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Groove Runner Turntable Speed Control

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Graham Slee View Drop Down
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    Posted: 02 Jul 2018 at 6:03pm
Groove Runner Turntable Speed Control

(this design and others was discussed at length at https://www.hifisystemcomponents.com/forum/turntable-speed-control_topic4359.html)

This is a preliminary introduction to the Groove Runner Turntable Speed Control or Synchronous Motor Driver as I prefer to call it.

Because it will require some DIY skills, if only in the fitting of the plug, I have decided to offer it as a DIY kit of parts project, with the option of having it built for you.

Even so, with most motors, some DIY tweaking could/will be necessary.

By making this direct supply only, under my DAK brand, it removes certain profit margins, making it more affordable.

It is designed to work with existing mains type synchronous motors which are mostly 110V made to run on 230V where the mains is 200 - 250V, or left as is for 100 - 125V mains. This means you don't have to buy a new motor provided the one you have is good.

The Groove Runner (aptly named because it "runs the groove" by driving the motor) is quartz crystal locked to the required frequencies to make the motor spin at its designed RPM.

For example, on its 33.1/3 50Hz setting it will simply turn the motor as it would by being connected to 50Hz AC mains. Except that the mains frequency can sometimes drift off, whereas the Groove Runner is always locked on frequency.

A switch is provided to make it do 45 rpm without moving the belt from the 33.1/3 pulley, and for motors with pulleys meant for 60 Hz, the frequency switch is simply set to 60Hz, where it will also do 33.1/3 and 45 rpm.

It does not have any speed adjustment other than the preset 45 rpm and 60Hz alternatives. If the mechanism of the turntable has been properly engineered you would not need to adjust the speed. I have heard it said that some Rega's run fast. Well mine does too if I just put a strobe disc on the platter and observe it steadily advancing. But as soon as the stylus is in the groove it runs extremely close to 33.1/3 rpm.

So if that's what you want the Groove Runner is the motor driver for you.

Its output is independent of your mains. The outboard power supply self adjusts between 100 and 250V, and between 50 and 60 Hz. It supplies the Groove Runner with 15V DC.

This means that the Groove Runner generates its own voltage, and in standard form that is 110V (nominally - there is a trimmer inside for fine adjustment).

The rotary control allows it to be wound down to around 90 volts AC. It may improve your sound by reducing motor vibration.

The output is a pure sine wave, and is from a transformer I had specially made for the job. It is not a mains transformer connected backwards.

The transformer is driven by a chip bridge amplifier with in-built protection and a resettable in-line fuse between it and the transformer.

It has been tested on a Rega Planar 3 230V wired motor (standard PCB), which with rotary control fully clockwise, will slowly start it turning (yes at 110V), but mostly needs a push. Once moving and with record in play it will keep correct speed.

Quickly switch to 45 rpm and it will gradually pick up speed.

If you want it to self-start every time, the 10k 5 watt resistor on the motor PCB has to be shorted out with a link, but you need to ensure you remove it before connecting to 230V. I cannot take responsibility for the user's forgetfulness!

I found the Rega motor worked well with only one component - a 0.15uF (mains rated) capacitor between its phases - as the motor is specified for 110 V AC.

Wired like this it self started on 50Hz 33.1/3 and 45 rpm, as well as 60Hz 33.1/3 and 45 rpm with no noticeable vibration. Obviously not having the 60Hz pulley it did more than the rated speed, but a 60Hz turntable will have the right pulley, and will rotate at the right speed.

The motor discussed so far is the Premotec/Allied Motion/Philips/Airpax 9904 111 31813, which has the same specification as the 9904 111 31819 L*nn use.

I have also tried it with a couple of other motors:

Premotec/Allied Motion/Philips/Airpax 9904 111 31104 with 0.1uF and 1.8k resistor in series for the phasing. This motor is rated at 220V but runs extremely well and quiet at 110V and self starts just as quickly as a standard Rega Planar 3 on 230V mains.

Premotec/Allied Motion/Philips/Airpax 9904 111 32311 is a push start motor designed to operate stalled, and found on Nottingham Analogue for example.

The output is what I would call "simplex" as it does not drive both phases - hence the need for the phasing capacitor (or network as discussed above).

A "duplex" drive seems to be the next logical step for those who want to be really precise in control. An output might be taken from the Groove Runner frequency divider and stepped 90 degrees in a second Groove Runner, not having a frequency driver, but all the other required items. There would be some duplicity of controls, but it could be the basis of a "duplex" design proper.

Estimated price for the ("simplex") Groove Runner: Parts kit £348 inc. VAT plus shipping; Pre-assembled and tested £398 inc. VAT plus shipping.

Questions?




Edited by Graham Slee - 02 Jul 2018 at 8:56pm
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ICL1P View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ICL1P Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2018 at 7:12pm
Pictures?
Ifor
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Reflex M, CuSat50, Majestic DAC, a Proprius pair.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2018 at 9:10pm
Happy to oblige with the preliminary front panel drawing...



Final artwork being approved. Metalwork to follow.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richardl60 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2018 at 9:44pm
No plans this entend the power supply to the Technics (21v I believe) Graham?

Reading online (yes I know it can be dangerous) the SL1200/1210 appear to benefit from an improved 
Power supply?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jul 2018 at 9:39pm
Allegedly taking the transformer out, extending its wires, placing it in some sort of enclosure for obvious safety, makes a "great improvement".


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 2018 at 12:32am
I moved the SL1210 transformer out as Graham suggested. It makes a difference but must be done safely. I have since moved the rectifier and smoothing out.
Jon

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 15 Aug 2018 at 4:04pm
Here it is in the flesh...



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