A gift for you guys: Big Muff v2 PNP transistor gains and voltages

[runmikeyrun]

I recently had this to repair and my God does it sound good, it really roars.  So good, in fact, that I measured the components and transistor voltages and also obtained the hfe readings for each transistor. 

The schematic from kitrae for V2 PNP is mostly accurate as far as the resistor/cap values; i didn't find any discrepancies from there except the input cap (C1) is labeled as 1uF.  This pedal has a 10uF.  It's possible this was a replacement or factory, who really knows.  This does have a ton of low end and saturates heavily so I'm sure that helps.

Anyways, being PNP this one uses 2N5087 transistors and the gains/voltages are as follows.  Note: battery voltage was 9.18v

Q1: hfe 370
E 0.84
B 1.45
C 4.25

Q2: hfe 310
E 0.04
B 0.65
C 4.29

Q3: hfe 377
E 0
B 0.68
C 4.62

Q4: hfe 420
E 0
B 0.61
C 7.08

PLEASE NOTE: these are numbered corresponding to the markings on the original circuit board and the schematic posted below.  They are the reverse of the traditional left to right "order" that transistors are listed.  For example, the Q4 I posted is the first gain stage and Q1 is the last gain stage after the tone control.  Please make sure you read your schematic correctly. 

I'm thinking I may throw one together and use trim pots on both the collector and emitter resistors to get the voltages shown here.  Something tells me I'm gonna need to sort through a decent quantity of 5087 transistors to find four with gains similar to these, although I did have a couple already kicking around and one of them is 370.  So, who knows.  Good thing they're cheap. 

I'll post a build report when I get something together and let you guys know.  In the meantime I hope someone finds this useful. 





Ham fisting my way through one build to the next since 2003.