Analogguru - FET-Booster

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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modman
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Post by modman »

Again, I ask: Did anybody breadboard this yet?


modman wrote: I did, using a J201 transistor, and I got a very good clean boost from this circuit. However, although I followed and checked over and over:

- the bias pot functions as a gain control (bias is 5.13V at maximum gain and 8.70V at minimum gain (8.87V battery)
- the gain pot doesn't influence the sound or level in any audible way.
- the gain pot crackles!
- BF2415C (didn't have BF245A as suggested) didn't work (GSD pinout I know)
- Jfet that work are 2N5457 (less gain) and then I suppose MPF102, but didn't try that.

Note that gain and bias pot are parallel pots. 5KB for bias pot (functioning as gain control) work better than lower values, but about to just drop the original 'gain control'

Can anybody see what's going on here. I might have been stupid but it's boosting perfectly with a pot, cap and resistor less.

Maybe I should create my own project "Crackling JFETSHO"? I just hope AG doesn't find out or he'll sue me. You know how he is... :wink: You know you only need one building block to get started...
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Barcode
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Post by Barcode »

anyone try my layout yet?

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soulsonic
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Post by soulsonic »

I did an entire DIY project dedicated to this circuit.
https://solgrind.wordpress.com/2008/01/21/jfet-boost/

Sorry, I did not use your layout because I built mine on perf.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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soulsonic
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Post by soulsonic »

I just built a variation of this using a 2SK880 FET. It sounds fantastic. The circuit isn't exactly the same; a few changes here and there. Instead of the gain control, the 10uF cap is fixed across the Source resistance so it's high gain and I used a 100K audio taper pot after the output capacitor as a volume control. Also used a smaller value for the output cap, 1uF. Still plenty of low end, but it doesn't get mushy the way a SHO has a tendency to do (at least the ones I've built :lol: ).
I built this on my new universal booster board, which I'm in the process of testing out... schematic here:
JFETBoost1.JPG
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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soulsonic
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Post by soulsonic »

It sounds like this!
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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