An alternative to the mains for your CD player?

Posted by: wal riley on 30 May 2003

I did ask this question a few weeks ago but it appeared to sink without trace!
Maplin have 2 models of power inverter on sale at the mo', (one of them a higher power rating than the other) and the prices are pretty good. Just in case anyone isn't clear about what an inverter does, it takes the 12 volt D.C. supply from a car battery and converts it into 240 volts A.C. to enable the running of things such as portable tellies in your caravan. However, would this not make a good source of clean mains power for something such as a CD player or pre-amp? Obviously, this would mean that you would have to buy a car battery as well, but one of those and the cheaper inverter would still come in at about £70 quid,(not including a charger!)
Anyway, it sounds like a good idea, what with having a stable power source that is unlikely to spike and shouldn't suffer any R.F. pollution, but has anyone ever tried this and, if so, did the results live up to expectation?
Posted on: 01 June 2003 by John Luckins
I've tried it Wal but not under very exacting test conditions.

I used an invertor to powera DVD player and TV system with Nait2 and KEF speakers once. It was in Central Africa and there was no mains power in the village I was in so I had to use solar power and batteries. I used two 12 volt 50 Ampere Hour batteries in parallel and the best quality Maplin invertor I could get. The results were quite respectable but the sound souce was a bit of a limitation. Seems a bit silly to me to go from 12 volts DC to 240 AC only to drop back to 24 volts DC for the Naim kit. The principle advantage of the mains is the drop in supply impedance when you transform down to the 24 volts DC from 240 volts. All that extra kit in between seems like overkill. I have often felt that for low power kit it would be worthwhile uing an AC equivalent of a low pass filter. Something like a flywheel fitted between a small AC Motor and an alternator or AC generator. This would filter the mains of all the high frequency interference from other kit in much the same way as the heavy platter on a turntable does. Bit tricky for high power kit though.

John
Posted on: 01 June 2003 by JeremyB
Wal,

I think Julian dismissed the battery option which IIRC was all the rage about the time the Naim pre-amp came out.

The problem is that the constant chemical reaction that produces the emf is fairly slow and noisy and would require filtering making it worse than the mains.

Jeremy
Posted on: 02 June 2003 by BLT
"The problem is that the constant chemical reaction that produces the emf is fairly slow and noisy and would require filtering making it worse than the mains."
A friend of mine worked for Linn, designing amplifiers, in the late 80's he had come to exactly the same conclusion; batteries are simply not the ideal source that they are often touted as.
The inverters are basically cheap SMPS - I really don't see the point of converting DC to (noisy) AC and then back to DC again. The mechanical filtering may be worth looking into, but unless you use a large generator/motor set, you will end up with a much higher impedance supply than you would if you simply used the normal mains.