troubleshooting a splitter/blend pedal - 18V too much for a TL072?

[rollo greb]

Hi, this is my first thread here. I've built a number of pedals but have just recently ventured into opamp based effects, so I'm still learning. I found this schematic floating around the internet and decided to try building it, it seems to be based on the idea of the GGG parallelyzer which splits a signal into four and then blends back together:



I'm having trouble with the output section - without the TL072 installed I'm getting -9V at pin 4 of the socket like I should have. When I install the chip I get +0.6V at pin 4. I've tried two chips and gotten the same result. Have also triple checked my wiring, with a meter as well as visually - it's built on perfboard but everything seems fine. Could the +/- 18V be too much for the TL072? I see on its datasheet that 18V is its max rating, but I think the TL074's are rated the same and they seem fine in this circuit.

I can measure and post the voltages at the other pins of the chip if it helps.

Also, comparing the schematic above to the GGG mini mixer, everything looks similar (apart from the higher voltage I'm using).

[frequencycentral]

TL072 is fine on 18V.

[Jordan A.]

To add to FCs post, the maximum supply for a TL07x is +/- 18 volts, meaning a total of 36 volts.  At +/- 9 volts you are only half way there.

Double check that it's not in backwards?  That seems like the most likely culprit, otherwise check for the usual stuff, hard to see shorts, wrong resistor value, shorted cap.

cheers,

jordan

:edit: if the IC is in the right way, maybe try it with two 9 volt batteries, to eliminate the charge pump from the equation?

[rollo greb]

Thanks for the replies. Good to know the chip should be fine with +/- 9V. The chip is definitely in the right way around, and I've checked every resistor and cap in that section of the circuit with a meter, as well as checked for any possible shorts with a meter and have come up totally empty.

[R.G.]

Debugging: what to do when it doesn't work

[rollo greb]

Problem solved - after staring at the datasheets for a while I noticed the schematic is drawn wrong. The positive and negative inputs should be flipped in the second section of the TL074's (after the return jacks). Works like a charm now, and wow parallel mixing is a lot of fun! I would definitely recommend this project to anyone interested in that kind of thing.