Distortion mod issue (help pls) - diyAudio
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Old 9th March 2013, 06:44 PM   #1
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Default Distortion mod issue (help pls)

Hoping someone can help.

So I had pickedup a DOD Death Metal Distortion dirt cheap, as it had the core crunch sound I was looking for. However the op amps were a bit too noisy and there was no gain control. So first up I swapped ina pair of TL082 op amps, and then I added a gain control by swapping out the 120K gain resistor with a 100K POT.

It actually did ALOT more to the sound then I expected. I did lose some gain, but that's ok considering the sound I did get which is alot closer to the sonic distortion but with alot more adjustability. The amps were quieter and alot less sloppy without the static sound. It's been workign great for over a month, then last night, the stupid thing will not disengage. It stays on, the gain is virtually nothing, but it is heavily distorted and not in a good way. I can't even begin to describe how horrid it sounds. It's like the circuit comes and goes, but at the same time, it has this god aweful sound I can't begin to describe. Something has HAD to of let go. Nothing looks burnt though.

The day before it did this, and the day it did this, there was kind of a funky smell, but I couldn't tell if it was coming from the pedal or somewhere else. I live in a 60 year old mobile home so there are always some interested scents. Plus the neighbors tend to um "cook" some rather interesting "food" that smells rather interesting alot of the times. It's not dope or anything, they really are cooking their sustenance, just most of what they could probably hasn't been smelled anywhere on earth before. So i haven't discounted that the scent could have come from them. However it didn't smell like silicon or carbon burning out. Nothing on the pedal looks burnt. If need be I can get an audio sample of how it sounds. In the meantime I took a buncha photo's(I also stripped the case and painted it as the black with red spiderwebbing looked horrid), I still need to put WWII Naval Aircraft decals on it to make it look better.

Due to their size I'm posting a link to the photo's. Please these are NOT 56K friendly or even slow DSL friendly. I also do photography and these are fullsize images from a Canon 550D 18MP DSLR camera. It took me 5 years to be able to get this camera before I had the $$$. I wanted the upclose detail though.

Guitar Effects Stuff Photos by redneck_chevy_psychopath | Photobucket
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Old 11th March 2013, 11:10 AM   #2
Tesla88 is offline Tesla88  Italy
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Click the image to open in full size.

Schematic
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Old 11th March 2013, 11:13 AM   #3
Tesla88 is offline Tesla88  Italy
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From what i understand , the pedal stay On and never go on ByPass , right?
First check the supply , are u using 9V battery or ac adaptor?
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Old 11th March 2013, 07:26 PM   #4
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Sound like you may have blown an opamp, but i can't tell for sure. You could try *carefully* to feel around for hot components when it's running, or trying to sniff out the area of the board that has that smell. You might try cleaning off some of that flux from your soldering job as it might be leaking current to another part of the circuit.

Please use a battery when troubleshooting. Many pedal adapters can really push some amps.
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Old 11th March 2013, 09:45 PM   #5
Tesla88 is offline Tesla88  Italy
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I won't bother about the horrible sound is making , you should start from the fact the unit don't go in bypass

Quote:
the stupid thing will not disengage
If still not disengage (bypass) the problem coulb either the 4007 IC or the switch , anyway a low voltage can also be the cause.

So first check voltage across ICs , you must have 4.5-5V between pin 7 and 14(+) of 4007 IC , and 9V between 4 and 8(+) of op-amps (TL072)

If voltages are ok , i will start by changing CD4007 , it's the responsable of switch unit on - off ...

Bye
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Old 12th March 2013, 03:22 AM   #6
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I always use a battery to power my pedals, I've checked the voltage on the battery and it's right up there where it shouldbe, as I suspected as it's brand new but always check the simple stuff first. I'll check the voltages on the op amps. I'll give the switch a test too. Def don't want to go back to the old op amps, they sound like crap. May order a couple of 4558's if I can find them and these are toast. The TL082's sound REALLY close to the 4558's with just a bit more gain and a bit less harsh. The junk that came in this pedal though just sound like garbage all the way around.

I'll check that stuff when I get a chance, but I just found out a kid I've known sicne he was 3 was just murdered last night, so that's kind of onmy mind right now. Hard to concentrate on anything else.
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Old 15th March 2013, 06:46 AM   #7
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Ok well i popped everything apart, appears the problem of the pedal not turning off was an issue of the foam rubber pad shifting which I have now glued in place inside the plastic foot pedal part.

However it still has same same crappy sound. Felt around for hot components, and nothing. Nothing smells off this time when I'm trying it out, so it's not the pedal. None of the components smell off either.

Voltage accross pins 4 and 8 ont he two 8 pin Ic's are the same as on the 14 pin IC. Right about 8 volts, regardless of where I set the gain control.
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Old 15th March 2013, 06:48 AM   #8
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Oh also forgot, I have a small pinpoint IR thermometer that's pretty accurate I use it to make sure I don't fry my Radio control stuff and that I don't blow up the house when charging lithium batteries, and the temp accross all the componenets are within 2 degrees of each other, and that is about the same as the rest of the room or any other average item i point it at in the same room so nothing is getting warm.
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