A little MkII/Supa Fuzz help

[Bret608]

Hi all,

This summer I build a Marshall Supafuzz according to the layout at Tagboard Effects. See below:

http://tagboardeffects.blogspot.com/2012/02/marshall-supa-fuzz.html

It did work initially (quite rocking, actually), but I was having some scratchy sounds when I tweaked the volume knob. I hypothesized that I had a bad input cap (since I grabbed electros of unknown age where I work), so changed it out two or three times. Each time when I put it on my test rig (which I power with an Ibanez wall wart, so have to reverse the power and ground leads for this PNP circuit), it would sort of "charge up", come to life and then be fine other than the scratchiness coming back.

So this week, I swapped out all the electros for fresh ones that I got in my last Small Bear order to see what would happen. Same sound-fading-in behavior, only this time it didn't get up to full fuzz. On a whim I soldered in a battery clip--black lead to the board, red lead attached to the board and pot ground wires with an alligator clip. I only used the in and out leads on my test rig. Instant improvement! Less noise and no scratchiness. But the sound is basically clean, and the pots are acting weird. The volume pot has the same volume level, all the way down to zero. It just makes the tone brighter or darker. I can't tell the gain pot is doing anything, other than an increase in background hiss at max rotation. Also, the bias on the Q3 collector is about a volt lower than when I checked it this summer--about 5.7v rather than 6.6v.

So my question is, am I hooking this up wrong, now that it's not on wall wart power? Or have I broken a wire internally (can't see any visible breaks)?

[Bret608]

Sigh...I just have to bump this--even if no one has any tips, it's so weird that I feel it bears sharing.

I discovered this morning that this thing passes the same loud, clean signal whether or not there are transistors in the sockets! Would a working MkII pass a signal in this state? Stumped...

[Cortexturizer]

Hey hey I am not on the computer do can't do a search for you but thereis a great topic started by jakefuzz and possibly one by timbo if I recall correctly, I did a lot of posting there too try to find it
What you have described so far makes me believe it's the bias nothing else
And given that you were doing a lot of desoldering and putting components in and out, you might wanna do it all from the start again. Really, with the fuzz face, and the bender I've found that a tinny bit of dirt can make BIG problems, parts being really close to each other and all sorta stuff really. Just build the thing again, trust me. Since I've heard it I try to follow juansolo's advice - with a circuit that simple if you can't see where the culprit is in 15 minutes time it's just better to build it again.

[Bret608]

Luckily, I do have enough vero to build it again!    Thanks and I may indeed go that route.

[Bret608]

Well, actually, I got this working again. The way I was trying to hook it up with a battery on my test box was wrong. I just went back to the wall wart but this time put a 100r resistor in series with the -9v input--similar to what Tim suggested in the other thread. I bet I could have gone up to 220r or 470r like he mentioned, but this does help as it is.