Wooly mammoth clone problem

[franfranky]

Hi, i'm new on this forum, I live in France (nobody's perfect...) and I'm beginner in builting of DIY pedals ( but I'have some skill in electronic).

I have try to start with the built of an bass fuzz pedal, the famous "wooly mammoth".
I have find this model: http://2.bp.blogspot.com/-lYIkG8l6u5g/TVnFxKNs8cI/AAAAAAAAAVQ/tH1nDAr3mvA/s1600/ZVex+Woolly+Mammoth+-+smallest.png

Yesterday I'have built the pedal, all its good (leads, componants, wiring, ground...) but when I test the pedal on my bass I have a problem:
-the sound is "spongy" like a big noise gate ( when I attack the string the fuzz effect is present but the volume deacrease quickly and  the signal turn off).
-this variation of volum is different depending the note (the signal is very very low on the C of the G string) and make like a modulation ( the signal decrease and increase).

What do you think about this problem? a problem of bias with the two transistors (2N3904 no matched...)?


Thank you!

François

[craigmillard]

This does sound like a bias problem with the transistors, triple check all your resistors to make sure they are the right values and check for any solder bridges between the copper tracks...

A good tip is to run a Stanley knife over the gap a few times..

[franfranky]

I'have check all resistor value: it's OK
I have'nt find shortcut on the board.
for info I'have use 0.25w metal oxyde resistor, xicon MPP 0.01uF and 0.22uF (too big!), 100uF Elna RFS 25V (polarized).

I have scratch the board with a cutter between the cooper stripes.

[craigmillard]

Can you get some voltage readings off the transistors with a multimeter?

[franfranky]

I have check the voltage on transistors:
battery voltage : 8,93 v

Q1 (see the layout)
C: 1,65V
B: 0,65V
E:0V (strange??)

Q2
C:8,53
B:1,65
E:1,12

[WaveshapeIllusions]

It is a heavy gated fuzz, so that kind of sounds like what it should be doing. What is the level of the 'pinch' (q2 emitter to q1 base) pot set at. A higher resistance would make it awfully gated sounding. Mine does a similar thing at that level.

On the other hand, the voltages seem a bit odd. Q1 emitter should be at ground, base should be about tjat much higher. Collector usually biases low. Q2 base is right (same as Q1 collector), emitter is s bit high though. It should be at least 0V65 below the base, or it won't conduct. Also the collector should not be that high. I would look at Q2's collector resistor again, it might be an incorrect value?

Hope this helps.

[Jaicen_solo]

Double check your wiring to the pots. Also make sure you are using a fresh battery.