I just built an Opamp Muff Fuzz with a 3mm Red LED and a 1N4148 for the clipping diodes -it works fine- but I just wanted to ask these two questions about tweaking the tone:

1)  How can I stop the "gating" type effect that's chopping the sustain short and sucking the guts out of palm muting?  I read about something like "putting a resistor across the diodes", but what does that mean?  Which resistor value would be used and where exactly is it connected to?  I've used the PCB design from GGG.

2)  I'm using a piggybacked LM833 and LM4558 for the opamp, but I also found a TL072 to try and it doesn't seem to work.  All that happens when it's socketed is the clipping LED lights up really bright and there's no sound at all.  What gives?  :shock:

Anyhows, thanks if anyone can help.

> I'm using a piggybacked LM833 and LM4558 for the opamp, but I also found a TL072 to try and it doesn't seem to work. All that happens when it's socketed is the clipping LED lights up really bright and there's no sound at all. What gives?

What does this mean? Do you have the output of an LM833 into LM4558? Do you have a blocking capacitor in between? If not, please check the voltage going into the input of the op amp with the LEDs.

By piggybacked, I meant the two opamps stacked on top of each other in parallel ie David Barber style.  I didn't know how else to describe it  :oops:

The problem with the TL072 is that when I put it in the socket by itself like any other Opamp -it doesn't make any sound and just lights up the LED (4.39volts).  The LM833 and LM4558 work fine and sound great whether by themselves or in parallel -so I'm guessin' the TL072 might be busted.  

The other opamps sound great anyway so I'm not that fussed about the TL072 not working (unless it sounds angelic or somethin')...the crummy gating is what's really bugging me.

OK, if the 4558 works and the 072 doesn't , then yes, maybe the 072 is damaged I guess.

Quote2) I'm using a piggybacked LM833 and LM4558 for the opamp

Pardon my ignorance, but is that literally what it sounds? on physicaly on top of the other (or am I on to much ganja...) ?

Oops, only the first line is a quote... sorry... the second is my question...


definantly too much ganja...

Perhaps using a very large resistor in parallel with the LEDs would solve this.

I'm guessing for some reason, the LEDs are shutting off when there's no signal, causing the gating effect. Being a FET input opamp, the TL072 pulls basically no current through the LEDs. Putting a 10M resistor would keep a DC path there even when the signal falls below that LED threshold.