Author Topic: Diaz Style Fuzz Bias Issue  (Read 153 times)


Diaz Style Fuzz Bias Issue
« on: February 26, 2021, 09:43:20 AM »
Just threw together a quick test circuit to put together a Diaz style square face fuzz. Using some GE OC44s - everything seems to be hooked up ok and it seems to sound pretty good, but the bias on Q2 with the stock values sits right around -6.6v and would take increasing the 8.2k resistor way up to around 20k to get it to down to the -4.5v range. Just curious as to why this might be, the transistor gains are up around 115 (which is around what most original diaz pedals I've had were) and both have low leakage. Curious as to whether this is natural for this circuit, the main resistor swap is 470 to 1.2k and 2k Fuzz pot. I did notice that the 'hendrix mod' is basically the same circuit and it has the 8.2k resistor swapped out to 18k which makes more sense given my situation. Every original diaz I've owned has the 8.2k in place.



Re: Diaz Style Fuzz Bias Issue
« Reply #1 on: February 26, 2021, 10:00:18 AM »
The 4.5VDC at Q2 is something the web seems to reinforce and seems to limit what people will try .

I often set a ff like circuit 2nd transistor collector >6VDC.

Look at different FF like fuzz circuit voltages.

I often add bias controls to circuits I build try different operating points on the transistors.


Re: Diaz Style Fuzz Bias Issue
« Reply #2 on: February 27, 2021, 04:12:43 PM »
4.5V is not a magic number. Maybe not close. Perhaps not likely.

8.8V would be wrong. Too close to 9.0.

6.6V is quite workable and likely very playable. It leaves 2.4V of swing, way more than we need, and the usual output network makes this about 0.16V which is enough to rock the clock.