Strange Build Issue - Need A Little Help.

[timd]

I'm attempting to complete an easy build - just a 386 based dirt box with few components on vero. I have tested the final finished product with a quick and dirty setup (9V DC female plug for power, in and out 1/4 jacks) and it works fine, so the board works. When I take this board and wire it up as a pedal with true bypass, etc. the circuit doesn't work and the 386 chip gets really hot after just a second or two - hot enough for me to smell the super glue that holds the board to a pot!

This is the second time I have tried this build. The first one didn't work either, and I think I fried out the 386. The circuit is one of my own, and I have made it before with no issues. I have looked over everything. The LED lights up. There is 9.4 volts coming in. I don't know what the issue is at all, but it seems to be an issue with an off board component. I just can't see why a stompswitch, pot, Led, 1/4 jacks, or power plug would cause a circuit to fail and a chip to heat up. Anyone have this happen?

[PRR]

Here's a cave-man debug:

Solder-up the off-board stuff with power on. Yes, this is a bad idea. But 9 Volts won't kill you. Use a battery, it won't throw any big sparks or burn the carpet. You might lose a part, but you already doing that.

Solder, sniff, feel; solder, sniff, feel;....

When you solder and get super-smell, that's a Clue. Un-do that wire and see how many other wires you can solder without problem.

[mistahead]

Love that debug method... wonder how it would go with a ~50V  and the wife not pre-warned mwhahahahahaha.

But at the original point, differential troubleshoot - what has changed in the mounting process, you're clearly shorting something (fast heat build up indicates this). What enclosure material? I'm going to guess metal and that off board knobs/switches are fine until you mount them in a big 0R box and create new cicuits from the hardware's housing against the metal enclosure...

Or at least that is what I would have done! 

[Jdansti]

Are your 386 chips from a reputable dealer?

Edit: you said they fail when you add external hardware, otherwise they work fine.

Do you have a drawing, even a hand sketch of the circuit?  I'm off tomorrow babysitting air conditioning installers at my house, so I could give it a try and see what happens.

[timd]

@PRR - Great debug tips. That will come in handy for this and for future build issues.

@Mistahead - You mentioned the enclosure, which is one thing I hadn't considered... It is metal - a salad bowl type thing. What is an "0R" box? Maybe as the first part of the debug, I'll leave everything soldered and take it all out of the enclosure and see if it works.

@Jdansti - The chips are from Tayda, and I've never had an issue with them before. Basically the failure is somewhere when I add the extra components/enclosure. I've gotten this circuit to work before as a pedal. In fact, its been on my pedalboard since I made it - its the Onyx:
http://www.diystompboxes.com/smfforum/index.php?topic=99943.0
Sketch/video will be found there.

[armdnrdy]

Please excuse this stupid question but....are you using an isolated power jack (plastic) or a metal one?

I had an issue similar to what you described so I had to ask.

[mistahead]

Short hand to remind me that I have to remember the circuit beyond the circuit board:
"0R" = Zero Ohm resistor
"xR" = My Finger


Frustration makes my logic break so I have to have some tactics to drag it back into play - heat sounds like shorting, the differential is between board and enclosure (assuming no other changes, knobs/etc were on cicuit on board), something about the enclosure is shorting..

[timd]

Please excuse this stupid question but....are you using an isolated power jack (plastic) or a metal one?

I had an issue similar to what you described so I had to ask.

Its an isolated one.

[Jdansti]

If the power were shorting to ground, then your power supply or battery would be hot. You must be doing something else that the 386 doesn't like.

Here are a few possibilities that come to mind:

Reverse polarity-possibly at the chip and not the power jack.

Output shorted to ground.

Switch miswired and you're applying 9V to the input or output pins.

[Jdansti]

Well I breadboarded this today and liked it. I added a 1k pot between pins 1and 8 of the 386 to give me some control over the gain. If I box this, I'm considering calling mine "Spirit in the Sky" because it reminds me of the extra fuzzy guitar on Norman Greenbaum's tune by the same name. Here's a little bit of poorly played "Spirit in the Sky" using the Onyx:

http://soundcloud.com/john-danna/spirit-3-from-ampkit/s-k3one

[timd]

That sounds really good! The gain can be really crazy without that pot and/or a resistor to tame it. Spirt in the Sky is one of my favorite thick recorded fuzz tones as well as American Woman (Guess Who's version of course). I hope to have some time soon for DIY stuff - my basement caught a bit of water and I've been busy with that.

[kingswayguitar]

pretty cool

[timd]

After some exhaustive debugging, I found the answer...which should have been easy to spot. I was using a bowl shape enclosure and the lugs of the pot were touching the enclosure, causing chaos to ensue. I had a rubber washer laying around that I used to lift the pot just a bit so it didn't touch. Problem solved.

[mistahead]

Ermahgad ERMAHGAD - I HELPED SOMEONE!!!!

We're all royally *******d now...

[Jdansti]

Congratulations!  It's always the easy fixes that are the hardest to diagnose!