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Fishman Model G acoustic preamplifier [Schematic]
Posted: 28 Dec 2019, 11:54
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.
Basically 10M JFET input buffer into inverting amplifier into active baxandall.
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 28 Dec 2019, 18:17
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.
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 28 Dec 2019, 19:03
by dylan159
LF353. I didn't manage to make the schem neater but it's there!
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 28 Dec 2019, 22:14
by karul
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 29 Dec 2019, 09:42
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.
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 29 Dec 2019, 09:43
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?
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 31 Dec 2019, 15:45
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?
Re: Fishman Model G acoustic preamplifier [Schematic]
Posted: 31 Dec 2019, 17:39
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"