Fuzz Face, True Bypass and 2N2369A... @$%#%$

[mac]

I want to share this funny and annoying experience...

I finished to solder a new FF with smooth pot at the input, variable input capacitor, bias pot, no gain pot and transistors sockets. It was intended for a pair of 2N388, 2N1114 Ge.
To be sure it was working fine I tried it with a pair of Motorola 2N2369A and guess what?: horrible sound and RF interference. I checked the voltages and they were as expected. Everything was ok, except that even at 4.5V on Q2 there was a strange sound when the notes were fading away, some kind of broken transistor sound mixed with the normal fuzz, strange indeed. And if I put my hand closer to the circuit the DC bias changed!!! Also the true bypass was not working, though it was wired ok. In bypass mode the RF interference typical of the 2N2369 found a way to the amp, I guess through the case. I disconnected the pull down resistor and the bypass switch to be sure, tried a direct connection between the jacks but the RF and tone sucking were there. The only way to have true bypass was grounding the input. I had other 2369 from another brand but it was the same.
I changed transistors, a pair of MPSA42. Now the RF noise was gone, the bypass without input to gnd was bypassing and no tone sucking, and the strange artifacts when the notes were decaying almost vanished. I suspected some bad solder for this one. After resoldering the sockets it is working fine, but the 2369s still refuse to work.

And it is a pity since the 2369 fuzz nicely.

I've seen that there are two bypass wirings, one with input to ground, the other with the input unconnected. I always use the second one and never had problems until now.
Is it advisible to ground the input?

mac

[petemoore]

 Something else I would tend to guess.
  And/or weird.
   Generally those type ff observations/problems are associated with placing higher gain transistors, the 2369 is LG IIRC.
 

[mac]

I tried bc549C hfe 480 and had a lot of oscillations and wierd things.
The circuit is on a perfboard and has 4 pots, maybe too much wiring acting like an antenna and helping RF transistors... the most annoying thing was to hear shakira's fuzzy hawlings on the background...

Today I checked the circuit once more and there is no mistake. It works bad with RF and/or high gain transistors, but with BD139, MPSA42, 2N2219A it works fine.

mac

[petemoore]

  Hard to say what...sounds like FF w/high gain transistor problems, which can be sort of intractable, lower gain somehow maybe, or try little HF rolloff caps say from B/C or the Axis Fuzz LP Trick [.1uf or so across the 1k resistor].
 

[mac]

It has the roll off caps, 47pf & 100pf.
What still surprise me is how the signal gets through the amp in true bypass mode.
I'm goin to build a new one with input grounded in bypass as in GGG schematics.

I flushed it. It is now on its way to the Atlantic Ocean. 

mac

[petemoore]

  Chiclets, wafers and worms, I'm sure the fish will be pleased !

[mac]

I hope some big shark eats the gremlins inside the board and the 2369!!! And survive to that toxic meat.
Mmmmhhhh... poor sharks, I better put my hand in the flush and recover it, and trash it.

mac

[Paul Perry (Frostwave)]

A ferrite bead on a transistor leg usually stops it oscillating at RF.
If that is the problem.

[mac]

I put a ferrite bead at the input jack with no results. Did not try a ferrite bead on a transistor leg... Next time.

mac