[Fuzzy OneThree]

After having my cMoy for nearly a full year, I decided I was going to case it correctly in an Altoids tin (originally it was in a large and, frankly, a quite ugly wooden case). When I did that, I also rewired it with navship's silver wire so that it would fit. When I switched it on, the op-amp quickly heated up. The sound was barely audible, even when everything was turned up all the way. The weirder thing was that there would still be that small amount of sound even when the amp was turned off and even when I completely removed the battery. Albeit, the sound was extremely distorted, like when your battery got low on power and the opamp needed more power, but to a greater extent.

I picked up 2 op-amps at Radioshack for testing. The first one was LM386N which didn't overheat. Granted, it wasn't correct for the application and there was still the low volume when plugged in and distorted sound without the battery and no sound in the left ear. Next up was TLE082. This one heated up just like my original OPA2132PA.

So, still not having a solution, I took the next logical step. I built a new one from scratch. I followed tangent's instructions and it still had the same issues.

Now, pics. The first 3 pics are the original cmoy; next 2 are the new one.

P.S. They are louder when the battery is unplugged.

P.P.S. Battery is at 7.87 v, v- to ground is 4.74, v+ to ground is 3.10 for the new one. This is with no op-amp. R1 + is 4.70 ohm, R1 - is 4.68 ohm

 

[tangent]

The LM386 is not an op-amp. It probably contains an op-amp, but it doesn't present to the outside world as an op-amp. Even if it were, it's a single, and that layout calls for a dual.

Your symptoms suggest you have something shorted out, which I would guess would be something ground-related, since it happened after moving to a metal case. Removing everything from the case should fix the symptom if so.

 

[Fuzzy OneThree]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif The LM386 is not an op-amp. It probably contains an op-amp, but it doesn't present to the outside world as an op-amp. Even if it were, it's a single, and that layout calls for a dual.

I haphazardly picked one at Radioshack. It said something like "dual audio op-amp", so I wrongly assumed that it was a good substitute. The more important fact, I think, is that it didn't overheat.

Quote:

Your symptoms suggest you have something shorted out, which I would guess would be something ground-related, since it happened after moving to a metal case. Removing everything from the case should fix the symptom if so.

The bottom of the tin has covered with a felt sheet the entire time. And plus, the second cmoy didn't even ever go into the altoids tin. I'll rework all the joints that go to the ground, but I find it weird that it happened twice

 

[Anonanimal]

Fuzzy-

I've had similar experiences when building amps and I'm going to agree with Tangent that you've probably got one of your connections shorted to ground. Sometimes you'll have just the tiniest bit of solder or a single strand of wire causing the problem and it's hard to see.

Good luck with your repairs and let us know how it goes!

 

[NightOwl]

Quote:

Originally Posted by Fuzzy OneThree /img/forum/go_quote.gif The bottom of the tin has covered with a felt sheet the entire time. And plus, the second cmoy didn't even ever go into the altoids tin. I'll rework all the joints that go to the ground, but I find it weird that it happened twice

You do know that felt is often made from wool and can hold and discharge static electricity?

 

[tangent]

Quote:

Originally Posted by Fuzzy OneThree /img/forum/go_quote.gif The more important fact, I think, is that it didn't overheat.

Actually, that fact is completely unimportant. It's the wrong kind of chip, so what it does when plugged into that socket means precisely zilch. If it were otherwise, you could get useful data by plugging an 8-pin microcontroller in, too.

Quote:

The bottom of the tin has covered with a felt sheet the entire time.

An inadvertent connection between virtual ground and one of the power rails would explain your symptom. Doing so through a metal case is one popular way, but not the only way.

What do you get for the measurements described in this article: Basic Troubleshooting for Headphone Amplifiers

Also, try cleaning the board, also recommended in that article, with references to how to do it right.

 

[rembrant]

Well LM386 is a single supply only chip anyway. So you might as well toss that idea right now. It wont work in a CMoy circuit. I mean not at all. You may hear sound but it certainly isn't working.

 

[Fuzzy OneThree]

I realized last night that I wired the battery (and I presume the LED) backwards on the new one. The black wire from the battery holder should go into the V- power side. Oops. I don't think that was the only problem, but its a start. Could that have fried my op-amps rather quickly?

 

[liltehood]

yes, i think thats the thing that burned ur opamp

 

[Fuzzy OneThree]

Yup, the backward battery clip was the problem. Now, after I get some parts to finish out the amps, a lucky head-fier will get a cMoy.