Silicon FF is getting crazy when Fuzz pot fully up

[yeeshkul]

I made a silicon FF and it sounds quite decent, but when i turn the fuzz pot fully up then a strange whistling noise starts . Guys would anyone some advice how to get rid of it?
All the bias voltages are all right, everything works fine, just the bloody craziness at the top of the fuzz. When i turn it down a bit it stops but there is also much less sustain, so i don't wanna just turn it down ...

[GREEN FUZ]

Hmm..I had this problem also. If I remember correctly it happened when using high gain transistors. Since using lower gain trannies and installing a tone pot the problem disappeared.

[Jaicen_solo]

Putting a small cap between the base of Q2 and ground seems to help subdue oscillation too.
What type of battery are you using?

[yeeshkul]

both my trannies have hfe 190. I am using a super heavy duty 9V battery.
I will give a try to that trick, thanks

[yeeshkul]

i tried the cap but no change . I tried even different transistors... . I also inserted a big cap parallely to the battery. Still the same madness

[tcobretti]

The classic trick is a 50-100pf cap from base to collector on Q1.  My Mondo Fuzz uses MPSA18s and doesn't oscillate because of this trick.

[Gus]

This kind of problem is kind of common with a FF.

Layout and battery internal resistance and how well the connections are made between the cells inside.  First the battery I have "fixed' a few effects by just changing the battery.  Some batterys can do strange things.  One partal fix is using a good Al electrolyic cap across the power supply.  Have you seen how a 9V battery is put together?

Next the harder one Layout.  This is what you go to school, read books and do tests to understand.  You need to get you head around currents and phase and other stuff.

  This kind of problem is why I do not use stripboard constuction.  I don't like stripboard.

  I perf most circuits and wire every thing point to point I use no busses.  Wires that run parallel can cause crosstalk: However clever designers sometimes use traces in parallel (Top and bottom of a 2 sided board) to make small value caps.  There are lots of things you need to know to get good at this stuff.

Sometimes it could be the bypass switch with crosstalk.  Often when I build a new effect for the first power up it is not in a box and the jacks are wired direct to the in and out no bypass switch.  Have you tried the FF without the bypass switch?

Another kind of fix "bandaid" is to use a 47, 100 ohm etc  smallest value that works  resistor between the node of the "top" of the pot and feedback resistor and the emitter of the 2nd transistor.

[yeeshkul]

Thanks Gus, i will check it out and if it doesn't help i guess i am gonna built a new one from the scratch.

[yeeshkul]

actually the small res (100) helped completely! But, isn't this the same thing like to turn the fuzz pot down? I guess i am gonna build another one on a big layout