killing fizzies with mosfets...

[MetalGod]

ok, I've been reading up on various biasing methods with mosfets and decided to build a single stage mosfet overdrive.  what do you know, it turned out alot like the booster on Jack Orman's website 

Anyway, there is some fizzyness in the tone that I want rid of - anyone got tips?

My initial thoughts are to try small (100-500pF) caps accross the drain resistor and maybe a larger (22nF cap) from the output to ground.

Anyone?

[petemoore]

ok, I've been reading up on various biasing methods with mosfets and decided to build a single stage mosfet overdrive.  what do you know, it turned out alot like the booster on Jack Orman's website
  So...it's not a mosfet boost, but almost is...how's the bias on that Q?
Anyway, there is some *fizzyness in the tone that I want rid of - anyone got tips?
  This doesn't sound like a descript of the MB.
My initial thoughts are to try small (100-500pF) caps accross the drain resistor
  Worth a try just to see what it does, My guess is it'd pass more current through drain to V+ at freq's it passes...not sure what result would be.
   and maybe a larger (22nF cap) from the output to ground
 
  This should kill the signal.
  Try small cap from D/G or tone pot/cap from output to ground, replace the chosen potvalue with fixed R later ?

[MetalGod]

thanks for the reply.  it's setup like this...

G= 2v
S= 0.4v
D= 4.5v

[lovekraft0]

Using a small cap in parallel with the drain resistor will work - V+ is ground for an AC signal. The ROG May Queen uses a cap across the Q3 drain resistor to tame highs, and Fender (among others) has used a small cap across the occasional plate resistor to prevent squealing in some of their more troublesome tube amps.

[MetalGod]

thanks for the replies - I'm ok with putting small caps across the plate, err, I mean drain resistors - I was just wanting to see if there were any other common 'tricks'. 

I'm going in reverse on this stuff - I've worked on valve amps for the past six years after starting out building pedals in summer '97.  Made alot of 'clones' and now I'm more interested in making my own stuff.  (like with valve amps), chances are that it'll end up like something that's already out there   

[petemoore]

and maybe a larger (22nF cap) from the output to ground
  DAFT I Can't read...
  I Read 22UF...you said 22 nF...Me dummy says...yes This WILL let some highs 'out' to be shunted to ground, and will take egde of Fizzies...