Please help.
I've been trying to finish my Doubelganger 2.1d and I've been getting bypass signal through the pedal fine but I lose the guitar signal when I turn the effect on. Depending on the position of knobs and switches, I got various sounds, mostly oscillating noise.
I've looked at the solder joints and double checked orientation of things on the PCB. I checked my switch wiring against the instructions. I embarked on a mission to track down the problem with an audio probe but I think I'm in over my head. I traced the guitar signal through many of the components but I get lost. As far as I got, the guitar signal gets louder or softer, dryer or wetter, but it seems to still be present. I jumped over to IC1 and IC2 just for kicks and both of them only have ticking coming out of them. I really don't know what I'm supposed to hear where so I'm hoping for some more direction.
I took some pictures in case that helps and I can take some voltages too if that would be useful.
(http://i1286.photobucket.com/albums/a609/dsteidtman/Mobile%20Uploads/20170710_094346_zpsyirzq1g3.jpg)
(http://i1286.photobucket.com/albums/a609/dsteidtman/Mobile%20Uploads/20170710_094357_zps913podra.jpg)
(http://i1286.photobucket.com/albums/a609/dsteidtman/Mobile%20Uploads/20170710_094418_zpshxqggbhr.jpg)
I can't see your photos. Maybe it is just that I'm looking on a cell phone.
Looking at the schematic ic1 and 2 are part of the lfo circuit.
If it was me I would triple check the switch wiring. Then I would focus on the top part of the circuit. Ic3 and ic4. Start at in and just keep following that line to the right as well as all components and lines that junction off from there. Find where the sound goes out and you'll probably find a bad or wrong value component
Quote from: bsoncini on July 10, 2017, 09:56:58 PM
I can't see your photos. Maybe it is just that I'm looking on a cell phone.
I see them on my post. I wonder if I'm the only one who can see them. Image Shack started holding my pictures for ransom so I tried posting the link from my Google drive as an alternative.
I'll give the probe another try. It's just easy for me to get lost between the schematic and the board.
It looks like you should have a signal on every pin on ic3 (except pwr and gnd of course). Maybe start there. Do you have a signal of pin 3 of the blend knob?
Post some voltages and I'll give you mine when I get time.
I tried putting the pictures on photobucket. Maybe that will show up.
I'll try to get some voltages and work on the probe some more today. Thanks.
Ok. I was able to gather some more information and I reposted the photos above from Photobucket. Hopefully this helps.
I do have signal at Blend #3. I also have signal on IC3 pins 1,2,3,5,6,7,8,9,10,12,13 and 14 (although there's a lot of squeal on 9 and 13). IC4 only has signal at pins 1,2,3 and 7.
Voltages (as best I could get with the thing on):
IC1:
1 4.2v
2 4.2v
3 4.2v
4 8.4v
11 .4mv
5,6,7,8,9,10,12,13 and 14 were kind of up and down all over the place when I measured.
IC2:
1 up and down
2 4.2v
3 4.2v
4 .3mv
5,6 and 7 are up and down
8 8.4v
IC3:
1 3.98v
2 3.98v
3 3.98v
4 7.96v
5 3.97v
6 3.99v
7 3.98v
8 3.98v
9 3.97v
10 3.97v
11 .3mv
12 3.98v
13 3.99v
14 3.98v
IC4:
1 3.98v
2 3.98v
3 3.26v
4 .2mv
5 3.97v
6 3.98v
7 3.98v
8 7.96v
Well you have a signal at pin 7 on ic4. That is almost at the output. There is a 10 uf cap right by pin 7 the schematic doesn't say which number. Do you have a signal on both sides? Do you have a signal at r41 which is right after the cap?
I don't recall if I checked the cap but I know I had signal at R41. That's pretty much the whole audio path, correct? Out of curiosity, can you see the pictures now?
Yes. I can see them.
Do you have a signal on the a1 pad that goes to the bypass switch? Have you tried toggling the true/spec switch?
I do have signal at A1 to bypass. Spec and True bypass both are ok and I do hear the difference between spec and true bypass. I cranked up the amp and discovered that there IS a very faint signal coming through but it's pretty much silent at the normal volume setting that I used when probing it.
FYI, I have it hooked up to my test box now but I also tried it plugged into the wired-in jacks and there didn't seem to be any difference.
Just to clarify. Your signal at your output jack is much lower than when you probed the audio signal throughout your circuit? Even at a1 pin?
What I noticed is that, with the effect on (bypass switch turned on), there is a faint signal I can hear. That signal gets louder when I probe through the circuit. So.. probing=normal volume. Not probing=hardly any volume. I don't know if that's normal or if it's a clue.
I would make my way back through the circuit and see where the signal gets much louder and check all components around there. Start at the output jack. Go to a1 pin of the bypass switch, pin 7 on ic4. Are the all the same volume? Maybe you put a 330k instead of 330r for r41?
Should the signal be pretty much the same volume all the way through when I probe or should I expect it to be louder or quieter in some spots?
Could I have messed up my switch wiring somehow? I've checked and double and triple checked that it matches the revised wiring diagram but I wonder.
I think I may have found it. I think my bypass switch is not working. Duh. Maybe that should be at the top of my troubleshooting list. I'll update if I manage to fix it.
Got it. I must have overheated one tab on the bypass switch. It's good now. Thanks for all your time and help. I got a little better at troubleshooting on this one. Now... to make a box.
That is good news. Put alligator clip across the a1 and output wire to test. Test the switch on the continuity setting of your multimeter.
Glad you figured it out. It's always nice to have builds work right away but you don't really learn anything. I built one of these recently and probably didn't even look at the schematic once.