Distortr PCB Weirdness

[jeffwhitfield]

Ok, so I must be the King of finding weirdness with PCB boards.

So I got a Distortr and a CrackleJack and built a dual pedal out of them. CrackleJack turned out fine...but the Distortr didn't. Turns out that I got the order of the Gain and Subs switches wrong. I'm not good at desoldering switches (much less the rest of the components!) so I just opted to start over from scratch.

Second Distortr build was still problematic. I installed the wrong pots for Volume and Drive....or did I? The board itself was correct...but the documentation off the Distortr page shows the opposite orientation (with Drive on the left and Volume on the right). After flipping them back, both worked.

However, while the pots work, the switches don't. Subs switch doesn't seem to do much of anything. And the Gain switch does something..but I can't say it's a gain difference. Seems more like a tone difference. And yet the prior board is clearly wrong with the opposite switch placement. So...which is it? Which one gets the on-off-on?

I think the problem is that this particular PCB has seen a revision. The version shown in the documentation is Revision 08.20.17 and shows a pic of a PCB with a very different layout. The current one doesn't appear to be the same PCB. So, me thinks there might be an issue with the current board...possibly with the switches themselves. The rest seems to work...it's the switches that are the problem.

Kind of bummed.

 

[Feral Feline]

Look at the subs switch on the schematic. There are three caps — C5, C6, C7 — the latter is in the circuit at all times, ie the middle "OFF" position of the on-off-on. When you switch the on-off-on toggle to an "ON" position it is engaging either C5 or C6 to run in parallel with C7. Parallel caps sum, so add the value of C5 or C6 to C7 to get your sub's value.

If you look at the schematic again, the gain switching shows two paths to ground from Q3's drain. If it were to have an on-off-on switch it would interrupt the the source completely, which would be bad. Gain gets the on-on.

If you apply a DMM to your board, you'll be able to figure out which SPDT switch on your board has a link directly to ground and another to R13 — this will be the on-on SPDT (Gain). If you find the switch you're testing to link to C5, C6 or C7 then of course you've found where the on-off-on SPDT goes.


Lay down the solder-tip so it's across all three lugs of the switch you may have better luck wiggling the switch out. Do it a little bit at a time and let the switch and surrounding components cool off between increments of removal — otherwise you may need new switches and or parts if you overcook 'em. Once you've got the switches out test them with your DMM and manually operate them to see if they're still workable or have sustained damage from the heat. If the PCB's SPDT pads are still clogged with solder, you can now unclog them easily one at a time with your iron, solder wick and/or solder-sucker.

Can't say anything about your drive and vol pots problem, as my distortr board is packed away somewhere and all I've got to go on is the 8.20.17 build doc. However, in the pictures you posted, you've got the C5k and A100k swapped from what they should be according to the printing on your board — hard to make out beneath all that flux, but looking at the component side it definitely shows C5k on left and ?00? on the right.


I'd definitely go with what's printed on the PCB and swap the pots around, as build docs may take some time to be updated after a board receives a revision.


It's a cool pairing for a dual-pedal so I hope you're able to get it all squared away; are you running the Cracklejack first to push the Distortr over the top, or after as a cleanish boost?

 

[PJS]

Nothing to do with the switches, but if you are not using the LED you would be far better to just leave it out than to short the 2 pads together.

 

[Robert]

 

[jeffwhitfield]

View attachment 17338

Ah, cool! This helps! Is the schematic the same? Or is there a revision on that as well?

 

[jeffwhitfield]

Ok, so I debugged some things a bit. Yeah, I already knew I got the pots backwards. Fixed that and made sure the switch orientation is correct (Which it already was! Yea!). So far, everything appears to be working...except the Subs switch. Not getting any noticeable change in tone with it.

I traced the signal and checked the continuity of the switch. Between the switch and R14 (47K) continuity appears to be working just fine. No signal from pole #3 or #1 in the middle position. And I get signal from each pole when switched. All good there!

While reflowing the solder joints, I heard a weird sputter from C5 (820n) so I switched it out and tested it. Yep, it was deader than a doornail! Even with the switch though, the Subs switch still doesn't reveal any noticable change in tone.

So...what could it be? Any suggestions on how to go about finding the culprit component?

Being that this is a board revision, is there any change in the circuit itself? Just wondering.

 

[jeffwhitfield]

Alrighty, so I did a bit more testing on this one. Board is working and sounds pretty good. However, the MIDS switch still doesn't work. I ran the pedal through an oscilloscope on my Mac and used a few different tones. Switching does change the sound...but only slightly it seems. Doesn't appear to be dramatic, much less audible.

I had a similar problem with another pedal, the AionFX Aphelion. That ones has a similar setup with it's Tone switch: a 10n cap inline with a switch that adds either a 1n or 470pF cap. And, like this one, Tone switching revealed no audible change in tone. Kind of perplexing.

So, now I'm super curious as to what it could be. Is it a buffering issue? Well, probably not considering I set it as the first pedal in my chain and it still didn't work. Maybe an impedance issue? Both of my guitars (a Gretsch and Ibanez) both have hum buckers so....could that be it? Hmm...inquiring minds want to know.

 

[juice886]

Okay, bumping this thread up as I got my hands on the Distortr. I have the same kind of issue as jeffwhitfield, the subs switch has very mild effect on the bass response. Luckily I have an original Zvex Distortron. I'm not going to reverse engineer it or whatever, knowing it has SMD components but a quick comparison test shows the Subs switch in the original has much more prominent effect and overall has more bass content in the 3rd position and much less bass in the middle position. My guess is that the values of C5, 6 and 7 could be different in fact from the schematic that is floating in the global internet matrix but that's only a guess. I'll come back later when I have results of simulation in Microcap.

 

[juice886]

So I can confirm that the PCB is absolutely okay.
Though when I compared my clone to the original I noticed an obvious difference in the tone control curve. Then I googled and there are suggestions that C8 is 100n, not 10n. And it makes sense, 100n and 82k give 19Hz so it doesn't roll off bass making possible to control bass frequencies at the input of the tonestack with C5, C6, and C7. So I changed C8 to 100n and it became much closer to the original. Still I don't like the original tonestack response, first 50% sounds muddy and dark and that's exactly how the original pedal behaves. So I changed C9 to 10n in my clone but that didn't give much of improvement, probably it is worth to lower C9 even further. I also modified C7 (56n) to 22n and R18 (82r) to 15r.

 

[john kurzweg]

Has it been confirmed that C8 should be 100n ? Seems that might be right from glancing at other related schematics--- Also, should the C5K pot be reverse log? It doesn't indicate that in the build doc -- Any other values on the PCB that might be incorrect? I am a BIG fan of the Distortron , but mine stopped working after 15 years , so I thought I'd take a shot at building one - I've populated the PCB and was about to start hooking up pots etc when I saw some of these concerns--I'm still a newb with trying to suss this stuff out!--Thanks in advance.