Ibanez GSR200 Onboard Bass Preamp

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars
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Kyosanshugi
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Post by Kyosanshugi »

Hello all,

So a while back I picked up an Ibanez Gio GSR200 bass off of craigslist for cheap, and though it sounded kinda like crap with everything on it stock, I got infatuated with the onboard preamp it came with, especially after opening it up and seeing that it was a relatively simple circuit. Well, I've been working on tracing it for a while, and after a good amount of trial and error, I finally built a working copy and drawn up a schematic. The circuit is compact and fits comfortably in the body cavity of many basses. I'm about to build like three more of these things and put them in other basses and also my Dano baritone, for kicks. Enjoy!

ibanez new_s1.png
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ibanez new_layout.png
(original image: https://img.photobucket.com/albums/v11/ ... layout.png)

ibanez new.png
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davidmochen
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Post by davidmochen »

Hi, anyone care to describe the role of IC1B in this circuit?

george giblet
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Post by george giblet »

It's part of a gyrator (IC1B, R6, R9, C8). It looks like a 1.0H inductor in series with 1k (R9) and in parallel with 2.2M (R6)

For this circuit you can ignore the 2.2M part. What you have is a 1H inductor in series with 1k and that's in series with C7 (4.7uF)
and the three elements form a series resonant circuit. The resonant frequency is 72Hz. The way it's wired gives a peaking bass boost
at 72Hz.

R10 and C5 give a shelving type treble boost.

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