Identify this onboard guitar circuit!

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Bside2234
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Post by Bside2234 »

Does this look familiar to anyone? It was found with a bunch of old guitar stuff. There are a couple of 1M pots hooked up to it. The bottom of the board is potted with this green epoxy stuff so there isn't any help there.
It's not mine or I would have dissected it.
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chicago_mike
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Post by chicago_mike »

Thats not an old Starz Guitarz preamp is it?
Skyline FX 2013

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EddieTavares
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Post by EddieTavares »

I guess that it is a Sting Ray circuit or varitant cause It has the same number of components.

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Bside2234
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Post by Bside2234 »

With 4 diodes though? I would say it's not Stingray related just based on that.

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EddieTavares
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Post by EddieTavares »

Bside2234 wrote:With 4 diodes though? I would say it's not Stingray related just based on that.
OK, I think your could be correct but there is a little possibility that it uses glass capacitors like below:

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Why it is using 4 diodes? One of them could be used to prevent dc reverse flow but what about the others the others?
If it uses two diodes in the input to prevent overflow so it sounds very strange as it has to be used inside the instrument where its very uncommon to have overflow.

Clippers?

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Bside2234
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Post by Bside2234 »

You could be right and I don't know why it would use 4 diodes. The owner scratched off a little of the epoxy and revealed what looks like rectifier diodes. I wish he would send it to me and
I can take all that epoxy off and we can see what's going on there.

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astrobass
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Post by astrobass »

You can use diodes to bias a transistor, but that's using an op amp. Still, maybe to provide Vref? Two diodes to provide Vin, one to provide Vref? As long as the forward voltage is highly consistent between diodes and it's relatively high couldn't that work?

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astrobass
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Post by astrobass »

Just following up that post and I'm pretty sure that's a terrible idea and it would bleed the battery dry in very little time if it would even work which who knows it probably wouldn't. The glass caps idea seems more likely. Glass resistors also exist but why would they be present alongside more common types

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galmar
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Post by galmar »

Maybe diodes are used to protect the IC from certain voltages. :scratch:

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