TL072 type opamp behaivior.

[served]

Hi.

I had some PCBs made and there is an error somewhere.
I would like to ask some questions about the TL072 operation.

If I power it with +/-17V. Should the out pin have a voltage on it even if there is no signal on the input.
The opamp is run as inverting buffer. (-)Input has 10k feedback resistor + 10p cap and input resistor 20k. (+) input is to ground. There is nothing loading the output.

If I power the circuit I have ca 15V on the output. Even if I have no parts on the pcb except the IC I have that voltage on the output.
Tested different Opamps 5532, Opa, TL072 taken from working systems.

If I take the Opamp out. The voltage is gone.

[thelonious]

If you had PCBs made, you should have both a schematic and a layout easily accessible. It would help a lot if you posted those so we can more easily identify the problem. When you get 15 volts on the output, are you measuring between ground and the output pin? Have you properly terminated the unused section of the opamp?

[antonis]

The opamp is run as inverting buffer. (-)Input has 10k feedback resistor + 10p cap and input resistor 20k. (+) input is to ground.

Maybe you have to post a rough schematic because it seems to me more like a booster (X 1.5) rather than a buffer...

[slacker]

Max safe supply voltage for a TL072 is +-15 Volts, I don't know if that explains your problem though. 

[merlinb]

Max safe supply voltage for a TL072 is +-15 Volts, above that it might not work correctly.

The data sheet says +/- 18V
http://www.ti.com/lit/ds/symlink/tl074.pdf

[slacker]

I've always been led to believe that the recommended max was +-15V, seems like a fairly common belief. Maybe it's an old wives tale, or like a lot of things it was something that used to be true back in the day. Does seem like the datasheet makes no mention of it, looks like I stand corrected.  

[GGBB]

Max input is +-15V - max supply is +-18V.

[served]

I have tested all the ICs after inserting inside this circuit. They all work.
After remeasuring.
I am getting -15V on the out put. If I desolder the feedback resistor and feedback cap input looses its voltage. But the output pin still has that -15V, so I guess it is coming somewhere. Its is there even if I ground all the Opamp inputs.

The stage looks like this
http://chrisgammell.com/wp-content/uploads/2008/08/inv_opamp.jpg

I have eagle files and everything but as its a double sidded board there is no good way to present the PCB layout as the IC is on the other side.
I guess I have to figure this one out myself. I will do some more investigation.

I took another board (I had many made) and only soldered an IC socket and installed the opamp and also the PSU. The result is the same -15V on the output of the opamp stage.. So I think the boards are faulty.

[bool]

The most useful "opamp data" for a DIY builder would be imho: How close to each rail an opamp can swing at the output, precautions wrt the useful input stage voltage range (and protection), and the average current consumption. Gbwp, open-loop gain and slew rate, thd ... are usually slightly less important in pedals imho.

[slacker]

Probably a stupid question but you haven't switched the inputs have you. That would make it a comparator and the output would tend to go negative.
I would take a blank board and continuity check  that all the opamp pins are connected how you think they should be.

[served]

Thank you!
As stupid as it can be, this is the issue here.
The board has total 20 ICs on it and managed to mess up the easiest IC.

Ohh well, thats the fun of the proto run anyway.

Thanks!
I hope I can manage to fix it now.

[antonis]

If I desolder the feedback resistor and feedback cap input looses its voltage.

Quite right if there is a coupling capacitor before the inverting input...

But the output pin still has that -15V, so I guess it is coming somewhere.

Maybe a short-circuited decoupling cap in power line..

edit: Didn't read the above about pin swapping..