chip (11/27/82)
A friend of mine just bought yet-another-trinket for his Lynn Sondek turntable. It's a little circuit card that connects between the motor and the 120 volts AC (normally the motor is connected directly to the AC). The circuit is supposed to re-synthesize the 60hz AC using a crystal reference to obtain super-accurate speed control. I was always under the impression that the 60hz coming out of the wall was pretty-damn-accurate. Am I wrong about this? Does the power company play tricks with the 60hz? Could there be some other benefit in having this ($130) circuit that I'm not aware of? I have a Lynn Sondek copy (Ariston RD11s) and I'd consider getting one of these circuits if it's really worth it. Any thoughts/info? Chip Hoover ...!mcnc!chip
wm (11/27/82)
The 60Hz that comes out of the wall is only accurate over a long time interval, i.e. so your clock will stay fairly accurate over long periods of time. Short term fluctuations in frequency accuracy can be quite large, although they rarely are. Most of the time the frequency error out of the wall will drift slowly one way until it is inaccurate enough (in the long term, again) and the control operator or computer or whatever will nudge the control a little the other way for a while to make up for it. Personally I can't see any reason for a device to resynthesize 60Hz. If you are that worried, get a turntable with a servo drive, or any other form of drive rather than a synchonous motor. Wm Leler - UNC Chapel Hill
ark (11/27/82)
(1) If you have a device that re-synthesizes 60 Hz, you can change the frequency a little to get deliberate speed variations. (2) I think that while power companies control long-term frequency variations very tightly, there can be some short-term drift. I doubt this would be enough to bother, but you never know. This only works, of course, if you have a turntable with a synchronous motor.
rjk (11/27/82)
Andy is right (rabbit!ark) - the power company does maintain long-term frequency stability, so your clocks won't be off an hour per year. The frequency standard is at Ohio Power and Light in the Akron/Canton area. While doing EE lab projects in the power area, I found some frequency variations that could produce turntable wow, but decent tables have platters with enough mass to carry them through those times. Randy King
spence (11/29/82)
#R:mcnc:-138400:harpo:18700002:000:522 harpo!spence Nov 29 10:36:00 1982 I've designed clocks that count down the electric company's 60hz to derive the time. It is very accurate over the course of a day, however this is just the average. The EC does vary the frequency over the course of the day usually on the order of 1 hz. So it may vary from ~59 to ~61 hz. You probably have to have a VERY good ear to notice the difference, but there IS a difference. Unless the rest of your system is top oof the line, top notch, etc., it probably is not worth your while. Steve Spencer harpo!spence