[einolu]

Can I use one of the 12v rails from my computer powersupply to pwer a cmoy? seems like it would be a good idea to me. Might build one into a floppy drive frame!

~EO

 

[Stephonovich]

You could, but there's people that will tell you that the RF and EMI inherent with a computer will ruin the sound. Myself, I'm pretty sure that with a decent power supply (hook a multimeter up to the 12v rail and ground with it running, and put a decent load on it, like a lot of hard drive access and CPU usage... if it doesn't go below, say, 11.8 and above 12.2 than you're a lot better than most wall warts) it wouldn't matter.

(-:Stephonovich

 

[Sycraft]

I'd say probably a bad idea. The Cmoy looks to be quite sensitive to PSU noise and I'd bet most PSUs have it in spades. Just doesn't matter much to a digital device so it's not worth sepnding the money to minimise. Also most 12v rails in most computers are under pretty heavy load, and a load from a number of vaired devices like HDs and such that will spill noise back on the rails.

If you were to do such a thing, it would probably be a better idea to get a design that goes through some regulation first.

Best of all is just keep out of the case. There's a reason why the big daddy soundcards come in external boxes with seperate power, computers just aren't clean. I have an external soundcard, but I power it over firewire. If I turn my PPA up to the point I can hear the noise, I hear the hiss from the D/As, but louder than that I hear a whine on the frequency of the harddrives comming from the computer. It manages to get pack on the rail, into the firewire power, and through the regulation in the soundcard (granted at a very low level). I wouldn't want to hear it straight off a rail in the case.

 

[Stephonovich]

Methinks it depends on your source (I'm assuming the computer, if it's mounted in a drive bay...) and headphones as well. I mean, there's people who claim that anything other than battery power is sacrilege, as you can hear noise in AC power. There's also people that claim you can hear the difference between different chemistries of batteries. I'm not saying it's all bunk (although it sounds suspiciously so), but it's quite possible that with a fairly low-end setup (like mine; read my sig), you wouldn't hear said noise. You can always try it, at least.

(-:Stephonovich

 

[Sycraft]

Well I know you can hear PSU noise. As I said, I can hear it in mine. It's not a, barely, I think I can, sort of thing, when I turn the volume up, I can hear it clearly. It sounds the same as the harddrives and isn't present when the firewire cable isn't plugged in, so I know what the source is too.

I remember on my SB16 I could hear so much noise, I could tell things about the computer's state by listening, like how hard the processor was working, if the disk was reading, etc. It had very little dampening of the noise that came in so you could hear it even at moderate volume levels.

I can't say for sure it owuld be problematic in a Cmoy, but I suspect so. I mean it has little in the way go circutry to deal with PSU noise and being right on the rail, right in the case is going to be worst case.

I'm not saying a headphone amp in the case is an impossibility, but you'd probably want to add some regulation and stick it in a metal case to try and shield it.

I mean my SB Audigy 2 produces enough noise that if I turn the volume on my mixer past unity, it reads as -30dBu on the meters.

 

[breez]

If the computer is used as the source, you cannot use +12V from it for a CMoy because of the virtual ground design.

 

[Garbz]

The said noise is not some crapply quater percent measurable type noise. It's REAL noise.

Yes batteries are good, but this is in a whole different league. I highly recomend seeking some external power source. That will also solve the ground problems between the cmoy and the computer case. A computer is a horrible environment for an amp.

 

[guzzler]

Quote:

Originally Posted by breez If the computer is used as the source, you cannot use +12V from it for a CMoy because of the virtual ground design.

not entirely true, but you have to isolate the virtual ground from any metal part of the case, doing so shorts the output to ground. PRR had an AC coupled CMoy over at Headwize which might be of interest

computer PSUs are switch mode designs meaning they do have a lot of switching noise on them. You can attenuate this by using an LRC filter followed by a regulator, but you'll never have an ideal power supply from the computer

g

 

[breez]

But computer ground = signal ground = virtual ground.

 

[einolu]

Ill stick to batterys than, heh. thanks for all the insight!

~EO

 

[guzzler]

Quote:

Originally Posted by breez But computer ground = signal ground = virtual ground.

no, virtual ground is half way between the computer ground and +12V. Signal ground is virtual ground, so by connecting to signal/virtual to computer ground, you are, to the opamp, effectively shorting the output to 0V

g

 

[breez]

Yes. Most (if not all) consumer level soundcard signal ground is indeed the computer ground. No way around it unfortunately.

 

[stereth]

There have been many threads on Headwize about this, including several with single-ended Cmoy variants designed to work where V- is signal ground.

Worst case, toss an 8xAA holder in the bay. It'll last for about a week and a half of constant use.

 

[Sewer Guy]

Sewerguys basic rules for hi quality audio circuits: 1. Only linear psu's are to be used (no switching psu's, under any circumstance). 2. No tantalum capacitors are to be used; even as power bypass caps. 3. All rotary controls
ie volume, tone, etc. shall use conductive plastic or hot molded pots. No carbon contorls shall be used (this includes all of the alps pots).

I won't go further here; these rules if followed will help to produce quality audio.

 

[bitWrangler]

Quote:

Originally Posted by stereth Worst case, toss an 8xAA holder in the bay. It'll last for about a week and a half of constant use.

Along that vein, couldn't you build a recharging circuit to run off the 12v internal and use rechargables, then you wouldn't have to worry about it until the rechargables fail to hold a charge (could be a nice long time if the charging circuit were intelligent enough)?