[jchanhm]

I have been staring at my board for a long time, but I have no idea what is the problem, or what could be the problem.

I've assembled my whole pimeta according to tangent's guide, but there are two problems that occur:

1) the ground buffer BUFG heats up when there is an input signal. It heats up faster the more i turn up the volume
2) the right ear has no sound output, but it grows very warm.

I've already pretty much killed the right ear, but I dont mind since its a test pair of headphones.

I've double checked my soldering on the board, and I'm pretty sure that there are no short circuits anywhere. Does anyone have any ideas of how to debug/what the problem might be?

thanks very much

 

[kklee]

Have you tried Tangent's troubleshooting steps?

http://tangentsoft.net/audio/trouble.html

 

[odoe]

Are your buffers stacked?
If so, try reflowing the solder on the buffer stack.
Maybe swap the buf with another on the board to verify if it is the buf or the ground socket. I had a similar problem on mine and I don't know if that's the best way of troubleshotting it, but I did find I had one stack that needed to have the the solder reflowed as the pins weren't completely touching.

Best of luck.

 

[tomb]

The PIMETA uses an active ground channel with an opamp and a buffer. If you have the output grounded to the case, and your input and pot are also grounded to the case, the ground channel will see the output ground as a short. Some opamps will drive right on with this condition, others will protest noisily and with lots of heat. So, check to make sure your output is not grounded.

 

[vixr]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif others will protest noisily and with lots of heat.

sounds like my daughter when she is grounded

 

[jchanhm]

Thanks for pointing to Tangent's troubleshooting tips. I had forgotten about that page.

For starters, I have a little more info about the problem.

First - There is a very loud audible click when the pimeta starts up in the -right ear only- . The left ear works perfectly. According to the guide, this could be due to the DC offset at the output of the amp.. However, my multimeter is cheap and I can't measure in millivolts, so I cant test it very well.

I also took the amp out of the case when I discovered it had problems, just so I knew for sure it had nothing to do with grounding problems. Also, I did not stack my buffers since I didn't want to deal with complicated things like that...

Probably the main problem is the ground buffer. I tested the amp again without a source plugged in, and BUFG still heats up very quickly. I swapped buffers as well, and I still get the same problem. So I've determined that its not the chip.

Since the pimeta is built on a PCB, then the only thing I can think of that can cause problems in the circuit is if I have a thread of solder short circuiting the circuit. However, I can't see any short circuits on the bottom of the board, even with a magnifying glass. Some of the sockets that looked 'iffy', I even cut the section with a knife, just in case.

Of course, if I did everything correct, then probably there would be no problem.

Basically, all the suggestions you guys brought up, I've decided are not the cause of the problem... I guess I'll just keep tinkering and hoping. Thanks a lot for the advice.

 

[tomb]

What opamp are you using for the ground channel? If it's not unity gain stable, it will cause big problems. Even if it is, not every combination of opamp works in the ground channel with the L&R channel. What works in L&R may not necessarily work in GND.

 

[MisterX]

Fix the problem with the right channel first.
I would not be surprised if the issue with the ground channel disappeared once that was sorted out.

 

[jchanhm]

I am using a BUF364P chip for the L&R and the ground buffers. Is this fine?

MisterX: Oh, I thought that the right channel problem was occurring due to the problem with the ground buffer. I'll take a look at the right circuit when I get a chance tonight. [Edit: although I'm not sure what to look for... =[ ]

 

[tomb]

Quote:

Originally Posted by jchanhm /img/forum/go_quote.gif I am using a BUF364P chip for the L&R and the ground buffers. Is this fine?

Of course - but what are your opamps? They can cause problems in the buffers if there is a mismatch, particularly in GND.

As for your right channel, I agree in principle that may be the problem. However, depending on your pot, I've seen a huge buzz occur on whichever channel is not tracking exactly when there's a mismatch with the ground opamp.

Let's hear more about your configuration, first - iow, tell us the opamps you're using, please.

 

[jchanhm]

For OPAG I am using an OPA132PA , for OPALR I am using an OPA2132PA chip.

[edit: At least, I think it is an OPA132PA for OPAG.. the chip is a bit weird. It says OPA132P A , with white text for the "OPA132P" and the "A" kind of faded and in a different font. I bought these off ebay since digikey didn't have them anymore >_> ]

Also, I am using the alps RK27 pot, two 9V batteries in series as power supply. no JFET cascode yet, but I plan to add it once the amp works, and also no input capacitors ( I am wondering if I should add them, or if its safe enough to go without them, since from what I understand, not having them makes a big difference in quality )

 

[tomb]

Hmm ... that opamp is very stable. Like you, I am a little suspicious of the Ground opamp, however. I was not aware that you could even get an OPA132 "P" version anymore. All I've ever seen in the single channel version are SOIC-8 "U" versions in singles. Still, assuming it is genuine, your choice of opamps would not be the issue. So, unless its a fake/bad chip, your problem is elsewhere.

Usually when we get to this point in a troubleshooting thread, photos are warranted. Could you post some of the top and bottom of the board? There's always a chance someone will spot something.