Linn Valhalla on Thorens turntable

[G Doggett]

I have just installed a Mose power supply to a friends Linn LP12 mainly so that he could play some of his 45 records.
He has offered me the original Valhalla circuit board which is in perfect condition and I was wondering if anyone had installed this into a Thorens TD160.
Is this likely to be a sonic improvement over the Thorens basic resistor and capacitor wiring, considering that in New Zealand we have a fairly stable 240 volt 50 Hz power supply.
I am considering placing it in a separate box rather than under the turntable, but don't want to go to all his trouble if the difference is minimal.
Keen to hear from anyone who has done this and what was the outcome.
Graham.

[G Doggett]

ANYONE ??????

[G Doggett]

Well I went ahead with this project and it works fine.
I had a project box that was just the right size for the Valhalla circuit board.
The output wires are connected directly to the Thorens motor and supply a clean 85 volts to the 2 windings. Start up is fine and the motor is smooth and quiet.
The second photo is my test run with a spare motor to confirm it would work.
Because of the heat generated by the 2 resisters on the circuit board I provided ventilation holes for airflow.
First listening impressions are quieter background and a slight increase in bass.
The difference is only minor but real, so I wouldn't rush out to buy a Valhalla unit but as I had one already it was a worthwhile upgrade.
Graham.

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[JaS]

A very tidy job there It's useful to know that it will work with that motor, rather than just Airpax/Premotec.

Regards,
JaS

[Trackside]

AFAIK it just supplies a 'synthesised' lower voltage AC at mains frequency so it should work fine with any mains driven motor. Looks like a neat setup in that box Many LP12 owners ditch the Valhalla for better PSU's one of which is Naim's 'armageddon' which is just a big step down toroid in a box which is even easier to do as a DIY project than this.

[G Doggett]

I had planned to build a DIY 'Armaggedon' but when I scored the Valhalla I figured I might as well use it.

The success of this project has got me thinking that an improvement in sonic performance could be achieved on many turntables that use a similar 110 volt synchronous motor.
While a good deal of the improvement must come from the 'cleaned up' AC supply, some must come from simply dropping the voltage down to 85 volts which reduces the motor cogging effect resulting in steady platter rotation.
A simple mod could involve nothing more than fitting a dropping resistor into the motor supply circuit.
Makes you wonder how many turntables could be measurably upgraded with a 20 cent resistor and a bit of soldering !!!!
I might try this on my almost finished Logic DM101 rebuild.
Any suggestions as to the value of the resistor to use ?
Graham

[JaS]

It depends what wattage the motor is? A Variac works well as you can tune the voltage down to the minimum required to keep the motor spinning, and tweak it up a bit to get it started. A 3 way switch (off/start/run) with different resistors for starting and running might work too

Regards,
JaS

[Trackside]

I've heard it claimed that one of the reasons the armaggedon mod works is it provides a low impedance power supply so adding a resistor to drop the voltage ( which it won't do in an AC circuit ?) may not be very effective. Also smoothing the cogging has much to do with the value of the cap used which may not be the same as the one used by the manufacturer. On my Systemdek I changed the factory spec .22uf cap to a .39uf and the motor vibration disappeared. There are some data sheets on Airpax and Premotec motors which you can download which describe the correct phase change cap values and also indicate that trim pots may be required on the windings to balance the power delivery between the coils for optimal smooth running.