big muff pi is excellent! (op amp)

[plexi12000]

wow...what a killer pedal.  well...pretty much.  just built a typical op amp version.  the distortion part of it is just INSANE.  it is BITCHIN. Big, chunky, fat....and all that.   WAAAAAY better than any of my TS-808's distortion.

i'm sure the BMP purists are gunna verbally assault me for saying this......but i'm not really a "fuzz" fan.   hahahaha

can i build another.....and either tame or eliminate the fuzz aspect?   i'm tellin ya....the distortion is just that good.

[Derringer]

I too am a fan of the opamp version. That's the one on my pedal board now. The transistor version I built I gave to a friend.

Anyway, instead of 1n914 silicon diodes, I used the mosfet+1n34 setup on my opamp muff. That seemed to make things sound a bit less fizzy and bit more "amp" like. Otherwise, toy with your tonestack, or even maybe just adding an additional low pass filter between the tonestack and the volume pot would do the trick. Something like a 10K resistor and a 3300pf cap to ground. You might need to bump the volume pot up to 100K then though if you lose too much volume.

Otherwise, try lowering the input capacitor to 0.1 uf ... assuming the version you built has 0.15uf in there now. You'll lose some low end, but it'll tighten up and won't be as fuzzed out on the bottom.

[MuffinFlop]

My all time favorite distortion.
My preferred mods are changing the three coupling caps (C1, C7, C10 in the schematic below) and 10u (C5) to ground all to 100n, removing the cap (C9) from the feedback loop of the clipping stage and, then completely removing the tonestack (C11, C12, C14, R15, R18, R19), C10 being connected straight to lug 3 of the volume pot. This turns it into a huge, cutting fuzz machine with excellent sustain and chord clarity (think Violet Ram's Head, not Green Russian).
On my latest, I also wired the sustain pot to max, so I only have a volume control and a toggle switch to move the connection of the 47R from directly to ground or through the 100n cap to ground, it's descirbed in the document as AnaolgGuru's mod. In one position, it's huge yet clear. In the other, it's more the typical wall of Muffy doom.
http://pedalparts.co.uk/docs/ICMuff78.pdf

I'm also using TL072 and TL071, though I don't hear that much of a difference compared to the 4558/ 741 pair of the stock values, if any at all.

[plexi12000]

derringer----muffinflop

yeah man-- i think its absolutely smokin distortion. one of the best i've ever had.   and i don't "put down" anyone's choices/preferences....because everyone is different and likes different tones.

but for ME....oh yeah, it's outstanding to me. 

Derringer: WOW- thats interesting! My knowledge is limited so let me see if i understand.  You're using MOSFETs for clipping, instead of the 914 diodes? 

MuffinFlop---  thanks for the link bro--  i'll give er a look.   I'm TRYING to learn more....(it takes me a while- lol) ....so I really appreciate the info!!!!!

T

[plexi12000]

Derringer---- forgot to ask you.....  have you ever tried using a BS 170, connected as a diode, for clipping?   i have a couple on hand that i might monkey around with.

[Derringer]

yup

basically like this but pay attention to the pinout of your BS170's. It may be different from the IRF520 mosfet diagrammed here.

and that pic is from this page that you may want to bookmark for future reference:
http://www.diystompboxes.com/pedals/schematics.html

wire two of them in that configuration with gate and drain tied together and the source connected to the germanium diode's cathode (the end that the stripe is closest to) and reverse polarity with the pair like you would any other pair of diodes in an opamp's feedback loop.

Fulltone did it with 2n7000's in the OCD ... well with one of the them anyway.

BS170 should work fine.

[plexi12000]

Derringer----  or anyone else! lol

-- the info i have for using the bs170 as a diode is to use the gate and source pins and the drain in not used.  i'm assuming this way or the one you provided is suitable.

I wonder if there is a significant difference in tone?  i've read that using the different 'chips' in a transistor can produce tone differences.   i haven't gotten to experiment on this yet.

thanks! 

[Derringer]

i think you can make the mosfet work as a diode with different configurations, but what I posted above is what I did with mine

breadboard it, try different configurations and check the voltage drop over the whole mos+germ diode to see if it's actually working as a diode
then see what they sound like in the circuit and let your ears decide

[plexi12000]

cool-- thank you Derringer!