Fishman Model G acoustic preamplifier [Schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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dylan159
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Post by dylan159 »

I've traced this little clip-on piezo preamplifier for fun. Seems like a simple yet nice design (aside from those ridiculous electrolytic coupling capacitors a bit everywhere and the wimpy decoupling, which should be fine for battery power). I haven't seen many acoustic guitar preamp schematics around, hope this gives a nice starting point to diy builders.
fish.PNG
Basically 10M JFET input buffer into inverting amplifier into active baxandall.
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Ichabod_Crane
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Post by Ichabod_Crane »

Thank you!
What is the opamp? I found an image of that preamp, but it's not so clear, it seems to me a LFxxx.

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dylan159
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Post by dylan159 »

LF353. I didn't manage to make the schem neater but it's there!
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karul
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Post by karul »

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Fishman Model G (2).jpg

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dylan159
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Post by dylan159 »

Exactly the same! Same random mix of metal film and carbon film (actually in different positions than mine), and mind has no greenies and the op amp is one of those pretty old ones with the silver band.
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Ben N
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Post by Ben N »

Thanks, this looks really handy.
Anybody have any thoughts on whether the first opamp might double as a mixer for a (buffered or unbuffered) mag pickup input by way of a suitable (10k-20k?) mixing resistor to the (-) input?

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Yazoo55
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Post by Yazoo55 »

This is another picture I found online without the greenies.

Just a query - the capacitor on the power/voltage divider to give the reference voltage is bigger, maybe 100uF(?) from what I can make out.

Any chance you could upload a picture of the copper side of the board please?
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Fishman G.jpg

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dylan159
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Post by dylan159 »

Yazoo55 wrote:This is another picture I found online without the greenies.

Just a query - the capacitor on the power/voltage divider to give the reference voltage is bigger, maybe 100uF(?) from what I can make out.

Any chance you could upload a picture of the copper side of the board please?
Sure, I'll upload some as soon as i can in a few days if you're interested.
It seems to me that their philosophy for populating the board is "whatever they had around"
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Post by TwinBeech »

Can you explain the hookup for the trimmer and Volume pots? Is the wiper and both ends connected or is one end left open.

Thanks. It looks like a pretty good amp.

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