One Knob Fuzz Squealing?

[edlamb0306]

Heya,

I built up a one knob fuzz on a pedalparts board (http://shop.pedalparts.co.uk/Thug_Fuzz/p847124_7840055.aspx) but changed a few values as per suggestions on this page http://tagboardeffects.blogspot.co.uk/2013/04/1-knob-fuzz-bonanza.html

I have a couple issues:

1: I've tried loads of different combinations of transistors as per that tagboard page (BC107, 8, 9's, TP2222 etc), but can only get output if i use a combo of 2N3904 and BC182L.  Why is this?

2: I'm getting an uber loud squeeling noise and heavy radio interference when I switch on the pedal.  However, If I slam the input with another pedal (say, an overdrive with lots of volume) and then turn off the preceding pedal - all the noise is gone.  What's causing this?  Something to do with one of the components on the input before the first transistor like the input cap?

The values I used are

Resistors:
R1 - 18K
R2 - 820R
R3 - 4.7K
R4 - 1K
R5 - 120K
R6 - 1M

Caps:
C1 - 100u
C2 - 680n
C3 - 470p
C4 - 47p
C5 - 220nf
C6 - 10u

Cheers,
Ed

[notnews32]

Re: swapping transistors and not having any output... have you checked the pin layout of the transistors you're using? Check the pinout of the working 2N3904 and BC182L transistors and be sure to keep that arrangement consistent when trying different transistors. If the working transistor is plugged in the order BCE, make sure the substitute transistors follow that arrangement as well. Connecting the pins out of order/incorrectly will definitely assure silence (unless you're Death By Audio).

Also..99% of the time the following wouldn't totally kill the sound, but make check out the characteristics of the working transistors (voltages, hfe, currents) and make sure you're not overloading/underwhelming the circuit when you swap in a different transistor. If the circuit requires a transistor with an very large gain factor and you're trying to use a unity gain transistor, you may not generate a big enough signal to overcome certain threshold components like a diode or something. Just something to consider.

Re: the second issue.. I'm guessing that your pedal isn't properly grounded. Circuit ground and PS ground should be connected somewhere on the metal enclosure, like the ground lug on the input or output jack. When you do this, the enclosure itself is at ground potential and acts as a shield against hum and radio freqs. If you've ever seen ferrite beads in a high-gain layout before, they're typically used because they increase impedance to radio frequency signals while providing little resistance to the dc power. Try adding a ferrite bead or two to the signal input wire between the jack and the board. Adding a small capacitor to ground at the signal input may also help.

[Gus]

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0