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Simpler JFET amplifier stage question
Old 3rd December 2019
Gear Maniac

Simpler JFET amplifier stage question

I set a J201 up as a self-biased common source amp with 24V DC supply.

I have about 15dB of clean gain, pleasant symmetrical clipping as input amplitude of a 1kHz sine increases beyond 400mVAC, and no noise.

Does that sound about right? I'd like to build a simple guitar preamp. I know there are so many treatments of guitar buffers and preamps online but I wanted to have a crack at designing from measured JFET parameters and making use of the 24V rather than the assumed 9V.
Old 5th December 2019

With a 24v supply, you should be able to get more output if you want. I liked the overdrive I was able to get out of a MMBFJ201 without a bypass cap on the source resistor.

For more gain in my design, I added some BS170 E N-MosFETs. I was able to get about 25dB from them when the source resistor is bypassed - but I'm working with 9v.


Old 6th December 2019
25 db of gain is about all I can get with some fets running at 9 volts. Use two in cascade and you get 40 db or more.
Old 8th December 2019
Gear Maniac

Great! Thank you both, I might have missed something or mis-measured then.

I can see now how you get hooked on analogue signal processing.
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