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In Reply to: RE: What type of controls work with this Garrard 401? posted by Ugly on January 14, 2017 at 19:19:53
Hi Ugly,
It has taken me a while to respond as I have been thinking about this for a while.
As Steve said, your machine has a speed control already. It is not closed loop or tied to a quartz oscillator but it is loosely tied to your mains frequency. You have an induction motor with a rotor designed to slip at a speed proportional to torque load. There is an eddy current brake which puts a torque load on the motor which is proportional to speed. If your mains power is decent that should be good enough. If your power is nasty there is the very $pendy power source which Steve suggested. I'm pretty sure that will provide good clean power with low phase noise and quartz stability. This may very well improve the short term stability of your machine. You will however still not be closing the loop around the platter and the long term stability will still be somewhat determined by the eddy brake and the motor.
If you really want to close the loop on the platter and reference it to a quartz clock, something like that Roadrunner setup which Pheonix Engineering sells may do the job. You would set the speed of the eddy brake a bit high and let the speed box do what it does.
One issue you will have to deal with is that the Roadrunner setup puts out 5 Watts maximum. Your machine requires ~16 Watts. Either you will have to rig an amplifier between the Roadrunner and your motor or talk to them about making you a custom unit.
Phil
Follow Ups:
Thank you for the informative post, Phil. It really helps my understanding along to realize it is a form of induction motor I have.
When I look at my grid it looks mostly sinusoidal but there is a distinct lumpiness to it most of the time. Hard to say what the definition of "good" is...I think it looks pretty bad. It is the wild west out here after all. No harmonics initiative in my neighborhood.
Since I have no idea what this or any other 401 sounds like stock or what others are doing with theirs to get them running optimally I figured now would be a good time to try and find out if this disappearing Phoenix Engineering hardware should be of any interest to me. It is a neat old looking turntable that I had hoped to one day give some love to to find out if I like it.
Since I think I may already own one I would love to learn Garrard 401 owners get the best speed control results from the stock eddy brake rather t5han some aftermarket solution.
I think the Eagle Power Supply is a larger drive capable of 3phase output at 25W per phase and can take the velocity feedback from the Roadrunner product to close the automatic velocity control loop.
I don't know all the details but I recently read rumor some type of induction motor controls can be done with the Phoenix stuff.
It may be tho whole point is moot now that there is no support with questions in my mind such as : is the closed loop bandwidth, tach resolution, etc sufficient for doing an idler drive speed control? For all I know the Phoenix speed control stuff may have been targeting belt drive systems but again, I have no idea.
I guess the distinct lack of a response on this forum to my query from anyone doing what I'm asking may be evidence not many, if any, are doing this.
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: 01/17/17
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
I am very interested in this discussion because I recently purchased a Phoenix Falcon PSU. As soon as I learned they were shutting their doors I quickly bought the Roadrunner plus an extra sensor. These are hooked to an upgraded Rega P25.
I bought the extra sensor thinking that would die first but then I was thinking about putting the extra sensor on my Thorens 124. Then I started thinking about finding the upgraded Eagle PSU for the Thorens motor. So I'm hoping there is more discussion on this topic
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