Looking for a DIY way to boost CV level

[SuperMutate]

Actually, I think your first time surface mount soldering looks pretty good. The only thing I saw that looked odd was the square pad under C6, make sure your cap leads are not solder bridged to that pad. (Kinda weird to put a big hole under an SMT cap??)

Check that ground traces are not shorted to power pins, start at the Euro power header... same with plus and minus power, test for a short between them.

For 2x gain, your opamp feedback resistor is usually 2x the value of the resistors for and aft of the op-amp in the signal path. Example: 100k into op-amp, 100k out of op-amp, 200k in op-amp feedback path.

[Haralds:Werk]

The signs for the orientation differs from manufacturer to manufacturer. In your case the circle on the left lower side indicates pin one. So the orientation is correct. In the tNames_OVL the side of the OpAmp with line is the side with pin one. If you don't have a voltmeter to measure the voltages you can use your softscope for that as well, if it is DC coupled. Just power the module up and put the probe on pin 4 and 8. You should see +12V and minus 12V there. If this is fine, follow the signal path. Apply a signal to one input and check the signal on pin one. You should see a inverted signal there with the same signal level as the input. Do this for all three.

[aspertime]

Thanks.
I checked the C6 pad and although it's not pretty, the solder points are not touching.
I checked the power pins with a multimeter and got a beep when touching the negative pins and the ground pins, so this might be it. (touching the positive and ground did not cause a beep)
Unfortunately the inputs on my audio interface are not DC coupled so I can only use a software oscilloscope for testing audio.
So, what is the next step?

[Haralds:Werk]

Sounds as if you have a short between ground and the negative rail. This means a solder bridge somewhere. Follow the negative rail and check all points where it comes near to the GND rail. Use magnifier glass. You can see the traces through the solder mask.
Particularly check the pins 3 and 4 on the OpAmps and C12-C16.

[Haralds:Werk]

Start with C13.Llooks as if there is to much solder.

[Haralds:Werk]

I forget to ask is it just a beep or a constant sound. If it is only a short beep it is caused by the loading current of the electrolytes. If it is constant it is a short.

[aspertime]

Progress was made, thanks.
Fixed the caps, so no more shorts.

Channel 2 boosts the signal nicely, it distorts past about 3 o'clock, but I can live with it.

Channel 1 and 3 are still not boosting. I checked the opamps' soldering and it seems fine. Also did not notice any bridged components upon close inspection.
What's the next move?

[Haralds:Werk]

Progress was made, thanks.
Fixed the caps, so no more shorts.

Very good.

Channel 2 boosts the signal nicely, it distorts past about 3 o'clock, but I can live with it.

If this happens then your input signal is to hot. You should be fine over the full range when the input signal is below 5Vpp. You can see this with your scope. Feed a sine in the input and look at the output.

Channel 1 and 3 are still not boosting. I checked the opamps' soldering and it seems fine. Also did not notice any bridged components upon close inspection.
What's the next move?

Follow the signal path with your scope. Check the signal at the whipper of the potentiometer. This is the middle one. You should see a inverted version of your input signal which changes when you rotate the pot from zero to same value as your input signal level. If there is no signal then the fault is before the pot otherwise behind the pot. Now with one part working you can compare the other two with your working one.

[aspertime]

Thank you.
I see that there's no other way to troubleshoot DIY builts, but getting an oscilloscope.
Ok, I will do so and see where it gets me.

[Haralds:Werk]

Meanwhile you can try it with your synth. Instead of an o-scope use the tip of a patch cable connect to VCA or other module and listen to the output. So you can detect if the fault is before or behind the pot.

[aspertime]

Meanwhile you can try it with your synth. Instead of an o-scope use the tip of a patch cable connect to VCA or other module and listen to the output. So you can detect if the fault is before or behind the pot.

I did do that. Channel 1 and 3 attenuate the signal but do not go beyond unity gain.
Channel 2 boosts and distorts. The strange thing is that the distortion on channel 2 (when the pot goes over 3-4 o'clock) happens regardless of the inut gain, and happens for both audio and cv. The audio sounds like a narrowing pulse wave and the cv turns a sine into square.
I re-soldered all caps and most of the resistors on channel 1 but got similar results.
Could it be a faulty batch of op-amps?

[Haralds:Werk]

Meanwhile you can try it with your synth. Instead of an o-scope use the tip of a patch cable connect to VCA or other module and listen to the output. So you can detect if the fault is before or behind the pot.

I did do that. Channel 1 and 3 attenuate the signal but do not go beyond unity gain.
Channel 2 boosts and distorts. The strange thing is that the distortion on channel 2 (when the pot goes over 3-4 o'clock) happens regardless of the inut gain, and happens for both audio and cv. The audio sounds like a narrowing pulse wave and the cv turns a sine into square.
I re-soldered all caps and most of the resistors on channel 1 but got similar results.
Could it be a faulty batch of op-amps?

Ups, I am sorry I did not mean the whole circuitry. I wanted to wrote:
Meanwhile you can try it with your synth. Instead of an o-scope use the tip of a patch cable to check the signal on the whipper of the pots connect to VCA or other module and listen to the output. So you can detect if the fault is before or behind the pot.
From your description I think it is more likely that you mismatched some resistors. You wrote you own a softscope. Why not using this?

[aspertime]

I double checked all resistor values, did a reflow or resolder for all components and checked with a multimeter all paths to and from the ICs.
The reason why I'm not using a scope is because it's a plugin in my DAW and my audio interface only has DC-Coupled outputs, while the inputs are AC-Coupled. I can use it for audio but that's about it, unless I'm missing something.

The multimeter beeps if I touch the middle leg of the potentiometer that works and the resistor right below it (R9) but if I test the other two pots with their respective resisotrs (R4, R14) I'm getting no beep, just some numbers on the screen. Could that be a hint?

[Haralds:Werk]

Yes, you should get a beep on the other two as well. The numbers implies that you have some resistance here. The common reason here is a cold solder joint. Or a broken trace.

[SuperMutate]

What is going on with the ten pins (power header?)
Above one pot and next to C13 ??
Some cold solder joints where solder has flowed around the pins, yet not melded with the pins. One seems to have a hole there with really minimal solder.
Suggest reheating those pins and adding just enough fresh solder for the rosin inside to flow the joint again.

Added: if it is the power header, then don't be afraid to get those pins Hot, (can't hurt nothin').
Ideally each of those pins should look like a miniature Mount Fuji when done.

[aspertime]

I removed the pot and tested the middle hole with resistor R14. I got a beep when touching the resistor's right side, but touching its left side I get no beep, just numbers. Tried replacing the resistor, got same results. Maybe the pcb print was faulty?
As for the power pins, as can be seen in the pic, they're quite solid.

[Haralds:Werk]

I removed the pot and tested the middle hole with resistor R14. I got a beep when touching the resistor's right side, but touching its left side I get no beep, just numbers. Tried replacing the resistor, got same results. Maybe the pcb print was faulty?

No, everything is fine. The beep told you that the trace is OK. And the numbers you get on the other side shows you that t he resistor is ok. The numbers should be around 10k as the printing on the resistors says. So, when you got no beep as you wrote before from the whipper to the resistor then you have had a cold solder joint on the whipper to the PCB. Reflowing the solder joint should have done the trick. Put it back in and test.

[aspertime]

I reflowed the solder joint and reconnected the pot. Same result.
You are correct that I get 10k after the resistor, the strange thing is that I do get a beep after the resistor on the one channel that works.
Oh well. I think I might just re-start this whole build with new components because nothing seems to change.

[Haralds:Werk]

You are correct that I get 10k after the resistor, the strange thing is that I do get a beep after the resistor on the one channel that works.

This explains the distortion you get after 3 o clock. You shortened our the 10k resistor.

Oh well. I think I might just re-start this whole build with new components because nothing seems to change.

Well, it is a learning curve. I think it is better to get the current one running and learn what went wrong. You already have a working one. Clear the short on the 10k resistor. The distortion should disappear. Then work from this working one. Compare measurements. And, very important, think about what you expect to measure before measuring. Lookup the theory. Learn! It's worth it.

[aspertime]

I appreciate your spirit, Harald. Thank you for the encouragement to stride on.
I re-soldered the 10 resistor, and now it doesn't beep, however it also doesn't amplify any more and simply attenuates, similar to the others.

[Haralds:Werk]

So now you have three active attenuators. Not to bad. This proves that your signal path is correct. Now only thing to fix is the amplification. The amplification depends on the value of R2, R7 and R12. Check the values. To get an amplification of 2 they must be 20K.

[aspertime]

Ok, I verified that all three resistors are 20k.
Also verified a connection between the IC's 6th and 7th leg to the resistor. (the multimeter beeps) What should I look for next?

[Haralds:Werk]

Let's go for the OpAmps. Pins 3 and 5 of every OpAmp should be connected to GND (Beep).
Pin 4 to -12V pin8 to +12V (Beep).
Check all other pin connections to resistors if not done yet (Beep).
Then use your Voltmeter. Connect common to GND and measure the voltage at pins 4 and 8. Should measure -12V at pin 4 and +12V at pin 8.
If all of above is fine then it might be the OpAmps. Remove all and replace only one.

[aspertime]

I removed one of the opamps and tested the pads against the GND, 3 is connected to GND but 5 is connected to +12
4 is good at -12 and 8 is connected to GND
again, no IC, just bare pads.

[Haralds:Werk]

Check the datasheet and lookup the right counting for the pins for dual OpAmps.