Hello
I have a synthesizer which I enjoy playing, but it is lacking enough output volume compared to others. I am willing to build a small, simple stereo preamp for it, and I am looking for advices.
My needs would be :
- +12 to +18dB of clean boost, with no bass or treble attenuation;
- stereo operation;
- The boost device would not add (too much) additional noise;
- Maybe +9 to +18V for increased headroom (not mandatory);
- Maybe a "dirt" switch for some slight coloration when needed (not mandatory);
I am hesitating between transistor and opamp design, and I think there are plenty schmeatics and veroboard layouts out there, but I don't know which one to chose...
- I have considered building two EQD Black Eye (or two modded Red Llama) into a single stereo enclosure;
- I am searching the web for veroboards of stereo preamps, but I am mainly finding "audiophile" preamps so far...
- I have the feeling that I could mod this Klon-style buffer (https://stompboxschematics.com/circuits/dual-opamp-buffer-on-veroboard/) into a stereo booster, but I don't know how to do (and if it would be a good idea)
Would you have any advice or recommendation?
Thank you in advance!
My go to is a pair of MXR microamps, which can run on 18v.
http://www.tonepad.com/project.asp?id=28 (http://www.tonepad.com/project.asp?id=28)
hi, Idy
Thank you for your suggestion : This is also what occured to me after browsing the web for a while :icon_wink:
I will investigate.
Maybe building a stereo version with a dual opamp ?
And maybe featuring a switch adding leds to the circuit, for a transparent/overdriven switch?
+1 what idy said. A simple dual op-amp (even on 9V) will give you minimal noise and can definitely achieve the clean boost you need.
Thank you, Electric Druid.
So let's go for a dual MXR MicroAmp then.
I am considering adding either diodes/leds on a switch, or an EQD Speaker Cranker on top of it when a slight dose of saturation is needed ;)
I will suggest that you aim for optimum headroom by using a +/-12V supply. Even if this one is low, by comparison to others, synths tend to put out some pretty hefty signals, applying 12db boost may exceed what a 12V supply can provide in the way of headroom. And should you ever venture into the realm of Eurorack, you'll have a +/-12V supply ready.
It's a synth. Therefore, a low impedance output (I'm guessing, do you have any specs?). How low is the output? If you have a sine oscillator on it (I'm guessing a triangle would work fine too) then you can measure its output with a simple multimeter on AC mode (it will measure the RMS value, you need to multiply it by √2 to get the peak value, twice this for peak to peak - if the sine is not a sine, true peak values will be lower). +12 to +18dB means a gain of 4-8.
This means maximum output needs to be, at 9V, about 6V swing / 4-8. (Opamps clip usually at about the supply rail +/-1.5V, so subtract 3V from the supply voltage). That is, 0.75 to 1.5Vpp (about 0.26 to 0.52 Vrms).
18V supply instead: 15V swing / 4-8. Therefore 1.875-3.75Vpp (so, about 0.66 to 1.32Vrms).
18V makes it easier to use many opamps (many of which are not specified for operation at 9V) but unless you are looking for extremely low noise, and assuming a low source impedance, a bipolar input opamp such as the NJM4580 can be a good choice. It's cheap and it works at low(er) voltages. Otherwise the NE5532 is cheap and almost top of the class.
In both cases, assuming a low source impedance, the parts count is, just as a quick calculation... LED, 3.6k or so current limiting resistor, diode for reverse polarity protection, the opamp, the 0.1u MLCC bypass capacitor, two 220u caps, four diodes for input overvoltage protection (or not :icon_smile: ), two 10u input caps, four 10k resistors for biasing (two for the voltage divider to set Vref, two as biasing resistors - 10kohm input impedance per channel), then, another two resistors + a cap per channel for the feedback path (for instance, 2.7kohm + 47uF for the ground path and either a 8.2kohm or a 18kohm feedback resistor from output to Input-), a 100ohm or so resistor on the output of each channel, another two 10u caps on the output, two 100kohm resistors to ground after the caps. Four TS jacks (or two TRS ones) and a DC barrel jack. That's it. Should work fine. You probably should add in a 100p or so ultrasonic limiting cap in the feedback, parallel to the feedback resistor, per channel. All in all, about 30 components. Should expect about 0.01% THD or less. If you want complete flatness in band go bigger with the big caps (uF) and smaller with the small ones (pF), these are already overkill anyway. Oh, all caps should be rated for at least three times the DC voltage they will be subject to. If you're supplying 18V, then the 220u power supply cap should be at least 50V, all the others 35V. (25V can work fine too).
Don't know if you can make any sense of what I said. Also, I might be talking bollocks. I'm an amateur.
PS: if you go with a dual supply - but you'll probably have to build it yourself, and you might as well go with +/-15V - there is no Vref to set but another 0.1uF MLCC bypass capacitor from V- to ground. If you're building your own power supply, you might want to use voltage regulators.
While I understand people's desire for more headroom, the initial problem was that the synth is quiet. If it were boosted to the point just before it starts to clip on a 9V supply, we'd be looking at about 6Vpp output, or perhaps a touch more. There's *no way* a 6Vpp signal is "quiet" in any normal situation, so moving to 18V headroom seems like overkill. Even +4dBu "Pro" line level is only 3.5Vpp, so 6Vpp is more than enough to whack the inputs of most gear.
About the only exception I can think of is if you're feeding it into a modular synth that's expecting +/-10V (20Vpp) levels. In that situation, it might be a bit quiet!
I suppose the other question is whether there might be something wrong with the synth that's making it quiet? Dodgy volume control? Bad output? It could be we need to *fix* it, rather than boost it.
FWIW, powering a NE5532 (and alike) with 36V (+/- 18V) supply is like you're asking for trouble..
Thank you all for your replies.
I will try to answer everything :
@Mark : Yes, I do have a small Eurorack system with a symmetrical +/-12V power supply. However, in the studio the synth will not be very close to the Eurorack (and I wouldn't want to use the whole modular system just for beefing up the Blofeld weak output level). I'd rather build an internal +/-12V daughterboard if needed.
@Fryingpan : Wow, thank you for all the technical information!
Yes, NE5532 is what I had in mind (this, or either a TL071). I have several 5532 in a bag, so I think it is what I am going to use.
About the capacitors : according to this website (https://www.electrosmash.com/mxr-microamp), there should be no need to increase the size of input capacitors ;)
(https://www.electrosmash.com/images/tech/microamp/mxr-microamp-all-signals.png)
@ElectricDruid : Yes, that's it. The synth is too quiet. It's rather boring, because it's really not on par with the other synths in the studio, so I'm willing to build a small "set and forget" boosting device so I won't have to worry about it anymore.
It's a Waldorf Blofeld (https://waldorfmusic.com/blofeld-en/). It's a lovely synth, but the weak output level is a known issue (or "feature?"), and I don't think there is anything which can be done to improve it.
(https://i.postimg.cc/y3ZHthBZ/blofeld.jpg) (https://postimg.cc/y3ZHthBZ)
Quote from: snk on October 01, 2024, 02:55:59 AMThank you all for your replies.
I will try to answer everything :
@Mark : Yes, I do have a small Eurorack system with a symmetrical +/-12V power supply. However, in the studio the synth will not be very close to the Eurorack (and I wouldn't want to use the whole modular system just for beefing up the Blofeld weak output level). I'd rather build an internal +/-12V daughterboard if needed.
@Fryingpan : Wow, thank you for all the technical information!
Yes, NE5532 is what I had in mind (this, or either a TL071). I have several 5532 in a bag, so I think it is what I am going to use.
About the capacitors : according to this website (https://www.electrosmash.com/mxr-microamp), there should be no need to increase the size of input capacitors ;)
(https://www.electrosmash.com/images/tech/microamp/mxr-microamp-all-signals.png)
@ElectricDruid : Yes, that's it. The synth is too quiet. It's rather boring, because it's really not on par with the other synths in the studio, so I'm willing to build a small "set and forget" boosting device so I won't have to worry about it anymore.
It's a Waldorf Blofeld (https://waldorfmusic.com/blofeld-en/). It's a lovely synth, but the weak output level is a known issue (or "feature?"), and I don't think there is anything which can be done to improve it.
(https://i.postimg.cc/y3ZHthBZ/blofeld.jpg) (https://postimg.cc/y3ZHthBZ)
I have that very synth. It's quiet. Also a bit noisy. A great synth otherwise.
If you use 5532s you can get away with 12V (single supply). Of course not 18V dual, the most you can do with an NE5532 is 15V dual (30V single).
If you want some dirt, you could add two sets of two 1N4148 series / antiparallel diodes, maybe with a 22n cap before or after the antiparallel pair, and a switch. Of course, in the feedback path of each opamp. This way, you'd be looking at some mild soft clipping over 400Hz or so. (If you go with +18dB gain, if you go with +12dB a 6.8n cap works).
Quote from: fryingpan on October 01, 2024, 04:35:44 AMOf course, in the feedback path of each opamp.
Not necessarily.. :icon_wink:
Of course, it's a matter of taste but, IMHO, that set of diodes with a series resistor (for off-seting clipping threshold) from op-amp out to GND could "sound" better in such a preamp configuration..
(at least, for guitar/bass..)
Quote from: antonis on October 01, 2024, 05:24:45 AMQuote from: fryingpan on October 01, 2024, 04:35:44 AMOf course, in the feedback path of each opamp.
Not necessarily.. :icon_wink:
Of course, it's a matter of taste but, IMHO, that set of diodes with a series resistor (for off-seting clipping threshold) from op-amp out to GND could "sound" better in such a preamp configuration..
(at least, for guitar/bass..)
Yes, I employ it myself in a number of designs... The series resistor could be anything from 2k to 10k (or beyond).
Ok, I will be building the circuit this evening or tomorrow.
Once built, I will consider adding a switch with diodes, but since I already have several dirt and coloration devices, my main goal here is to make the synth "just louder", so I might decide to keep it simple ;)
One question : the Electrosmash website states that
QuoteThe 500K potentiometer R5 is Reverse Log. You can still use a Linear potentiometer but the action of it will not be evenly spread across the whole pot range. As you can see in the table below, everything occurs between 0 and 50K (and thats why a Reverse Log pot is needed):
R5(kΩ) GAIN
0 21.7
50 2.06
100 1.54
150 1.36
200 1.27
250 1.22
300 1.18
350 1.15
400 1.13
450 1.12
500 1.11
So, wouldn't it be best to use a 100K pot ?
https://www.electrosmash.com/mxr-microamp#link12
I am struggling to find a dual gang antilog 500k pot, and since my synth already features a volume pot, I think it might be easier and smarter to go for a fixed boost (or two values on a switch).
Am I right assuming that replacing the 500k antilog pot by a 12K resistor would give me roughly 12dB of amplification, and that a 5.1K resistor would give me +18dB (gain x8)?
with Gain = 1 + 56k/(R5+2k7)
Quote from: snk on October 01, 2024, 01:06:05 PMAm I right assuming that replacing the 500k antilog pot by a 12K resistor would give me roughly 12dB of amplification, and that a 5.1K resistor would give me +18dB (gain x8)?
with Gain = 1 + 56k/(R5+2k7)
Yes, that's right.
Here's an alternative approach using linear pot. A dual 100K linear pot should be easy to find.
(https://i.postimg.cc/tY14TTVh/Non-Inverting-Op-Amp.png) (https://postimg.cc/tY14TTVh)
(https://i.postimg.cc/gxHFkF4V/Non-Inverting-Op-Amp-Gain-Response.png) (https://postimg.cc/gxHFkF4V)
Ok, it's not totally even, but it'll be fine for +12 or +18dB. It gives you a bit more control for the lower gain settings.
Not again.. :icon_mrgreen:
(lost post..)!!!
Gagh, PostImg is not playing ball at all... >:(
Let's try again...
(https://i.postimg.cc/tY14TTVh/Non-Inverting-Op-Amp.png) (https://postimg.cc/tY14TTVh)
(https://i.postimg.cc/gxHFkF4V/Non-Inverting-Op-Amp-Gain-Response.png) (https://postimg.cc/gxHFkF4V)
Aha! That's better!
Oh, now *everything* suddenly appears... :icon_eek:
Oh well.
Quote from: ElectricDruid on October 01, 2024, 03:48:19 PMOh, now *everything* suddenly appears... :icon_eek:
Yours *everything*, not mine..! :icon_mrgreen:
Thank you so much both, that's super useful ! :D
But after thinking about it, I think I like the pot-less design even more (so I can have the boost enclosure somewhat hidden, at least not like something I would be tweaking. It's less clutter in the studio, "set and forget" and voilà :)
(but the circuit you posted may be useful for another project I have - a stereo Red Llama, which I haven't build yet-, and for which I don't have dual gang 1M lin and 10k log pots -while I have many dual gang 100k pots)
Anyway, do get rid of those high value resistors. 10M, 22M, those are far too high. More noise, more susceptibility to noise on the supply, more offset.
Make R1 1M or smaller. R2 10k and C1 10u¹. R7-R8 22k, and C4 100u or 220u. You could make R10 larger, like 100kohm, since you will be plugging into a 10kohm input. The 5532 has plenty of drive, but the bigger the load, the better. I would also add overvoltage diodes on the input, just before R3. You can do this several ways. The easiest is an antiparallel pair to ground of a 1N1418 series with a (reversed) zener diode around 7V breakdown. The Blofeld won't get anywhere near frying the opamp's input, but should you use it with something else, better to be safe than sorry.
¹ : you don't need to make it that big for bandwidth reasons. Even 3.3u would probably suffice. That said, electrolytics are best chosen, like, at least three times larger (some say ten times).
Quote from: antonis on October 01, 2024, 02:32:49 AMpowering a NE5532 (and alike) with 36V (+/- 18V) supply is like you're asking for trouble..
Where are youse guys buying your '5532??
The '5532 family is rated 44V, +/-22V. Yes, even in the 21st century. That is one of its best features.
https://www.ti.com/lit/ds/symlink/ne5532.pdf table 7.1
We DO know 5532 specs but we've also experienced of those op-amps getting pretty warm at about 35V..
(after all, we don't sacrifice peace of mind for a couple of dBs more headroom..) :icon_wink:
Also, under Table 7.1, TI declares:
<Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions is not implied.>
At Table 7.3 here (https://www.ti.com/lit/ds/symlink/ne5532.pdf), TI lists +/- 15V as Recommendend Operating Conditions
Quote from: fryingpan on October 01, 2024, 04:44:52 PMAnyway, do get rid of those high value resistors. 10M, 22M, those are far too high. More noise, more susceptibility to noise on the supply, more offset.
Make R1 1M or smaller. R2 10k and C1 10u¹. R7-R8 22k, and C4 100u or 220u. You could make R10 larger, like 100kohm, since you will be plugging into a 10kohm input. The 5532 has plenty of drive, but the bigger the load, the better.[...]
¹ : you don't need to make it that big for bandwidth reasons. Even 3.3u would probably suffice. That said, electrolytics are best chosen, like, at least three times larger (some say ten times).
Thank you very much for all those advices.
I understand the need for lower R1 and R2 values (less noise).
I understand the need to increase capacitors values (more power filtering).
But could you elaborate about the advantage to make R7-R8 22k and R10 100k?
I see
R7-R8 are needed for biasing : woudn't changing their values also change the biasing?
And wouldn't increasing
R10 to 100k, despite changing the impedance (which I guess it the goal of mod), also change the output volume?
Are these mods safe in every way volume-wise and bandwidth-wise? (I mean : is there any other side effects)?
Quote from: snk on October 02, 2024, 06:42:07 AMBut could you elaborate about the advantage to make R7-R8 22k and R10 100k?
I see R7-R8 are needed for biasing : woudn't changing their values also change the biasing?
No, as long as their ratio is retained.. :icon_wink:
(by lowering their values you result into a more "stiff" resistive voltage divider..)
Quote from: snk on October 02, 2024, 06:42:07 AMAnd wouldn't increasing R10 to 100k, despite changing the impedance (which I guess it the goal of mod), also change the output volume?
It will raise output volume about 4.5%..
( compare 10k/(10k+470R) to 100k/(100k+470R), considering op-amp output impedance almost zero..)
You can use a 100k pot in place of R10 as an output Volume control.. :icon_wink:
Quote from: antonis on October 02, 2024, 05:10:48 AMWe DO know 5532 specs but we've also experienced of those op-amps getting pretty warm at about 35V..
(after all, we don't sacrifice peace of mind for a couple of dBs more headroom..) :icon_wink:
Also, under Table 7.1, TI declares:
<Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions is not implied.>
At Table 7.3 here (https://www.ti.com/lit/ds/symlink/ne5532.pdf), TI lists +/- 15V as Recommendend Operating Conditions
That's what I remembered too. Anyway, 30V is plenty (about 18dB headroom relative to +4dBu). I suppose that +/-18V (36V) is doable too with a heatsink.
There are a few criteria here you need to look at. The NE5532 isn't exactly the most modern device and there are better options out there when it comes to noise and power consumption. Also, it's got a regular BJT inut, which means input impedance is low even in a non-inverting configuration.
The OPA1642 is a great low noise, high input impedance JFET dual opamp. Great for things like buffers in guitar signals or clean gain boosts as a utility. With the high input impedance, it doesn't matter what the output impedance of your synth is (could be really low with modern designs or unusually high for arbitrary reasons, can't see anything in the waldorf manual).
Are you planning on designing a PCB for this or are you perfboarding it (OPA1642 is smd only)? And have you decided on how you are powering the circuit?
Quote from: antonis on October 02, 2024, 07:07:31 AMIt will raise output volume about 4.5%..
( compare 10k/(10k+470R) to 100k/(100k+470R), considering op-amp output impedance almost zero..)
You can use a 100k pot in place of R10 as an output Volume control.. :icon_wink:
Also, the intended load is 10kohm (a line input). With an already existing 10kohm load, that becomes 5kohm (10kohm//10kohm), which the 5532 can certainly manage fine, but the higher the load, "the best it feels", so to speak. The noise should mostly be "absorbed" by the low output impedance of the opamp, similarly to how a 1M input resistor rarely causes noise when you plug in a guitar.
Quote from: mzy12 on October 02, 2024, 09:57:41 AMThere are a few criteria here you need to look at. The NE5532 isn't exactly the most modern device and there are better options out there when it comes to noise and power consumption. Also, it's got a regular BJT inut, which means input impedance is low even in a non-inverting configuration.
The OPA1642 is a great low noise, high input impedance JFET dual opamp. Great for things like buffers in guitar signals or clean gain boosts as a utility. With the high input impedance, it doesn't matter what the output impedance of your synth is (could be really low with modern designs or unusually high for arbitrary reasons, can't see anything in the waldorf manual).
Are you planning on designing a PCB for this or are you perfboarding it (OPA1642 is smd only)? And have you decided on how you are powering the circuit?
If I were to swap opamps (but the 5532 is mighty fine) I'd go with the 4562 honestly, considering that it's intended to be used with a low source impedance. That opamp is basically silent and very low input offset too (not that it matters in this application). And it can be found through-hole too. With SMD devices there are loads (well, relatively) of opamps to choose from.
Quote from: fryingpan on October 02, 2024, 10:06:32 AMconsidering that it's intended to be used with a low source impedance
The 'problem' is we don't know the output impedance of the blofeld. At least I couldn't find anything on the internet about it.
I'd also recommend moving R10 of the MXR microamp 'behind' R9, to avoid creating a resistor divider on the output, unnecessarily dumping the output volume. And of course increasing the value of the power supply filtering caps and adding a 100nF ceramic cap as close to the opamp power rails as possible between power and ground (that's just good practice to do all the time).
Quote from: mzy12 on October 02, 2024, 10:40:57 AMQuote from: fryingpan on October 02, 2024, 10:06:32 AMconsidering that it's intended to be used with a low source impedance
The 'problem' is we don't know the output impedance of the blofeld. At least I couldn't find anything on the internet about it.
I'd also recommend moving R10 of the MXR microamp 'behind' R9, to avoid creating a resistor divider on the output, unnecessarily dumping the output volume. And of course increasing the value of the power supply filtering caps and adding a 100nF ceramic cap as close to the opamp power rails as possible between power and ground (that's just good practice to do all the time).
Waldorf says nothing, but a Greek website says it is 550 ohms (1100 ohms stereo, which makes no sense). Regardless, it would be weird if the output impedance were much higher. The DAC's output is connected to an opamp and then to the line out.
Quote from: fryingpan on October 02, 2024, 01:08:49 PM1100 ohms stereo, which makes no sense
Stereo, twice the impedance, twice the goodness! :icon_lol:
So I built a version on veroboard today and it is not working... Obviously I made a mistake somewhere, so I will try to debug the build... I will let you know how it goes!
Here's a quick schematic for a bipolar power supply with a 'clean' gain of 10. It's optimised for low noise as best my knowledge allows me. I still haven't decided on what ferrite bead would be the best choice for this application. Also ignore the suggested opamp and use what you want, that's just what I was building it around :icon_biggrin:
Schematic (https://postimg.cc/ZCtvbCY6)
EDIT: Images aren't working lol
EDIT AGAIN: Just inserted a link.
Quote from: snk on October 02, 2024, 05:13:13 PMI built a version on veroboard today and it is not working...
Distorting, dead silent, oscillating, smoking..???
Quote from: antonis on October 03, 2024, 04:39:32 AMQuote from: snk on October 02, 2024, 05:13:13 PMI built a version on veroboard today and it is not working...
Distorting, dead silent, oscillating, smoking..???
Sorry, I didn't give any detail (it was late, and I didn't take much time to investigate).
By "not working", I meant "no sound at all". It is not buzzing, oscillating, distorting or smoking.
But since I had built it on veroboard, from a layout I did myself (and I am by no means an expert), with a dual gang pot at the output, there are plenty reasons why it could not work :icon_redface: :icon_biggrin:
I need to take some time to check the wiring first.
I can also post my layout, but I don't know if it would be useful?
Quote from: snk on October 03, 2024, 09:49:21 AMI can also post my layout, but I don't know if it would be useful?
it is always useful. but with a circuit diagram. and photos of your build. easy peasy. please.
Quote from: snk on October 02, 2024, 05:13:13 PMit is not working...
Longshoremen went out on strike this week. (https://www.nbcnews.com/news/us-news/ship-queue-grows-us-ports-dockworker-strike-enters-third-day-rcna173772)
EDIT strike on hold for now.
Quote from: mzy12 on October 02, 2024, 08:34:48 PMHere's a quick schematic for a bipolar power supply with a 'clean' gain of 10. It's optimised for low noise as best my knowledge allows me. I still haven't decided on what ferrite bead would be the best choice for this application. Also ignore the suggested opamp and use what you want, that's just what I was building it around :icon_biggrin:
Schematic (https://postimg.cc/ZCtvbCY6)
EDIT: Images aren't working lol
EDIT AGAIN: Just inserted a link.
I never understood how this overvoltage protection approach works. I mean, it will limit input voltages by V± ± 0.7V but the absolute maximum limits for many opamps dictate input voltages no higher than the supply.
Quote from: fryingpan on October 03, 2024, 06:58:20 PMI never understood how this overvoltage protection approach works. I mean, it will limit input voltages by V± ± 0.7V but the absolute maximum limits for many opamps dictate input voltages no higher than the supply.
"No higher" can't mean 0.000,000V- that would imply some kind of zero offset or a perfect rectifier. Also any series resistance prevents infinite/very-high current, the real culprit.
Yes, we can blow-up gear with the 'protection' shown. But it is not so easy.
Quote from: PRR on October 03, 2024, 08:59:48 PMYes, we can blow-up gear with the 'protection' shown. But it is not so easy.
"Pretty difficult", even!! And usually that's enough. We're mostly trying to avoid being heavily penalised for our inevitable moments of stupidity, not protect the thing against deliberate attack.
Quote from: duck_arse on October 03, 2024, 10:35:03 AMQuote from: snk on October 03, 2024, 09:49:21 AMI can also post my layout, but I don't know if it would be useful?
it is always useful. but with a circuit diagram. and photos of your build. easy peasy. please.
Hello
This is already a first post with the layout I designed : it is the dual version of the verified layout by TagboardFX (https://tagboardeffects.blogspot.com/2010/10/mxr-microamp-compact-layout.html) (which is obviously mono/single channel, like the original).
I have included the suggested mods (capacitors and resistors values, etc).
I made it dual channel.
I used a fixed resistor value (5.1k) instead of the antilog 500k pot.
I used a 100k dual gang output volume pot.
I also added some components at the input for polarity protection (a 1n5817 diode) and decoupling (100R resistor and capacitor).
(https://i.postimg.cc/56RZpbLv/dual-microamp.jpg) (https://postimg.cc/56RZpbLv)
Later today I will be able to post images of the build, and run some further testings on my (not working) build.
Dunno if I missed something but what's the reason of implementing 2 single op-amps instead of a dual one..?? :icon_wink:
Can't see either the need nor the implementation of single op-amps extra pins for compensation/off-set trimming..
Quote from: antonis on October 05, 2024, 05:57:49 AMDunno if I missed something but what's the reason of implementing 2 single op-amps instead of a dual one..?? :icon_wink:
Can't see either the need nor the implementation of single op-amps extra pins for compensation/off-set trimming..
It's just that I don't know how to do it :icon_redface:
I thought about it, it occured to me, but I don't have the knowledge to design such a circuit. And as the Mxr Microamp circuit was very simple, I thought it would be ok and easy enough to gather 2 of them into a single enclosure.
Quote from: snk on October 05, 2024, 06:02:58 AMIt's just that I don't know how to do it :icon_redface:
Fair enough.. :icon_wink:
If we do it for you in the schematic form, are you willing/able to "transfer " it on layout board..??
Quote from: antonis on October 05, 2024, 06:31:47 AMIf we do it for you in the schematic form, are you willing/able to "transfer " it on layout board..??
At least, I'd be willing to try ;D
Thank you a lot for the kind proposition :)
I can't guarantee that it would be fine at the firt attempt, but I can try, it doesn't seem that much complicated.
Quote from: snk on October 05, 2024, 07:58:23 AMQuote from: antonis on October 05, 2024, 06:31:47 AMIf we do it for you in the schematic form, are you willing/able to "transfer " it on layout board..??
At least, I'd be willing to try ;D
Thank you a lot for the kind proposition :)
I can't guarantee that it would be fine at the firt attempt, but I can try, it doesn't seem that much complicated.
It's actually easier.
your bias setup doesn't work. on your layout I see a 100k from each oppie pin 7 to a 47k to ground each. that's not what the circuit shows. then I stopped trying to follow.
Quote from: duck_arse on October 05, 2024, 10:39:56 AMyour bias setup doesn't work. on your layout I see a 100k from each oppie pin 7 to a 47k to ground each. that's not what the circuit shows. then I stopped trying to follow.
Yes, you're right : I obviously messed up the values (it should be the same values : 100k on the original schematic).
(https://i.postimg.cc/CdJyYNVh/irma-bunt-debugging-01.jpg) (https://postimg.cc/CdJyYNVh)
also, while we are discussing backwards electros - that 3u3 on the input - you have 1M [or something - 22M?] pulling one end to ground and the other end connected to about half supply. check which end connects where ....
Quote from: duck_arse on October 05, 2024, 11:54:10 AMalso, while we are discussing backwards electros - that 3u3 on the input - you have 1M [or something - 22M?] pulling one end to ground and the other end connected to about half supply. check which end connects where ....
Ok, I think I get it. I had the + towards the audio input, but it should "look" towards the biased current. So a 180° rotation is required. Right?
Quote from: snk on October 05, 2024, 07:58:23 AMAt least, I'd be willing to try ;D
Thank you a lot for the kind proposition :)
I can't guarantee that it would be fine at the firt attempt, but I can try, it doesn't seem that much complicated.
Here you are.. :icon_wink:
(there are some items values mods and electros correct polarity..)
(https://i.imgur.com/YkP98Ay.png)
Hello
Thank you all for the help! Life has gotten a bit too busy these last weeks, so I could not test any further this project. But I am not giving up, I just to find some free time to mess around with it :)
I will let you know how things work !