Serendipity-no drive

[slimtriggers]

Just built up a Serendipity and it's not giving me any love.  I get signal in bypass, signal when it's switched on, LED works, but no drive.  The drive control acts like a volume control.  The volume control also acts like a volume control. The voice pot seems to be working properly, and it's hard to tell if the tone knob is doing anything.

I did sub a TL072 instead of the AD712.  So far the only thing I've tried is switching the transistors around in case I had the pinout backwards.  No change when I switched them, though.

I'll go through and double check my resistor values tonight.  I probably should check to make sure I don't have the pots mixed up, too.

Any other suggestions?

[cjkbug]

did you use 2n700's or some other fet? I had a stubborn vero build of this circuit with similar behavior. it was a problem with the fets. I replaced them and it was fine. bs 170's work great in that circuit too.

[madbean]

What brand of 2n7000 are they?

[cjkbug]

mine where cheap ones from tayda. I bought a bag of 100 and I've had a few duds

[madbean]

It's a bit of a pain slimtriggers, but socket the two transistors and try putting in some diodes there like 1n914. If you get distortion then it's a matter of either different pinouts or perhaps bum transistors.

[slimtriggers]

Yeah mine are from Tayda as well.  I socketed the transistors, so swapping them with diodes will only be a minor inconvenience.  I'll give that a shot. 

I'll let you know how it goes

[slimtriggers]

I tried 1n4148's in place of the transistors, but no change.  I tried 2 more transistors (off the same strip, though) but no change there either.

All the resistors check out, and my pots are correct.  Maybe I'll try a 4558 just in case...

[gtr2]

hmm... it's almost like there is a short somewhere in the neg feedback loop of IC1A.  A solder bridge perhaps?

This is a weird one.

[slimtriggers]

Tried a 4558, but no change.  Would an IRF510 work if I could finagle the leads appropriately?  That might be a tough one to try out, though.  I only have 1 BS170, but I may switch it into both spots to see if there's any change.  BS170 has pinout opposite of a 2n7000 if I understand correctly.

I would take some pics, but I haven't seen my camera since we went to Gettysburg a few weeks ago

[jimmybjj]

Can you post hi res pics of both the component and solder sides inclusive of the wiring?

[madbean]

Voltages on the IC are in order, as well.

[slimtriggers]

No way to take a pic right now, but here are the voltages.

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[slimtriggers]

Volts at the transistors:

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[slimtriggers]

OK.  Found the camera

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[slimtriggers]

Good Lord the soldering looks ugly all blown up   I already see a couple of spots that may be suspicious.

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