Black Russian Big Muff + 2N5089's

[stephenMF]

Yet another big muff question:

I had an old Black Russian (with green lettering) Big Muff reissue and I finally decided to change it up a bit.

I ordered MPSA18 and 2N5089 transistors.  

First, I replaced every transistor with the MPSA18's.  I turned it on, and I had almost no fuzz/gain/distortion whatsoever.  

Then, I replaced all those with 2N5089's.  This was a little better, but to even have the softest amount of crunch, I have to turn volume and gain knobs all the way up.  It's like these transistors have removed every bit of gain/sustain that I had.  

Is the 2N5089 a low gain transistor?  I noticed that the original transistors were bigger in size.  


(PS, I cannot find a schematic for the Black Russian Big Muff anywhere.  In all schematics I have seen, the Volume pot is the last thing the signal goes through.  From what I can see, on my pedal, it is the first thing.)

[p1_ind]

Make sure that the pinout of the transistors is the same.
If I am not mistaken the pinout of the transistors of the Russian reissues
is the opposite of 2N5089 and the MPSA18.

The pinout of the transistors in them I think is C B E instead of E B C as on
the 2N5089.

Adam

[Mark Hammer]

Adam's observation is likely correct.  The MPSA18 and 2N5089 are both quite high gain devices.  Hfe readings of more than 700-800 are not uncommon at all.

[petemoore]

Use a transistor BM schematic and see if the R values are close to whats on your circuit board.
 This should help you identify the Emitter and Collector connections.

[jimbob]

I did this mod a while back- bout a year- I think theres a theread here that someone told be the correct pinout because the original ones had Russian lettering on them..

ANyway- mine now has a lot more gain--but a little less compression

[aron]

Yes, it sounds like the transistors are oriented incorrectly.

[stephenMF]

Adam was absolutely right.  Russian transistors are backwards.  Emitter Collector and Base were labeled in Russian letters on the bottom of the board.  I just assumed that if the flat side faced the same way, it would be correct.
So I added some sockets and flipped all the transistors around and now it is very loud =)

[aron]

Does it sound good?

[stephenMF]

Ugh

The distortion sound is great.  I really can't tell how much better it is though because I don't have another black russian big muff to compare it with side by side.  

However, I have an additional problem.

(Note:  I had taken the LED out so that I could attempt a true bypass.)

The problem is that I still hear some distortion when I have the pedal turned off.  If I un-plug the battery, I can still hear the guitar and the distortion noise goes away.  That's how I know that I have semi-bypassed the effect circuit.

While the pedal is off with battery in, if I link the center terminal of the sustain pot to ground, the noise goes away.  But if I have this connection when the pedal is on, it cuts everything out -- no sound.  

I used to do this automatically with the footswitch when in the off position.  However, that side of the switch does not work anymore.  It was DPDT, and now it is SPDT =/  I'm not sure what happened, but only 3 terminals work, instead of 6.  


I can fix this if I buy a new switch, but I was wondering, why does some of the effect "leak" onto the clean signal?  And, is there a better way to fix this?

[p1_ind]

I have a green reissue which has a DPDT switch one side switches the output (on to the output of the effect and off to the input) and the other side switches a ground wire ( on to the LED ground and off to the lug of the distortion pot ) so that it grounds the input and keeps distortion from bleeding through.

The Black reissues at least the ones I have worked on have poor quality DPDT switches.
I would buy a 3PDT switch from Aron and install it.
On a high gain ciruit like the Big Muff I use the bypass method that grounds the input to keep distortion from bleeding through.

Adam

[petemoore]

Sounds like the switch is 'intermodulating] [werd]]
 possibly...eliminate the switch and get the input and output wires away from each other and see if that eliminates it.
  High gain pedals can have RF feed from the input switch lug to the switches output lug.
 Did you say you're using an SPDT? Maybe try a 3PDT and use the middle part of the switch for nothing or the LED, this separates the input and output [according to reports] enough to eliminate the bleedthrough.

[stephenMF]

Thanks again guys!

My switch is still malfunctioning as SPDT, so I still can't ground the effect output when the pedal is off.  BUT, (yeah, maybe I should have known) when I put it back in the box and grounded it to the metal, it stopped leaking.

So now, it sounds fine, but I do need to get the 3PDT.