[Sinbios]

I've had nothing but problems with my MINT, but I think I'm getting closer. Right now, both channels are emitting a whine, and DC offset on both channels are ~1.5V! Neither the opamp nor the buffers are getting hot, and I've replaced both several times, with the same results. The part I'm suspecting is the rail splitter, which gets very hot, but the problem persisted even when I replaced that one with a brand new splitter. Where could the problem be?

 

[MisterX]

You got this in a case?
If so do you have a isolated DCjack?

It sounds like you are shorting V- to the in/out ground

 

[Sinbios]

This isn't in a case, and the various jacks are just floating about in thin air.

 

[MisterX]

Have you cleaned the flux off and all of that other stuff (like checking the voltages)?

 

[n_maher]

Quote:

Originally Posted by Sinbios I've had nothing but problems with my MINT, but I think I'm getting closer. Right now, both channels are emitting a whine, and DC offset on both channels are ~1.5V! Neither the opamp nor the buffers are getting hot, and I've replaced both several times, with the same results. The part I'm suspecting is the rail splitter, which gets very hot, but the problem persisted even when I replaced that one with a brand new splitter. Where could the problem be?

I'd suggest posting pictures, detail pictures, of both sides of the boards along with a list of component values used. We're operating blind here, under the assumption that you did mostly everything correct, which based on your results may or may not be the case. So whip out the digicam or find someone who's got one. We'll get you straightened out.

Nate

 

[Sinbios]

Quote:

Originally Posted by MisterX Have you cleaned the flux off and all of that other stuff (like checking the voltages)?

Yes, I've cleaned the flux and checked both the voltage and resistances. I'll try to get some pictures taken tonight

 

[Sinbios]

Ok, finally solved the problem - all three of the opamps I tried were fried in one fashion or another. They were all brand new when I started this project. $25 down the drain, damn. I'd like to try to salvage them and turn them into single-channel chips, since some of them has one channel working. Is there an easy way to determine if an opamp is dead or not without soldering it into an amp?

 

[n_maher]

Be careful, you may have found a solution but not identified the problem. I'd suggest some careful observation of DC offset for a while. Maybe even run the amp with a dummy load for a couple of days and then recheck it. I'm seriously paranoid when it comes to my cans.

Nate

 

[__redruM]

Quote:

Originally Posted by Sinbios Is there an easy way to determine if an opamp is dead or not without soldering it into an amp?

http://tangentsoft.net/elec/opamp-tester.html

Wow and offset of 1.5V, now that'll hurt you earphones, I hope you tried it with a cheaper pair.

 

[tangent]

You need to determine whether you killed the chips (static, overheating, etc.) or the amp killed them; you can bet all three didn't come from the factory dead. Failing to nail down the ultimate cause is likely to lead to more problems down the road.

 

[Sinbios]

Quote:

Originally Posted by tangent You need to determine whether you killed the chips (static, overheating, etc.) or the amp killed them; you can bet all three didn't come from the factory dead. Failing to nail down the ultimate cause is likely to lead to more problems down the road.

How could I find out? I have a new chip in there now and it's working so far...

 

[tangent]

Quote:

Originally Posted by Sinbios How could I find out? I have a new chip in there now and it's working so far...

We can provisionally rule out the amplifier, then.

It's quite likely that your technique improved with each chip. It's not hard to kill chips by overheating them when not being quick with the iron. It only takes about 5 seconds with a temp-controlled iron at minimum working temperature, and probably less with a hotter iron. Ideally, you want to make each joint in about a second, less if you can manage it.

As for static, you tell me. Do you habitually ground yourself before touching ICs? I emphasized that because I find myself now unwilling to even accept a DIMM handed to me by a co-worker without looking around for something to ground myself against first. Maybe I'm in a bit of a different situation from you, though: I live in New Mexico (humidity? what's that?) and work in places without anti-static carpet. Some days you will get shocked every time you get up and move around at all. This is a necessary habit I've cultivated.

 

[Sinbios]

Quote:

Originally Posted by tangent We can provisionally rule out the amplifier, then. It's quite likely that your technique improved with each chip. It's not hard to kill chips by overheating them when not being quick with the iron. It only takes about 5 seconds with a temp-controlled iron at minimum working temperature, and probably less with a hotter iron. Ideally, you want to make each joint in about a second, less if you can manage it. As for static, you tell me. Do you habitually ground yourself before touching ICs? I emphasized that because I find myself now unwilling to even accept a DIMM handed to me by a co-worker without looking around for something to ground myself against first. Maybe I'm in a bit of a different situation from you, though: I live in New Mexico (humidity? what's that?) and work in places without anti-static carpet. Some days you will get shocked every time you get up and move around at all. This is a necessary habit I've cultivated.

It's probably the iron, then. I probably left it on too long while trying to remove the chips from the board, since I had another problem earlier and suspected the opamp.

I do ground myself when I work with chips, and even go as far as keeping a bare leg on the metal leg of the chair at all times when I'm handling chips, thought I'm not sure if that's enough.