thinking 10K instead of 12K to go from 1,447Hz to 15,915Hz and have a bit more control over the "air" part of the spectrum... What do you guys think? 1.4K~13.3K or 1.4K~15.9K? Low end is almost the same (1,421Hz vs 1,447Hz), but I do gain a lot in the highs...
QuoteWhat do you guys think? 1.4K~13.3K or 1.4K~15.9K? Low end is almost the same (1,421Hz vs 1,447Hz), but I do gain a lot in the highs...
Since it's for voice and those parametrics have a low Q (wide bandwidth) the change would help more than it hurts. Like you could just use 10k resistors on all ranges.
FWIW, at the low frequency side the pot resistance tolerance comes into play so the frequency limits of the real unit could be higher or lower than the calculations.
Quote from: Rob Strand on May 25, 2020, 07:37:52 PM
QuoteWhat do you guys think? 1.4K~13.3K or 1.4K~15.9K? Low end is almost the same (1,421Hz vs 1,447Hz), but I do gain a lot in the highs...
Since it's for voice and those parametrics have a low Q (wide bandwidth) the change would help more than it hurts. Like you could just use 10k resistors on all ranges.
FWIW, at the low frequency side the pot resistance tolerance comes into play so the frequency limits of the real unit could be higher or lower than the calculations.
I decided to use 12K in all the frequencies. My reasoning is that, since I ran out of 10K resistors, I would use 12K resistors. :icon_biggrin:
At the end of the day, I will use a tone generator to tune the frequencies if necessary (I doubt it will be necessary, but at least to know the limits!).
I am still waiting for the C100K dual gang pots to arrive, but here is the breadboard minus the pots:
(https://i.postimg.cc/G3FptpB0/20200530_002338.jpg)
I so want to try it! By the way, the CUT / BOOST pots right now are linear taper; I wanted to go with audio taper, but I did not have any on hand (I thought I did, but I don't!). For this purpose, is it better linear or audio taper (my logic already failed me with the dual gang ones!)?
Quote from: jfrabat on May 30, 2020, 01:31:07 AM
By the way, the CUT / BOOST pots right now are linear taper; I wanted to go with audio taper, but I did not have any on hand (I thought I did, but I don't!). For this purpose, is it better linear or audio taper (my logic already failed me with the dual gang ones!)?
I'd say they have to be linear taper, because they have a centre zero. Any other pot type will finish up with the zero position being off to one side or the other.
while you have that much of it on the bb, TEST IT! sub 2 x 47k resistors for each missing section of the missing pots - test what you have while you wait, y'no, just in case .....
Quote from: duck_arse on May 30, 2020, 10:46:44 AM
while you have that much of it on the bb, TEST IT! sub 2 x 47k resistors for each missing section of the missing pots - test what you have while you wait, y'no, just in case .....
Not a bad idea, actually... I will do that.
Well, this is what we got so far:
Power Stage seems to be working fine. The power supply I am using (says is 12V 100mA) actually puts out 16.4V when plugged to the system (16.9V when unplugged). My regulated power supply with linear regulators seems to be working fine, as the voltage prior to D2 is 12.1V (not sure about noise yet, just testing voltages). V+ measured at 10.45V, and V- measured at 8.5V (I am still a newb, but those values seem perfectly reasonable to me, at least).
Sound Stage:
Obviously, I do not have the caps yet, so I could not test much of what the circuit is actually intended to do, BUT... I get no sound coming through. I will have to check all the equalization circuit again. Not that I expected anything different, and at least I have something to do over the weekend while I wait for the pots to arrive. I will bust out my audio probe and chase the sound signal.
> I'd say they have to be linear taper
For perfectly even spacing they want to be an "S-taper". {Edit: W-taper?}
It REALLY is easier to buy than to build. But we need to keep Felipe off the streets and healthy.
Quote from: PRR on May 30, 2020, 04:13:17 PM
> I'd say they have to be linear taper
For perfectly even spacing they want to be an "S-taper".
Ah, the infamous W taper... I hate it when they are required. Not easy to get those locally.
Quote from: PRR on May 30, 2020, 04:13:17 PM
It REALLY is easier to buy than to build. But we need to keep Felipe off the streets and healthy.
Buying is nowhere NEAR as distracting for my mind... and not NEARLY as satisfying to play!
QuoteFor perfectly even spacing they want to be an "S-taper".
You can do OK with linears for the boost/cut. There's probably some tweak you can do to the 47k to ground to tweak the dB's for the mid-way boost and mid-way cut positions (around 9 O'Clock and 3 O'Clock)).
Well, first thing first... Let me get the line to actually go through first. Then I will ask you how to do this.
I got 3 pedals on the build table; this one, a phaser (which has been a HEADACHE to troubleshoot, but we are almost there!), and a tube screamer clone (waiting for parts on that one). Also had an OCD Overdrive, but that one I finished this week. So I need to go one step at a time to avoid getting ahead of myself.
QuoteSo I need to go one step at a time to avoid getting ahead of myself.
You're not the only one. I've got a whole heap of stuff that suddenly died as well.
By the way, just to check my logic, I need to place a 47K resistor in place of each part of the pot, right?
(https://i.postimg.cc/k4y1FrZw/PAi-A-9303-4-Band-EQ.jpg)
So 2 resistors per band, right? For example, in band 1, I would put one between R7 and C13 (on the non grounded side), and another from C13 (same side) to C14, right?
QuoteSo 2 resistors per band, right? For example, in band 1, I would put one between R7 and C13 (on the non grounded side), and another from C13 (same side) to C14, right?
Yes. You connect a resistor in place of a pot. One resistor for each 'gang' of the pot. It's like the pot is stuck on one setting.
OK, checked my board. Found a few small errors (last OpAmp V+ was not connected, and, for some reason, I soldered the signal of the output jack to the ring part of a stereo jack; I also had D3 connected to the wrong row). I now get signal coming through the circuit, but I am hearing no amplification (the signal comes out very faintly). The signal loses strength through the circuit. Also, I feel that the cut part of the system is working, but the boosting is not.
Question; in the scheme I posted, the OpAmp's port 4 is connected to V-, which in this case, is actually 5V (the other day I measured and it was 8.5V, but today it is 5V now; guess D3 had something to do with that. V+ is now 8V, BTW). Shouldn't pin 4 of these OpAmps go to GND?
I also need to check the first pot, as the signal goes through only with that pot at minimum. I checked it against the schematic, but it seems to be connected OK. Pot itself also checked out. Not sure what it is, but I will check it tomorrow.
Quote
By the way, just to check my logic, I need to place a 47K resistor in place of each part of the pot, right?
[your sch]
QuoteQuestion; in the scheme I posted, the OpAmp's port 4 is connected to V-, which in this case, is actually 5V (the other day I measured and it was 8.5V, but today it is 5V now; guess D3 had something to do with that. V+ is now 8V, BTW). Shouldn't pin 4 of these OpAmps go to GND?
The power section in that schematic has some problems.
In the original schematic,
(https://i.postimg.cc/0NVFx9jS/4-band-equalizer-question.jpg)
The power supply works by taking the AC from one winding of a transformer then it creates a DC supply with both +12V and -12V. The two diodes and the two 100uF form a doubler circuit. The following two 150R and 100uF caps provided extra filtering to remove ripple/hum from the DC rail. The main point here is the supply is a bipolar supply with +12V and -12V.
In your schematic: a *single* *DC* rail is applied to the DC jack then it is passes through the 12V regulator. In short you won't get +12V and -12V. Also the diodes and caps in you schematic can never produce +12V and -12V. With a DC rail that diode + cap doubler actually makes not sense as it *only* works with an AC input. So you will need to remove all that stuff - but that won't make it work.
As far as a solution goes. It depends if you want to input 12V AC or 12V DC on the power jack. So the options are:
1) 12V AC in. Use diode + cap doubler circuit like the original schematic. If you want to use 12V regulators you will need to replace the 2x 150R + 100uF with a LM7812 and a LM7912 to get +/- 12V; will need to add some caps for the regulator
2) 12V unreg DC in ---> 12V regulator (LM7812)
----> negative supply generator circuit ---> -12V regulator (LM7912)
A slight variation is to connect the negative supply generator to the output of the 12V regulator.
The negative supply generator will be a whole other circuit.
3) Using only a single 12V supply rail. And convert the whole circuit to single supply.
Connect the opamp +Vcc to 12VDC.
Connect the opamp -Vcc to 0V (ground)
Add a Vcc/2 circuit like most pedals have with a resistive divider and cap to ground to create Vref = Vcc/2
Change circuit *signal* grounds to 0V (ground)
The more involved part is to detach some of the points which are currently connected to ground and wire those
to Vref Vcc/2 so the opamps are biased correctly.
Add coupling caps where you need to separate the DC and ground
Add coupling cap to the signal input.
Add coupling cap to the signal output.
Maybe a few other points I haven't elaborated on but that the general idea.
I suppose you have to choose which way you want to go. Solution (3) loses headroom since the supply is 12V = +/-6V but the true bipolar supply is +/- 12V.
I want to emphasize that when using 12V regulator you will need an unregulated input supply which really produces about +/-16 to 18V. You need a DC input greater than 15V to ensure the regulators work.
Ah, that explains a lot... OK. So, my best course of action is to get a 12V AC-to-AC transformer and delete all that regulated power supply with linear regulators part; either that, or place it and a mirror of it on V+ and V- (and I would need a 7912 for that one, and figure out how to use B1 - B2 in this case - correctly for -12V).
What would you recommend? Leave out the regulated supply part? I looked om Amazon, and the have 12V AC-to-AC transformers (https://www.amazon.com/Reliapro-ACU120100D0531-Adapter-Transformer-Straight/dp/B00B8861T2/ref=mp_s_a_1_3?dchild=1&keywords=12V+Ac+Power+Supply&qid=1590905478&sr=8-3)... and 16VAC (https://www.amazon.com/NORTEL-T41160500A010G-A0619627-Adapter-Transformer/dp/B07D591K9V/ref=mp_s_a_1_4?dchild=1&keywords=16V+Ac+Power+Supply&qid=1590905591&sr=8-4) if I will use the regulated supply part (times 2).
Would you be willing to guide me in this process? I am still learning all this...
So if I keep the circuit like this:
(https://i.postimg.cc/4drmQ123/PAi-A-9303-4-Band-EQ.png)
And use one of these power adapters (https://www.amazon.com/gp/product/B00B88621O/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1), I should be OK, then?
PD: I just noticed I need to move the + side of the bypass LED to the 12+ signal...
QuoteAnd use one of these power adapters, I should be OK, then?
If you follow the original, without the regulators, then I'd go for a 12VAC plug-pack for sure. The 16VAC will produce quite a high voltage on the DC side.
Probably a good idea to beef-up the caps C5, C6, C7, C8 to 470uF 25V to 35V.
FYI: One thing about these doublers is they usually cause a power-up "bang" in the audio because one side of the supply always starts before the other. With R3 and R4 in place and larger C7 and C8 it slows down the speed the DC side rises and hides some of the "band".
On your new schematic, 12VAC2 needs to connect to the ground between C5 and C6. When you wire it up you need to physically wire it exactly that way as well.
R1 and LED1 aren't wired correctly. The original wired the LED to AC but I'd probably power both LED's from the DC rail(s). So R1 and LED1 go from ground to -ve C6, R2 and LED2 go from ground to +ve C5. All I'm doing here is dividing the LED currents between the + and - rails.
Quote from: Rob Strand on May 31, 2020, 07:10:13 PM
Probably a good idea to beef-up the caps C5, C6, C7, C8 to 470uF 25V to 35V.
OK, I got 220 & 1000uF, but both are 16V. Should I go all the way to 1000? I do not have 470uF...
Quote from: Rob Strand on May 31, 2020, 07:10:13 PMFYI: One thing about these doublers is they usually cause a power-up "bang" in the audio because one side of the supply always starts before the other. With R3 and R4 in place and larger C7 and C8 it slows down the speed the DC side rises and hides some of the "band".
Sounds like a good idea. I do not want a "bang" on powerup, so better to increase. So increase all 4 caps, right? Not only C7 and C8, but C5 & C6 as well, right?
Quote from: Rob Strand on May 31, 2020, 07:10:13 PMOn your new schematic, 12VAC2 needs to connect to the ground between C5 and C6. When you wire it up you need to physically wire it exactly that way as well.
So not just connected to ground, but LITERALLY between the 2 caps? So make the board like this:
(https://i.postimg.cc/QN9FqFQ9/PAi-A-9303-4-Band-EQ-BOARD.png)
I forced the trace between the 2 caps (C5 & C6)
Dual gang pots will be off board (I just needed the holes to be in the board). Single gang pots will be in the other side, as usual. For the On/Off Toggle, I am still debating if to use a ON/OFF/ON that is the same size as the the other switch, or use the ON/OFF I have (which has a little smaller toggle lever). Either way, both fit...
Quote from: Rob Strand on May 31, 2020, 07:10:13 PMR1 and LED1 aren't wired correctly. The original wired the LED to AC but I'd probably power both LED's from the DC rail(s). So R1 and LED1 go from ground to -ve C6, R2 and LED2 go from ground to +ve C5. All I'm doing here is dividing the LED currents between the + and - rails.
So, replacing 100uF caps for 1000uF caps, and changing the LED layout (please check if polarity of LED is correct!), the schematic should look like this then:
(https://i.postimg.cc/V5PQqGjR/PAi-A-9303-4-Band-EQ.png)
DELETED (duplicated)
QuoteOK, I got 220 & 1000uF, but both are 16V. Should I go all the way to 1000? I do not have 470uF...
QuoteSounds like a good idea. I do not want a "bang" on powerup, so better to increase. So increase all 4 caps, right? Not only C7 and C8, but C5 & C6 as well, right?
C5 and C6 can be either 220u or 1000uF, up to you, slight advantage with 1000uF. Making C7 and C8 1000uF will help tame the turn-on thump/bang.
16V is pushing the caps close to the limit, especially C5 and C6. It will work but it will reduce the life of the cap.
I just want to be clear that it is quite difficult to remove *all* the power-up thump when using those doubler circuits. You can certainly reduce it. Completely removing it will need extra circuits with transistors. Most single supply circuit thump a small amount.
QuoteSo not just connected to ground, but LITERALLY between the 2 caps?
You want the transformer wire to go to the centre of two caps C5, C6 on it's own track, not through the ground plane. How you did it looks OK. You can then connect another track from the center of the caps along to C6 and C7 and then from that point to the ground.
You still have a bug on your power supply 12VAC to ground is still going to the diodes. You need to remove that line. One side of the transformer connects to both diode and the other side of the transformer connection to C5, C6.
Also you could connect the LEDs to C5 and C6 instead of C7, C8. The idea is it helps stop the LED1 current changing the +ve supply voltage to the opamps due to it loading the power rail.
LED polarities look OK.
That's as far as I got this evening.
Quote from: Rob Strand on June 01, 2020, 07:24:45 AM
C5 and C6 can be either 220u or 1000uF, up to you, slight advantage with 1000uF. Making C7 and C8 1000uF will help tame the turn-on thump/bang.
OK, 1000 it is then for all 4 of them.
Quote from: Rob Strand on June 01, 2020, 07:24:45 AM16V is pushing the caps close to the limit, especially C5 and C6. It will work but it will reduce the life of the cap.
I will start then with 16V until I can get higher voltage.
Quote from: Rob Strand on June 01, 2020, 07:24:45 AMI just want to be clear that it is quite difficult to remove *all* the power-up thump when using those doubler circuits. You can certainly reduce it. Completely removing it will need extra circuits with transistors. Most single supply circuit thump a small amount.
Understood. I will have the bypass switch (hopefully no THUMP there!) to work with as well...
Quote from: Rob Strand on June 01, 2020, 07:24:45 AMYou want the transformer wire to go to the centre of two caps C5, C6 on it's own track, not through the ground plane. How you did it looks OK. You can then connect another track from the center of the caps along to C6 and C7 and then from that point to the ground.
You still have a bug on your power supply 12VAC to ground is still going to the diodes. You need to remove that line. One side of the transformer connects to both diode and the other side of the transformer connection to C5, C6.
I am having a real hard time getting Eagle to separate the 12VAC2 from GND, because, to Eagle, they are directly connected and thus are the same thing. In the schematics, it does not really matter, but when doing the board, it is a REAL PITA! So I added a 0 Ohm resistor to dived the segments... I can use it or use a jumper in the final build.
Anyway, here is what the new board looks like:
(https://i.postimg.cc/mZNmQvqK/NEW-BOARD.jpg)
I tried going from the 12V AC on the right, to the middle of C5 (1) & C6 (+), and from there a point where C7 (-), C8 (+), D1 (cathode), D2 (anode), Switch 1 and R10 (which I had to add to trick Eagle) all are connected. I really had to wiggle my traces in there!
Quote from: Rob Strand on June 01, 2020, 07:24:45 AMAlso you could connect the LEDs to C5 and C6 instead of C7, C8. The idea is it helps stop the LED1 current changing the +ve supply voltage to the opamps due to it loading the power rail.
LED polarities look OK.
Here's the new schematic showing this as well:
(https://i.postimg.cc/3NPV0mWm/PAi-A-9303-4-Band-EQ.png)
Please review to make sure I did not screw it up anywhere. Also, about R10, should I use a 0 Ohm resistor, or just a jumper?
0 ohm resistor or jumper doesnt really matter ;)
Deng bro, that is nót the nicest pcb drawing i've ever seen :o
You should check if the NE5532's and the jacks can actually be fitted physically on your bord...
I think I would use a full-wave rectifier (so 4 diodes), not sure whether yours will work as expected actually :)
Quote from: niektb on June 01, 2020, 03:02:58 PM
0 ohm resistor or jumper doesnt really matter ;)
Deng bro, that is nót the nicest pcb drawing i've ever seen :o
You should check if the NE5532's and the jacks can actually be fitted physically on your bord...
I think I would use a full-wave rectifier (so 4 diodes), not sure whether yours will work as expected actually :)
You realize you are looking at both sides at once, right? Pots go on one side, ICs on the other...
I agree it is not my best board, but it is not THAT bad...
Jacks and double gang pots go offboard, by the way. And yes, I got plenty of space. It is all checked.
As for the rectifiers, I had them, but took them out as a result of this board using AC. I could use them in V+ and V-, but that will depend on how the breadboard works.
QuoteI am having a real hard time getting Eagle to separate the 12VAC2 from GND, because, to Eagle, they are directly connected and thus are the same thing. In the schematics, it does not really matter, but when doing the board, it is a REAL PITA! So I added a 0 Ohm resistor to dived the segments... I can use it or use a jumper in the final build.
That's a normal problem. You shouldn't really add a 0R just to get around that. Yes, is does break the two NETs but there's no real reason circuit-wise to add that 0R resistor. I'd just use the GND for that TX wire and leave it. Use separate text to label the connector.
In your updated schematic you have a new problem the AC input at the diodes is shorted to the AC input to ground. Follow the original schematic and you will see what I mean.
Also R2 (to LED2) should go to C5.
Quote from: rankot on May 22, 2020, 02:53:15 AM
It is also better to have regulated power supply with linear regulators.
Quote from: niektb on June 01, 2020, 03:02:58 PM
I think I would use a full-wave rectifier (so 4 diodes), not sure whether yours will work as expected actually :)
You know, I do have some W01G 100V 1.5A rectifiers... should I go in that direction?
I think I will try it on the breadboard as it is and see what's what. After all, it is almost ready to try (of course, i need to wait for the power source, and I am using 47K resistors instead of the dual gang pots).
(https://i.postimg.cc/bwV77mXY/20200601_211913.jpg)
But let me know your ideas.
Quote from: Rob Strand on June 01, 2020, 10:19:30 PM
That's a normal problem. You shouldn't really add a 0R just to get around that. Yes, is does break the two NETs but there's no real reason circuit-wise to add that 0R resistor. I'd just use the GND for that TX wire and leave it. Use separate text to label the connector.
I tried, but when making it to the board, instead of having the ground plane be ground, it was V- or 12VAC. This is the only way I managed to get it to work. I can always just put a jumper there, but this is the only solution I had to make the board work...
Quote from: Rob Strand on June 01, 2020, 10:19:30 PMIn your updated schematic you have a new problem the AC input at the diodes is shorted to the AC input to ground. Follow the original schematic and you will see what I mean.
Also R2 (to LED2) should go to C5.
I see what you mean. The LED original circuit threw me off there. I kept the same connections, but without a diode and a resistor, I guess it works different! :D
This is the latest schematic incorporating the solutions mentioned. Correct me if I misunderstood your meaning, please!
(https://i.postimg.cc/7ZTvygqg/PAi-A-9303-4-Band-EQ.png)
And here is the board with the corrections of the schematic:
(https://i.postimg.cc/dtfMXWcs/NEW-BOARD.jpg)
I also corrected the breadboard, as it had that same short...
QuoteI can always just put a jumper there, but this is the only solution I had to make the board work...
It's more to do with the software than an electronics problem.
Quote
Correct me if I misunderstood your meaning, please!
All looks good.
Some bigger picture issues are:
- Do you want to add some input and output coupling caps?
- Also are you happy with the fairly low input impedance? If you plug a guitar or bass into that circuit directly it will load the pickups.
Educate me a little here..
Quote from: Rob Strand on June 01, 2020, 11:38:33 PM
Some bigger picture issues are:
- Do you want to add some input and output coupling caps?
These are the caps we put at the input and output to filter the signal, right? Blocking DC and allowing AC to pass (at the cost of low frequency). Is that right?
What is the upside and downside of using them vs not using them for this application (voice mostly)?
Quote from: Rob Strand on June 01, 2020, 11:38:33 PM
- Also are you happy with the fairly low input impedance? If you plug a guitar or bass into that circuit directly it will load the pickups.
What do you mean by "loading up the pickups"? I intend to use this mostly for voice (microphone in any case). Chain will be Mic to PreAmp to Compresor to EQ (this pedal) to Audio Interphase (or mixer console if live).
Now, if I can make it switchable (increase impedance with a toggle) then that woult be an interesting addition... then I have the option to use it for guitar! But I have no clue how to do that.
QuoteThese are the caps we put at the input and output to filter the signal, right? Blocking DC and allowing AC to pass (at the cost of low frequency). Is that right?
What is the upside and downside of using them vs not using them for this application (voice mostly)?
The goal is more about blocking DC than cutting low-frequencies. Ideally you want to choose large enough capacitors so the signal is unaffected.
Why you would put them in is more of a bigger picture view of reducing problems in different scenario's. In an ideal scenario you could leave them out and the equalizer will still work. An example of non-ideal scenario is you connect it to another device, where someone has left out the very same caps, or the caps are faulty, and there is DC on the output. When you connect that device to an EQ with no input caps the DC feeds into the EQ and that could reduce the headroom of the equalizer and cause unexplained early clipping. Another scenario you connect it to a faulty device and the DC output from that devices blows up parts in your device. If all devices use input and output caps it reduces the risk of weird stuff happening.
QuoteWhat do you mean by "loading up the pickups"? I intend to use this mostly for voice (microphone in any case). Chain will be Mic to PreAmp to Compresor to EQ (this pedal) to Audio Interphase (or mixer console if live).
Earlier on you mentioned you might use it with an instrument. In the case where you connect the instrument directly to the EQ the low input impedance of the EQ will load down the pickup. As is the EQ is more of a 'line level' device as opposed to an instrument compatible device (like an EQ pedal).
In order to make it an instrument compatible device you need to add a buffer to the front end. You get the idea for the input buffer from section "A" on this schematic, although I'd probably make the 470k's higher. Notice the input stage here has an AC coupling cap. The resistor across the input stops "pops" when you connect it to another devices.
https://www.schematics.com/site_media/media/project/previews/55855-preview2x.png
The output side of this circuit in section "B". This circuit has an additional opamp, which you don't need. The things to take note of are: the resistor in series with the output of the opamp, which helps stop the opamp oscillating when connected to cables, and the capacitor and resistor to ground which provide the AC coupling at the output.
If you hunt around on the web you will see a lot of circuits which use the same ideas for the input and output stages.
Quote from: jfrabat on June 01, 2020, 06:26:31 PM
You realize you are looking at both sides at once, right? Pots go on one side, ICs on the other...
I agree it is not my best board, but it is not THAT bad...
Jacks and double gang pots go offboard, by the way. And yes, I got plenty of space. It is all checked.
As for the rectifiers, I had them, but took them out as a result of this board using AC. I could use them in V+ and V-, but that will depend on how the breadboard works.
Yes I totally noticed that but depending on the pots, you might not have space for the opamp pins on the other side... But if you're sure about that, then it's okay :)
I think the biggest thing that's bugging me is your routing. It's much neater if you use only angles of 45 degrees (and you should totally avoid angles of 90 degrees and higher, especially when using high-speed signals, as it degrades your signal :))
If your board is using AC then you need something that rectifies right? (using a special rectifier or 4 diodes doesn't really differ a whole lot but a special rectifier can often handle more current/voltage)
Quote from: Rob Strand on June 02, 2020, 03:03:08 AM
The goal is more about blocking DC than cutting low-frequencies. Ideally you want to choose large enough capacitors so the signal is unaffected.
Why you would put them in is more of a bigger picture view of reducing problems in different scenario's. In an ideal scenario you could leave them out and the equalizer will still work. An example of non-ideal scenario is you connect it to another device, where someone has left out the very same caps, or the caps are faulty, and there is DC on the output. When you connect that device to an EQ with no input caps the DC feeds into the EQ and that could reduce the headroom of the equalizer and cause unexplained early clipping. Another scenario you connect it to a faulty device and the DC output from that devices blows up parts in your device. If all devices use input and output caps it reduces the risk of weird stuff happening.
So it seems like a good idea to add them. Is there any downside to adding them? How big should I go?
Quote from: Rob Strand on June 02, 2020, 03:03:08 AM
Earlier on you mentioned you might use it with an instrument. In the case where you connect the instrument directly to the EQ the low input impedance of the EQ will load down the pickup. As is the EQ is more of a 'line level' device as opposed to an instrument compatible device (like an EQ pedal).
If I do increase impedance, will it affect using it as a line level device? That is the part I am not sure of. If it has no negative effect, then I prefer to increase the impedance and be able to use it for guitars as well. But if it does, then I will leave it as is, as the main purpose is to use it on a line coming from a Mic (after the preamp and compressor).
Quote from: Rob Strand on June 02, 2020, 03:03:08 AMIn order to make it an instrument compatible device you need to add a buffer to the front end. You get the idea for the input buffer from section "A" on this schematic, although I'd probably make the 470k's higher. Notice the input stage here has an AC coupling cap. The resistor across the input stops "pops" when you connect it to another devices.
https://www.schematics.com/site_media/media/project/previews/55855-preview2x.png
The output side of this circuit in section "B". This circuit has an additional opamp, which you don't need. The things to take note of are: the resistor in series with the output of the opamp, which helps stop the opamp oscillating when connected to cables, and the capacitor and resistor to ground which provide the AC coupling at the output.
If you hunt around on the web you will see a lot of circuits which use the same ideas for the input and output stages.
If my previous knowledge is correct, the buffer would be R2, R3, R4 and C1 (input), right? I can't find the output one... (by the way, there are 4 sections A and 4 section B)
Quote from: niektb on June 02, 2020, 03:06:27 AM
Yes I totally noticed that but depending on the pots, you might not have space for the opamp pins on the other side... But if you're sure about that, then it's okay :)
Then it is OK. I measured it and it works out.
Quote from: niektb on June 02, 2020, 03:06:27 AM
I think the biggest thing that's bugging me is your routing. It's much neater if you use only angles of 45 degrees (and you should totally avoid angles of 90 degrees and higher, especially when using high-speed signals, as it degrades your signal :))
OK, I took your advice. I re-routed the board. Here is the new board:
(https://i.postimg.cc/FzNkbcQM/NEW-BOARD.jpg)
Still not pretty, but better. I took out all the weird angles in the traces.
Quote from: niektb on June 02, 2020, 03:06:27 AM
If your board is using AC then you need something that rectifies right? (using a special rectifier or 4 diodes doesn't really differ a whole lot but a special rectifier can often handle more current/voltage)
The original drawing uses the diodes and caps for that. I tried "improving" it with rectifiers, but I ended up screwing up the circuit. So I went back to the original.
By the way, I just noticed I made the resistor size a little too small in Eagle (physical size). I have 3 options:
1. Delete all resistors and replace them with the correct size (best option, but time consuming)
2. Squeeze the 1/4W 7mm long resistors into holes 5mm apart
3. Use 1/8W resistors (which I have)
Would 1/8W be enough for this pedal? Technically, it drains 100mAh, so 1/10W should be enough, right? To be honest, I am leaning towards #2 because I do not want to waste all the resistors I already got on the breadboard (I would save them, of course, but they will be out of the carton holder, so they would easily get misplaced). Everything else checks out size wise.
Sorry about the A/B thing. It's a bit weird the way they have marked the opamp segments as large A's and B's outside of the opamp. So what they means is U1A and U1B.
QuoteSo it seems like a good idea to add them. Is there any downside to adding them? How big should I go?
QuoteIf I do increase impedance, will it affect using it as a line level device? That is the part I am not sure of. If it has no negative effect, then I prefer to increase the impedance and be able to use it for guitars as well. But if it does, then I will leave it as is, as the main purpose is to use it on a line coming from a Mic (after the preamp and compressor).
No real downside, other than adding more parts. You could argue adding a buffer adds a bit of noise, but really with so many opamps in the circuit it's not going to be noticeable.
Adding a buffer will have little effect on the line-level.
For the schematic link I posted:
For the input, add buffer U1A use say: R2=2M2, C1=100nF, R3 =2k2, R4=1M
For the output, around U14B, use say R59=100 ohm, C18 = 10uF to 47uF is fine, R60=100k.
The values are not absolutely critical.
Even without the buffer a circuit with so many opamps will add noise, especially for the instrument case. The way that is combated is using pre-emphasis and de-emphasis circuits. Take a look at the Boss GE-7 schematic for example. For the mic case you have a preamp so it's going to boost the signal and help the signal to noise. For line-level signals you don't really need pre-emphasis and de-emphasis.
QuoteIf my previous knowledge is correct, the buffer would be R2, R3, R4 and C1 (input), right? I can't find the output one... (by the way, there are 4 sections A and 4 section B)
That's correct.
The thing to realize about all this is you can just take a circuit and built it, or, you can tweak it. However, when you tweak it you have to make design decisions and that means thinking about a whole lot of stuff you might not have considered, or even known about.
Quote1. Delete all resistors and replace them with the correct size (best option, but time consuming)
That's probably the right thing to do but it's a total pain in the butt. Options 2 and 3 are up to you.
QuoteWould 1/8W be enough for this pedal? Technically, it drains 100mAh, so 1/10W should be enough, right? To be honest, I am leaning towards #2 because I do not want to waste all the resistors I already got on the breadboard (I would save them, of course, but they will be out of the carton holder, so they would easily get misplaced). Everything else checks out size wise.
For modern LEDs resistors R1 and R2 at going to be too low and will make the LED too bright. You could probably use 4.7k resistors there. The 330Rs are going to get hot but the 4.7k's will not.
The power supply resistors R3, R4 would be best left at 1/4W (maybe even 1/2 W to handle turn-on peaks).
Quote from: Rob Strand on June 03, 2020, 07:43:08 PM
No real downside, other than adding more parts. You could argue adding a buffer adds a bit of noise, but really with so many opamps in the circuit it's not going to be noticeable.
Adding a buffer will have little effect on the line-level.
Sold! Buffer is going in.
Quote from: Rob Strand on June 03, 2020, 07:43:08 PM
For the schematic link I posted:
For the input, add buffer U1A use say: R2=2M2, C1=100nF, R3 =2k2, R4=1M
For the output, around U14B, use say R59=100 ohm, C18 = 10uF to 47uF is fine, R60=100k.
The values are not absolutely critical.
So, Something along these lines then?
(https://i.postimg.cc/LsgqDcVz/PAi-A-9303-4-Band-EQ.png)
Quote from: Rob Strand on June 03, 2020, 07:43:08 PM
Even without the buffer a circuit with so many opamps will add noise, especially for the instrument case. The way that is combated is using pre-emphasis and de-emphasis circuits. Take a look at the Boss GE-7 schematic for example. For the mic case you have a preamp so it's going to boost the signal and help the signal to noise. For line-level signals you don't really need pre-emphasis and de-emphasis.
Quote1. Delete all resistors and replace them with the correct size (best option, but time consuming)
That's probably the right thing to do but it's a total pain in the butt. Options 2 and 3 are up to you.
QuoteWould 1/8W be enough for this pedal? Technically, it drains 100mAh, so 1/10W should be enough, right? To be honest, I am leaning towards #2 because I do not want to waste all the resistors I already got on the breadboard (I would save them, of course, but they will be out of the carton holder, so they would easily get misplaced). Everything else checks out size wise.
For modern LEDs resistors R1 and R2 at going to be too low and will make the LED too bright. You could probably use 4.7k resistors there. The 330Rs are going to get hot but the 4.7k's will not.
The power supply resistors R3, R4 would be best left at 1/4W (maybe even 1/2 W to handle turn-on peaks).
Since I am adding the buffer, I will need to reroute anyway, so I deleted the resistors and added 2 more mm of spacing so that the 1/4W resistors fit fine. Already cutting it close on the cap voltages, so I don't want to gamble with the resistors as well. I will get to work on the board once I know the schematic is correct (Hint, hint! Waiting for you! LOL!). For CLR, I will start at 4.7K on the breadboard, and work from there.
Quote
So, Something along these lines then?
That's just about it.
You don't need to add U1B. The output can come off IC5B.
Just move R41, C2, R42 to the output of IC5B.
So, the changes would be, including shuffling the part designations down,
- Remove IC1B, R39, R40
- Make R27 100R
- Connect C2 to R27. Note: need to make C2 a larger value 10uF to 47uF
- Connect 100k (call it R39) from C2 to ground.
QuoteFor CLR, I will start at 4.7K on the breadboard, and work from there.
Sounds good. The LEDs brighness is easy to tweak.
Quote from: Rob Strand on June 04, 2020, 02:15:46 AM
- Connect C2 to R27. Note: need to make C2 a larger value 10uF to 47uF
So C2 will need to be electrolytic (the highest film I got is 1uF)? What would be the polarity then? Negative towards output?
So, we are talking about something along these lines?
(https://i.postimg.cc/ZnSYpc4m/PAi-A-9303-4-Band-EQ.png)
NOTE: I renumbered automatically based on the board layout, so numbers have changed form last schematic.
If that is so, I will modifiy the breadboard (power supply is on its way, by the way). Here is the board layout for that schematic:
(https://i.postimg.cc/526JHGLv/NEW-BOARD.jpg)
If it all checks out, I will get this board printed...
(https://i.postimg.cc/hjCM7C9z/Board-Mockup.jpg)
I know, I still got to polish the silk screens, but I am getting excited about this project!
QuoteSo, we are talking about something along these lines?
Yes, looks good.
QuoteSo C2 will need to be electrolytic (the highest film I got is 1uF)? What would be the polarity then? Negative towards output?
1uF is a bit small, I'd say that would be the smallest you would want to use in that position and I'd probably not go for a 1uF in that part of the circuit.
So the easiest solution is an electrolytic. You might see people complaining about putting electros in but really there's zillions of pieces of equipment with Electros on the output. The only only to do is make sure it's a large value to prevent the voltage on the cap increasing. Say 10uF to 47uF.
As for the polarity. In you case there is a 'more' correct orientation for the cap. Put the negative towards the opamp and positive towards the output.
The reason for cap having a correct orientation is:
- Opamp IC1A an NE5532 which has a transistor input stage which causes the output to sit at a negative voltage,
say -0.2V.
- the rest of the circuit is non-inverting overall so the output opamp ends up at -0.2V.
- so the conclusion is the -ve terminal on the cap is best connected to the opamp.
Here's more technical stuff making life difficult:
The reason why IC1A sits at a small negative voltage is because the opamp has transistors at the input. The base current of these transistors causes a voltage drop across the 1M input resistor. That voltage drops ends-up at the output of IC1A.
The best prevent the DC voltage is to no to use a NE5532 for IC1A. Use a JFET input opamp like a TL072. JFET input opamp do not pull current through the 1M resistor. If it were building it for myself I'd probably go that way.
The cons of have the DC voltage through the circuit is the boost/cut pots have more of a tendency to go scratchy. Each of the EQ stages inverts so it will have -0.2V on the input and +0.2V on the output; alternating in sign after each stage. So that means there's 0.4V across the EQ boost/cut pots. When the pot gets old that DC voltage flickers and you get scratchyness.
So if you wanted to keep the NE5532 *and* reduce pot potential scratchyness there are a number of options. The best would be to put another coupling cap between the output of IC1A and where R5, R6 and the first Boost/Cut pot join. You can reduce the offset by half by dropping the 1M to 470k but that's only reducing the problem. There's a few other ways but to be the best solution is to use a JFET input opamp like a TL072.
I do have TL072. I even have TL082, which I understand is more HiFi than the 072 (and also JFET). Should I drop the TL082 in there? In this case, keep polarity with negative towards output?
QuoteI do have TL072. I even have TL082, which I understand is more HiFi than the 072 (and also JFET). Should I drop the TL082 in there? In this case, keep polarity with negative towards output?
The TL072 is supposed to have better noise and the TL082 is a generic part (a little cheaper in the old days), in practice they seem close. It will work no problems.
The polarity of the caps shouldn't matter so much, negative to output is the default.
I will go with TL072 then.
By the way, I just got the power supply today. I plugged the breadboard in, but I am getting no signal. I did not have time to troubleshoot, but I did checked voltages. I am getting 13.8VAC at input, +8.65VDC at V+, -8.65VDC at V-, 0V at ground. So those all look good. I did find it odd that the LED connected to C6 is getting -17.65VDC... is that normal?
Tonight or tomorrow I will go through it with the audio probe to see what is going on with the signal.
Felipe
PS: I also got my FMR RNC 1773 and the Presonus TubePre V2 that will go before this in the signal chain. The RNC was supposedly not working; turns out, it will not work with a DC power supply, so I got a good deal on it! Just get a new $10 power supply, and PRESTO!
Almost ready to start some serious recording!
QuoteI am getting 13.8VAC at input, +8.65VDC at V+, -8.65VDC at V-, 0V at ground. So those all look good. I did find it odd that the LED connected to C6 is getting -17.65VDC... is that normal?
The 17.65V looks fine, 16V to 18V is very normal. The 8.65V looks a bit low. From experience I would have guessed the supply was about 12V. However, no need to guess, we can calculate what it should be.
Supply current:
Icc = 4 x [NE5532 current (both opamps) ] + [TL082 current (both opamp)]
Using typical values from the datasheets,
Icc = 4 x 8mA + 2 x 1.4mA = 34.8mA ; NE5532 species total current but TL082 specifies one opamp.
Expected voltage drop across 150 ohm,
Vdrop = 150 * 34.8mA = 5.22V
Expected opamp supply voltage,
Vcc = 17.65 - 5.22 = 12.4.V
If we look at the *maximum* current for the NE5532 it is 16mA; the max on the TL082 won't make a big difference.
Repeating, the calculations we get Icc = 66.8mA, Vdrop = 10V, Vcc = 7.65V
So typically we would have expected 12.4V, which seems very reasonable. However,
because of opamp tolerances we might see as low as 7.65V. Your 8.65V is in this range
so the opamps are in spec but they are on the high side of good and causing the
supply voltage to drop.
For a one-off build like this the solution is very simple, just reduce the 150ohms to about 100ohms.
That should give about 12V.
Quote
PS: I also got my FMR RNC 1773 and the Presonus TubePre V2 that will go before this in the signal chain. The RNC was supposedly not working; turns out, it will not work with a DC power supply, so I got a good deal on it! Just get a new $10 power supply, and PRESTO!
Very cool, sometimes you can be lucky.
Quote from: Rob Strand on June 09, 2020, 10:43:06 PM
The 17.65V looks fine, 16V to 18V is very normal. The 8.65V looks a bit low. From experience I would have guessed the supply was about 12V. However, no need to guess, we can calculate what it should be.
Supply current:
Icc = 4 x [NE5532 current (both opamps) ] + [TL082 current (both opamp)]
Using typical values from the datasheets,
Icc = 4 x 8mA + 2 x 1.4mA = 34.8mA ; NE5532 species total current but TL082 specifies one opamp.
Expected voltage drop across 150 ohm,
Vdrop = 150 * 34.8mA = 5.22V
Expected opamp supply voltage,
Vcc = 17.65 - 5.22 = 12.4.V
If we look at the *maximum* current for the NE5532 it is 16mA; the max on the TL082 won't make a big difference.
Repeating, the calculations we get Icc = 66.8mA, Vdrop = 10V, Vcc = 7.65V
So typically we would have expected 12.4V, which seems very reasonable. However,
because of opamp tolerances we might see as low as 7.65V. Your 8.65V is in this range
so the opamps are in spec but they are on the high side of good and causing the
supply voltage to drop.
For a one-off build like this the solution is very simple, just reduce the 150ohms to about 100ohms.
That should give about 12V.
I replaced the resistors. I am now at 12.87V (+ and -). Should I leave it there or increase resistance slightly to lower voltage closer to 12V?
As for the sound, I still have not had a chance to troubleshoot...
QuoteShould I leave it there or increase resistance slightly to lower voltage closer to 12V?
Absolutely fine at 12.87V.
Great! Will try to troubleshoot it tomorrow; we just finished a REALLY FRICKING LONG video conference! I am exhausted!
A couple of updates.
1. The old breadboard was working all the way to the 3rd band; I could control the frequencies up or down, and it was noticeable. There was an issue in the 4th band, but I decided to redo the whole breadboard on my larger breadboard, as the old one did not have the buffer, and space was so tight, troubleshooting was going to be an issue.
2. Since I had taken out the pedal I was working on in the large breadboard, I moved everything over, and included the buffer.
This is the new breadboard:
(https://i.postimg.cc/jdB7ztRP/20200612-121959.jpg)
As you can see, I am also using the dual gang pots (B100K) in this iteration, instead of the fixed resistors. And ignore the Cap number written in the power side of the caps; those were the old numbers... Oh, and I also changed to 10K the resistors in the last band's Wien Bridge to reach a bit higher fequency.
Here is the current schematic, for quick reference to the numbering:
(https://i.postimg.cc/bv3Ksznf/PAi-A-9303-4-Band-EQ.png)
In this new breadboard a couple of things came about, with which I need some help:
- Is it normal for R27 and R35 to get hot? Is this something I need to worry about?
- In order to more or less balance V+ and V-, this time I had to use different values in R27 and R35. My guess is that the switch (which I included) is changing the resistance; does that make sense? I am now getting +12.03V for V+ and -11.73V at V- (also note that I went with 120 and 91 Ohms in the Schematic, which is showing current values in the breadboard)
- Currently signal is not making it through the system; I have noticed (by using the audio probe and a line level signal) that the low end frequencies get filtered (a little more with each band) if I listen to the sound on Pin 1 of the cut/boost pots. But once I get to pin 7 of IC1, the sound is gone.
- Unlike the previous BB, my cut/boost pots are not cutting or boosting. My frequency select pots ARE working, but the cut/boost seems to be "stuck"
I am going to go over the entire BB once again matching it to the schematic. But I wanted to share where I am currently at.
I have to ask, since I feel kind of responsible for sucking you into this vortex-of-trouble, when it works does it do what you needed?
Yes, it does. And don't feel bad, I am actually happy to have gone this route. I am learning, and that is valuable. Plus, once I get this working, the sense of accomplishment will be even more valuable to me!
A couple of things up front. Make sure all opamps are getting power, both + and -. You should check the DC voltages on all opamp pins. They should all be less than 0.1V, probably less than 20mV.
If the DC voltages are wrong you need to sort that out first. If the DC voltages are out in an earlier band, say band 1, it will affect the DC voltages from that point on because the stages are DC coupled.
Quote1. The old breadboard was working all the way to the 3rd band; I could control the frequencies up or down, and it was noticeable. There was an issue in the 4th band,
It's possible your band-4 opamp had a problem and when you moved the circuit that opamp is now on band-1 and stopping everything.
QuoteIs it normal for R27 and R35 to get hot? Is this something I need to worry about?
Yes it is expected to get warm. Since your circuit is pulling twice the expected current it has made things a little worse.
QuoteIn order to more or less balance V+ and V-, this time I had to use different values in R27 and R35. My guess is that the switch (which I included) is changing the resistance; does that make sense? I am now getting +12.03V for V+ and -11.73V at V- (also note that I went with 120 and 91 Ohms in the Schematic, which is showing current values in the breadboard)
Doing that is fine.
QuoteCurrently signal is not making it through the system; I have noticed (by using the audio probe and a line level signal) that the low end frequencies get filtered (a little more with each band) if I listen to the sound on Pin 1 of the cut/boost pots. But once I get to pin 7 of IC1, the sound is gone.
Perhaps check the DC voltages first. They often show-up problems.
If you have wiring issue then obviously that's going to cause problems and doing a thorough check by eye certainly helps.
When you have a largish circuit like this sometimes it is useful to get one band working at a time. You do that by wiring the buffer to the input of each EQ stage (don't forget to disconnect the input of the EQ from the previous stage.) then wire the EQ stage output to the output jack.
Quote
Unlike the previous BB, my cut/boost pots are not cutting or boosting. My frequency select pots ARE working, but the cut/boost seems to be "stuck"
See how you go after checking the wiring. (I can't quite make out the wiring from the photo but when I first looked it looked like pins 1 and 3 are not going to the right place in all cases.)
You can try a few other things:
- disconnect the wipers of the boost/cut pots and see if the circuit comes to life.
Once you disconnect the boost/cut wipers the circuit should just pass signal.
- If you are really keen you can pull out the boost cut pots. The circuit will then just pass
signal as each stage looks like an inverter.
When you mentioned the supply voltages were low a few posts back I kind of assumed the unit was working. It is possible the extra current is because of a problem, or a faulty opamp. Extra current can also be caused by oscillations.
Went through the whole breadboard again. Found some errors, and corrected them (apparently, if you leave out some resistors, the pedal does not work as it should; who would have thought!). Anyway, if there are any other errors, I have not caught them. And I am still getting issues.
Now the signal is actually making it through, and bands 2, 3 and 4 are working as they should. But band 1 is not cutting or boosting. Also, if I turn the pot all the way up or down, it cuts the entire signal off very suddenly.
Here is a short video:
Now, mind you, the speaker I am using is the guitar amp, so forget about HiFi!! LOL!
So, in summary, everything is working as it should except Band 1's 2 issues:
- No cut/boost function
- Sound cutting at min and max (all audio signal)
Any ideas how to troubleshoot these 2 issues?
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
A couple of things up front. Make sure all opamps are getting power, both + and -. You should check the DC voltages on all opamp pins. They should all be less than 0.1V, probably less than 20mV.
If the DC voltages are wrong you need to sort that out first. If the DC voltages are out in an earlier band, say band 1, it will affect the DC voltages from that point on because the stages are DC coupled.
All OpAmps are gettingaround +11.75V and -11.75V. I will check Band 1's OpAmp in all the pins shortly.
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
It's possible your band-4 opamp had a problem and when you moved the circuit that opamp is now on band-1 and stopping everything.
I switched the pot, but did not think about switching the OpAmp... I will try with a new one.
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
Yes it is expected to get warm. Since your circuit is pulling twice the expected current it has made things a little worse.
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
Doing that is fine.
Good to know!
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
Perhaps check the DC voltages first. They often show-up problems.
If you have wiring issue then obviously that's going to cause problems and doing a thorough check by eye certainly helps.
When you have a largish circuit like this sometimes it is useful to get one band working at a time. You do that by wiring the buffer to the input of each EQ stage (don't forget to disconnect the input of the EQ from the previous stage.) then wire the EQ stage output to the output jack.
Will go over Band 1.
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
See how you go after checking the wiring. (I can't quite make out the wiring from the photo but when I first looked it looked like pins 1 and 3 are not going to the right place in all cases.)
You can try a few other things:
- disconnect the wipers of the boost/cut pots and see if the circuit comes to life.
Once you disconnect the boost/cut wipers the circuit should just pass signal.
- If you are really keen you can pull out the boost cut pots. The circuit will then just pass
signal as each stage looks like an inverter.
When you mentioned the supply voltages were low a few posts back I kind of assumed the unit was working. It is possible the extra current is because of a problem, or a faulty opamp. Extra current can also be caused by oscillations.
Let me try with the new OpAmp in Band 1, and we will see
Quote from: Rob Strand on June 12, 2020, 06:42:32 PM
When you mentioned the supply voltages were low a few posts back I kind of assumed the unit was working. It is possible the extra current is because of a problem, or a faulty opamp. Extra current can also be caused by oscillations.
When you are right, you are right...
Checked voltages of OpAmp for Band 1, and the first amplifier was reading around -10V all around (pins 1, 2 and 3). Replaced it, and now Band 1 works. Also, voltage is now up +13.6V for V+ and -13.5V for V-. I will replace the resistors to bring it down to 12V again.
QuoteChecked voltages of OpAmp for Band 1, and the first amplifier was reading around -10V all around (pins 1, 2 and 3). Replaced it, and now Band 1 works. Also, voltage is now up +13.6V for V+ and -13.5V for V-. I will replace the resistors to bring it down to 12V again.
I was just about to post something then you made a new post.
Good news indeed, well done!
My guess is 150ohm and 120ohm might do it.
Quote from: Rob Strand on June 12, 2020, 07:20:21 PM
QuoteChecked voltages of OpAmp for Band 1, and the first amplifier was reading around -10V all around (pins 1, 2 and 3). Replaced it, and now Band 1 works. Also, voltage is now up +13.6V for V+ and -13.5V for V-. I will replace the resistors to bring it down to 12V again.
I was just about to post something then you made a new post.
Good news indeed, well done!
My guess is 150ohm and 120ohm might do it.
I JUST finished with that same combo. +12.6V and -12.5V. All done!
THANKS TO ALL FOR THIS GREAT JOURNEY!
Now, time to send to have the boards made!!!
Very cool.
Just for the sake of documentation, here is the final schematic:
(https://i.postimg.cc/DfLTz97j/PAi-A-9303-4-Band-EQ.png)
And this is the board layout in Eagle:
(https://i.postimg.cc/2jc5Qpsz/NEW-BOARD.jpg)
Dual-gang pots, and all jacks are off board. Idea is to fit it in a Hammond 1590Q enclosure (in theory, it fits; will make sure once the boards arrive!).
And this is how the boards will look like:
(https://i.postimg.cc/hv5PcxLJ/Board-Prototype.png)
I just noticed the schematic has both A and B tapers for the Boost/Cut pots.
They should be B taper (Linear).
Quote from: Rob Strand on June 12, 2020, 11:30:24 PM
I just noticed the schematic has both A and B tapers for the Boost/Cut pots.
They should be B taper (Linear).
Absolutely! And they are in the BB. I will edit the schematic above to show it correctly. And actually, the dual-gang ones are A also (could not find W in dual gang)
Hi, guys. One last question about this. I built the PCB, and have the enclosure drying. A couple of things came out unexpectedly, but I managed to work all but one of those out.
1. My frequencies were in the opposite order (lows to the right, highs to the left), but I ended up flipping the board around to fix it (had to use a bit longer wires, but that is about it).
2. This also helped another issue; my switches were also backwards (up was down/bypass, down was off/engaged)
3. 1000uF caps were a little too tall for the enclosure, so I had to desolder them and use new ones but laying them out flat instead of sticking up. Problem solved!
4. Even though I downloaded the template from Mouser, turns out the 3PDP switch did not fit in the holes; I had to cut the switch leads and solder legs from components used in the board. It is not a pretty fix, but the switch is working, and it is soldered to the board! This, of course, led to the switch being a bit higher than intended (the legs I soldered are not PERFECTLY centeres!), so I had to do a similar mod (only no cutting) on the on/off switch so that it would be at the same height (pots I could get at the right height without extensions).
5. This is the one that is throwing me off... Everything is working, but if I boost to max the highs, and select the highest frequency, I get a high pitched tone coming out. It only happens in the last pot, and only at max boost with the highest frequencies. In the last Wein Bridge I used 10K instead of 12K resistors in the other 3; should I go back to 12K in the highest frequency?
Here is the board:
(https://i.postimg.cc/SNS2gJm3/20200701_173231.jpg)
I will post a pic of the finalized pedal once I finish it. Maybe even a video.
Nice work, and appreciate the ongoing followup.
I hope the two legs of C16 are not touching as they appear to be in the photo.
It is an optical illusion from the angle. They are about 1/4 inch apart (a bit less, but more than enough to not make contact)...
Quote5. This is the one that is throwing me off... Everything is working, but if I boost to max the highs, and select the highest frequency, I get a high pitched tone coming out. It only happens in the last pot, and only at max boost with the highest frequencies. In the last Wein Bridge I used 10K instead of 12K resistors in the other 3; should I go back to 12K in the highest frequency?
It's probably some marginal stability issue and the unit is oscillating. It could also be made worse if the input and output wires are not kept far enough apart.
There's a few common things that help. In weird cases they can make things worse.
Assuming the problem is only *caused* by the last stage:
1) The place to start would be to add 100pF across R7.
This is a very common fix for these problems, so if it works leave it at that.
2) Next would be to add a 100pF across R12. You can try it with and without the cap across R7.
I'm not 100% happy about this one if you don't need it.
Assuming the real problem is throughout the whole unit and is exposed by setting the boost pot to maximum:
3) Add 100pF across R7, R5, R9, R30
Again this isn't an uncommon configuration.
I'm hoping (1) is good enough and the other items are just things to try.
Quote from: Rob Strand on July 01, 2020, 11:34:39 PM
1) The place to start would be to add 100pF across R7.
This is a very common fix for these problems, so if it works leave it at that.
Just in parallel to R7?
Yes parallel.
You can see the same sort of thing used on the Boss MT-2 pedal,
(https://electricdruid.net/wp-content/uploads/2016/01/Parametric-Mid-tone-control.png)
(The 330R resistor could be helping but I wouldn't go that far at this point. Many working circuits don't have these.)
It did not work... Will try with the other options. Starting with 100pF across R7, R5, R9, R30...
QuoteWill try with the other options. Starting with 100pF across R7, R5, R9, R30...
Worth trying. In fact even if the caps across R7, R5, R9, R30 don't work it might be worth leaving them in for now as they help reduce secondary issues.
Another thing you can try for an overall problem is a 100pF across R29 (1M).
It's weird the prototype worked. Maybe the 10k on the last band was enough to push it over the edge.
Quote from: Rob Strand on July 01, 2020, 11:34:39 PM
It's probably some marginal stability issue and the unit is oscillating. It could also be made worse if the input and output wires are not kept far enough apart.
There's a few common things that help. In weird cases they can make things worse.
Assuming the problem is only *caused* by the last stage:
1) The place to start would be to add 100pF across R7.
This is a very common fix for these problems, so if it works leave it at that.
2) Next would be to add a 100pF across R12. You can try it with and without the cap across R7.
I'm not 100% happy about this one if you don't need it.
Assuming the real problem is throughout the whole unit and is exposed by setting the boost pot to maximum:
3) Add 100pF across R7, R5, R9, R30
Again this isn't an uncommon configuration.
I'm hoping (1) is good enough and the other items are just things to try.
Tried 1, 2 and 3... No change. I did decide to leave the caps in (well, not 2; that one I took out, but the others) for good measure, though. I also tried changing R4 and R22 to 12K, thinking that if I cut the top frequency, it would go away, but still same issue. It is not a HUGE issue, as I doubt I will be boosting the top frequency for either vocals or guitar, but it would be nice to have it working properly...
Quote from: Rob Strand on July 02, 2020, 12:03:28 AM
QuoteWill try with the other options. Starting with 100pF across R7, R5, R9, R30...
Worth trying. In fact even if the caps across R7, R5, R9, R30 don't work it might be worth leaving them in for now as they help reduce secondary issues.
Another thing you can try for an overall problem is a 100pF across R29 (1M).
It's weird the prototype worked. Maybe the 10k on the last band was enough to push it over the edge.
You know, I am not sure I tried max gain in highest frequency. So maybe it was there in the BB... And the breadboard had 10K resistors for that one. One difference I did notice when building the OCB is that R28 was 100 Ohm instead of 100K in the BB (I fixed that), but that change should not make this happen.
QuoteTried 1, 2 and 3... No change. I did decide to leave the caps in (well, not 2; that one I took out, but the others) for good measure, though. I also tried changing R4 and R22 to 12K, thinking that if I cut the top frequency, it would go away, but still same issue. It is not a HUGE issue, as I doubt I will be boosting the top frequency for either vocals or guitar, but it would be nice to have it working properly...
At least you gave it a shot.
QuoteYou know, I am not sure I tried max gain in highest frequency. So maybe it was there in the BB... And the breadboard had 10K resistors for that one. One difference I did notice when building the OCB is that R28 was 100 Ohm instead of 100K in the BB (I fixed that), but that change should not make this happen.
Well, it wouldn't hurt to try increasing R28 to 1k.
Another thing which can affect things is grounding the chassis of the pots.
It's seems like a tricky problem, where is the cause is a little deeper than the common problems.
If you are really keen you could try putting a TL072 in locations IC1 and/or IC2. The TL072's are a little less susceptible to weird oscillations that the NE5532's.
Quote from: Rob Strand on July 02, 2020, 01:01:45 AM
Well, it wouldn't hurt to try increasing R28 to 1k.
I already put everything in the enclosure, and it takes a little persuading to get the board to line up just right, so I think I will just leave it as is...
Quote from: Rob Strand on July 02, 2020, 01:01:45 AM
Another thing which can affect things is grounding the chassis of the pots.
If you are really keen you could try putting a TL072 in locations IC1 and/or IC2. The TL072's are a little less susceptible to weird oscillations that the NE5532's.
These I could try; the grounding of the chassis of the pots (the dual gang ones, at least) is simple enough without having to take the whole thing apart. Same with the chip change. I used the NE5532's because they are supposed to be cleaner than the TL072 (remember this is mainly for vocals, not guitar). Is my understanding correct?
By the way, here is the "final" (not really, because I need to change the knobs, and they have yet to arrive!) product working:
QuoteThese I could try; the grounding of the chassis of the pots (the dual gang ones, at least) is simple enough without having to take the whole thing apart.
I'm assuming the metal enclosure is connected to ground? If that's the case the pots should already be grounded.
QuoteI used the NE5532's because they are supposed to be cleaner than the TL072 (remember this is mainly for vocals, not guitar). Is my understanding correct?
If you don't clip the signal they should be pretty much the same. I used a lot of NE5532s for HiFi stuff but the idea is not to clip in the first place. When clipping they do have minor differences, perhaps very slightly in favor of the NE5532. If the TL072's fix the problem I'd be more inclined to go with them. After listening to the video I don't think that's the problem!
That oscillation sounds quite angry. I would fix it. It really sounds like outright oscillation. I suspect you might even be able to tune the pitch with the frequency pot. One possibility is frequency cap or frequency pot tolerances are causing the problem. The way some of those EQs work is they push the gains close to oscillation. That would be compensated for by:
- reducing R12 to 9.1k
- OR, increasing R21 to 51k
- OR perhaps increasing only R22 to 12k.
If you have a wrong resistor value or cap value on that band it could also cause that problem.
You could test the idea by adding a large resistor or pot in parallel with R12. Adjust the value until the oscillation goes away. Then measure the added resistor value with a multimeter. After after that just solder a fixed resistor of that value or slightly lower in parallel with R12.
When you measure the added resistor value it will give you a good idea how close the gain is to the point of oscillation. If it is quite low I'd really start looking hard for wrong part values.
Quote from: Rob Strand on July 03, 2020, 06:52:23 AM
I'm assuming the metal enclosure is connected to ground? If that's the case the pots should already be grounded.
Ah, good point. The input and output jacks should be grounding them anyway. And since the enclosure is not even painted (I just polished it a little), the contact should be pretty good.
Quote from: Rob Strand on July 03, 2020, 06:52:23 AM
If you don't clip the signal they should be pretty much the same. I used a lot of NE5532s for HiFi stuff but the idea is not to clip in the first place. When clipping they do have minor differences, perhaps very slightly in favor of the NE5532. If the TL072's fix the problem I'd be more inclined to go with them. After listening to the video I don't think that's the problem!
OK, I understand. I will keep the 5532s then.
Quote from: Rob Strand on July 03, 2020, 06:52:23 AMThat oscillation sounds quite angry. I would fix it. It really sounds like outright oscillation. I suspect you might even be able to tune the pitch with the frequency pot. One possibility is frequency cap or frequency pot tolerances are causing the problem. The way some of those EQs work is they push the gains close to oscillation. That would be compensated for by:
- reducing R12 to 9.1k
- OR, increasing R21 to 51k
- OR perhaps increasing only R22 to 12k.
Well, I measured caps and resistors prior to installing. Caps are within 1nF from spec, and resistors were also very close. At least the Wein bridge ones, anyway (those were the ones I measured).
Quote from: Rob Strand on July 03, 2020, 06:52:23 AMIf you have a wrong resistor value or cap value on that band it could also cause that problem.
You could test the idea by adding a large resistor or pot in parallel with R12. Adjust the value until the oscillation goes away. Then measure the added resistor value with a multimeter. After after that just solder a fixed resistor of that value or slightly lower in parallel with R12.
When you measure the added resistor value it will give you a good idea how close the gain is to the point of oscillation. If it is quite low I'd really start looking hard for wrong part values.
I will try increasing R12 and will report back. I may even go back to 10K in R4 and R22 (although, to be honest, the highest frequency is already pretty high, so it is not absolutely necessary)
Before replying, I decided to check all the resistors in the last stage; all measurements are taken with the resistors in the board (I know you are not supposed to measure with them in, but for simplicity sake I did it like that). Here is what we have:
R3: 6.6K (should be 10K) - Not in series, so not sure what it should read; color code correct (Brown, Black, Black, Red)
R4: 11.73K (should be 10K) - This one I replaced with 12K, but will bring back to 10K
R7: 6.65K (should be 10K) - Not in series, so not sure what it should read
R11: 98.1 (should be 100) - OK
R20: started at 7K and rises; waited until 14K and got bored, but it was still going up (should be 47K; color code matches R21, so it seems to be correct)
R21: 46.7K (should be 47K) - OK
R22: 9.87K (should be 10K) - OK
Here is R20 and R21:
(https://i.postimg.cc/jqw41HLm/20200703_114020.jpg)
Lost track what plan you are working to, but....
> R3: 6.6K (should be 10K)
I have not seen a -33% tolerance resistor since before I was born.
That sure smells like 10k with a 20k across it. You can't measure soldered-in resistors without studying everything they are connected to.
Quote from: PRR on July 03, 2020, 09:22:31 PM
Lost track what plan you are working to, but....
> R3: 6.6K (should be 10K)
I have not seen a -33% tolerance resistor since before I was born.
That sure smells like 10k with a 20k across it. You can't measure soldered-in resistors without studying everything they are connected to.
As I said, that circuit is not in series; it has other routes, so the resistance varies with a bunch of other resistors, so I wont even start to calculate. Besides, colo code is right...
Is that R20 soldered properly? From the photo it looks like the solder hasn't flowed into the hole completely. Sometimes that's no problem if it's well soldered on the bottom, but other times it indicates a bad joint.
QuoteThat sure smells like 10k with a 20k across it. You can't measure soldered-in resistors without studying everything they are connected to.
That one might make sense because the boost/cut pot and R7 appear in series.
Then you get the same effect when measuring R7, which also shows up in the measurements.
I had a look at how close the circuit is to creating a wein-bridge oscillator on its own:
As far as an oscillator goes U1B has a gain of 2, U1A has a gain of 1.21, then the Wien network should have a gain of 1/3. The total loop gain is 2 * 1.21 * (1/3) = 0.81. It would need to be about 1 for it to oscillate on its own.
A loop gain of 0.81 looks like it should have enough slack in it to fend off some degree of tolerances. If there was a wrong part then that's an obvious cause but the measurements don't look too bad. If the tolerance were way off in a worst-case combination it would struggle to get to a loop gain of 1. Under normal circumstances, the mis-tracking of the pot taper would be the most likely candidate for the gain to be off, perhaps helped along with capacitance tolerances.
One possible key point is the upper band only oscillates when the frequency pot is at the upper frequency settings. Please correct me if I am wrong here. If the band oscillates at the lower frequency setting and at maximum boost that would definitely point to a part value or other circuit issue. The fact it *only* occurs near at the upper frequency setting might mean the opamps are involved.
For the sake of sanity, I definitely think it is worthwhile at least trying a TL072 for U1. That would at least confirm the opamps are involved.
As far as a work around I can only suggest the tweaks I made in Reply#111. Note the idea of changing R22 to 12k is to leave R4 at 10k. What that does is reduces the loop gain a bit at the high frequency settings only, which should deter oscillations by a small amount. The other suggestions directly reduce the gain and are likely to be more successful.
Quote from: Rob Strand on July 05, 2020, 12:00:59 AM
QuoteThat sure smells like 10k with a 20k across it. You can't measure soldered-in resistors without studying everything they are connected to.
That one might make sense because the boost/cut pot and R7 appear in series.
Then you get the same effect when measuring R7, which also shows up in the measurements.
I am proud to have realized this on my own! I am finally learning here! :)
Quote from: Rob Strand on July 05, 2020, 12:00:59 AM
As far as an oscillator goes U1B has a gain of 2, U1A has a gain of 1.21, then the Wien network should have a gain of 1/3. The total loop gain is 2 * 1.21 * (1/3) = 0.81. It would need to be about 1 for it to oscillate on its own.
A loop gain of 0.81 looks like it should have enough slack in it to fend off some degree of tolerances.
Haven't learned THIS much yet, though! :o
Quote from: Rob Strand on July 05, 2020, 12:00:59 AM
One possible key point is the upper band only oscillates when the frequency pot is at the upper frequency settings. Please correct me if I am wrong here.
You are not; what you say is correct, it only oscillates with the frequency pot at max and the boost close to max (a hair before max, it starts oscillating). If the frequency pot is, say, ad the 12 o'clock position, and I go to max boost, there is no oscillation.
Quote from: Rob Strand on July 05, 2020, 12:00:59 AM
For the sake of sanity, I definitely think it is worthwhile at least trying a TL072 for U1. That would at least confirm the opamps are involved.
That is simple enough to do; I will give it a shot and report back.
Quote from: Rob Strand on July 05, 2020, 12:00:59 AM
For the sake of sanity, I definitely think it is worthwhile at least trying a TL072 for U1. That would at least confirm the opamps are involved.
Tried it, and no fixing the issue. The TL072 does exactly the same thing. So it is not the OpAmp. Must be something else. I also soldered all the suspicious resistors from the top, and still, no change.
Also, noticed something odd; when I connected it to my interface, the tone comes in even earlier; as soon as I boost even a little (while at max frequency), the shrill starts. Maybe I could just not hear it in the speaker, not sure...
QuoteTried it, and no fixing the issue. The TL072 does exactly the same thing. So it is not the OpAmp. Must be something else. I also soldered all the suspicious resistors from the top, and still, no change.
It was definitely worth trying.
QuoteAlso, noticed something odd; when I connected it to my interface, the tone comes in even earlier; as soon as I boost even a little (while at max frequency), the shrill starts. Maybe I could just not hear it in the speaker, not sure...
That's not good. Perhaps the load of the interface on the last opamp is making the oscillation come in earlier, or perhaps making it come in at a frequency you can now hear.
Given the load might be having an effect it might be worth increasing R27 (schematic on reply #77) from 100R to 1k.
I'm starting to run out of ideas. At this point, there's a couple of things I would probably try if it was my unit:
- Change the caps on say band #2 so the frequencies are the same as band #4. Band #2 is currently working and the idea is to see if there is some inherent problem with the design when frequencies are high.
- Built a single band on the bread-board and try to debug it.
It is still worth checking over the board, tracks, soldering. Maybe check the frequency pot is actually working and is soldered correctly. If one gang is broken it could cause this problem.
Decided to just leave it as it was... Except for the knobs. I will just work around the issue (it should not affect what I am trying to do). Here is the final version:
(https://i.postimg.cc/qvDk3Sn5/20200709_121442.jpg)
And installed in my PC with the other stuff:
(https://i.postimg.cc/hPr4SfGg/20200709_121638.jpg)
Very nice.
Now, since I feel some responsibility for pushing you in this direction, I have to ask: does it do what you wanted and needed it to do?
Yes, it does. If it where not for that high freq issue, it would have been as good as anything In2ould have been able to buy (for my needs) with the flexibility to use it also with my guitar!
Hello,
Very nice build / journey and result. After reading the whole thread, I have some questions.
Q1. What is the max current draw of such a circuit ? (PAIA's documentation states that the wall mount transformer must be min 100mA)
Q2. How "bad" would be the impact when using +/-9V instead of +/-12V (does it differ in a voice vs instrument context, is there a big risk of clipping) ?
Q3. If the headroom provided by a +/-12V power supply is required, Would it be possible / ok to power the NE532s using a 9VDC power supply with a (or multiple) charge pump(s) + inverter(s) ? (i.e. to obtain +18V with -9V virtual ground to have a "similar" headroom). What would be the best way to achieve this (If I'm not wrong, the TC1044SCPA is capable of providing 20mA, would it be possible to use N times a TC1044SCPA ? is there a better way to achieve this) ?
Q3. If using a 12VDC power supply, what would be the best (and cheapest) way to invert the voltage ? (I was thinking for instance about LT8331, but it's quite expensive ~8x the price of a TC1044SCPA)
Thanks a lot for your answers !
Michel
Quote from: kraal on July 14, 2020, 04:33:23 AM
Hello,
Very nice build / journey and result.
Thanks!
Quote from: kraal on July 14, 2020, 04:33:23 AM
Q1. What is the max current draw of such a circuit ? (PAIA's documentation states that the wall mount transformer must be min 100mA)
Not sure; did not measure it. I am using a 500 mAh power source, but I think the 100mAh would do fine.
Quote from: kraal on July 14, 2020, 04:33:23 AM
Q2. How "bad" would be the impact when using +/-9V instead of +/-12V (does it differ in a voice vs instrument context, is there a big risk of clipping) ?
Have not really tried it, but I would imagine you would loose headroom boost.
Quote from: kraal on July 14, 2020, 04:33:23 AM
Q3. If the headroom provided by a +/-12V power supply is required, Would it be possible / ok to power the NE532s using a 9VDC power supply with a (or multiple) charge pump(s) + inverter(s) ? (i.e. to obtain +18V with -9V virtual ground to have a "similar" headroom). What would be the best way to achieve this (If I'm not wrong, the TC1044SCPA is capable of providing 20mA, would it be possible to use N times a TC1044SCPA ? is there a better way to achieve this) ?
Here you are going above my knowledge... not sure what would happen, to be honest.
Quote from: kraal on July 14, 2020, 04:33:23 AM
Q4. If using a 12VDC power supply, what would be the best (and cheapest) way to invert the voltage ? (I was thinking for instance about LT8331, but it's quite expensive ~8x the price of a TC1044SCPA)
Same here... Sorry I could not be more helpful!
Quote from: kraal on July 14, 2020, 04:33:23 AM
Q3. If the headroom provided by a +/-12V power supply is required, Would it be possible / ok to power the NE532s using a 9VDC power supply with a (or multiple) charge pump(s) + inverter(s) ? (i.e. to obtain +18V with -9V virtual ground to have a "similar" headroom). What would be the best way to achieve this (If I'm not wrong, the TC1044SCPA is capable of providing 20mA, would it be possible to use N times a TC1044SCPA ? is there a better way to achieve this) ?
By adding series-pass transistors should be more space/cost efficient configuration..
(in case of a V
BE (+/-) loss in headroom should be acceptable, of course..)
Just wanted to update you guys; my daughter (who recently got a PC in her room) wanted to make her own recording setup. She bought an interface, but she wanted some more gear (you know, cause daddy can make it!). So I decided to make her (among other things) a copy of this EQ (I had 2 boards of it laying around, because the minimum order is 3). Anyway, I just finished populating the board (only the LEDs are missing), and lo and behold, this one does not have that high frequency oscillation that the original one has. So it is certainly an issue with one (or more) component(s) in the original build rather than a design issue.
Now with the new board, I will go measure component by component and compare (with pots all the way down in both cases so that I know it is the same) and see if I can find the culprit.
Quotethis one does not have that high frequency oscillation that the original one has. So it is certainly an issue with one (or more) component(s) in the original build rather than a design issue.
Good to know.
Quote from: jfrabat on August 19, 2020, 04:55:18 PM
Just wanted to update you guys; my daughter (who recently got a PC in her room) wanted to make her own recording setup. She bought an interface, but she wanted some more gear (you know, cause daddy can make it!). So I decided to make her (among other things) a copy of this EQ (I had 2 boards of it laying around, because the minimum order is 3). Anyway, I just finished populating the board (only the LEDs are missing), and lo and behold, this one does not have that high frequency oscillation that the original one has. So it is certainly an issue with one (or more) component(s) in the original build rather than a design issue.
Now with the new board, I will go measure component by component and compare (with pots all the way down in both cases so that I know it is the same) and see if I can find the culprit.
Swap yours with hers... assuming her box is the same as yours... :icon_lol:
Jokes aside, its always good to see people do a one-try success in pcb populating etc. ;D
Quote from: 11-90-an on August 19, 2020, 11:55:18 PM
Swap yours with hers... assuming her box is the same as yours... :icon_lol:
I am sorry... Did I leave any doubts that my intention was to swap them? :D :D :D
Quote from: 11-90-an on August 19, 2020, 11:55:18 PM
Jokes aside, its always good to see people do a one-try success in pcb populating etc. ;D
Well.... SORT OF! LOL! You see, I had marked the pots (cut/boost) as A10K in the schematics, so, obviously, I used A10K pots... And, OF COURSE, I had swapped them out for B10K pots in the original. So now parity is at about 70% turn. I am still debating if I will remove the pots and replace them (probably will)... but not right now. I am tired! I feel so dumb for pulling that little stunt! Oh, and did I mentioned I only got 2 B10K pots in my stash? In the words of a famous philosopher (Homer Simpson), "DOH!"
New update; since I had to order the pots (B10K), and shipping is expensive, I figured, the right thing to do would be to order MORE stuff so that the shipping makes sense, right? Sounds like a logical plan, right? (For some reason, my wife thinks it does not; cannot see why she feels that way! LOL!) ANYWAY, as some of you know, I am making myself a compressor (https://www.diystompboxes.com/smfforum/index.php?topic=125167.0), for which I had already purchased some parts... But both the compressor and the interface have a frontal panel, and my EQ has a top panel. It just does not match! SO, since I had an extra board for the EQ laying around (3 unit minimum order and all that jazz), I ordered myself some additional Hammond 1402B enclosures (https://www.hammfg.com/part/1402b) so that I can have the compressor and the EQ in matching cases with frontal panels on both (which makes A LOT more sense considering where they are located on my desk!).
So I started building my pedal while I wait for the enclosure. This is it so far:
(https://i.postimg.cc/dVF32vh3/20200823_123436.jpg)
As you can see, I had to drill 3 holes at the corners that had space for the holes to mount the board to the new case (no pots to hang from on this one!) that I will use nylon mounts (which I already have) to attach to the bottom plate of the enclosure to keep it from rattling about or shorting out the bottom of the board. As for how the front panel will look like, it will be something along these lines (ignore the colors; those are just layers in AutoCAD):
(https://i.postimg.cc/rwQK93Xk/Front-Panel.jpg)
I will carry on the idea of having different color knobs for each band, as will the compressor, which will have different color knobs for the compressor controls and the gate controls, but, unlike the original on top, I will be using smaller anodized aluminum knobs of these, as they make more sense size-wise. And as you can see, deign-wise, it will be a nice match to the compressor:
(https://i.postimg.cc/VNxZZ7n7/Front-Panel.jpg)
I also ordered a DP-1010 Mic Preamp Kit (http://micpreampkit.com/) from Fivefish Audio and the vented version of the enclosure (the Hammond 1402BV enclosure (https://www.hammfg.com/part/1402bv)) so that it will all match. In fact, I will have an additional non-vented enclosure, and the idea is that if the compressor works well, I will make myself 2 compressors and chain them for smoother compression. The FMR Audio RNC1773 I have uses 4 when using the Super Nice mode, and I like that a lot (that compressor would be given to my daughter for her recordings, along with the PreSonus TubePre V2 I currently use).
Oh, and the name changed from 4TWEQ to 4 TweEQ at the suggestion of my wife (she says 4TWEQ sounds more like 4TWECK and that makes no sense).
Looks impressive!
What's the final schematic for this?
Quote from: rankot on August 24, 2020, 05:09:55 AM
Looks impressive!
What's the final schematic for this?
Quote from: jfrabat on June 12, 2020, 10:54:25 PM
Just for the sake of documentation, here is the final schematic:
(https://i.postimg.cc/DfLTz97j/PAi-A-9303-4-Band-EQ.png)
Just use B10K pots instead of the A10K pots listed and B100K pots instead of A100K pots.
Thanks!
Not sure how I manage it, but I do! I built the 2 other boards for this project, and each has different issues from the other! LOL! On the one in the Hammond 1590Q case, band #3 is not working. On the one in the Hammond 1402D case, nothing is working right!
I am starting troubleshooting them now, but it is frustrating how I manage this!
Here is how the 1402D case looks like, by the way:
(https://i.postimg.cc/Y25ZyDhs/20200831_163824.jpg)
Now, I just noticed that I wired ALL the pots backwards, so I have to fix that, but I think there is more troubleshooting in store after, as it currently sounds like the frequencies got both cut and boosted at the same time (if that makes sense). But I will start by wiring the pots the correct way and work up from there... Oh, and I messed up a pad to the bypass switch, so I had to wire the input wire directly (so at least bypass now works!).
The 1590Q one I already damaged the finish (almost identical to the original, but brushed aluminum instead of polished and changed the word TwEQ for TweEQ). So, 3 exact boards built, and 3 different issues! Tomorrow I will re-solder the pots of the 1402D, then move to the other pedal to try to get band 3 working properly (at least this one is not oscillating in band 4!). After that, it is back to the 1402D one... The original I will leave as a memento, as it has that oscillation, and I only got 2 12VAC power supplies!
I'm ashamed to say that I've not been following this thread as closely as I might, but this . . .
(https://i.postimg.cc/Y25ZyDhs/20200831_163824.jpg)
. . . is eye-poppingly incredible! Top work, Felipe. Well done. :icon_cool:
Quote from: bluebunny on September 01, 2020, 03:54:10 AM
I'm ashamed to say that I've not been following this thread as closely as I might, but this . . .
(https://i.postimg.cc/Y25ZyDhs/20200831_163824.jpg)
. . . is eye-poppingly incredible! Top work, Felipe. Well done. :icon_cool:
Thanks, but top work will be when it actually works! (It will, but I need tontrouble shoot it!) As of now, it is just a pretty but expensive paper weight! But it will look really cool once all the studio harware (compressor, de-esser and 2 preamps) are finished with a similar finish and the same type of enclosure. The compressor is next... PCB just got manufactured and is on its way. I also got one of the preamps half built (waiting for some parts to arrive).
I will post a pic of the other version of the EQ as well (the one I am making for my daughter).
The brushed aluminum makes it look a lot nicer.
But, Lordy, those enclosures are pricey! Is there a source for, shall we say, less "pedigreed" 1/3-1/2 rack size enclosures?
Quote from: Ben N on September 01, 2020, 09:13:59 AM
But, Lordy, those enclosures are pricey! Is there a source for, shall we say, less "pedigreed" 1/3-1/2 rack size enclosures?
They are. I was looking for 1/3 or 1/2U, but did not find any, so if you do, let me know!!!
Now, (AS USUAL!) I need some help figuring out what the heck I did...
Of the 2 pedals, the 1590Q is working fine now (I had a small short in band 3 that has been corrected). I am very proud of myself for finding that one on my own; I am getting better at this!
As you can see, no issues with oscillation in any of the 4 bands. Of course, the 2 gang pots being Audio taper, the frequency sweep is a bit of a thing, but it works fine.
Here is the pic of that one:
(https://i.postimg.cc/25Cz2Vhc/20200901_150957.jpg)
As you can see, there is a lot of damage to the sticker from taking this thing apart so many times! You may also notice it is the same design as the original, but I went with brushed aluminum look instead of polished, and the name was tweaked (pun totally intended!) to sound better.
So, the 1590Q is officially finished.
The 1402B, however, is not! AND I NEED HELP! I AM STUMPED!!!It is exactly the same board (print 3 out of 3), using the same components, except:
- Violet LED's instead of white
- CLRs increased resistance dim the LEDs a bit (my daughter wanted to spotlights; I told her I was going to adjust them, but she said no. Go figure!)
- Dual gang pots are A100K in the 1590Q and B100K in the 1402D
- 12K resistors are from a different batch (Mouser 5% in the 1402B and cheap Chinese Amazon 10% in the 1590Q)
Apart from that, the changes between the 2 are:
- Pots wired off board (all 8 in the 1402B, and only the dual gang in the 1590Q)
- AC Jack (they both use DC jacks, really, but the one in the 1402B is the smaller type while the one in the 1590Q is the one with the provision for a battery, which is not used obviously)
I did a comparison of values between the 2; here is the final circuit, so you can trace the values:
(https://i.postimg.cc/P5tsk1cH/eq.png)
And here are the values:
(https://i.postimg.cc/xTDfZxSF/IC-Measurements.png)
I also measured resistance. Normaly, I would not bother measuring resistance when everything is in the board, but since I have 2 identical boards, I figured it would make a good comparison. For this, I turned the pots all the way to the left (all 8 of them) to have a consistent reading in both EQs:
(https://i.postimg.cc/jdHxYHxq/REsistor-Measurements.png)
Here is a shot of the interior in case it helps:
(https://i.postimg.cc/WprFtJNC/20200901_172742.jpg)
Excuse the rats' nest! I tried to tidy things up a bit stuffing the extra cable under the board so that you can see clearly all the components...
Here are the symptoms of that one:
Any ideas on what to do will be greatly appreciated. Becasue I ran out of ideas. I did find some errors (like the dual gang pots being wired backwards, and the cut/boost ones being wired wrong), but I cannot dins anything else, and the problem persists! I imagine the issue is in the last band (AGAIN!), but I cannot narrow it down!