Simple onboard guitar preamp

[CJ]

after trying a million stomp boxes ,

nice to have one cord and easy access,

9 volt battery in the cavity,

crazy thing is the 0.01 cap on the output, thought it would kill tone but this thing sounds better than any of the stomp boxes i tried,

thanks to Gus for the 30K idea,

 

[JohnRoberts]

I thought J201 was a junction FET, it looks like you drew an insulated gate mosfet.

JR

 

[CJ]

i was just testing to see who knew their stuff around here,

i changed it to a tube, now you won't know if i made a mistake,

 

[musipol]

Is there a specific reason for that 30k gate stopper? Does it oscillate without it? Just curious.

 

[Matador]

On the J201's I've tested, most were clustered around -0.9V VGS(off) and IDSS of about 0.6mA. With those values, center bias with the drain at 4.5V comes out to a drain resistor of about 27k and a source resistor of 2.7k. Given the diode's it looks more like an overdrive, so maybe ideal values don't matter.

The 30K rolls off high frequency gain into the Miller capacitance of the JFET.

 

[CJ]

Yes it is right in between a clean boost and light distortion box, the diodes are there as a limiter but turned out to add a nice compression to the boost,

 

[Tubetec]

Look at the bright input on a Hiwatt , 500pf is the coupling ,sounds shrill unless your hitting it with a vintage humbucker ,doesnt work with single coils at all .
Bright input generally works better with humbuckers , normal input with single coils to give back a bit of fattness .