Jfet/Mos/Si Matchbox [Q1]

[petemoore]

  Matchbox circuit built, but with 2n7000 [what I have] it sounded too sharp, glassy.
  Subbed right in different Si's, smoother than the mosfet [strong recommend for BS170 in article].
  Then I biased in a Jfet [2n5457] for Q1, since I'm mostly looking for the tone of the circuit, using it with other gainers, It's suited very well for what I'm doing.
  I clipped the 1m off the gate to V+, and diddled with the Drain resistor and the Jfet is biased in there nicely..if I ever get a BS170 or workalike..which I probably should..I can mend the 1m and pull the Jfet drain 'bypass' resistor [the Jfet I have likes 5k6, original value is 15k] from the extra socket lug I have there for the drain, just for cases like this !!
  Maybe I need to rethink the source resistance and rebias drain?
  Anyway it's biased in there and the circuit performance has improved for my tastes so far...and sounds great. Gotta love the amp sims for 'improved' amp sound through an amp .
  for some reason the Si, biased with same values as Mosfet [shown values] was producing hiss.

[petemoore]

  Thanks to Doug, the guys at ROG, and everyone who'se done work on these amp emulators.

[stm]

AFAIK the BS170 and 2N7000 are very similar.  I would rather expect the differences in sound come from one having more gain than another and thus exhibiting more or less clipping in the first stage (this clipping can be hard!).

Some other possible workarounds I see are:

1) If you have a bunch of 2N7000's try them all and see if you find a lower gain device that sounds better

2) Simply reduce tha gain of the first stage to a level where it sounds OK.  To do this, lift the 22uF capacitor from source to ground and place a 1K pot in series.  I think a value between 47 ohms to 330 ohms will set gain just right.

3) Use a J201 in the first stage (cutting the 1Meg resistor to V+ and retuning the drain resistor as you did with the 2N5457). These are "darker sounding" than the MOSFETs cited and the 2N5457--in practice their clipping characteristics are softer (more round) and thus generate less agressive harmonics.

Regards.

[MartyMart]

The matchbox does sound wonderful eh ?
I used a BS170 and when completed, tried about 12 more.
I couldn't tell much between them, so stayed with number 12 !!
Descriptions are so "lame" but I'd say it's quite a bright "spanky" tone
and makes the gtr very "Present" sounding.
Clear and not over crunched ..... but .......

It's not a "shrinking violet" 

MM.