noisey BC108 when put on switches

[tjmicsak]

I took a BYOC fuzz face and added tranny pads and switches so I could select out of two Ge and two Si pairs for both Q1 and Q2 using three 3PDT switches on each side of the unit. The resluts were that there is actually not a great deal of difference now between the seperate Ge sets or the Si sets as there was when replacing them on the board pads themselves, but I still understanably have a gain increase when going from Ge to Si sets.
It seems that the wiring leads for the switch configuration is "buffering" the neuances of the different transistors. On top of that, the real problem is that now when selecting the Si trannys (but only when using them in BOTH Q1 and Q2) they now exhibit a kind of ocilation sine wave noise right in the sweet spot sweep range of the bias as though I am turning the tuning dial of a short wave radio. This goes away if the fuzz control is set back from 10 to about 9.5.
Should I have used shielded wires for the switches?
How can I eliminate the issue?

[darron]

shielded wire to the switches would be a horrible pain, wouldn't it?

is this the circuit that you are working on? http://www.buildyourownclone.com/fuzz.html

putting massive filtering caps on the power rails of a fuzz face seem to help with oscillations. ie. 1,000uF.

[R.G.]

You have successfully turned a Fuzz Face into a radio frequency oscillator.

The BC108 has a gain which extends up through the FM radio band, over 100MHz.
Wires have inductance; not much, but some, even straight wires.
Wires have capacitance to other wires. This can form a feedback loop you can't see.

Decoupling your power supply with both an electrolytic cap of about 100uF and  0.01 ceramic disk may help. Shielding the wires would help, at the expense of possible treble loss because the capacitance of wire to wire is turned into capacitance to ground (the shields).

The real answer is Lesson 1 about electronic layout: keep signal wires short and direct. The higher the frequencies involved, the shorter and directer you have to keep them.

[tjmicsak]

I had a pretty good idea it was the wires as I had tried all the trannys in the two pads on the actual board and had no issues.
Well I removed much of the wiring and switches down to one set of Ge and one set of Si, soldered the pad sockets righ on the switch terminals by breaking them out of the tri-pad plastic, and used minimum wire from the board pads to the switches. No more problems and I still have option of Si or Ge for Q1 and Q2.

Anyone know where I can get snap-in hole fillers for the switches I removed?