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-   -   Use +12V PC molex connector to power headphone amp? (http://www.diyaudio.com/forums/headphone-systems/212509-use-12v-pc-molex-connector-power-headphone-amp.html)

1c4ru5 11th May 2012 09:57 PM

Use +12V PC molex connector to power headphone amp?
 
First of all,I'd like to say hello, and that almost everything I've read on this forum goes over my head. I searched for molex power supplies, and a few other versions of that statement, in multiple categories and couldn't really find any answer that seemed to fit my particular goal. That having been said,my question is as follows: My headphones simply aren't loud enough sometimes on my PC - certain things are mediocre at best, and the rest is worse. A cmoy amp seems like a fun project for somebody of my experience, i.e. almost none - I can solder and read diagrams but don't you dare ask me to come up with anything more complex than a light switch. The complication here is that I'd like to use a 12v molex connector from my PC to power this thing, and PC power supplies are switching, if I'm not mistaken. So, what I want is a way to reduce noise from the 12V pin - can this be done with a TLE2426 IC Rail splitter, and a huge capacitor, or will something go laughably, and probably expensively wrong with that plan? Does it need to be isolated? If so, can that be done with a simple 1:1 transformer, and still fit inside of an altoids tin?

Avro Arrow 11th May 2012 10:49 PM

I would steer clear of using the computers power supply...very noisy.
CMoys are typically powered by one or two 9 volts batteries, but
a wall wort will do just as well. You can often find wall worts at thrift
stores for a dollar.
Here is a page to get you started, contains lots of good information
and videos for beginners.

Good luck and don't forget to ask lots of questions!

1c4ru5 11th May 2012 11:04 PM

hmm, so there's no way to curb that noise? One of these really seems like it should do the trick http://www.ti.com/lit/ds/symlink/tle2426.pdf

What specifically makes a PC power supply so noisy? I know there are a lot of components in the PC drawing various current, and that it is a switching supply, but surely there should be a way to flatten the signal?

Avro Arrow 12th May 2012 12:28 AM

It's not just the power supply generating the noise, it's all the inner workings of the computer as well.

The TLE2426 is just a rail splitter...it in no way is meant to be a noise suppressor.

I'm sure you could filter the PC power to something you could use with enough resistors, capacitors and inductors, but it would be much simpler to use a DC wall wort.
You may find you want to use the amp away from the computer as well.

wwenze 12th May 2012 01:04 AM

LC, LC, and more LC.

Actually, nah, I've compared computer PSU vs wall-warts for powering my sound card, and this is the result:

Which of these power supplies is best for Xonar STX?

Granted, STX may not behave like CMOY, but I guess the general trend should be the same.

1c4ru5 12th May 2012 01:04 AM

I went digging through my box of misc electronics junk, and found a big heavy brick labeled for use with sony audio equipment. I checked the connector against the wall plug, and got absolutely no connection between either end, so i am assuming it's isolated - is there an easy way to figure out if it's regulated?

Would still like to know how to try to brute force the molex connector into submission though- I have a breadboard and I'm not afraid to use it.

DigitalJunkie 12th May 2012 01:26 AM

You might be able to clean up the PC supply with loads of filtering,as mentioned.. I was also thinking that several stages of LC filtering might be needed.

Assuming you could get the HF noise under control,you might be able to regulate it down to 9V or something,so that the regulator 'chops off' the ripple centered up around 12V. This assumes that the high freq noise is already somewhat under control,and that the regulator won't simply pass it on to the output side. Many common regulators don't have the greatest HF rejection.

PC's really are very (electrically) noisy environments,IME..I'd say they're only second to automotive electrical systems.(Even more noisy and 'hostile'.)

1c4ru5 12th May 2012 01:41 AM

I found a probably suitable wall wart - based on meter readings I am pretty certain it is isolated, any way to tell if it's regulated?

I would still like to look into using a molex power connector though. How would I filter the signal? can I get a doodled diagram for this? I assume i involves at least one inductor, and some big capacitors?

wwenze 12th May 2012 02:27 AM

To tell if it is regulated, just measure the voltage without any load, and voltage at rated current draw. If it is about the same, then it is regulated.

Just use the molex, add filtering if it is too noisy.

rjm 14th May 2012 06:35 AM

Quote:

Originally Posted by Avro Arrow (Post 3020351)
I would steer clear of using the computers power supply...very noisy.

Except that something like the Onkyo SE-200PCI runs off the computer power supply, from the PCI bus, inside the computer chassis ... and sounds absolutely excellent. No noise, no interference, just great sound... with the measurements to back it up, too.

So the computer power supply can be tamed. Unless you are a Japanese engineer working for Onkyo, however, you may find the job difficult.


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