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Powering CMOY with a power supply

post #1 of 15
Thread Starter 

So years ago I built a tangentsoft CMOY shown here:




I used the OPA2132PA opamp, which accepts up to 36V.


I used 35V caps for future plans of possible external power source.



Seeing this tweak listed:






My dad knows of my plans for external power for the amp and found an electronics surplus store in Oregon, and picked up a Lambda 24V 1.2A power supply for me. He works as a stepper technician for various chip manufacturers and says that the Lambda supplies are pretty good, but does not know if it would be linear-regulated or not.


My question is, would this power supply be a good choice to power my CMOY without lots of noise? Or, would it even work?


Power supply in question:



post #2 of 15

It's a switch-mode power supply.



You should try it anyway, you can't hurt anything by trying it.  Might just be quiet, the better switch-mode supplies are pretty clean.

post #3 of 15

As my article says, the big question is isolation, which isn't addressed by the product's data sheet.


The simplest way to test this is, with the supply sitting on the bench, unplugged from everything else, measure resistance between each of the V+ and V- outs and all the other connections. That's 8 separate measurements, with this supply.


If you get high resistance or no conductivity at all with all of these measurements, it's probably isolated.


If it isn't isolated, it will likely be because V- is connected to FG, ACG, and/or N, but check all combinations of outputs to inputs and grounds anyway.

post #4 of 15

FWIW, I build a OPA2132 CMOY some time ago, after trying some of the self switching power supplies I got the best out of the chip with LDO LT1085/LT1033 regulators, dual bridges with ISL9R460PF2 diodes and Elna SILMIC2 capacitors....

Edited by Konstantin690 - 8/9/13 at 6:41am
post #5 of 15
Thread Starter 

Hmm, may be toying around with the amp again after I get the PSU wired in!

post #6 of 15
Thread Starter 

Tangent: I got the unit yesterday, got around to testing it today, as you stated. I have "connectivity" between V+ and V-, but that's it. None of the other connections ohm out (aka, no resistance or connectivity). Good to go?

post #7 of 15

You shouldn't have conductivity between V+ and V-, unless it's already connected to the CMoy amp, in which case you'd be measuring 2x the voltage divider resistor value. (R1+/- in my schematic.)


You probably can't damage anything by just trying it.


(The point of doing the tests is to avoid wasting time on something that can't work.)

post #8 of 15
Thread Starter 

Hmm. That test is with it sitting on the bench before anything is connected. The unit does seem to work, I am getting 24.5V with just a power cord connected and the unit on.


What type of damage am I looking at if I were to go through with it?

post #9 of 15
Thread Starter 
Well I went ahead and tried it out, works like a charm! No noise, at least no more than the basic dual 9v would have. Sounds a bit punchier in the lower tones on the 24v dc supply, as well.

I have added diodes to the board, and setup the "diode OR bridge" circuit you have on your page. Works like a charm, everything tested well with the meter.

Now to build another enclosure!
post #10 of 15

I'm glad it's working for you.


However, you seem to be mixing up voltage and resistance tests.  Obviously there should be 24V at the output, but what I asked you to test is resistance between all combinations of input and output terminals, while the power supply is disconnected from both the wall and the amp.


If you did that and I am just unclear on it, there's no need to respond. I just don't want to leave this dangling string unpulled.

post #11 of 15
Thread Starter 
There is resistance between the v- and v+. Ot starts low and builds up to infinity. Is that normal?

Testing v- against all inputs there is no connectivity, and the same for v+.
Edited by PintoDave - 8/20/13 at 8:53am
post #12 of 15

That's just the output capacitors charging up.  "Continuity" would mean there is a constant near-zero resistance.

post #13 of 15
Thread Starter 

Ahh, I see. Thank you for clarifying that, I was getting confused!


I hope to build a couple more CMoy amps. My brother wants one, and my friend has one I built like mine but doesn't use it much due to the lack of a wall supply. Now I have a source for the power supplies that I know work, and diodes are not an issue since I have a stock pile of them in my parts bins.

post #14 of 15

Hello PintoDave.
I don't know if is a little late... :P
The last year I bought 3 differents cmoys.
I don't like the switching psu, so I did my self one with differents items from ebay.
I would recommend to you see on ebay :
My cmoys work perfectly and I can't hear underground hum.
Good luck!


Edited by fuens - 2/25/14 at 4:00pm
post #15 of 15
Thread Starter 
Nice! I will have to keep this in mind for future projects that I can't get the same supply I used for this one.
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