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DIY Stompboxes => Building your own stompbox => Topic started by: jfrabat on August 18, 2019, 10:08:59 AM

Title: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 18, 2019, 10:08:59 AM
Hey, guys.  I am looking to add Bass, Mids and Trebble control to a distortion/overdrive pedal I have (schematic below):

(https://i.postimg.cc/ydyy6Kng/Schematic.jpg)

How do you recommend I go about doing it?  3 filters with one pot each was my idea, but what do you think?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Mark Hammer on August 18, 2019, 11:27:09 AM
Do you want the tonal adjustments to change how the distortion occurs, or simply filter out what the clipping circuit provides?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 18, 2019, 11:53:48 AM
Hi Felipe,

the obvious question here is: are you sure you need a 3-band EQ? A reasonably good 2-band EQ is going to be more complicated than the whole rest of your circuit. 3-band is quite a bit more complex still. Tom has a good article on the Boss Metal Zone on his home page, which has a very flexible 3-band tone control with semiparametric mids (can be easily converted to non-parametric by changing 1 stereo pot to two resistors). See here:
https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

You could at that to the end of the electra distortion. If that really is what you want. I would instead suggest to go with a Big Muff style tone control with switchable mids and a buffer at the end. If the frequencies are chosen wisely, that is usually more useful than a full 3-band and A LOT simpler.

Cheers,
Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 18, 2019, 01:34:31 PM
Hi Felipe,

the obvious question here is: are you sure you need a 3-band EQ? A reasonably good 2-band EQ is going to be more complicated than the whole rest of your circuit. 3-band is quite a bit more complex still. Tom has a good article on the Boss Metal Zone on his home page, which has a very flexible 3-band tone control with semiparametric mids (can be easily converted to non-parametric by changing 1 stereo pot to two resistors). See here:
https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

You could at that to the end of the electra distortion. If that really is what you want. I would instead suggest to go with a Big Muff style tone control with switchable mids and a buffer at the end. If the frequencies are chosen wisely, that is usually more useful than a full 3-band and A LOT simpler.

Cheers,
Andy

Thanks, Andy.  Let me read it, and, if I understand it, breadboard it.  I was reading this (http://www.geofex.com/article_folders/eqs/paramet.htm) article, but I took about as much from it as if it would have been written in Chinese!  I did not understand ANYTHING!
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 18, 2019, 03:14:09 PM
Hi Filipe,

hmmm... R.G.'s article on EQs and gyrators is generally considered essential reading (and understanding) around these parts if you want to design an EQ that is more complex than the standard passive tone stacks. Here is a good online calculator with visualization for many different simple EQ types:
https://www.guitarscience.net/tsc/info.htm

My recommendation: Build a Big Muff tone stack and play with the values. See what you like and dislike about it. Then move on to a 2-band (like the James), do the same. If you still feel you need that third band,try a Fender or Marshall tone stack. If that still won't cut it, start thinking about gyrators and semi-parametric stuff.

After a passive tone stack and before the volume control, you will want a buffer. Without a buffer, the ton stack will interact with the volume control and not do what it is supposed to, depending on the volume setting. Here's a good resource:
http://www.muzique.com/lab/buffers.htm

Hope that helps,
Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Mark Hammer on August 18, 2019, 04:26:33 PM
Note that if the tone controls are active, that will require additional semiconductors, whether chips or transistors.  And if the controls are passive, there will be some signal loss, which will also require a gain-recovery stage.

That's one of the reasons why I ask whether you anticipate changing the tone before or after clipping (or maybe even both), since that will determine not only where any active stages are situated but also what form they take, and how complicated the final circuit would be.

The simplest possible configuration would be one in which you use a 3-position toggle to change the value of C1 and achieve different bass rolloffs before the clipping, and a second 3-position toggle to select caps placed in parallel with the clipping diodes and tame the treble.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: PRR on August 18, 2019, 04:31:20 PM
> add Bass, Mids and Trebble control

Always steal from the classics.
(https://i.postimg.cc/tYzTGfGp/jfrabat-14.gif) (https://postimg.cc/tYzTGfGp)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Mark Hammer on August 18, 2019, 06:16:20 PM
That will certainly "work", Paul.  But will it have any oomph to it unless gain and volume are dimed?  Most likely not.  I'm not saying it is inappropriate for this circuit, just insufficient.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 18, 2019, 09:14:53 PM
I am actually thinking of skipping the VOLUME pot, and go directly to a HIGH/LOW tone ontrlo from Boss:

(https://electricdruid.net/wp-content/uploads/2016/01/High-and-Low-tone-controls-1.png)

And then into a sweepable mid control:

(https://electricdruid.net/wp-content/uploads/2016/01/Parametric-Mid-tone-control.png)

Then the Volume pot  (would I need an output buffer?).  Let me see if I can draw it in eagle
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: pinkjimiphoton on August 18, 2019, 09:37:41 PM
check out barry's tonetwEQ circuit on guitarpcb.com nice useful versatile circuit, small foot print too if ya use his boards.
i use it a lot in dirt boxes these days if i need three band tone controls.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 19, 2019, 03:41:06 AM
I found in the tone twEQ an atttractive active 3-band equalizer project, but I didn't try it, yet.
I have a 2-band Baxandall tone stack board, (that I guess it's a good possibile 2-band eq for jfrabat in case he wants to do something easier), and bass and high work really fine.
About the tone twEQ, I'm still wondering how much is effective the mid control. I hope it works fine as well the other controls.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: pinkjimiphoton on August 19, 2019, 10:58:21 AM
i've built a bunch of them, standalone or in other projects, they work great. the mid control works fine, ya get +/- 15db i think.
if ya need more control, you could probably add a bigger mid pot, but it may change the slope of the eq some. i've used "Wrong" pots in a few of them, still seem to work well... 50k, 250k even 1m, tho at 1m it can oscillate some.

i use one of these sitting standalone on top of my amp, last thing in line as a buffer so i can tweak stuff without having to try n see the amp settings live. pretty groovy circuit.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 19, 2019, 01:32:46 PM
check out barry's tonetwEQ circuit on guitarpcb.com nice useful versatile circuit, small foot print too if ya use his boards.
i use it a lot in dirt boxes these days if i need three band tone controls.

Oh, I LIKE IT!!!  This is what I was looking for!  Do you typically use it before or after the gain stage?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Ben N on August 19, 2019, 02:02:02 PM
That's very similar to the tone stack in the JHS Angry Charlie v3, which comes after the distortion.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 19, 2019, 04:23:16 PM
So something like this should work, right?

(https://i.postimg.cc/ZYBcx4Dm/2019-08-19-3-20-PM-Office-Lens.jpg)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: pinkjimiphoton on August 19, 2019, 05:49:28 PM
i would use it after the distortion. depends on the circuit, like most things it will do different things depending on whether pre or post. it will drive the distortion harder before, but probably be more useful after.

in my applications, if i use it, i usually use it to replace tone stack stages, like in a big muff pi. works great.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 12:20:39 AM
Thats how its setup in the schematic above.  I am still new at this, so I took out what I think was the filter from from the Tone TwEQ diagram (the overdrive alreaady has one, right?) but I need someone with more knowledge than me to check it.

By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Anyway, let me know if this will work...  I intend tonstart breadboarding once I get back home Thursday!

Felipe
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 20, 2019, 07:29:29 AM
By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Input cap forms a high-pass filter together with Emitter resistor + emitter intrinsic resistor in parallel with 2M2 NFB resistor,  the later seen A+1 times lower, where A is individual stage gain.
Output cap makes exactly the same with OUT pot, in parallel with next effect input impedance..

If you make the respective calculations for both extreme low & high pots settings, you can verify (or not) if 68μF is adequate for the frequency band of your interest..
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 20, 2019, 08:15:33 AM
I love your drawing style, Felipe. That schematic is beautiful. :)

T.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 08:53:40 AM
I love your drawing style, Felipe. That schematic is beautiful. :)

T.

I will consider it beautiful if it actually works!   ;D

Input cap forms a high-pass filter together with Emitter resistor + emitter intrinsic resistor in parallel with 2M2 NFB resistor,  the later seen A+1 times lower, where A is individual stage gain.
Output cap makes exactly the same with OUT pot, in parallel with next effect input impedance..

You lost me here...  Noob issues...

If you make the respective calculations for both extreme low & high pots settings, you can verify (or not) if 68μF is adequate for the frequency band of your interest..

How do I do this?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: 287m on August 20, 2019, 10:20:06 AM
that drawing need voltage divider/bias for pin 3 and 5
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Ben N on August 20, 2019, 11:17:27 AM
... and Vcc to pin 8.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: pinkjimiphoton on August 20, 2019, 12:28:12 PM
Thats how its setup in the schematic above.  I am still new at this, so I took out what I think was the filter from from the Tone TwEQ diagram (the overdrive alreaady has one, right?) but I need someone with more knowledge than me to check it.

By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Anyway, let me know if this will work...  I intend tonstart breadboarding once I get back home Thursday!

Felipe

hey felipe, nice work, man.  68uF is really big to use for input and output caps. gonna let a lot of subharmonics thru that likely will just make it unstable, muddy, and prone to motorboating.

i think you mean 68nF, not uF. 68n/.068uF <same thing for our uses> is plenty for guitar. since you're gonna breadboard the circuit thursday, i'd suggest just trying different value caps til you like it.

generally anything from about 10n/.01uf to 4.7uF should be fine for the input filter of the fuzz part. you are right, since you already have an output cap on the fuzz, you can skip the input cap of the eq part of the circuit.

tonally, 4.7n input cap to the fuzz will make it a treble booster, as you climb the scale, it will get more and more dirty the bigger the cap is... more bass gets thru, more bass = more fuzz.  you can also limit the bass at the end of the circuit, too if needed.

i generally like about 47n-100n for input caps usually on most of the stuff i cobble together. or, google up faking a variable cap... in that case,  use a pot of 100k-250k or so and a small and a large cap... then you can vary the input capacitance and control the overdrive tone of the fuzz somewhat, and make it versatile enough to sound good from a rickenbacker to a les paul... just turn the knob to the sweet spot.

love to see peeps learning to roll their own like this. awesome job, brother. ;)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 03:15:13 PM
that drawing need voltage divider/bias for pin 3 and 5

... and Vcc to pin 8.

How do I do this?  Any advice?

i think you mean 68nF, not uF. 68n/.068uF <same thing for our uses> is plenty for guitar. since you're gonna breadboard the circuit thursday, i'd suggest just trying different value caps til you like it.

generally anything from about 10n/.01uf to 4.7uF should be fine for the input filter of the fuzz part. you are right, since you already have an output cap on the fuzz, you can skip the input cap of the eq part of the circuit.

I did mean 68nF...  Sorry!

Love to see peeps learning to roll their own like this. awesome job, brother. ;)

Thanks!  It is a lot easier to try and do stuff when help is just a post away, so thanks to all of you!
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Ben N on August 20, 2019, 04:52:46 PM
that drawing need voltage divider/bias for pin 3 and 5

... and Vcc to pin 8.

How do I do this?  Any advice?
Look at the power supply part of the Tone TwEQ schematic--the part that is connected to +9v. There is some filtering and a polarity protection diode hanging off the 9v line, and then a pair of 10k resistors to ground, with a tap off the junction of the two 10ks going to "Vb". That is your bias voltage, which is half of the main supply voltage, and it goes to the non-inverting inputs of the two opamps, pins 3 & 5 - just like it shows on the schematic.

You need a bias voltage because the opamp is designed for a bipolar supply, in which a positive voltage is connected to Pin 8, a corresponding negative voltage is connected to Pin 4, and the whole thing is referenced to ground through the non-inverting inputs 3 & 5 (in an inverting configuration). But we only have +9v, so we "fool" the opamp by treating the midway point between 0v and 9v as the reference (i.e., "ground"), and 0v as the "negative supply"--creating, in effect, a +/-4.5 volt bipolar supply around the artificial "ground" at +4.5 volts--the bias voltage. I hope this makes sense.

Pin 8 is the main supply (+9v) to the opamps, which is also shown on the schematic but a little less clearly. Between D1 and R11 in the bias supply (i.e. post filtering and polarity protection) there is a line down--that is the connection to Pin 8, and you will notice, there is also a connection from Pin 4 to ground. Pin 4 is the connection for the negative power supply, which, in our case, is 0 volts==true ground, as explained above.

You could just connect the power supply for the eq as drawn to the raw 9v power source, although you might be able to save some caps by combining the two power supplies for the drive and the eq.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: iainpunk on August 20, 2019, 05:42:15 PM
there were some wonky biasing mistakes in the drawink, i fixed it.
also, dont forget to hook up the power and ground for the opamps
(https://i.postimg.cc/n9KvcPF7/2019-08-19-3-20-PM-Office-Lens.jpg) (https://postimg.cc/n9KvcPF7)

EDIT: I MADE A MISTAKE AND OVERLOOKED THE FACT THAT THE SECOND OPAMP IS INVERTING, ONLY ADD THE CAPACITOR IN THE BOTTOM CIRCLE, NOT THE BIAS IN THE TOP CIRCUIT
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 08:55:04 PM
OK, I will redraw the circuit with the proposed changes so that we can review it.  But question; if I fix the voltage dividing / bias from the original Tone TwEQ, do I still add the bias corrections iainpunk is suggesting?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: PRR on August 20, 2019, 10:19:01 PM
> So something like this should work, right?

Where did you get those cap values? They all look 10X-100X too big.

Almost like you confused "n" for "u".

http://www.zen22142.zen.co.uk/Circuits/Audio/3bandton.gif

Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 10:37:14 PM
Almost like you confused "n" for "u".

I did; I mentioned that above...
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 20, 2019, 11:56:55 PM
OK, so if I understood everyone right, this is what I need to breadboard:

(https://i.postimg.cc/VvV4gn7w/20190820-215437.jpg)

Is this right?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 21, 2019, 01:48:15 AM
Is this right?

Nearly. You've lost the 100uF cap that you had on the Vb supply. That's important. It should go between Vb and ground.

Also Iainpunk corrected their original post - you *don't* need that 100K to Vb on the tone control circuit. Like he said, it's an inverting op-amp arrangement.

The cap values all look much better!
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 21, 2019, 05:43:51 AM
Also: your second opamp half has two non-inverting inputs. That's not a thing. You want the upper inputs in your schematic to be the inverting (-) and the lower ones to be the non-inverting (+) inputs. For both opamp halves.

Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 21, 2019, 05:56:06 AM
A rough (by heart) calculation says that 68nF Input cap sets HPF cut-off frequency at about 230Hz..
(with a, rough again, estimation of total input impedance of about 10k..)

If you want all guitar frequencies unaffected, raise about 10 times input cap value..
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 21, 2019, 07:37:32 AM
I have some questions becuase I want to use a Baxandall or a Tone TwEQ after a preamp.

1. The Active Baxandall layout and the Tone TwEQ has the 1M from input to ground (pulldown resistor). In the schematic drawn above that resistor has been omitted. Is it necessary or I can we omit it without any problem?
2. I'm using large 10uF input and output caps. Is the cap in front the TL072 be necessary non-polarized? I would like use a 10uF polarized there even there.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 21, 2019, 09:40:54 AM
1. The Active Baxandall layout and the Tone TwEQ has the 1M from input to ground (pulldown resistor). In the schematic drawn above that resistor has been omitted. Is it necessary or I can we omit it without any problem?

If you wire your 3PDT switch with Input grounded when effect by-passed, you shouldn't have any problem by omiting pulldown resistor...

2. I'm using large 10uF input and output caps. Is the cap in front the TL072 be necessary non-polarized? I would like use a 10uF polarized there even there.

Use of non-polarized cap isn't necessary..
It mainly depends on HPF cut-off frequency (here set at 13Hz with 220nF & 56k) hence cap's capacity value..
(10μF cap there should be useless in the mean of low frequencies filtering..)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 21, 2019, 09:42:04 AM
You've lost the 100uF cap that you had on the Vb supply. That's important. It should go between Vb and ground.

OK, now I am confused; I changed the voltage protection I had for the power module of theTone TwEQ.  In theory, that one should be complete (it does have a 47uF electrolitic to ground; not sure if that is the one you mean?).  Or should I ad a 100uF directly to Vb (after the 10K resistor)?

Also Iainpunk corrected their original post - you *don't* need that 100K to Vb on the tone control circuit. Like he said, it's an inverting op-amp arrangement.

Got it. I will only keep the 220nF cap

Also: your second opamp half has two non-inverting inputs. That's not a thing. You want the upper inputs in your schematic to be the inverting (-) and the lower ones to be the non-inverting (+) inputs. For both opamp halves.

Thanks, Andy.  If I understand you correctly, you are talking about the 2 + signs, right?  If so, the top one was a drawing error (you can see in the pic that I tried scribbling the - in).

A rough (by heart) calculation says that 68nF Input cap sets HPF cut-off frequency at about 230Hz..
(with a, rough again, estimation of total input impedance of about 10k..)

If you want all guitar frequencies unaffected, raise about 10 times input cap value..

Maybe I will increase to 100nF, but I want to limit that somewhat.  The Tone TwEQ uses 220 and that includes usage for bass...  I can always play with it once on the breadboard.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 21, 2019, 10:15:16 AM
How about now?  And do I need to include the 100uF cap that is dotted?

(https://i.postimg.cc/y86v0Zwp/2019-08-21-8-07-AM-Office-Lens.jpg)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 21, 2019, 10:36:36 AM
Better but no cigar yet. The second Opamp half (the one in the EQ section) is correct now but the first one before the EQ is still not. Flip the + and - and that is fixed. The numbers are correct, by the way. But port 2 is the minus (which should be on top as the 2 is in your schematic) and port 3 is plus (again, the 3 is in the right position but it should have a + beside it).

The dotted cap is not necessary, strictly speaking, but it will greatly improve stability and therefore reduce unwanted additional distortion from the EQ section. So definitely put that in there. Make it large enough so that the two resistors, which it is connected to, which should be 100k each, in parallel form a RC low pass with the cap with a corner frequency below the audio band. Terrible sentence. Make the resistors 100k each and the cap 1u or larger, is what I'm saying. 100u is definitely unnecessarily large. Just takes up more space than necessary for no added benefit.

Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 21, 2019, 10:44:27 AM
Vb must have a cap to GND..  :icon_wink:
(both for voltage stability & AC grounding..)

Just exchange places between 47μF & 100μF..

P.S.
It should be advisable to lower enough voltage divider resistors values (down to 10k say..) and place a series resistor of 470k - 1M between them & Vb point..
(noise issues prevention..)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 21, 2019, 10:46:42 AM
Terrible sentence.

Indeed...!!!  :icon_lol: :icon_lol:
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 21, 2019, 10:56:12 AM
Vb must have a cap to GND..  :icon_wink:
(both for voltage stability & AC grounding..)

Just exchange places between 47μF & 100μF..

P.S.
It should be advisable to lower enough voltage divider resistors values (down to 10k say..) and place a series resistor of 470k - 1M between them & Vb point..
(noise issues prevention..)

+1 what Antonis said. Make the two Vb resistors 10K and use the 47uF cap for the dotted cap. The 100uF will do a good job in the position of the 47uF.

Aside from that, there's only the reversed "+" and "-" symbols on that first op-amp, but as Lime said, the pin numbers are all correct.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 21, 2019, 01:40:44 PM
Vb must have a cap to GND..  :icon_wink:
(both for voltage stability & AC grounding..)

Just exchange places between 47μF & 100μF..

P.S.
It should be advisable to lower enough voltage divider resistors values (down to 10k say..) and place a series resistor of 470k - 1M between them & Vb point..
(noise issues prevention..)

+1 what Antonis said. Make the two Vb resistors 10K and use the 47uF cap for the dotted cap. The 100uF will do a good job in the position of the 47uF.

Aside from that, there's only the reversed "+" and "-" symbols on that first op-amp, but as Lime said, the pin numbers are all correct.

-1 what Antonis said  :icon_wink:
The non-inverting inputs of the opamps should go straight to the intersection of the two resistors and the cap, without an additional 470k-1M resistor. That would only apply if you were using the opamp in non-inverting configuration. That technique is known as noiseless biasing but it does not apply here. The non-inverting input of an opamp used as an inverting amplifier (which is what both of your stages are) needs to be nailed to Vb with no extra resistance if you want it to behave linearly, which you do. Also: If (and only if) you will be using only the two halves of a single TL072, 100k bias resistors are fine in my oppinion, because the TL07x series has absolutely tiny input bias currents (as all JFET opamps do). if you were using, say an NE5532, RC4558, or even NJM4556, somethink like 10k or 22k would certainly be advisable. if I were you and I were set on the TL072, I'd go with the 100k-100k-1u combination. But going 10k-10k-10u (or 47u) would give you mere flexibility for swapping opamps. It will suck more juice from the power supply though, which would be an issue only if you plan on using it with a battery.

Cheers and don't let us confuse you,
Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: iainpunk on August 21, 2019, 04:02:08 PM
i just noticed that the led is always on when the pedal is powered, it that what you want or is the switching jut not drawn?

on the same topic, this might be interesting to read
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 21, 2019, 06:11:02 PM
i just noticed that the led is always on when the pedal is powered, it that what you want or is the switching jut not drawn?

on the same topic, this might be interesting to read

Ah, I had not noticed I did that!  So it would be technically a pad for soldering the LED lead, and the negative would go to the stompswitch.

Here is the latest draw:

(https://i.postimg.cc/prWx3nRS/2019-08-21-4-07-PM-Office-Lens.jpg)

Any other issues you see?  Do I move to breadboarding?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 21, 2019, 06:44:18 PM
-1 what Antonis said  :icon_wink:
The non-inverting inputs of the opamps should go straight to the intersection of the two resistors and the cap, without an additional 470k-1M resistor. That would only apply if you were using the opamp in non-inverting configuration. That technique is known as noiseless biasing but it does not apply here. The non-inverting input of an opamp used as an inverting amplifier (which is what both of your stages are) needs to be nailed to Vb with no extra resistance if you want it to behave linearly, which you do. Also: If (and only if) you will be using only the two halves of a single TL072, 100k bias resistors are fine in my oppinion, because the TL07x series has absolutely tiny input bias currents (as all JFET opamps do). if you were using, say an NE5532, RC4558, or even NJM4556, somethink like 10k or 22k would certainly be advisable. if I were you and I were set on the TL072, I'd go with the 100k-100k-1u combination. But going 10k-10k-10u (or 47u) would give you mere flexibility for swapping opamps. It will suck more juice from the power supply though, which would be an issue only if you plan on using it with a battery.

Cheers and don't let us confuse you,
Andy

Thanks for spotting the bit I'd missed about the resistor to Vb - totally right, they're not required. (Isn't it the case that you can use them in an inverting configuration too, to try and help balance offset voltages at the two inputs and therefore the output? - for audio this mostly doesn't matter, since we don't care and AC-couple the output anyway).

I think you worry too much about the 10-10K-1u versus 100K-100K-47u. 20K across a 9V supply is 0.45mA - not a huge amount. I admit 200K across a 9V supply is significantly less! And back when we used to use batteries by default, I *did* use to worry about stuff like this (and use TL062 and LF444s for jobs where they're weren't the best, but they didn't drain my PP3).
Either way will be fine...;)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 21, 2019, 11:23:19 PM
Noticed a couple of mistakes when I went to redraw it in Eagle.  Here is the latest schematic:

(https://i.postimg.cc/tRWXJpsJ/Schematic.jpg)

IMPORTANT NOTES:

So, can you guys spot any other thing that needs fixing?  Or something I may have missed when drawing it up on Eagle?  If not, it is off to the breadboard... and if that works, getting some boards done!
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 21, 2019, 11:49:59 PM
Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...;)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 22, 2019, 03:35:54 AM
1. The Active Baxandall layout and the Tone TwEQ has the 1M from input to ground (pulldown resistor). In the schematic drawn above that resistor has been omitted. Is it necessary or I can we omit it without any problem?

If you wire your 3PDT switch with Input grounded when effect by-passed, you shouldn't have any problem by omiting pulldown resistor...

2. I'm using large 10uF input and output caps. Is the cap in front the TL072 be necessary non-polarized? I would like use a 10uF polarized there even there.

Use of non-polarized cap isn't necessary..
It mainly depends on HPF cut-off frequency (here set at 13Hz with 220nF & 56k) hence cap's capacity value..
(10μF cap there should be useless in the mean of low frequencies filtering..)

Thank you, Antonis! ;)
But what I meant was the 1M input pulldown resistor in the Baxandall and in the TwEQ, but I have to put in front of one of the EQs an non-inverting opamp booster. So the will be not in the input, aymore. I don't know if I have to includede it or not. I can't notice changeing in the sound.
Actually, that pulldown resistor is missing in the schematics drawn here, distortion + eq (between the two sections). So, I assumed it's not necessary, but what happens if I include it?

About frequencies, I got these emulations:
(The three caps are input, output and the coupling cap in the middle of the Tone TwEQ. Just that circuit).

(https://i.imgur.com/Mm2Bkp3.jpg)

With the stock caps I got a line not very flat, but just with a slightly lack of mid/low end.

Nice topic, and sorry my interference. :)
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 22, 2019, 06:24:30 AM
Can't catch your diagram but pulldown resistors are only needed before IN and after OUT caps..
(the second only in case of Volume/Level pot absence..)

If you use Baxandall or Tone TwEQ as a separate, independendly chain activated effect, you might need them..
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 22, 2019, 06:32:38 AM
+1 what Antonis said.
-1 what Antonis said. 

Zero total shouldn't be considered as profit motive, should it..??  :icon_redface:

@Andy: Could we shake hands on keeping 10k/10k resistors and omit 407k - 1M bias resistor..??  :icon_biggrin:
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 22, 2019, 07:18:08 AM
+1 what Antonis said.
-1 what Antonis said. 

Zero total shouldn't be considered as profit motive, should it..??  :icon_redface:

@Andy: Could we shake hands on keeping 10k/10k resistors and omit 407k - 1M bias resistor..??  :icon_biggrin:
Sure! Like I said: -1. Not -2  :icon_wink: 10k/10k is fine, or 22k/22k, or 47k/47k. As long as we are not trying to squeeze out the last minute of service from a zinc-carbon battery, it really doesn't make a difference. I normally use the 10k/10k combination as well because I have lots of 10k resistors and never use batteries.

Cheers,
Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 22, 2019, 10:23:11 AM
Ok. I get that 1M resistor to the ground between my preamp and the Baxandall (or Tone TwEQ) is not necessary. But now I have it on the board.
I hope that the 1M resistor is just useless. Or is it better take it out?

I find the 10k/10k thing very interesting!
I'm using my preamp + eq on board, with the battery. I'm using a TL061 on the preamp and a TL062 on the EQ. Is in this case is advisable to use 200k/200k for the VB to reduce the battery consuption?

Thanks!
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 22, 2019, 11:46:30 AM
Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...;)

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 22, 2019, 02:51:23 PM
Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...;)

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.

Fixed!  Dont have the pic, though.

Quick question; can I substitute the 56nF cap in the power part of the schematic with 68nF?  I do not have 56nF in stock...  I got 47nF too, if that is better, but I think 68nF is OK, right?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Fancy Lime on August 22, 2019, 03:34:25 PM
Those op-amp inputs on the first op-amp (IC1A) have got flipped around again...;)

Crap!  You are right!  I will fix it tonight.  I will also start breadboarding.

Fixed!  Dont have the pic, though.

Quick question; can I substitute the 56nF cap in the power part of the schematic with 68nF?  I do not have 56nF in stock...  I got 47nF too, if that is better, but I think 68nF is OK, right?
47n or 68n are both ok in this position. In fact, any cap larger than 10n, which isn't an electrolytic is going to be ok. The purpose of the cap in this position is only to filter out high frequencies that the big 100u electrolytic cap can not catch because nothing is ideal and electrolytics have an increasing impedance at high frequencies. Film or ceramic caps do not have this particular problem, so together the two caps make up one "almost ideal" cap.

Andy
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 22, 2019, 09:51:21 PM
+1 what Lime said. I often use a 100nF ceramic in this position (they're cheap, I have lots around from logic decoupling duties). It acts in association with the electrolytic cap to make (as Lime neatly put it) an "almost ideal cap". Exactly. The 100nF deals with the stuff that the 100uF can't cope with, and vice versa. Together, they've pretty much got it covered.


Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 22, 2019, 11:23:29 PM
IT'S ALIVE!

OK, this is where we are at as of right now:

Schematic corrected with:

(https://i.postimg.cc/Xqwrf4hn/Schematic.jpg)

Here is the breadboard:

(https://i.postimg.cc/G24Yy0dp/20190822-215734.jpg)

Notice the transistor is in a reachable position so I can switch it to 2N222 or 2N5089 or something along those lines.  Also notice the diodes on the bottom; by only reconnecting one wire I can switch between 4 types (may play with it even more later on)

And the sound test (WARNING, English is not my first language!):



Overall, it is working as expected, but I do have a couple of small issues:
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 23, 2019, 04:02:13 AM
Maybe the high control boosts too much signal. I got something like that with the Active Baxandall. It's the same thing of the Tone TwEQ, but with differents value and without mid control. In my case I don't get any distortion, but I heard a lot of highs. In front I have a clean opamp preamp/booster.

About the mid control. Are you sure you connected it fine? I'm trying to find some circuit like this with a mid control. I tried to connect an external board of the mid control on my Baxandall, but I failed twice. I thought it was my fault.
I'm building it in these days, I was trusting in the Tone TwEQ, it should work, it must work! :o Someone built it with success. I guess.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: antonis on August 23, 2019, 05:43:06 AM
About the mid control. Are you sure you connected it fine?

Can't see any discrepancy between Felipe's & Tone TwEQ Mid control other than x10 underscaled pot wiper to virtual ground cap (C10)..
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 23, 2019, 06:32:32 AM
Indeed, C10 shoul be 33nF not 3.3nF. If on th breadboard there's the wrong cap jfrabat should get almost half cut/boost and higher frequencies of the mid.

It could be useful: https://guitarpcb.com/wp-content/uploads/2018/07/BD_Tone-TwEQ.pdf
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 23, 2019, 11:52:33 AM
Yup.  I did use 3.3nF on the breadboard.  I used the Eagle file as my build reference, so I defenetly used 3.3nF instead of 33nF.  Will replace it today.  Will check back with the update once it is done.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 23, 2019, 01:37:17 PM
Yup, that cap was certainly the issue.  I replaced it with 2 15nF ones (I was out of 33nF, so I measured my stock of 15nF, and used 2 that measured at 16nF), and VOILA!  Mid control works just fine.  Also the pedal is quieter; with single coils, if I use 2, there is little noise.

This is the schematic now:

(https://i.postimg.cc/QCjwjCSW/Schematic.jpg)

Again, I am adding the 2 parallel caps so that if I print it, I will just use what I already have.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 23, 2019, 01:58:03 PM
Great! :D
If it work for you I can't see why I will can't make work mine! ;D
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 24, 2019, 11:10:05 PM
Hi, Guys.

I got a couple more questions regarding the pedal (everything is working, but I am trying to personalize the sound to the taste of the user). 

On the breadboard you can see I got all kinds of diodes for clipping options:
I simply need to change one connection to switch it around.  I know a couple of those should not even be in the list, but my intention is to show him the effect of the clipping diode can have on sound.

As far as transistor goes, I am not sure how much the change the sound (have not tried it yet), but I am taking:
Do these really change the sound much?  Is it worth taking them?

I am also taking different caps for IN/OUT.  I have:
My understanding is that the lower the cap, the more treble will go through (or the least bass anyway), right?
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 25, 2019, 03:13:17 AM
I forgot to suggest you how try to fix that little issue that makes clip the signal with the Treble at max. How I told early, probably boosting the treble make to clip the signal, maybe even if you can't hear distortion in the signal there's a bit of gain. Did you use single coil guitar pickup? Anyway, you should try to raise up the 1.8k next the Treble pot. Some other configurations have 3.6k or 3.9k. Probably you will have a smaller range, but it could enough. ;)

Diodes.
If you want just to show the difference sound of the diodes just change them on the breadboard. Else, you need a rotary switch to select every pair of diodes.

Transistors.
Some transistors have higher hfe and some have lower hfe. This can determinate the gain level. But there's just a way to to know how a transistor sounds: try it! :D Those four transistors are rather common, if you are going to build something else I'm pretty sure you could use the three you don't use for this circuit in other project.

Input cap.
Changing the value of the input cap C4 (but also C5, C6, C7 and C12) change the cut of the low frequencies. Bigger cap cut less bass. A 1uF cap cut little bass, and maybe this circuit could work with a bass guitar. With a 1nF cap you can hear just the highest frequencies.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 25, 2019, 06:30:17 PM
Hey, guys.  Got together with the friend who asked me to make this pedal, and he is really digging how it is sounding.  This is the last schematic with the changes he liked:

(https://i.postimg.cc/K8qtt3sP/Schematic.jpg)

He was asking me if it is possible to make it have more gain.  I assumed I could just add another gain stage, so I tried that on the breadboard, but there is actually LESS gain when I add it AFTER the current gain stage, and it sounded like CRAP if I added it before (FYI, I used a 5.2K resistor to ground to kind of make that stage mid gain), so I took it out. 

So, a couple of educational questions:
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: jfrabat on August 25, 2019, 10:44:16 PM
Since I am no longer talking about the tone control, I am starting a new post for this part here (https://www.diystompboxes.com/smfforum/index.php?topic=122979.0).
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: Elijah-Baley on August 26, 2019, 02:51:36 AM
It's not necessary have the same value for those caps. The 10nF cap will cut bass.
Title: Re: Noob question - Bass, mid, treble control for overdrive/distortion
Post by: ElectricDruid on August 26, 2019, 06:14:04 PM
What is the best way to add more gain to this pedal?
You could make it more crunchy by using less diodes in series, or by using diodes with a smaller forward volt drop. If you just want it louder, you could increase R6.

Quote
If C4 and C12 are 10nF, I would be perfectly fine using 10nF for C5, C6 and C7, right?
No, that doesn't logically follow at all. C4 and C12 might be fine as 10nF, but that's because of the situation they're in. C5, C6 and C7 are in different situations and therefore probably require different values. Each and every cap needs working out for its particular situation.

Quote
Or would that change the tone in any way?
Yes, probably radically!