Doppelganger oscillation

[m-Kresol]

hey guys,

I’ve ran into some problems with my doppelganger build. It’s working, but not completely how it’s supposed to. First of, I get quite a lot of gain when strumming a little harder. Both, on my strat and my LP, with humbuckers or without and it’s even there in spectral bypass.
The other problem is that at certain knob positions (affected by all of the knobs as it seems) I get these spacey synth-like oscillations. I was really careful when soldering all components, reheating all joints after soldering in and measured all resistors, so they should be good.
other details:
* I used B2k pots for HF and LF span
* all pots are from tayda 
* futurlec 2A LDRs as recommended
* shielded cable for the output (missing in the pic, otherwise this is the final state)
Because of the amount of necessary wiring for testing (all of them, basically) I didn’t rock before boxing.
Any input on where to start searching for the issue is appreciated!

Thanks!

[muddyfox]

Nice noizemachine you have there!  My Dopp is not built yet so I can't help you with that, but I can help you with the YT link.
Click the YT icon and within the tags only insert the value after the "watch?v=".

[m-Kresol]

Nice noizemachine you have there!  My Dopp is not built yet so I can't help you with that, but I can help you with the YT link.
Click the YT icon and within the tags only insert the value after the "watch?v=".

thanks, that worked fine. now to the actual problem

[alanp]

Are you able to check the solder joints on the back? I've got a suspicion that R15 and C7 could have something going on, causing positive feedback going into oscillation, but don't quote me. I'd also check your component values.

The box looks really good

[m-Kresol]

UPDATE:
I checked all part values and they seem legit. As I said, I checked all resistors with a DMM before soldering, can't remember if I measured capacitors as well, but the source is reliable at least (musikding).
I swapped all opamps. I used TL072CP at first and used TL072IP when swapping. I had the impression that those were worse noise wise. I first thought that the problem might be IC4, which I think had the biggest impact (if any), but I'm not really sure about that. The oscillation noise turned to higher frequencies, I think.

Anyways, here's some voltages. If anyone could check those, I'd be really grateful
Source: 9.54 V
All voltages measure with the switches in the following positions: Phase mode, single LFO, NOT slow, sine wave, spectral bypass (the effect was engaged, just the switch if it matters), span pots maxed, speeds at about 1 o'clock, colour and blend maxed.
IC1 (TL074): some of the readings might be a little off, due to the varying voltages and the auto-range of my DMM
1-3: 4.35V
4: 8.79
5: 3.71-5.0
6: 3.71-4.87
7: 3.7-4.8
8: 2.6-7
9: 3.8-5.3
10: 3.4-5.6
11: 0
12: 2.3-9
13: 2.8-8
14: 0.4-9

IC2 (TL072)
1: 3.8-5
2: 3.8-5.1
3:4-5.3
4:0
5: 3.8-5.3
6: 3.9-5.3
7: 3.9-5.3
8: 8.7

IC3 (TL074)
1-3:4.17
4: 8.12
5: 4.15
6: 4.17
7: 4.17
8: 4.29
9: 4.24
10: 4.16
11: 0
12: 4.16
13: 4.7
14: 5.2

IC4 (TL072)
1-2: 4.19
3: 3.4
4: 0
5: 4.17
6: 4,13
7: 3.8-4.1
8: 8.09

I noticed that D9 is a little less bright than the others. I will switch that one out just in case.
What parts of the circuit is the signal passing in spectral bypass mode? since the issue is also occurring while bypassed we could probably get closer to the area causing problems.

Are you able to check the solder joints on the back? I've got a suspicion that R15 and C7 could have something going on, causing positive feedback going into oscillation, but don't quote me. I'd also check your component values.

I can't really check it without taking the board and therefore everything else, which I actually want to do if nothing else helps. I still think there could be something wrong with IC4... I also noticed that the colour pot is doing very little to the sound/tone.
Any input is welcome. Thanks!

[muddyfox]

I just came back from my vacation so things are crazy around here but I'll try to check the voltages tomorrow night when I get home.

Also, I know next to nothing about the circuit operation or what would make it self-oscillate so I'm gonna take potshots here and there and hopefully one will pan out.  Did you try shielding the vactrols from each other?

[m-Kresol]

thanks. A voltage check would be most awesome. I thought about it, but since all LEDs are out when bypassed and the problem is still present, I guess the problem is something else.
Note to myself: take photos of the solder side BEFORE boxing

[muddyfox]

Yeah... that's why it's called a potshot 
I missed that part about it acting funky in bypass as well. I'll get you those voltages tonight but take them with a grain of salt as I haven't compared it to Ian's video yet and it may not be all that it can be.
It doesn't self-oscillate though, I'll give it that! 

[m-Kresol]

much appreciated. But no hurries. I won't be able to check for anything tmr since a good friend is defending his phd thesis.

[muddyfox]

As good a reason as any to get plastered! Enjoy! 

[Govmnt_Lacky]

Something does not look right with your center 3PDT wiring. In the pic above... the right pole. It looks like you have NO wire going to the center lug.

Whats up with that?? 

Im gonna poop my pants if no one else caught that by now! 

[blearyeyes]

Something does not look right with your center 3PDT wiring. In the pic above... the right pole. It looks like you have NO wire going to the center lug.

Whats up with that?? 

Im gonna poop my pants if no one else caught that by now! 

I don't think he had finished installing the output wire (shielded) in this picture.
That is the post that goes to the out jack. Please don't poop your pants. 8-))

The crunchy breakup is the pedal when you strum a little harder?

In Spectral the whole circuit is still in. What I would look at is which LFO is the Oscillation being modulated by? I'll look at the video again

Ok it's being modulated by LFO1

Try pulling out the dry output run or shielding it. I didn't install it in mine and it looks like Lace didn't have it installed on his prototype. It is running to right before R7 and IC3A which puts it right before the modulation section. 

[m-Kresol]

thanks, I'll try that

Something does not look right with your center 3PDT wiring. In the pic above... the right pole. It looks like you have NO wire going to the center lug.

Whats up with that?? 

Im gonna poop my pants if no one else caught that by now! 

It isn't the final state. that shielded wire was the only thing still missing so I didn't take a new pic. I mentioned it in the first post. Sorry for my laziness. Thanks anyways

[alanp]

In spectral bypass, the LEDs that the LFO's are running are not connected to ground, and therefore do not light up at all. The signal is still running through the phase engine, though, which is why it sounds weirder than true bypass.

I'm inclined to think that the problem is in the audio half of the board, not the control half.

[muddyfox]

Felix, got you some voltage but still need to take care of something tonight.
Will type it up for you first thing in the morning.