Output from Pedal is Too Quiet

[tristanplaysguitar]

Hi

I'm building this pedal, an MI Audio Blues Pro clone. Everything seems to be working fine. I substituted the TL082 instead of the JRC 4558 because its what I had on hand. I'm ordering some other Op Amps to do a comparison.

However, when playing through the circuit, the output is really quiet. When I go straight to the amp it is loud, but the level through the pedal is low. Any ideas about what the problem is? Could it be the TL082, or is it something else?

Any suggestions/ideas on what to change to make it louder would be greatly appreciated.

Tristan

Schematic: http://tinypic.com/r/2zecpkg/6

[iccaros]

Tristan
Could you give us voltages around your opamp?

[Govmnt_Lacky]

Are you sure that your Volume pot is wired correctly? When looking at the BACK of the pot and the lugs facing DOWN, the ground wire should be going to the lug on the RIGHT.

Something quick to check. Otherwise, you need to do what iccaros suggests 

[tristanplaysguitar]

Are you sure that your Volume pot is wired correctly? When looking at the BACK of the pot and the lugs facing DOWN, the ground wire should be going to the lug on the RIGHT.

Something quick to check. Otherwise, you need to do what iccaros suggests 

Yup, it's wired correctly. When you guys say check voltages around the op amp - should I be probing for DC or AC voltages with my multimeter? No oscilloscope, sorry

Thanks

[nikooO_o]

Setting your multimeter to probe for DC will do the trick.

[tristanplaysguitar]

Tristan
Could you give us voltages around your opamp?

Pin 1 = -4.9
2 = 5
3 = 2.5
4 = -9.2

5 = -4.9
6 = -5
7 = -4.9
8 = -0.5

So, pin 8 is the problem, right? That should be the V+ for the op amp, which should be +9V, right?
Any other ideas/suggestions? Maybe a way to fix this? Do the other pins seem normal?

Thanks

[tristanplaysguitar]

Also, it may or may not be oscillating. It could just be a lot of external noise, as its on a breadboard. But there are some weeird harmonics coming through.

[iccaros]

first find out why pin 8 has no voltage on it?

It should read continuity to D3 and C11..
IF you not you have something miss wired there.

[tristanplaysguitar]

I've got continuity between D3 and C11. It seems like it should be getting voltage? Any other suggestions? I double checked that I wired the power section correctly.

[Jdansti]

If I may chime in, this would be a good point to post photos of the front and back of the board as well as the off board components.

Did you wire it point to point based on the schematic or use a particular layout?  If it's the latter, please post the layout as well.

[iccaros]

^^^^ +++ what JDansti said...




is you diode in backwards?

also since you have -9 volts on ground (pin 4) it suggest you have power plugged in backwards, wall wart or batt? check those connections..

[tristanplaysguitar]

So, the diode was backwards.
Now Pin 8 has 8.6VDC.
And Pin 1 = 4.3V,
2 = 4.3V,
3 = 2.1V,
4 = 0V,
5 = 4.3,
6 = 4.3V,
7 = 4.3V,
8 = 8.6V
Battery = 9.3V

Also, the guitar only comes through the amp if the volume pot is up all the way otherwise it all goes away, hum and everything. Also, the tone knob turns down gain. And the gain knob goes from nothing-crunch-super high gain crazy fuzz.
I'm wiring on a breadboard, no particular layout. I just built it as I went, point to point based on the schematic. Battery power.
It's still suuper quiet.

Any ideas?

Thanks,
Tristan

[Jdansti]

Do you have another IC you can substitute?  You might have fried it with the reverse polarity.

[tristanplaysguitar]

Do you have another IC you can substitute?  You might have fried it with the reverse polarity.

I tested it with an Ne5532. Same thing.

Tristan

[iccaros]

Breadboard can cause issues, but trace your wiring, see trouble shooting page to build an audio probe..

[tristanplaysguitar]

Breadboard can cause issues, but trace your wiring, see trouble shooting page to build an audio probe..

Argh I thought I was done with the troubleshooting, and into the "quick fix" phase. Come to think of it, there never is a quick fix phase though.

Thanks, I'll try and make the debugging probe and troubleshoot this weekend.

Tristan

[tristanplaysguitar]

Breadboard can cause issues, but trace your wiring, see trouble shooting page to build an audio probe..

So I probed the thing. Tracing my schematic as I went, this is what I got:

I'm not really sure what that part of the circuit even does other than some filters that I can see on inverting input B of the op amp. Anyone care to explain that portion of the circuit?
Also, I'm getting sound after the tone pot, but not right after either the 100K resistor, or the .022uF cap. Any ideas?

Thanks,

Tristan

[Jdansti]

Check the polarity of C10.

Can you post a photo of your breadboard?

[tristanplaysguitar]

Check the polarity of C10.

Can you post a photo of your breadboard?

Here you go: http://tinypic.com/r/330z5mq/6

C10 is correct. Also, the two IC sockets to the left don't have anything in them, just storing them in the breadboard.

Tristan

[Jdansti]

Two things look suspicious, but it might just be the way the photo looks.

R3 looks like it might be connected to pin 3 instead of pin 2 of the IC.

The other thing I can't verify is the little circuit containing R5, R6, R7, C6, and C8 and how they are connected to pins 6 and 7.  You might want to double check these.