What's on the workbench?

Robert said:
Hello darkness, my old friend.....

View attachment 64790

Yes, I know it's already been traced, but something didn't seem right so I bought an original to retrace....

Something is definitely different... and it's hiding under there.
Click to expand...
It appears to be D5 & D6 to my eyes but you should take a look under the Hood coz that's a lot of goop for 2 diodes!???
 
szukalski said:
Is it much of a difference from the drugscore trace? I know that trace had some 0R in series with clippers.
Click to expand...

Nope, our traces are the same aside from three two irrelevant things.

Upon A/B'ing the two I immediately noticed the original had MUCH more volume on tap, so I knew something wasn't quite right.

1) His Gain pot is drawn mirrored compared to mine. Not backwards, just mirrored. It still increases in resistance as you turn up the pot so it makes no electrical difference.

2) His Gain Width trim pot is backwards compared to mine. This one does actually behave backwards compared to the original, but it's a trim pot so that's no big deal.
 
Last edited:
That’s really interesting. Cheers for the explanation. I’ll give it a try once I’m back from holiday (in roughly 20 days, yay European holidays).

I never found the gain width that useful, so replaced the feedback loop with a different gain pot and resistor value. Now I’m keen to see if the diodes make much of an impact on things.
 
Robert said:
Nope,our traces are the same aside from three things, two which are (mostly) irrelevant. One however, makes a huge difference.

Upon A/B'ing the two I immediately noticed the original had MUCH more volume on tap, so I knew something wasn't quite right.

1) His Gain pot is drawn mirrored. Not backwards, just mirrored. It still increases in resistance as you turn up the pot so it makes no electrical difference.

2) His Gain Width trim pot is backwards. This one does actually behave backwards compared to the original, but it's a trim pot so that's no big deal.

3) This is the weird one.... In my original D1 and D2 are both oriented the same direction, cathode to VREF. This makes no sense to me, but I checked this multiple times before and after removing the goop. I noticed the odd voltage drop across the pair (0.24V in one direction, and effectively open in the opposite direction) before removing the goop. This is what I dug in to investigate.

These aren't zeners, both are schottkys.

Tomorrow I'm going to lift the diodes and see what the silkscreen indicates underneath them... This area was gooped so I know it hasn't been tampered with previously.

I flipped one of my diodes around to match the original and the volume popped right up and it sounds identical to my ears... Also the Gain pot actually does something now. It doesn't get clean by any means, but it at least has some effect when turning it.


Flip one of your clipping diodes around and tell me what you think. They should both be cathode to VREF.


@kanengomibako Any chance D1 and D2 were oriented the same direction in yours? It's baffling, but it's how they're installed in mine.
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1704276357590.png
 
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