Messages

thanks for your help, Jon and Bret. yes, "whine" is the better word here. when i try change r7 (Vr=25k) with feedback knob off - there is no whine or other bad sounds, just like intensity of effect is changed. maaaybe i have a mistake in pcb (it was rewritten to .lay format) - need to check it third time. with all values stock on powered pedal and effect in "Off" there are some values readings:
fb - pin1<- 7.62k-> pin2 <- 2.2k-> pin3 (border of whining)
r26 - 3,20k
r7 - 4.87k
when pedal in ON - r7 increases to 6.3k . i changed r26 to 12k but that also changed feedback usability. will try cap values soon.
Only increasing r7 doesn't help.
One more question - is difference of ~1v (+9V against -8.25v) could be a reason?

Hello all iron gurus!
Another "soldering by numbers" guy here. I'm stuck in debugging this great pedal. Layout is from bangerang101, pcb etched by local tech. Its (almost) all working fine except of bad oscillation if feedback knob turned about 3/4 CW  (7.6K between 1 and 2 lug). I use icl7660scpa inverter, 4558 chips (also tried  tl072).
Readings on ICs 1-4 are about these values:
-0.5mV  9.22V
+0.5mV  50mV
0           2mv
-8.23V    0

IC 5:
50mV   9.23V
40mV   3.3-3.8V
40mv    200mV
-8.25V   200mV

IC 6:
-6/+6V     8.55V
0             -3/+3V
-2/+3V     3mV
-8.25V      0

ICL7660s:
9.23V    9.23V
4.65V    7.46V
1mV     5.21V
-4.01V   -8.26V

I tried to change feedback pot, change values of r7 and r26 with no big success.
One finding while debugging is if I change R7 with variable resistor (10K iirc) i can tune some kind of "deepness" of the effect. Very nice mod for my ears, so i plan to make additional external pot for it.
I also read somewhere that lt1054 is a better option, but i can't buy for now.

Your help would be greatly appreciated.