CMoy DC PS Choices - Head-Fi: Covering Headphones, Earphones and Portable Audio

bmwpowere36m3 · 10-11-2008, 04:59 PM

Hey guys, just finished up my cmoy build and would now like to add a DC power supply to conserve battery power when using it at my desk. I'm currently running my cmoy off 2x 9V batteries and thought I'd add a DC jack (seperating PS from batteries with a set of diodes).

I have this PS at home now, off an old Yamaha 2.1 speaker system:

Class 2 Power Supply
Model: PA-M30
Input: AC120V 60Hz 30W
Output: DC 15V 1.2A

would it work or what other choices should I look at? Thanks.

rhys h · 10-11-2008, 05:52 PM

This will be fine, just look on the internet on how to use a cmoy with a rail splitter.

bmwpowere36m3 · 10-11-2008, 06:29 PM

Originally Posted by rhys h

This will be fine, just look on the internet on how to use a cmoy with a rail splitter.

The Cmoy is already built, not sure what rail splitter your talking about? I'm already using a TLE2426 to "split" the voltages on the CMoy.

cobaltmute · 10-11-2008, 07:01 PM

From what I read, using diodes as a switch won't work in this case as the voltage on the Power Supply is too low:Tweaks (from Tangents site on the CMoy)

bmwpowere36m3 · 10-12-2008, 05:20 AM

I could just wire in a selector switch... any other opinions on using that PS?

tangent · 10-12-2008, 06:25 AM

Have you checked that it's isolated?

Is it putting out 15V for real, or is it putting out something higher? If higher, it's unregulated, and so may inject noticeable amounts of hum into the amplifier. If regulated, it could be switching regulated, which will inject higher-frequency noise, again possibly audible. Chances are really low that it's linear-regulated, which would be the cleanest sort, generally best for this sort of audio circuit.

The voltage question depends on what battery setup you have. Care to share?

bmwpowere36m3 · 10-15-2008, 04:23 PM

Originally Posted by tangent

Have you checked that it's isolated?

Is it putting out 15V for real, or is it putting out something higher? If higher, it's unregulated, and so may inject noticeable amounts of hum into the amplifier. If regulated, it could be switching regulated, which will inject higher-frequency noise, again possibly audible. Chances are really low that it's linear-regulated, which would be the cleanest sort, generally best for this sort of audio circuit.

The voltage question depends on what battery setup you have. Care to share?

Yes it's isolated, but the actual ouput voltage is ~19V. So I'm assuming it's unregulated? What would you recommend for PS, since the ones listed on your site I couldn't find on Digi-Key or Mouser.

A3rd.Zero · 10-15-2008, 08:15 PM

At the bottom of the original CMOY project page on Headwize there is decent coverage on how to use a regulated transformer to power the CMOY.

HeadWize - Project: A Pocket Headphone Amplifier by Chu Moy

You can then add a regulator section to your transformer to drop it down to 12V or 9V, and smooth it out with some caps. It might be worth sticking it on a scope and seeing how smooth the DC coming out of that transformer is.

9 Volt 2 Amp PSU

Use the L78S09CV (9V 2A version of the 78S09) found for $.89 on mouser.

tangent · 10-16-2008, 03:57 AM

Originally Posted by bmwpowere36m3

I'm assuming it's unregulated?

Yes.

What would you recommend for PS

I'd try that one and see how it works. If you get audible hum, add a linear regulator of some sort between it and the amplifier. I offer the TREAD for this purpose. The suggestion to use an LM78xx will also work, but give about 4x the ripple; still good, just not as good. You can get most of the benefit of the TREAD by getting an LM317, a few resistors and a few capacitors from Radio Shack. Or, you can go nuts, adding Jung regulators and other such exotica.

Bottom line, starting from an unregulated supply like that is perfectly reasonable. The only question is how much regulation you want to add to it, if any at all.

bmwpowere36m3 · 10-16-2008, 08:25 PM

Originally Posted by tangent

Yes.

I'd try that one and see how it works. If you get audible hum, add a linear regulator of some sort between it and the amplifier. I offer the TREAD for this purpose. The suggestion to use an LM78xx will also work, but give about 4x the ripple; still good, just not as good. You can get most of the benefit of the TREAD by getting an LM317, a few resistors and a few capacitors from Radio Shack. Or, you can go nuts, adding Jung regulators and other such exotica.

Bottom line, starting from an unregulated supply like that is perfectly reasonable. The only question is how much regulation you want to add to it, if any at all.

The TREAD circuit looks appealing, looking over the circuit are: C5, B1, and the accompanying C1-C4 needed if I choose to use the above PS. Will they add any value or only when using AC wall-wart? How about using a 39uF C8, bigger is better as long as it fits the confines? Would it be sensable to run the output at 17V and could I just get rid of VSET and run: R1 120ohms & R2 1500ohms?