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I built a Ge Fuzzrite a year ago on tag and finally got round to testing it. I love the fuzz it does but when I turn the tone knob to anything much less than full, it starts to let unpleasant woofy low end frequencies through, especially if I hit the strings hard. I had the same problem when I breadboarded an Orpheum the other day. I think the tone knob blends between the first and the sum of the 2 gain stages....am I right? I don't have a 350kc pot so I've just used a 500ka. And as recommended by popular wisdom, I've got hfe 150ish for Q1 and hfe 30 for Q2.

Here's the schem and my layout...




Any ideas please?

Hi Ben!

A quick overview of your layout and I see that it doesn't exactly reflect the schematic.

C4 C6 R6 and Level lug 1 are supposed to be grounded...

edit: Your layout is perfect dude.. sorry I missed the ground symbol on the lug!

what is your voltage at Q2 collector, have you tried with different transistors.. or maybe a defective pot.

but when I turn the tone knob to anything much less than full, it starts to let unpleasant woofy low end frequencies through, especially if I hit the strings hard ... I think the tone knob blends between the first and the sum of the 2 gain stages....

I think so .. If I am correct, with tone control at full you only take signal from the first transistor, so the first stage seems to be correct. This also explains an hfe that low at Q2, maybe it can be adjusted by reducing R3 (a pot swapped here ?) .. or by adding some diode in parallel with R3, or a capacitor..

edit: I think I found your problem .. the schematic specify a "reverse log" pot for the tone control.. if you are using a standard log pot you have to wire it reversed (inverse the wires on lugs 1 &3) so the feel will be much better

hope this help

Maybe try unhooking C4 or changing it to a lower value. It seems that forms a low pass/high cut filter on the collector of Q2. Also you can try paralleling a resistor (1M~1.2M) across your 500K pot (outer lugs) to lower it to closer to 350K.

Thanks Doc and Mr. Head. I reversed the pot and strapped on a 1M and it sounds much better. Still some woofing though, I'll try messing with that filter - is it not a hipass though?

Ben79 wrote:is it not a hipass though?

Seems to me that this capacitor to ground arrangement rolls off some of the high end fizz, via a sort of lowpass-filter arrangement that the 100k and the capacitor form. it plays a role in governing the extent to which the transistor can "pull" current from the supply at various frequencies.

There is some funny experiments you can do:

Wire a second cap (using toggle switch?) in parallel with C4.

Change the 100k/47k series pair to 22k/100kb pot/27k. The 22k goes to one outside lug on the pot, and the other outside lug goes to the 27k. The wiper of that pot goes to C4, which in turn goes to ground.

The total series resistance of the resistors and pot remains constant, but what changes is the amount of resistance on each side of the pot wiper. That pot, plus a switch for the cap should provide a wide range of tones.

hope this help