Screaming MouseFET (The next MOS FF clone)

[Transmogrifox]

Here is the link to the fuzz I generated on my breadboard recently:


http://www.geocities.com/transmogrifox/MouseFET.html


If it doesn't link when you click it, then you may need to copy and paste into your web browser address bar.

[Transmogrifox]

The extra gain stage at the input allows for some wild sustain when you crank this thing up.

Let me know if you try it.  I'm quite pleased with the outcome.

[Marcos - Munky]

Thanks, this looks very cool.

[WGTP]

I've been running a similiar looking Tone Bender type circuit with a J201 for Q1 and 2N7000's for Q2 and Q3.  Lots of gain, big nasty sound.  I need to do some refining of the caps for a more useful sound.

[Transmogrifox]

Yeah, I find that clipping the lows tends to make it sound more nasty...more intermodulation distortion.  It clips off a lot of the higher frequency information, so it's good to limit the lows somewhat, I did it by setting the timeconstants on my filtering caps low enough to where the cutoff frequency was higher than usual.

Look at the Sweet Thing schematic for ideas.  It uses an in-line parallel RC get-up to attenuate the lows to a certain point, but not with quate as much rejection as the cap itself would supply to the lower lows.

[WGTP]

If your speaking of the 470K/470pf circuit, I have that between Q1 and Q2 with a 500K pot instead of the resisitor.  Sort of a gain/tone control.  I still need to reduce the input cap some.  Might also need some caps in the FF section to tame the highs.  Check out the article and scheme on Runoffgroove.com.  Mutant Tone Bender  

[Transmogrifox]

Thanks, that is very cool stuff.  It's funny how many of these fuzzes are so similar that minor modifications, amplifier stage additions and/or omissions can make it look more like one well-known circuit or another (I guess this goes for overdrives, too).  

Anyone could easily take this mutant tone-bender thing and turn it into a BMP clone with the addition of some diodes, an extra tranny stage and a simple tone stack.

[WGTP]

I realized since doing the Mutant Tonebender, that there is probably a cycle that nubies go thru when they arrive here and start learning stuff as I did.  Most of this ground has been covered before and the elders of the site sort of sit back and smile, while helping when they can.

Great place.

[Gary]

I tried the MouseFET circuit last night on the breadboard.  Pretty good sound.  I tweaked a little to suit my taste.  I simplified it a little, with minimal effect on the sound.  You can eliminate the resistor/cap on the source of M2. Take it straight to ground.   You can eliminate the resistor tying M2 and M3's drain resistors together.  Then hook the output cap directly to M3's drain.  Tune the resistors to get the biases you had before.  I also added an RC LPF to the output to tame the highs and make it a little more amp-like. I reduced the input cap a great deal to get more upper mids.  I reduced the coupling cap to M2 as well.   I hard-wired the gain pot at 4k7 and left it set for wide open.  I changed the bypass cap to 22uF.  It sounds great.  It doesn't clean up in a stellar manner, but the mid and high gain sounds are great.  Nice design, Transmogrifox.  This is a fun pedal.

[Transmogrifox]

Thanks for the reply, Gary.  If you send a schematic of your mods to me ( rjb@montana.edu ), I'll post them on that page.  I think I'll try your mods on my breadboard and see what happens.   Some of those extra parts had to do with my tinkering to get the biases right.  Actually, replacing the 5k pot with a 4k7 resistor was probably a perfect substitution to bias the  M2 drain more appropriately.  It takes only a small voltage change.

Either way, was your RC lowpass filter on the output a series RC to ground, or just a C in shunt to the output?

I'm glad you like it.  I agree it dosn't clean up very well.  You may want to reduce the input impedance, and it may help.  Just take that 510k Gate bias resistor out and short the input resistor divider to the gate.  That will reduce the input resistance to somewhere around 75 to 80k.  Usually, a guitar has a 500k volume pot, so you can see how much more easily one can roll off the input.  At 1/2 volume, you have a 250k in series with 250k parallel 80k resistor didvider....you probably get my drift.  It may clean up ok, but I did find that the threshold between clean and dirty is a very narrow line.  This is certainly not a "milkable"  tube-like sound.

[Gary]

I wouldn't say it isn't tube-like.  It doesn't have many shades, but the old Tone Bender didn't have that many shades, either.  This is a good circuit for high gain sounds.  Nothing wrong with that.

The RC was a dual series R/cap to ground setup.  See Doug Hammond's Meteor for inspiration.  I went pretty drastic with a 0.0047/15k setup repeated twice.  It takes off the buzzy sound.  You could go as small as 0.0022 and still be OK, but I wanted it smooth.

I changed the input stage around, too.  The best setup seemed to be source to ground, gate biased via two 1M resistors, 6k8 on drain.  Take the upper 1M from the 6k8/drain junction.

All the mods I made are in this email and the last one.  Feel free to use them if you like them.

[Transmogrifox]

Thanks again.  I was actually throwing around the idea of a drain/gate feedback resistor like that for fun.  I think I'll try your mods, then if I have any personal taste preference that differs, I'll run some numbers and try some stuff.  

I'm going to make a dual distortion pedal this afternoon with MouseFET and Sweet Thing enclosed with a switch between the two, so I'm going to try the Sweet Thing output buffer, tone stack and volume setup on the output of this Screaming MouseFET and see if that tone stack will tame the highs like your RC filter does.

If I like it, I'll just alternately set up the switching between MouseFET output and Sweet Thing pre-tone stack stage and save some money on pots and other random parts.  I'll let you know what I think of it if I get it done as planned.