Quick TT power supply

[scott wurcer]

I have an off the cuff idea to make a clean 60Hz (+-) power supply for my VPI TT.
I got out my clip on meter and measured about 60mA AC current draw on the TT which
figures out to be about 7.2W. The idea is to take an old rat shack 12.6 filament transformer connected backwards and a spare low power amp driven by a 30min.
(I have a bad habit of putting an LP on and going to bed) 60Hz CD cut generated in Cooledit. A little work with a strobe and I could probably get the speed spot on. The
numbers figure out to about 20 Ohms looking into the 12.6V tap so the 16 Ohm tap on an
old tube amp should work out too. This would eliminate the need for DC blocking.

Anyone tried/seen this before?

[CG]

I've seen this done before. In fact, at one time someone was selling a commercial version of this. At least the tube portion, not the Cooledit part.

For what it's worth, I've found that the motor supply is pretty much the most critical one in the set-up. Perhaps that's because everything else is filtered well with good regulation, current sources, and all that so that it is less sensitive. But, it does make sense since every little change in the wave form applied to the motor causes FMing of the motor speed. Unless you have a genuine class A power amplifier, the AC mains will have all sorts of power factor irregularities from the power amp gulping current to charge the filter caps. So in a way you have a feedback mechanism built into the ac mains system. That doesn't seem like a desirable thing.

There has been some vague suggestions by Harry Weisfeld (I hope I got the spelling okay) that a pure sine wave may not be the best source. I think he once mentioned that a small amount of 9th harmonic energy souned better. I have no idea of the science behind that.

Clarke

[GUILHERME]

Hi.

I've been designing an SDS-like device and I'll be making it public shortly, so you may consider waiting a bit longer.

There has been some vague suggestions by Harry Weisfeld (I hope I got the spelling okay) that a pure sine wave may not be the best source. I think he once mentioned that a small amount of 9th harmonic energy souned better. I have no idea of the science behind that.

Neither do I. But driving a motor with seperate phases and snippin' the phase-shifting capacitior is a large improvement on motor vibration (one that you can literaly feel in your hand right away). I've also played with the phase angle and it does appear that 90º may not be the best vibration-wise, but I want to be sure of this first before I commit to such statement.



Guilherme.