FF PNP info...pls

[rx5]

wired my PNP (ge) FF to be negative ground...AND it oscillates when FUZZ is set to full....  why the heck does it??

really like the sound but I couldnt make an electronic bypass for it...since electronic switches operate in positive supply , not negative supply...

hope someone out there who could help me....

[bwanasonic]

My first attempt at a FF wired that way did the same thing. I thought it was just me! I wish I could say I knew what it was, but I scrapped the whole negative ground idea and went *old-school* - PNP/pos. ground and no adapter. It works really well and battery life is hardly an issue. A carbon/zinc lasts forever.

BTW- the oscillations I was getting were not squealing high, but more low-pitched.

Kerry M

[ErikMiller]

Check your layout for what wires run next to each other. Keep the input and output as far apart as possible.

Fuzz Faces will oscillate if you merely route the hookup wires just right/wrong.

[rx5]

bwanasonic,
It would be no hassle at all if you had only CARLINGs available  :wink: my only problem was how to convert the JFet switching to positive ground, same with PNP fuzz  :lol:  I think that hasnt been done ?? yet?? convert to to Positive ground a Jfet switching scheme?? :wink:

Erik,
I think its not the wiring cuz it was originaly PNP and even though Its wiring was wired so ugly   :wink:   , I didnt hear oscillations when it was Positive ground... Until I came upon an article at AMZ bout converting PNP to negative ground...


peace..


-Ralph

[rx5]

another thing also, my (all Ge) PNP sounds GREAT in the morning and noon ....... as if it has no tone alteration(flat response).....but in evening comes, it sound totally different.... It sounds like the mid has been cut out... like "scoop" if you put it that way...hehehe :lol:

is this normal??  :lol:

FF rocks..... (change the 2.2uF)  :lol:      :lol:  :twisted:


-Ralph

[R.G.]

I know that there are several people who claim undying success in rewiring PNP FF and other fuzz circuits for negative ground, but I have run into several situations where this connection gives intractible oscillation that only quits when restored to positive ground.

I believe the problem is impedance in the power supply between + and - leads. A 0.1uf ceramic cap in parallel with a 1uF cap in parallel with a 10uF cap in parallel with a 100uF cap in parallel with a 1000uF cap might fix this. But maybe not. Your mileage may vary.

[Brett Clark]

I think the problem may be the input capacitor (2.2uF). The DC potential of the guitar input will be at chassis ground, whatever that may be. SO, in a standard FF, the input side of the 2.2 is slightly positive (the Vbe of the first transistor), but if you change the ground, it's (9V-Vbe=8.8V) NEGATIVE. So the cap should be reversed, and will need to be rated for at least 9V (whereas 6.3V would have worked before).

By the way, this may change the sound. Electrolytic caps are not very linear when the DC bias applied is very small (<1V). Changing to negative ground (and reversing the cap) changes the bias across the cap from about 0.2V to 8.8V. Personally, I think it's an improvement, as I like to change this cap to a film cap anyhow.

As for a (germanium) FF sounding different at different times of day: they are very temperature sensitive. The first transistor has no emitter resistor and will shift it's operating point with just a few degrees of temp change. Just touching it with your fingers for a few seconds will change the sound.