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post #481 of 627
Hi Tangent,
After running my Pimeta for a few days I noticed that the right side sound much lower than the left. Upon checking I discover the following:
1) High current draw from regulated 24 volts supply using LM317.
2) Voltage drop from 24V to about 12V (+/- 6 V on opamp)
3) R1/R2 on LM317 is hot.
3) Changing the opamp does not help.
4) I suspect it must be the buffer coz removing both opamp the voltage drop is the same.
5) How can I check the defective buffer without removing it.
6) Other than the buffer, any where else should I check. Is it possible for something else drawing the current, C3/C5 shorting out?
Thank you.
post #482 of 627

I doubt your buffer diagnosis, because the voltage setting resistors on the LM317 should never be hot, no matter what the load on the power supply is. The output current doesn't go through them, so the heat in these resistors should be constant.


I think your problem is in the power supply.


Easy test: disconnect the power supply from the amp. Does it bounce back up to 24 V, or does it stay sulking down at 12 V? If it bounces back, put a 470 ohm resistor across the power supply. (This gives approximately 50 mA, roughly equal to the draw of a PIMETA v2.) Does the voltage remain at 24 V, or does it fall to 12 V again?

post #483 of 627
Thank you. But why is that the left channel sound louder than the right channel even with opamp change. I don't have 470R and will get some. In the mean time will test using 2 fully charge 9V battery.
post #484 of 627
Using another 24 volts regulated power supply in series with 1R resistor, I measured current draw of 120mA with both opamp and 105mA opamp removed. No wonder using the earlier supply the voltage drop so much coz its only rated 100mA. The opamp is warm while all the buffers are quite hot to touch more than 30 sec. The DC offset tested on all output is almost zero. All measurement done with biasing switch off.

When I plug the headphone, the sound is ok except the right channel is softer than the left. I am rather worried with the heat generated by the buffers. Any suggestion?
post #485 of 627
post #486 of 627

Hi, I've just built the pimeta v2 but it doesn't work. Some days ago the led didn't even light up, but after a bit of troublshooting I found out that I made some ridicoulus mistakes. Now the led lights up, but there's no sound, so I've checked the voltages at OPAG, OPALR and BUF pins relative to the IG and on a couple of pins for each I have 4V. I use a 9V battery as power supply.


More info: I've built the pimeta avoiding the problem of the bias, for now, so no second led, no RBLIM ecc. and without BUF chips. So I've avoided everything possible.


What's wrong?

post #487 of 627

Post high-res pictures of both sides of the board. Also, go through the rest of the standard troubleshooting steps.

post #488 of 627




Here are some pics, I know I've built it really bad. 

EDIT: (troubleshooting referred to the tangentsoft preliminaries)

1) using a 9V battery I measure 8.77V at V+ and V-.

4) no more the 15mV ground and the L/R output.

Edited by acvtre - 11/20/12 at 9:25am
post #489 of 627

You have no op-amps and no buffers. These aren't optional components.


Well, the buffers are optional in a kinda-sorta way, in that you can short them, but you haven't done that, either. And if you do, you basically end up with a glorified CMoy Pocket Amplifier. Not that there's anything wrong with that, but a nerfed PIMETA v2 is a pretty expensive way to achieve that end. :)


You could short the op-amps, too, but then you'd just have a really expensive interconnect. Some audiophool companies call these "passive preamps", but you still don't want it.

post #490 of 627

Ok, I've got the opamp but not the buffers. I'll buy 'em sonner or later. In order to realize if it works, how do I have to short the buffers?

post #491 of 627

Connect each buffer's input pin to its output pin.

post #492 of 627
Originally Posted by tangent View Post

Connect each buffer's input pin to its output pin.

Ok, can you please show me input and output for each buffer chip?


post #493 of 627



Pin 3 is the input, pin 6 is the output.

Edited by MisterX - 11/22/12 at 9:21pm
post #494 of 627

Hello, I was interested in building one of these amps, but have a couple of questions. I was planning on including it into a casemod on my PC, and possibly powering it through 4 pin molex connectors. I was also thinking of connecting it to the motherboard's headers for the front panel audio, or even joining it to the jacks that already exist on the case. The problem is I am a complete newb, although I am willing to put the time in to learn. Would any of this be feasible? I am most interested in powering it through the PC power supply, but connecting it to the motherboard would be awesome too.



post #495 of 627
Originally Posted by Ongar View Post

possibly powering it through 4 pin molex connectors.


It's not as easy as you think it should be. A PC power supply is not isolated. You can't power it from USB, either, for the same reason. (Or from your car's cigarette lighter, yet another frequently-asked-and-shot-down-proposal.)


You basically have two alternatives:


1. Run power in from an external isolated source


2. Put an isolated DC-DC converter between the PC power and the PIMETA. You can buy these from the same place you get most of the other PIMETA parts. Expect a good one to run you at least $15 or so, and maybe a few times that.



I was also thinking of connecting it to the motherboard's headers for the front panel audio


Totally doable. You'd just have to find the pins, then build a suitable cable.


There's a tiny chance, these days, that you have a CD-ROM audio connector. If so, then you don't even have to build the cable. Just take the cable that already plugs into that connector, snip one end off, strip to taste, and there's your amp-side.

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