[fivefanband]

I just finished my Pimeta today:

- 8620 and 8610 op-amps
- 2-1-2 stacked buffers
- TREAD PSU hooked up to a 24V 400ma wall-wart
- Cerafin Caps from Tangent
- Q1 and Q2 populated by Tangent's cascodes

I turned the potentiometer all they way down then switched on the amp. It was silent for around 5 seconds until a loud grinding noise started coming from my cheap Sony headphones. I immediately switched off the amp and checked the op-amps and buffers, which weren't hot.

Has anyone had this problem before? Any suggestions would be highly appreciated.

 

[n_maher]

Quote:

Originally Posted by fivefanband Has anyone had this problem before? Any suggestions would be highly appreciated.

Have you had a look at Tangent's Basic Troubleshooting for Headphone Amplifiers? That'd be the best place to start.

Nate

 

[fivefanband]

After further testing/troubleshooting, I found that my AD8620 chip was actually getting extremely hot after around 10 seconds (I hadn't noticed since I had always just turned off the amp after the noise had become too extreme). Only the 8620 is getting hot, though.

In Tangent's troubleshooting guide it says that this means I've got oscillation, but I have very little idea of what that means and whether or not bypass capacitors are the only solution.

Again, suggestions are highly appreciated.

 

[Xakepa]

Make sure you mounted the chip the right way on the BrownDog and there are no shorts on the adapter. If you happened to have any other chip, try with it.

Also...make sure you didn't flipped the adapter. This way I killed my 843s in less than 10 secs.

 

[fivefanband]

Well, thanks for all your comments; I've found the culprit. I had absent-mindedly switched the AD8610 and AD8620 chips in their slots. After switching them back I found that I've killed the right channel of my AD8620, and my ground channel buffer is getting pretty hot, is it possible that i've fried that too? Is there any chance that I've fried my AD8610 as well?

 

[Pars]

Quote:

Originally Posted by fivefanband Well, thanks for all your comments; I've found the culprit. I had absent-mindedly switched the AD8610 and AD8620 chips in their slots. After switching them back I found that I've killed the right channel of my AD8620, and my ground channel buffer is getting pretty hot, is it possible that i've fried that too? Is there any chance that I've fried my AD8610 as well?

Quite possible. If it were me, I'd go down to Ratshack and grab a TL082 dual opamp, and whatever they may have for a single opamp (maybe even a 741

) and toss those in and see what your DC offset looks like (you DO have a DMM/meter? don't tell me you're building a Pimeta without one

). Don't risk toasting $13 opamps until you are sure the more mundane problems are fixed first. And no, oscillation would not be my first guess as to why your 8620 was getting hot, although it is a possibility.

 

[tangent]

Quote:

Originally Posted by fivefanband I turned the potentiometer all they way down then switched on the amp. It was silent for around 5 seconds until a loud grinding noise started coming from my cheap Sony headphones.

I hope you don't mind killing those headphones. A DC offset test would have found this problem, too, without the risk of killing the cans.

Quote:

In Tangent's troubleshooting guide it says that this means I've got oscillation

The guide assumes that you haven't killed the chips, which is what happened here.

Quote:

my ground channel buffer is getting pretty hot, is it possible that i've fried that too?

Not likely. You're probably just seeing it get warm as it drives or sinks lots of current due to the other problems in the circuit.

Quote:

Is there any chance that I've fried my AD8610 as well?

Also not likely.

 

[fivefanband]

Well, I've found all the problems, and new parts are on the way. Thanks so much for all your help!