SUNKING PROBLEM

[Klinq58]

I finished building the Sunking and am having some problems with it. The gain pot has a very small clean area at the beginning of it's rotation. It then abruptly transitions to pretty major overdrive. The sound of the overdrive is very sputtery as it decays and then the signal cuts off abruptly. There is also a crackly (noise) quality to the distortion. Also, if the strings are hit very lightly, the circuit almost seems not to engage. Hit a little harder and it is full-on. At this point I have replaced almost every part in the circuit and done the usual check for solder bridges. I have tried numerous chips as well. I audio probed the circuit, but in this case I am getting plenty of signal, just not the kind I think anyone would want. It seems to degrade at the gain control. At one point I had the gain pot out and measured around .88k on one and .94k on the other. I reversed the top and bottom pot wiring without much effect. My chip voltages are as follows:
IC1  1.  4.73  2.  4.73  3.  3.72  4.  0  5.  4.73  6.  4.73  7.  8.76  8.  9.44
IC2  1.  4.62  2.  4.73  3.  4.72  4.  -9.17  5.  4.72  6.  4.73  7.  8.46  8.  17.29
IC3  1.  9.44  2.  4.67.  3.  0  4.  -4.63  5.  -9.18  6.  4.88  7.  7.16  8.  9.44
I have tried two MAX1044 with little change.
If anyone has any thoughts on this or experienced similar, save my project. Thanx in advance.

[madbean]

Pin1 of IC2 looks pretty far off, at first glance. The other voltages look more or less correct to me.

Have you made any modifications with the wiring?

[Klinq58]

No modifications to the wiring. I remeasured the voltage on pin 1 and it is within range. I corected the above.

[madbean]

Hmmm. I'm thinking this is a bias voltage issue due to it being centered around the gain pot and also because of the crackling. Let me think on it for a bit.

[Klinq58]

This thing sustains like crazy, almost compressor like pumping until it abruptly sputters out. There also seams to be some pitch altering when it is going full bore. In bypass, I think it is working as advertised.

[madbean]

Congratulations, you've created a "Klon Factory"

It's possible the board is faulty. Generally, this is very rare, though. Any chance you could take a high-rez pic of top and bottom side of your build? It might help with the diagnosis.

[Klinq58]

I just sent you some high resolution pics via your email. Strange problem. Hopefully your experienced eye can spot what mine can't.

[madbean]

Okay, I'll have a look and get back to you.

[oldhousescott]

Pin 3 of IC1 looks low. It should be closer to 4.73 like pins 1 & 2. Pin 7 on both IC1 and IC2 looks high. They also should both be closer to 4.73 like pins 5 & 6.

[Klinq58]

I agree, they do look off. I am perplexed as to why. I replaced the entire power supply (and much more) of the circuit with no change, but it does seem to be a supply issue.

[madbean]

Regarding the pics you sent: what are the two extra jacks you have attached to the input/output?

[Klinq58]

I thought you might ask that. I usually attach mini phone jacks in parallel with the regular 1/4. This allows me to fit this size box in some very tight pedal boards. Do you think that could be a problem with this circuit? Out of 20+ double circuit boxes it has not been a problem. It probably causes a slight impedance change.

[Klinq58]

If it turns out that no one has any ideas as to why this is happening, I will order another board and start from scratch. I want to make it work so I don't trash the enclosure, but am worried that I might run into the same thing. Since others have not experienced this, I must have some component that is off. It may be that I have several from the same batch that are malfuntioning. I did check all resistors as they went in as well as diodes. I did not check the capacitors. I thought that my routing could be causing occillation, but have moved the wiring fairly far apart to no effect. I just tried it after a buffer with the same results. Sounds great for big heavy bar chords until the sputtering crackly decay at the end, but seems to have far to much gain with very little range on the gain control. 1/4 turn, no gain and then full on with little effect for the next 3/4's. I have not tried a real Klon, but from what I have read I would not expect it to be anywhere near as gainy as this thing is at present. It is loud so lots of signal is getting through and the volume and tone controls seam to be doing their job.

[madbean]

No worries, it won't come to that. We'll get this one working. I've built this circuit a few times, so I can attest to it functioning. While the actual board you have could have an unseen problem, I think the solution will present itself soon.

Looking at your voltages again, I did gloss over a couple anomalies. Most concerning is pin7 on IC1. Pay particular attention to the pads for pin7&8 underneath. Could there be a small solder bridge there?

Are these caps rated over 25v: C22, C20, C21, C15? Cap orientation looks correct. BTW.

I see a few little bits of solder mixed with some flux on the bottom side of the board. A dry, soft toothbrush brushed lightly over the surface will help clear away the debris. This might help IN CASE there is some tiny little solder bridge somewhere.

I see one wire that has its insulation a little burned up. Is that just surface damage? IE the wire is still intact and not broken or burned up?

Finally, check your voltage readings at these places to see what you have: Lug2 of Gain1, Lug3 of Gain2 (ie, Vb), R29/R30 junction.

BTW: these are not criticisms of your build---I'm only trying to explore every possibility. I don't think your parallel input/output jacks will cause any problem here.

[Klinq58]

I spent a lot of time really cleaning the board. It was getting kind off messy from all the rework. I had high hopes that that might fix it, but it is not to be.

C22, C20, C21, C15 ARE ALL 50v and have been replaced at least once.
Yes, the wire (actually a piece of heat shrink) got a little toasted during rework.
Lug 2 Gain 1: 4.72
Lug 3 Gain 2: 4.72
R29/R30 Junction: 4.72