On Fri, May 28, 2010 at 09:31:03PM +0100, Folderol wrote: > On Fri, 28 May 2010 11:13:46 +0200 > Jörn Nettingsmeier <nettings@xxxxxxxxxxxxxxxxxxxxxx> wrote: v> > > On 05/27/2010 06:36 PM, Bob van der Poel wrote: > > >> 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. > An Optima or other AGM car/boat battery would work well, but they are pricey and HEAVY. There are large Li/Ion batteries available that might work, designed for electric bicycle applications, but they tend to run at 24v or 48v or some odd voltage. Or, you could just buy a Crate busking amp. Those things are A/B amps (I think) can run forever on a few D batteries. -ken _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
