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In Reply to: RE: What type of controls work with this Garrard 401? posted by Ugly on January 16, 2017 at 20:28:29
Mark is/was a Garrard 301 guy, and he knows more about turntable motors and how to drive them accurately than anyone I aware of. You might search these archives for his posts on the 301 motor; they would apply to your 401, as well.I am no expert on Phoenix products, but so far as I know, the Roadrunner is "only" a tachometer for displaying platter speed. If you have both the RR AND one of their turntable power supplies, Falcon or Eagle, you can feed the output of the RR into either of those and thereby achieve a feedback control of platter speed. (The Falcon or Eagle increases or decreases platter speed, as needed, based on info it receives from the RR.) The Falcon does not put out enough power for the Garrard motor; you need a 25W Eagle, for sure. But this begs the larger question about whether those devices (RR + Eagle), which are designed to drive AC synchronous turntable motors, would be appropriate for the induction motor in your Gerrard. This is where you might benefit from reviewing Mark Kelly's old posts here.
Edits: 01/17/17Follow Ups:
I will study Mr. Kelly's posts. Thanks.
Hi Ugly and Lew,I as well an not an expert on the Phoenix products. I knew that there are two boxes
1. A tachometer which measures the platter speed by timing the period of a marker placed on the platter to make a revolution. The timing is done with circuitry referenced to a quartz clock so it is very accurate. The bandwidth has to be fairly narrow as it requires a full revolution to update. It can be used stand alone to simply measure platter speed.
2. An AC power supply which is isolated from the mains. The frequency is controlled by an input from the tachometer (Road-Runner) to hold the platter speed at the selected value.
I believe the system is intended for belt drive machines but I would expect an idler drive to be an easier problem since there is one less pole (delay) in the feedback loop. It is intended for synchronous motors which run at some sub-multiple and the mains angular frequency. An induction motor runs at near the same speed but "slips" by 5 to 10 % depending on rotor design and torque load.
If they have a power supply large enough for the Garrard I have to believe it will work fine. I think the eddy brake should be retained for short term stability (wow) but some tweaking for best loop stability may optimise the result.
Phil
Edits: 01/17/17
I found this paper on-line (see below) which addresses the subject nicely.You'd definitely need the later 25W version of the Eagle Power Supply, plus the RoadRunner. The early version of the Eagle was 15W. The Garrard motor requires 16 to 18W input power.
Edits: 01/18/17
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