the Pimeta-V2 thread - Page 14

http://focus.ti.com/docs/prod/folders/print/opa1641.html

OPA1641/OPA1642.

hmm that looks like a nice little opamp for the price

I am in the process of building my second Pimeta V2 (the first was built for a friend). During the power supply testing (using an 8V battery) I got 3.9V on Pin 8 and -3.9V on pin 4 of the OPR\L (as expected). I also found that I was getting -3.9V on pins 1 and 7, is this normal?

RC

Pin 1 on OPAG isn't connected to anything.  That may not be strictly true, I haven't checked the PCB layout.  Point is, it doesn't matter what the voltage is.

Pin 7's value is backwards.  It should be V+, not V-.

If you were using the pin numbers on the schematic, redownload the schematic.  The previous version's numbers were arbitrarily numbered 1-5.  Now they correspond to the actual package pin numbers.

Hello Tangent,

I am referring to OPALR not OPAG.

RC

Oh, I see.  In that case, it makes sense only if you haven't installed BUFL, BUFR, or the R7s yet.  If you have, these pins should be 0 V relative to IG.

Quote:

Originally Posted by tangent 

Oh, I see.  In that case, it makes sense only if you haven't installed BUFL, BUFR, or the R7s yet.  If you have, these pins should be 0 V relative to IG.

I haven't installed the buffers as yet, I am at the stage where I am checking that the supply voltages are correct. My next set is to install the buffers and opamps.

BTW I am going to be using 2 x 8.4V Lipo batteries. In the Pimeta V2 that I have already built I get 16.03V at C2 (when batteries are hot off the charger). With this voltage would it be safe to use 16V capacitors at C2?

RC

 

It's not a good idea to exceed the C2s' rated value, but they won't suddenly explode with 0.03 V over their rated voltage.  I'd be tempted to put a second diode in series with D2 to remove any possibility of risk here.

Here are a couple of pictures.  Finally got it done.  This is my second amp. 

It's a beautiful enclosure, evolo!

Are you going to leave it open on top?

Thanks tangent.  I will put a cover on it.  I might do magnetic attach cover or latch style.  Haven't decide yet.  I should have wooden knobs done soon also.  I have a second pimeta and ppa on the way also.  Can't wait to finish those.  This head phone amp stuff is really fun.

Why my Pimeta v2 burns both leds when I connect wall wart to it. I have it regulated. I have most as in schematic, I used SMD resistors. I currently have RLED 16K.

http://dl.dropbox.com/u/7337908/IMG_6830.JPG

I have cleaned the board but maybe the denatured ethanol leaves some residue. Amplifier works fine though. I run out of blue leds and soon those led pads will be destroyed if I don't soon find out what is causing that.

Leds work when wall wart isn't connected, with battery that is. Wall wart voltage regulated 22V.

Have you checked the wattage on your RLED?  You're dropping about 18V across it when your are on line, something funky could be happening with it.

I guess it is 1/8W like rest of the 1206 SMD resistors
 

Quote:

Originally Posted by cobaltmute 

Have you checked the wattage on your RLED?  You're dropping about 18V across it when your are on line, something funky could be happening with it.

Quote:

Originally Posted by Spacehead 

my Pimeta v2 burns both leds when I connect wall wart to it

May we see a top-side pic showing D1 and D2?

Clearly so.  As messy as it's left your board, I wonder if you wouldn't have been better off not cleaning it at all as use that stuff.  Instead of flux around the solder points, you have junk evenly spread over the board now.

I think you have little choice but to make another cleaning pass at it.  Try to find something purer: tape head cleaner, high-purity isopropyl from a drug store, etc.  

Heet gas additives are high-purity alcohol (yellow bottle = methanol, red = isopropyl), but I don't know how the 1% of "proprietary additive" affects its suitability as a PCB cleaner.

I also see the potential for several shorts:

• BATT wires, extra exposed length and solder splatter on the blue one
• several places around BUFG
• extra unclipped lead lengths and unshielded jumpers in the scratchpad area

Is that a scratch or wire strand near forward LED?