Help

[Guitarist335]

I am a newbie to electronics and am learning through trial and error.
I have been breadboarding the schematic diagram below, which is an overdrive unit.



For an op amp, i am using the TL081, only because it was recommended on another forum. I know very little about op amps. My goal is simply to successfully  create my first overdrive unit on a breadboard.

I have built this schematic three times now. The first two times, I had terrible buzzing.

On the third attempt, I got no buzzing and instead, got a nice clean sound. The good news is that the buzzing is gone, but the bad news is that i cannot figure out why i am not getting any distortion or overdrive sound.

I have wired the schematic I linked to very carefully. I suspect it is the op amp itself that i am wiring incorrectly, even though I think i am following the schematic correctly.

Can anyone provide any advice on what may be causing the op amp to pass the signal, but not treat it as expected?

Thanks for your time and expertise. I appreciate it.

[11-90-an]

hello and welcome...   

have you tried replacing the op-amp? it would also help us if you would picture your breadboard with the circuit on it....

I also recommend not only naming your thread 'help' as it (more or less) should give an idea of your problem... 

[willienillie]

C3 is backwards on the schematic.  Do you have C28 going to ground?  Vref?

[patrick398]

The pin out for the tl081 is different from the tl082. How are you powering it? 9v needs to go to pin 7 on the 081, rather than pin 8 on the 082

[antonis]

A nice clean sound indicates (besides good working op-amp) some short between output & inverting input (-)..
(op-amp works as a unity buffer..)

OR

Gain setting branch (R46/C28) is "open" (C28 lower leg not connected to any DC or AC GND) , as willienillie already said..

P.S.
Can't realize the reason for R3 (other than "stopper" resistor - useles for a circuit like this, IMHO) or as signal source internal resistance simulation..
Its actuall existence simply complicates input HPF calculation..

[Guitarist335]

Thanks to all for the advice on the circuit and tips on how to post here. I will try the ideas and report back once I have the chance.  At present, pin 7 of the ic is receiving + power and pin 4 runs to ground.  I will also post a pic later today. 

Thanks again fo.r your help. Will update this thread once I have had a chance to work with the ideas. 

[Guitarist335]

Hi folks:

Well, i checked everything that was mentioned in this thread, and I rebuilt the circuit from scratch, even trading out the Op amp.

I am convinced of one of the following:

Either:

1. The circuit itself is flawed- many people have commented on a capacitor being shown with reverse polarity- maybe that's it?

2. I may have burnt out a component along the way and that's what's causing it.

In any event, I am giving up on this circuit and I plan to start a new thread asking for a recommended circuit for the op amps I currently have.

I will make sure I title it appropriately. If anyone has any ideas, please look for my new thread.

Thank-you to all!

[Marcos - Munky]

1. just C3 is reversed, The circuit should work if you rotate it. The rest is fine.
2. the only thing that may be burnt is the IC. Everything else should be fine.

[antonis]

This circuit wll work (even for a limited lifetime..) despite C3 polarity..!!

[Digital Larry]

You never answered where the bottom end of C28 connects.  That's a fairly important detail.

[antonis]

You never answered where the bottom end of C28 connects.  That's a fairly important detail.

Probably more important than OP appraises..