Crowther Audio - Prunes & Custard

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Post by Bernardduur »

Check if pin 1 is connected to the big line that runs underneath the IC. I've debugged some versions of friends and all had that problem.
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Post by jazzercountry »

Ok, Pin 1 was not connected to that line, so good call there. I fixed that, but it's still not working. Here are voltages:

1 8.2
2 8.4
3 8.4
4 8.9
5 8.4
6 8.5
7 8.2
8 9.2

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Post by bajaman »

there's your problem - pin 4 should be connected to earth (ground) - it should read 0 volts - check your earth connections
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Post by jazzercountry »

Ok, that's fixed. Pin 4 is 0v now. I have sound when the effect is engaged now, but it's just the same as when bypassed. I'm guessing that I cooked the IC having juice running to all 8 pins? I'll try another TL072 and see if that fixes it.

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Post by jazzercountry »

Well, looks like I'll have to run to Rat Shack to get another TL072 - but before I make the trip, does that sound like a reasonable explanation? The volume control works when the effect is engaged, there's just no effect (clean sound only louder)

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Post by bajaman »

post some pics :!: - showing the wiring etc. and both sides of board.
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Post by jazzercountry »

Ok, pardon the mess on the trace side. I've been going over this thing so many times I'm starting to get the brown stuff. Anyway, I'm not sure if I was mistaken before or what, but I do get distortion now. It's definitely not the prunes & custard sound, though, maybe it's just the diodes clipping? Anyway, there's no distortion until the gain knob is almost maxed. Also, the switches and the mix control don't have much distinguishable effect. What's next to check?
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Post by bajaman »

Okay - assuming the wiring to the pots is correct and assuming the pots are the correct value, I would check for shorts between adjacent tracks - in particular the middle track under the op amp; it looks awfully close to the track connected to pin 1 of the op amp in your photo.
Do you have a ohm meter or digital multimeter??
Check for shorted tracks!
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Post by jazzercountry »

I have one, but it doesn't have a continuity setting. I checked the one you mentioned, though, and it's good. Am I crazy for thinking this IC is cooked? Would that have this effect?

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Post by JimiB »

wouldnt work at all with a bad ic

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Post by JimiB »

take a sharp pointed tool and scrape in between the areas I circled untill you are sure they couldnt be making a connection, and then try it again.
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Post by MWichni »

You should also clean the board up from colophony...

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Post by jazzercountry »

Any tips for getting rid of that colophony rosin mess?

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Post by Fuzzer »

I think alcohol will do, but I don't know what it will do to the board, ¿what is the problem with the colophony after all? :?:
¿Does it bring trouble on long term?

Paint Thinner will also bring down the Colophony.
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Post by MWichni »

Yes, alcohol will do the job. The colophony used to be tricky. Sometimes it can connect two traces while being on them. When colophony is melted on two traces it could have in it some tin solder and in that way can connect traces. Hope you understand what I am trying to say. :scratch:

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Post by Fuzzer »

Sure, thanks for the clarification MWichni.

So, you should try the alcohol Jazzercountry.
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Post by MWichni »

Alcohol will do nothing to the board, so don't be afraid about cleaning board using it.

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Post by jazzercountry »

Ok, I got it all cleaned off. Same problem, though. Switches and shape control have no effect. Volume works, but Drive is completely clean until it's turned up all of the way. I double checked my pot values, and the solder connections to the pots and switches. I'm not really sure what to do next. In the meantime I've finished a half dozen other projects that have fired up the first time, so that makes this one even more frustrating.

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Post by MWichni »

Well, you have empty places on your board. I don't know what should be in there but it is first suspicious.

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Post by jazzercountry »

Yeah, I was curious about those, but I'm pretty sure I followed the layout.

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