Pimeta V1 opamps - For higher impedance cans - Page 2

Your #2 point just tells us that the amp is clipping. Let's fix the clipping, then return to your other questions.

You should be able to get away with putting a second 9V in series with the existing one temporarily. The advice to select your caps to exceed your total power supply voltage (rather than half the total, which they normally see) is made with continual running in mind, not short tests where you can just lash out with your hand to break the power connection if your virtual ground somehow manages to collapse during the test.

And hey, if you blow the caps, you were thinking of replacing them anyway.

Depends on your desired run time and how long you want to spend charging the amp as well.

I'm happily running 1000mAh AAA.

Figure ~60 mA continuous for a PIMETA with LMH6321. 1000 mAh then gives ~16 hours of run time if you can fully drain the battery before you run into clipping. This is explained more fully here: Op-Amp Working Voltage Considerations

I wish I had found out about this before I bought additional BUF634's for stacking.
Since I have a couple of spare LMH6321's can I use them (modified) for L\R buffers and use a BUF634 for the ground buffer?
RC

Sure.

Not if you're being careful. Observe the limits in the datasheet: don't exceed 300°C or 10 seconds per joint. If you can't make the joint within those restrictions, stop for a sec, let the joint cool down, and try again.

Have you watched this: Surface Mount Soldering Techniques ?

Be sure it's not set to charge when the amp is turned on. The charging IC may add noise to the amp. Best to use a DPDT power switch, so that when the power goes off, the charger comes on. I describe something like this in my Low Noise Measurement Preamplifier assembly guide.

That IC is going to add noise to the circuit. The last 8-pin DC-DC converter I tried added lots of easily-audible noise. At best, it will add noise which happens to be inaudible for one reason or another.

If it were me, I'd run that amp straight off the batteries, nothing in between.

Just leave them alone if you're not clear about this. Some people, like jcx, don't like Jung multiloop, so he was telling you to take it out. My reply to that is simply that yes, it's legal, if that's what you want to do.

If the noise appears only when the source is plugged in, then the noise is coming from the source.

The PIMETA is amplifying it, right along with the music, so it's partly to blame. Yes, lowering the gain will help. You might also consider getting a better source down the road.

Then yes, your gain is clearly too high. I prefer to make my amps so that the typical volume level is above the 50% point for my least efficient headphones.

I think you will find that you need more like 28-29 V to actually charge those batteries fully. The difference matters if you ever integrate the charger into the amp so that it can charge while power goes to the op-amps.

Actually, the recommended max for the AD8610 is 26 V. Check the datasheet.

You're right on the edge of disaster here, not clearly over it. I would add a silicon diode in series between V+ and the amp. If you're using dual batteries to remove the need for the TLE2426 in the amp, add one in series with the V- line, too. (You can do it if you're still using virtual ground, but it's not necessary.) This will drop the supply voltage by another 0.7 V, giving you a little bit of safety margin without the complexities of regulation.

EDIT: This has the side benefit of being a more reliable protection against plugging the batteries in backwards than the crowbar PIMETA v1 uses.

Obviously, measure the batteries after they come off the charger to be sure. You might find that they're not okay to plug in immediately, but after a few minutes the voltage stabilizes below 26.7 V.

If you really had to, you could use multiple diodes in series, but at that point, I'd start looking at a linear regulator.