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DC Wall Power Supply for CMoy

post #1 of 14
Thread Starter 

First time here. Nice to meet you ! :-)

 

I've search this forum and I'm unable to find any serious replacement for the Elpac WM080 power supply. I should finish my first CMoy (Audiologica) later this week and, seriously, the only annoying part of this project is the D battery.

 

I plan to use my new toy everyday at work and I can't imagine I'll buy a new battery every next day. My first mod will be to cut the + and - wires going to the battery and plug it to a power jack of some sort. It's a 15 minute job at worst. But the problem is to find a suitable power supply.

 

Anyone has something to suggest? I prefer an entre-level power supply. I can't imagine I'll spend more on the supply than on amp parts and enclosure...

 

Thanks for your help !

post #2 of 14

How about one of these and a cheap wall wart...

post #3 of 14
Thread Starter 

Of course, it's the DIY way to go. There is many of these PS kits. As long as it fits in the battery compartment... not much room beside that in my case !

 

But is there any regulated wall PS available on the market ? Some cheapo things can be found on EBay. No one has ever tried them ? They say it's regulated, but at 5$, I'm not sure it's of any good.

post #4 of 14

Of course, there is always checking your "junk drawer" for unused wall worts from other equipment.

If you don't have anything, maybe your friends or family do...Free is always the best price...
 

Quote:
Originally Posted by Bingo View Post

Of course, it's the DIY way to go. There is many of these PS kits. As long as it fits in the battery compartment... not much room beside that in my case !

 

But is there any regulated wall PS available on the market ? Some cheapo things can be found on EBay. No one has ever tried them ? They say it's regulated, but at 5$, I'm not sure it's of any good.


Edited by Avro_Arrow - 11/11/10 at 6:27am
post #5 of 14

Audiophile quality regulation costs money.  On top of that, because most powered devices don't actually require audiophile quality regulation, such supplies don't sell in high volumes, further increasing their cost relative to the less good sorts that move by the millions.

 

The only cheaper linear-regulated wall wart I've seen mentioned here is the Jameco 174879, but I've yet to see anyone post test data, or even a subjective comparison of it and the WM080.

 

An amplifier is a power transference device: as goes the power source, so goes the amp.

post #6 of 14
Thread Starter 

What about this thing ?

 

http://www.sparkfun.com/commerce/product_info.php?products_id=9442

 

12$, shipping included. 12V is barely enough, 650 mA is way too much... price is good. Hassle-free.

 

Anyone has ever tried this product ?

post #7 of 14

That is a switch mode power supply.

Ideally you are looking for a linear regulated supply.

There is nothing to say it wont work but it might

not sound as good (there could be some switching

noise) as a linear supply. If you isolate is with a resistor

and cap then it might be fine.

post #8 of 14

A 24 ohm, 1/2 watt resistor and a 500uF cap at 16 volts should be enough.

 

Like this:

 

Isolation.JPG

 

You should be able to fit it in the battery compartment.

post #9 of 14
Quote:
Originally Posted by Avro_Arrow View Post

That is a switch mode power supply.

 

It's also likely not isolated.  (It could be, but they don't bother to link you to a datasheet, so there's no way of telling short of buying it and testing it.)
 

Quote:
Originally Posted by Avro_Arrow View Post

A 24 ohm, 1/2 watt resistor and a 500uF cap at 16 volts should be enough.

 

Resistors in series with power rails...yuck.  If this helps, you've done it by taking a noisy power supply and increasing its ESR, which is also bad.

 

I also question whether a corner frequency of 13 Hz is low enough.  This doesn't work like the CMoy's input filter, where we're trying to eliminate DC, which is an infinite number of decades below the corner frequency. 

 

If this wall wart adds audible noise to the output of the amp, it'll probably be in the 10 kHz sort of range.  Say it's quiet, -40 dBFS relative to the loudest music you can get through the system.  That's equivalent to quiet office noise.  If we simplify by saying the fc is 10 Hz or the noise is 13 kHz, that's 3 decades, buying us only 21 dB of attenuation.  That's still -61 dBFS, which puts it only at the "library noise" sort of level, far higher than we'd really like.

 

If filtering is the answer, I'd say CLC makes more sense.  But magnetics strong enough to get enough attenuation aren't cheap or compact. 

 

For serious attenuation, you have to go active.  I'd be happier to see a cheap ($6) unregulated wall wart followed by a naked LM7824 than either passive solution.


Edited by tangent - 11/11/10 at 10:18am
post #10 of 14

@Tangent

 

I'm not sure if you are trying to help the OP with this or just try to give me a hard time.

I know a resistor and cap are far from an ideal solution (I did already suggest a

regulated power supply to the OP). I did already mention I didn't think the switching

power supply was a good idea. An extra 24 ohms seems pretty trivial in a CMoy that

already has about 5k resistance in it's voltage divider and draws less than 50 mA.

I expected it to drop about 1 volt at maximum draw. At 50kHz it dropped a 1 volt noise

signal down to 265 uV. Seemed like a pretty good reduction to me. I was just trying

to present a solution to someone with a "CMoy" level of technology and apparently either

a small budget or unwilling to spend much money on this.

post #11 of 14

I'm not trying to give you a hard time.  I just don't like that idea, and I presented the ideas I like better.  That's all.

post #12 of 14

Just can't figure out why you don't use rechargeable batteries the whole idea of the Cmoy is it's portability and pocketablity ? :)

 

I noticed that Red Wine Audio favour batteries in their power supplies for their amplifiers.The Cmoy can carry 18V 2x 9V batteries more than enough power

for a small headphone amp - correct me if I am wrong but this seems more sound quality efficient then being mains feed only ???

 

It's possible to have a switchless DC power jack and still have both battery and wall power http://tangentsoft.net/audio/cmoy-tutorial/tweaks.html

post #13 of 14

The power supply for my laptop works pretty good, I haven't heard any hum with it.

post #14 of 14

Yep I'd go for one of those an intend to - I can't figure the above out ? Looks like a problem where there really isn't one haa !

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