linuxaudio.org

On Fri, 28 May 2010 11:13:46 +0200

Jörn Nettingsmeier  wrote:
> On 05/27/2010 06:36 PM, Bob van der Poel wrote:

quoted text
> >> A friend of mine was talking about how he would like to be able to busk with

> >> his keyboard, and I said I would look into the possibility of building him a

> >> battery powered PA for it. Does anyone have any suggestions for good ways of

> >> going about this? We would like to keep the cost as low as possible.

> >>

> >

> > How about an off-the-shelf UPS? Don't know how big you'd need, would

> > depend on the gig time, etc. There is probably a way to calculate that

> > :)

> >

> > The consumer UPS units I've see all have lead-acid (sealed) batteries

> > and are quite reliable.

>

> not really recommendable for a permanent setup. with an ups and standard

> mains equipment, you will waste battery (and carry dead weight) twice:

> in the inverter that generates grid voltage from the battery, and in the

> PSUs of your gear that will re-transform the precious grid voltage back

> into low-voltage DC. throw out the middle man.

>

> the nice thing about car equipment (as a previous poster has suggested)

> is that all the gear is standardized to work at 12 volts dc. many car

> radios have line ins these days (for file players etc.). it's easy to

> hook up a small mixer here - you should be able to find a cheap one by

> the Brand That Shalt Not Be Named or one of the other manufacturers they

> steal their designs from - i've seen a few that take 12v dc.

How much sound output power do you actually need? In bridge mode an

amplifier running off 12V can deliver a maximum of 18W RMS into 4ohms.
Here in the UK Maplins supply a suitable power module (they call it 40W

- that's peak power) very cheaply - 15.99ukp

http://www.maplin.co.uk/Module.aspx?ModuleNo=37737
It's actually a Kemco product. I don't know how available that would be

in other countries.
At 500mV sensitivity it will probably be a pretty good match for

direct connection to most keyboards. If not, a small buffer amp could

easily be patched in.
I don't recommend using a car battery. They are not designed for steady

discharge, but for short bursts and long recharge times. Although

initially more expensive you would do a lot better getting a sealed gel

type lead-acid battery with suitable charger.
--

Will J Godfrey

http://www.musically.me.uk

Say you have a poem and I have a tune.

Exchange them and we can both have a poem, a tune, and a song.

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