USB dac battery power adapter

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Hi, I just bought a M-Audio fast track pro (Emu 0404 USB not avail.). Love it... replacing a spdif out from evolution 5.1 to an old MSB dac... if you are in such a situation... do the USB switch... Oh my...

Anyway, the power adapter sells separately, and I'm thinking I might as well make a battery adapter for my dac. Power requirements are 9V, 500ma. Does anyone have a quick advice how to do this... I have some old courses in electronics (very old), so I need step by step. Maybe direction to another link...

Is the current requirement important?

Kind regards
answering myself then... but hellp

Ok so what I've learned so far, after hours of search, is that the unit will pull the current it needs, that the battery (SLA), should be about 7 mah to stay on about 14 hours.. that I should lower a 12v battery to 9v and regulate the thing. How to lower and regulate is still a mystery.From what I know, a resistor in series is probably the tric for that. A post was so old that the regulator proposed in it no longer exist at the web store... and I wouldn't know how to use that regulator.

I also learned that this kind of project is very ermetical in both Audio Asylum and DIY Audio... no answers so far.

There must be some help somewhere

" ... Is the current requirement important? ..."

Well, not as much as one would guess. The steady state "on" power consumption is much less than the 500 mA. ... M-Audio uses a switching supply wall wart here and they are quieter when not drained too hard. Internally there is a 5.0 volt regulator, similar to a linear '7805 so the PS noise gets pushed way down. A battery source instead might improve the noise figure some, but not so's you would notice.

If it were mine, and I wanted to power from battery, I'd get a healthy motorcycle 12 VDC lead acid type and put a '7809 or equal on it with a small heat sink ... That way you will have plenty of long term power and enough surplus power to run a few other gadgets too.

... as you say ...

'7805 is +24 VDC to 5 VDC linear regulator = common part # uA7805

'7809 is +24 VDC to 9 VDC linear regulator = common part # uA7809 <<<.>>> the one you want for this purpose.

National Semi makes a whole line of equivalent linear DC regulators to the (older) Fairchild uA78xx and uA79xx series regulators and they have cross references on their web site. Plenty of reference designs and circuits too.
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