old big muff problems

[newperson]

Hi,
I have an older plain silver big muff.  i think the one after the triangle one.  does anyone know the sizes of the pot that should be in here?  all three are numberd the same--> 1377403, date and manafacture and XM2184.  Does the XM2184 tell the size?  Or does anyone how a schematic showing the proper size?  The volume pot has a broken leg and it has no output for the sound.  I thought I should try to fix this first.  The pedal has 4 transistors in it.  They are marked--> FS36999 335 Q1,2,3 and 4.  They have sorta strange readings right now, but I figure the pot should be fixed first.  Here is a link to a photo of the board.

http://i48.photobucket.com/albums/f212/new_person/77d60a9d.jpg

<a href="http://photobucket.com" target="_blank"><img src="http://i48.photobucket.com/albums/f212/new_person/77d60a9d.jpg" border="0" alt="Image hosting by Photobucket"></a>




Thanks for any help,
Paul.

[newperson]

Also, it says 3003 on the board.
-p.

[newperson]

from digging around on the net and the search button i see several with 100k.  is this the correct pot?  and should it be audio/log?
thanks,

[Skreddy]

Mouser has 100k pots with long board-mounted legs that should fit.
Part #31VQ501
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=261835

ElectroHarmonix used all linear pots in those.  It wouldn't hurt to get audio for the volume pot, but not necessary.  You'd just get a more reasonable sweep than the original.

[Skreddy]

Damn; yours has a pair of germanium clipping diodes.  Will be much more distorted sounding with slightly lower volume than most...

[newperson]

stuck a 100k b pot in there.  and fixed some joints.  sounds good now.  does anyone know what diodes would be good for D1-4.  D1 and D2 are different than D3 and D4.  I am going to try to trace out the pedal and copy it.  Also what transistors will replace the ones in there and sound about the same?

Thanks,
Paul.

[Skreddy]

Normally they'd have 2 pairs of 1N914 diodes.

I wouldn't swap those transistors!  (or anything else; I'd just get it working good and keep it as original as possible)  But if you're looking to clone it, you can get some 2N5133's from Steve Daniels at http://www.smallbearelec.com .  Or, for a higher-gain tone, you can use 2N5088's.  Some people like even higher gains with 2N5089's.  Some like medium gains with BC549C's.

I'd be interested in seeing the variations in this one you have.  You can find a Big Muff schematic very easily.  Then just make notes of where yours is different from the common values.  I bet it sounds nice.  That particular model is in vogue now.  A few years back, it was the triangle-knob; then the green Russian version; now it's the ram's head.  And it looks like the black Russian model is probabably going to be the next popular version.  Funny.     But yours uses the transistors from the triangle knob, rather than the 2N5087s more common in the ram's head version.  So I bet it sounds creamier than most ram's heads...

stuck a 100k b pot in there.  and fixed some joints.  sounds good now.  does anyone know what diodes would be good for D1-4.  D1 and D2 are different than D3 and D4.  I am going to try to trace out the pedal and copy it.  Also what transistors will replace the ones in there and sound about the same?

Thanks,
Paul.

[newperson]

thanks for the help.  i am going to mess with tracing it more this weekend.  this pedal is not mine.  it is a friends that asked if i could bring it back to life.  i wish to try to copy it while i have it.  i am going to try the scaning method that i read about around here for the back side of the board. 

do you know why there are two different sets of diodes in this one?  and our the 1n914's the smaller ones in the picture?  i looked around and cannot find the original transistors (FS36999 335) anywhere.  are they just gone, or am i looking in the wrong place?  or will one of the 3 that you wrote about sound the same?

thanks again,
paul.

[Skreddy]

Yeah; you will not find those transistors.  I saw them one time in a parts listing for a TV repair place, but I wasn't able to actually get any. 

Those are basically 2N5133's that I mentioned you can get from SmallBear, though; so all is not lost.

The bigger diodes are the germanium ones, and, yes; the smaller ones are most likely 1N914's.  I suspect ElectroHarmonix was just experimenting with those at the time.  I prefer to use silicon diodes in a Big Muff; the germanium ones lose a lot of dynamics.

Good job getting it working.  Like I said; download a Big Muff schematic to help you trace the circuit.  There will be minor variations between yours and the schematic you download (not in the circuit itself, just in the specific values used).  Those differences give that pedal its personality; make a note of them and you'll have some clues about how to tweak that circuit to customize the tone. 

Have fun!

Marc

thanks for the help.  i am going to mess with tracing it more this weekend.  this pedal is not mine.  it is a friends that asked if i could bring it back to life.  i wish to try to copy it while i have it.  i am going to try the scaning method that i read about around here for the back side of the board. 

do you know why there are two different sets of diodes in this one?  and our the 1n914's the smaller ones in the picture?  i looked around and cannot find the original transistors (FS36999 335) anywhere.  are they just gone, or am i looking in the wrong place?  or will one of the 3 that you wrote about sound the same?

thanks again,
paul.