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!
(http://felix.kalium.org/upload/pictures/Pedals/doubelganger_guts_small.jpg) (http://felix.kalium.org/upload/pictures/Pedals/doubelganger_guts_big.jpg)
Thanks!
Nice noizemachine you have there! ;D 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=".
Quote from: muddyfox on August 17, 2014, 07:01:32 PM
Nice noizemachine you have there! ;D 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 ;)
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 :)
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 TL072
CP at first and used TL072
IP 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.
Quote from: alanp on August 18, 2014, 04:35:48 AM
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!
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. ;D Did you try shielding the vactrols from each other?
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
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! ;D
much appreciated. But no hurries. I won't be able to check for anything tmr since a good friend is defending his phd thesis.
As good a reason as any to get plastered! Enjoy! ;)
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?? :o
Im gonna poop my pants if no one else caught that by now! ;D
Quote from: Govmnt_Lacky on August 18, 2014, 11:16:11 PM
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?? :o
Im gonna poop my pants if no one else caught that by now! ;D
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.
thanks, I'll try that
Quote from: Govmnt_Lacky on August 18, 2014, 11:16:11 PM
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?? :o
Im gonna poop my pants if no one else caught that by now! ;D
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
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.
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.
Alright... here it goes. This is a c/p from your post and I'll add my values to the right and mark the obvious variations in red.
FWIW:
-all my ICs are TLxxxCN
-all LEDs light up the same intensity
Here's a picture of all switches' positions, just to make sure we're on the same page:
-rates on 1 o'clock
-spans, color, blend maxed
-square, slow to the right
-antiphase, true up
-phase on (I think ::) )
-one lfo (green LEDs light in unison, I suppose that's one lfo?)
(https://lh6.googleusercontent.com/-83krqjqL1vI/U_ZXwvGaxQI/AAAAAAAAB6s/GzQZ7Ze7L8U/w1068-h801-no/Dopp%2BFelix.JPG)
Source: 9.54V 9.33
IC1 (TL074):
1-3: 4.35V 4.29
4: 8.79 8.59
5: 3.71-5.0 3.8-5.2
6: 3.71-4.87 3.7-4.6
7: 3.7-4.8 3.6-4.7
8: 2.6-7 2.7-6.8
9: 3.8-5.3 3.8-5.2
10: 3.4-5.6 3.27-5.5
11: 0 0
12: 2.3-9 3.16-5.63
13: 2.8-8 3.6-5.3
14: 0.4-9 2.1-7
IC2 (TL072)
1: 3.8-5 3.7-4.5
2: 3.8-5.1 3.7-4.9
3: 4-5.3 3.8-5.2
4: 0 0
5: 3.8-5.3 3.8-5.1
6: 3.9-5.3 3.8-5.2
7: 3.9-5.3 3.8-5.2
8: 8.7 8.6
IC3 (TL074)
1-3:4.17 4.1
4: 8.12 8.1
5: 4.15 4.0
6: 4.17 4.1
7: 4.17 4.1
8: 4.29 4.1
9: 4.24 4.1
10: 4.16 4.0
11: 0 0
12: 4.16 4.1
13: 4.7 4.4
14: 5.2 4.1
IC4 (TL072)
1-2: 4.19 4.1
3: 3.4 3.3
4: 0 0
5: 4.17 4.1
6: 4,13 4.1
7: 3.8-4.1 4.1
8: 8.09 8.04
thanks a lot! The voltages look quite ok, I guess. I'll make sure that we have the exact same settings and measure the parts again, where they don't agree.
I guess I have no other option than to disassemble it this weekend and check the back of the pcb, check for solder joints and reflow everything.
Just fyi, swapping the LED that was not quite as bright as the others didn't help. It's the same brightness now, but the noisy breakup is still there.
Quote from: blearyeyes on August 19, 2014, 12:47:50 AM
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.
I don't really see how that could influence the signal tbh. I only put the dry out in for completeness' sake, but isn't it basically a wire to nowhere if nothing's plugged in? There is no circuit than I think. Correct me if I'm wrong. Or do you think something is coupling into the dry output wire which is then fed back to the signal?
I'm no brainiac but it looks like that connection is in the right place to cause an issue. It's in the audio path right before the modulation of LFO1 and from what I can see you're getting oscillation in the audio path that is being modulated by LFO1. So maybe something is feeding back through the wire.. It looks like it runs under the whole board. Seems like a wire to nowhere could be an antenna but I could be completely off base. Tbh I'm just guessing but that is something I would try.
thanks for the explanation. I ran the wire on the top side of the board above the pots, but I'll check it for sure.
Do you have a specific knob/switch position that you can set and get immediate oscillation or do you have to coax it out? I'd like to try and replicate it and your vid kinda makes it hard to see (or I'm just being dense today ::) ).
Also, I shielded my input as well although it wasn't asked for. If you're picking up some garbage on the input, maybe that's your problem that just runs away under certain conditions?
You removed the YT clip? Now I definitely can't replicate it. :)
The video is running fine on my computer. It's just some really specific settings as it seems that is kinda influenced by all knobs. I had to fiddle around to find it, but there seems to be more than one setting that produces different kinds of oscillations depending on the switch positions.
Huh... it's prolly something at work blocking yt in a funny way...
Anyhoo, I'll give it a shot again but no fiddling I did produced anything unusual the last time I tried it.
I fiddled with mine and never heard a peep. Plus the crunch issue sounds like a cold solder joint.
Look at the components in the audio circuit right after IC4a before the first LFO modulation occurs.
Look at the dry output and how it connects to the circuit on the schematic.
Audio probe would be really helpful as well. Might be able to find it without taking it out of the box.
Good luck hunting!
Hi there, I wasn't really in the mood for debugging on saturday and didn't have time today so I didn't really devote myself to the build. Yet, here's an update:
* I rechecked the voltages that were different from muddyfox' values. Mine were the same as before.
* I poked around with the audio probe of my testing rig. I found that the signal is fine till after the first opamp part (IC4). the output is still crystal clean, but starting after R44 (going to the dry out) or R7 there is some noise.
* I haven't taken it apart yet, but I hope there is only a cold solder joint somewhere at IC3. As the weird oscillation is just at very specific, hard to find positions I could actually live with that, but the scratchy noise is a no-go.
I'll keep you posted on the progress and thanks for all your efforts.
Try removing the dry out
Try replacing IC4 (nearly any dual opamp should work, for a certain value of work.)
UPDATE:
I'm super exited right now and I couldn't wait to tell you. I just removed the dry out and the noise is gone as well as the funky oscillation!! Thanks a ton blearyeyes. Next time remind me to just do what you told me all along first thing.
It sounds way different now as well. No clue how this is possible, but who cares :D
I'll use shielded now and report back.
Guys, first of: Thank you big time. Especially blearyeyes for guiding me to the real problem and muddyfox for taking time for voltage readings.
Now, here's a funny story:
I replaced the dry out wire with shielded cable and the noise was back. I was confused since I thought the noise issue was the result of some antenna effect of the wire running a long way around the enclosure. I just unscrewed the jack from the enclosure and tried again - without grounding the shield. No noise. Not a tiny bit. Crystal clear sound.
So upon closer inspection of the jack I finally found the culprit... as you can see in the pic in the first post, out and dry out are VERY close together. I feared there was an issue of touching metal parts, so I had put some insulating tape in between. Turns out the tape ripped just a teeny tiny bit at the edge thus making contact to the regular out. I guess some of the output signal was fed back through the dry out or something like that resulting in oscillation. I added some hot glue to insulate the jacks better and now it works like a charm.
This turned out to be an amazing day. I was productive at work (finished my conference poster for Istanbul); time flew by, so over 10 hours of work didn't bother me. I fixed the doppelgänger and tried my first attempt at toner transfer, which came out spectacular and now I'm just really happy with how the build turned out. I just gave it a quick try since it's already rather late, but the sound is amazing so far. Fixing the issue gave it a fuller tone, the colour knob is actually doing something and the build looks killer, if I might say so. :)
Thanks again! be ready for my build report :)
Glad you got it working, Felix! Good to finally hear some good nooze (as I can't seem to do anything right these days with pretty much everything I touch).
Excellent job, can't wait to see it!
figures it was a little tear in a piece of tape.
Thanks for all the cudos but please always trust your instincts because i really don't know what I'm doing and I figure the day I think I do know what I'm doing I'll have become a moron!
Excellent to hear good results ;D
I never would have guessed that the issue was the two output jacks being too close together, but I can definitely see how that would cause issues.