On Fri, 28 May 2010 11:13:46 +0200 Jörn Nettingsmeier <nettings@xxxxxxxxxxxxxxxxxxxxxx> wrote: > 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. -- 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. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
