Phuncgnosis sound

[zhx]

I just built the phungnosis and got it working. The sound kind of puzzles me though. Instead of an expected "woaw" I get a "rrrrrrrawh...(pop)". So a bit of distortion and a slight pop at the end. Could this be because of ceramic filter caps? I couldn't find polyester ones. The ic is a RC4558P. TL062 and NE5532 distorted too much.

[GibsonGM]

Hmm, could you post your voltages at each pin of the IC?  Sounds like a short somewhere, something like that.  It shouldn't distort.  Read the post called "Debugging", and be sure of your parts values....LEDs oriented correctly, the right value resistors biasing the opamp and in the gain feedback loop, that kind of thing. If one of those was off, you'd experience what you're describing.  Need voltages to see what's up, though....usually there's an assembly error. 

Ceramic caps won't do that (as long as they're good), BTW, they would just be less hi-fidelity and maybe create just a very small amount more hiss in the circuit.

[oldrocker]

I used ceramic caps in mine and it's fine.  I agree that it's most likely an assembly error.  For what looks like a simple project I was surprised how much effort it took to build it.  Again watch what LED's you use.  I used some I bought from an electronic store multi pack and they didn't work right.  Then I used the smaller yellow LED's from Radio Shack and it started working.  I think I used a 5532 in mine.

[zhx]

Thanks guys !

to GibsonGM: here are the ic pin voltages (1spot 9.53V)

pin1 8.83
pin2 7.11
pin3 1.59
pin4 0.00
pin5 7.06
pin6 1.88
pin7 6.36
pin8 9.53

to OldRocker: I used 3mm red leds. They're the same I used on my nurse quacky ... worked fine there.

The sound isn't that bad, just a little distorted and the slight pop at the end is kinda weird.


BTW: If I were to add a decay pot, that would probably be a pot - resistor combo parallel to one of the polarized caps to ground. Could I do this by substituting the 330K to ground with - say - a 50K res and a 500K pot?  Or am I way off here?

[zhx]

Oh, I just noticed that the 5M resistor connecting pins 6 and 7 is 4.9M instead of 5M. Could this be the problem?

[cab42]

My phuncgnosis also distorted very badly. I used a TL062 opamp in my original build and also tried a few 4558's.

Then I rebuild it using a TL072 and it quacked like a dream.

BTW: If I were to add a decay pot, that would probably be a pot - resistor combo parallel to one of the polarized caps to ground. Could I do this by substituting the 330K to ground with - say - a 50K res and a 500K pot?  Or am I way off here?

Mac suggested using a 1M linear pot instead of the 330K resistor. I tried that and it works fine. He also suggested a few other mods. If you search you should be able to find them.

Regards

Carsten

[zhx]

I added a 100K resistor to match up with the 5M. The pop is gone and the quack is good. Still distortion, but the sound is actually pretty good. With the filter turned down makes a pretty good OD. I still have the 330K/ pot fix to do, but I believe it will work fine.

[markm]

There may be other issues with your build if you are getting that much distortion from this circuit as it is pretty darn clean from my experiences with it.