Help Debugging Op Amp Distortion Prototype

[platypy]

So I'm trying to design a distortion for a friend (styled somewhat after the ProCo Rat, and other opamp distortions) and I've breadboarded it up, but I've run into a strange problem: the effect makes no sound, unless I unground the input and output, and then it just sounds clean, with the occasional hum from the ungrounded cables (the volume pot does nothing). I looked over my breadboard and found that I had connected a capacitor to the wrong pin of the IC, but I fixed that now and am still having the same problem. Could I have fried the IC? If so, is there a way to tell?

Here are the voltage measures for my IC (I'm using a TL071). My supply voltage was a battery that I measured at 8.49v
P1=0.15v
P2=4.17v (This pin was acting weird: as I held my multimeter on it, the voltage slowly dropped. When I took my multimeter away and put it back it reset to 4.17v and then started to drop again).
P3=2.07v
P4=0v
P5=0.15v
P6=4.25v
P7=8.49v
P8=0v

I also measured the voltages on both my diodes. Both the cathode and anode of each read at 0v.

This is the schematic of what I built:


If anyone can give me any advice on how to get this thing up and running, that'd be much appreciated. Also, my schematic should be fine, but I did piece it together from a few sources so if anything seems off there, I'd love to know.

Thanks!

EDIT: I forgot to include the value of the capacitor connected to ground in the voltage divider. I used a 10uf cap.

[GGBB]

the effect makes no sound, unless I unground the input and output

Taken literally, this is to be completely expected. Could you explain what you actually mean, or perhaps post photos of your work? This sounds like simple build mistakes.

Schematic looks fine, but note that you are not applying very much gain in comparison to typical distortion circuits (and especially in comparison to a RAT). I'd still expect some clipping, but not a lot, but I could be wrong. Is your clean signal any louder than bypass? Try changing the 100k off pin2 to 10k or lower. I doubt that you fried the IC, else you wouldn't get any sound.

[platypy]

Oh, I see how that was confusing. What I meant was, when I have my input and output jacks, with the tips attached to the circuit, and the sleeves grounded, absolutely no sound comes from the circuit. When I remove and connections to the sleeves, I get clean sound with a slight hum.
I can post some pics, if you want, but I've built it on a breadboard so it's really messy.
Since I built it on a breadboard, I also don't have any reference to a bypassed signal. I'll re-set it up and listen to the bypassed signal, as well as trying a 10k instead of a 100k.

[anotherjim]

The op-amp could be current limiting and/or oscillating, because you have a large capacitor followed by a very low impedance load from its output in the clipping diodes. There ought to be a series resistor in there before the diodes, say 1k.

To the inverting input, make sure you have that 10uF cap the right way round , negative to ground. I'm assuming it's electrolytic as it's the only one you haven't shown polarity for.

[duck_arse]

A-L-W-A-Y-S include the IC pin numbers on yer diagram. look them up on the datasheet, so you don't get them wrong. and once you've written them on your dia, recheck yr board, you might find something amiss.

and yes, we want photos.

I've built it on a breadboard so it's really messy.

there is no reason for a messy BB build. lay it out neat and ordered, less mistakes, easier to find when you make them.

[platypy]

Ok, so I re-did my breadboard nice and neat and added a 1k series resistor before the diodes, per anotherjim's suggestion. Now, instead of only getting clean sound when I unground the input/output jack sleeves, I get clean sound when they are grounded. The volume knob still doesn't work, though.

Here is my revised schematic, and some pictures of my breadboard. That green electrolytic capacitor connected to ground is non-polarized, by the way. Also, the purple jumper wire connects to output, and the blue connects to input.




Let me know if you need any more information or pictures. And thanks so much for the help!

[anotherjim]

Ha-ha! Those 2 film capacitors that you write as being 1nF, look like 100nF to me (the .1 on the top refers to 0.1uF value). 100nF is big enough to filter a lot of signal out. Try without them if you don't have 1nF.

[platypy]

Success! I removed the two 100nf caps masquerading as 1nf's and now the volume knob works. I also changed the 100k and 1M resistors off of pin 2 to lower values to increase the gain, so now I'm getting some (very bass-y) distortion! I'm gonna go rework the circuit now so it sounds more to my liking. Thanks  so much for all the help!

[GGBB]

I also changed the 100k and 1M resistors off of pin 2 to lower values to increase the gain

To what, may I ask? Gain is the value of the 1M over the 100k - changing both by the same factor - e.g. to 500k and 50k - won't change the gain - but it may change the frequency response. Keep the 1M, lower the 100k.

[platypy]

Right now I've kept the 1M and have the 100k changed to a 100R, but I'm still playing with it.