August 8th, 2008, 03:31 PM
I'm between guitar builds right now and in need of something to pecker around with so we got to thinking about modifying my EH Russian Big Muff that gets limited use. Upon opening the pedal one marvels at the fact that the Russians could produce mach 3 aircraft...the Big Muff employs some primitive technology but it works for the Muff.
The plan is to upgrade to germanium transistors and diodes,add bias and voltage controls,upgrade the pots plus add a 9 volt power supply jack which would eliminate the need to change batteries.
The required components are ordered, I'm looking forward to see how the project turns out.
August 8th, 2008, 06:35 PM
If your PCB is anything like mine (I've got a green one), you're in for a treat - the traces almost tear away just by staring at them!
Seriously - if you want to twiddle with that thing, I suggest desoldering braid big time. I've got an old ram's head that I can hit with a blowtorch, but not the MIR.
Most of the trannies used in the MIR are actually kinda cool - they have lower gain than other Muff variations. I suggest you save them - you might come back to them!
I've tried running the first clipper stage with all diodes pulled, but it was too much, so I settled on LED's instead. Even though the suggested cap upgrade for the one in series with the clipping pair is 1 uF, I find .47 uF to be sufficient. Stock Russian value is .1 uF - too low!
For the second clipper stage, I was running 1N4001's, but they are too loose, IMO. 1N14148's are actually okay if you pop up the 470 pF cap in series with the 470K resistor to .001 uF or even .0047, IMO.
The most cricital change, IMO, is to replace the 20K bass resistor with a 47K (stock MIA Muffs use a 39K), and the treble cap with a .022 uF (stock is .004). The MIR uses a 22K treble resistor in place of the stock 100K MIA value - I find it to work much better! I really don't like the dinky .004 treble cap - too much of a mid notch. The whacky stock bass is fine though, IMO.
Just be careful with all of the germ stuff - the Muff is very loose, as is.
And make sure you get ready for one nasty PCB, if you've got a greenie like I do.