AC motor power supply - Page 3

diymax62 · 19th August 2007, 04:30 PM

Hello Nanook, as far as I know the Valhalla supply should generate a stable, quartz-locked 50 Hz square wave, followed by a proper filter with a very high slope (probably a Chebischev one), with a 90 degrees phase shifter at the end to drive the second coil of the motor. I said "as far as I know" because I didn't received the scheme until now (but I absolutely don't want to force tkwou in any way).
The way to build a 60 Hz modified Valhalla should be easy enough, but I can't help you in any ways in the digital domain to generate a stable quatz-locked 60 Hz square wave. For the filter, you must change the value of the capacitors OR the resistors interested in the filtering job multiplying their values by a factor of 5/6 (e.g. a 120nF capacitor should be replaced with a 100 nF one, or, probably easier, a 12K resistor with a 10K one).
For the mechanical approach tkwou is absolutely right, it's too much simple to damage the motor without the rproper experience and tools to work that way.
The only thing that I can suggest (I made it a couple of years ago with a Thorens motor) is, if the pulley is a plastic one, to put the motor in a plastic bag and put it in the freezer for a proper amount of time to get an help from the thermal reduction of the size of the metal shaft, but it's a VERY delicate work, and don't forget that, after this, you must re-insert the new one...
The electronic way is reeeeaaly better...
A great salute

tkwou · 3rd September 2007, 05:36 PM

Thanks diymax62. This is certainly a viable option. Actually I have done this when I made a Valhalla to run at 45RPM. You just have to change the crystal and one resistor. To get the 60Hz output you only have to change the crystal. There were actually a few of these made by Linn when the Valhalla first came out so that people with existing North American LP-12's could update to the Valhalla without changing the motor. This didn't last long because it was easier and more profitable for Linn to have one single Valhalla board and one motor unit that could be used world-wide.

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19th August 2007, 04:30 PM	#21
diymax62 diyAudio Member Join Date: Nov 2004 Location: rome	Hello Nanook, as far as I know the Valhalla supply should generate a stable, quartz-locked 50 Hz square wave, followed by a proper filter with a very high slope (probably a Chebischev one), with a 90 degrees phase shifter at the end to drive the second coil of the motor. I said "as far as I know" because I didn't received the scheme until now (but I absolutely don't want to force tkwou in any way). The way to build a 60 Hz modified Valhalla should be easy enough, but I can't help you in any ways in the digital domain to generate a stable quatz-locked 60 Hz square wave. For the filter, you must change the value of the capacitors OR the resistors interested in the filtering job multiplying their values by a factor of 5/6 (e.g. a 120nF capacitor should be replaced with a 100 nF one, or, probably easier, a 12K resistor with a 10K one). For the mechanical approach tkwou is absolutely right, it's too much simple to damage the motor without the rproper experience and tools to work that way. The only thing that I can suggest (I made it a couple of years ago with a Thorens motor) is, if the pulley is a plastic one, to put the motor in a plastic bag and put it in the freezer for a proper amount of time to get an help from the thermal reduction of the size of the metal shaft, but it's a VERY delicate work, and don't forget that, after this, you must re-insert the new one... The electronic way is reeeeaaly better... A great salute

3rd September 2007, 05:36 PM	#22
tkwou diyAudio Member Join Date: Feb 2006 Location: Vancouver	Thanks diymax62. This is certainly a viable option. Actually I have done this when I made a Valhalla to run at 45RPM. You just have to change the crystal and one resistor. To get the 60Hz output you only have to change the crystal. There were actually a few of these made by Linn when the Valhalla first came out so that people with existing North American LP-12's could update to the Valhalla without changing the motor. This didn't last long because it was easier and more profitable for Linn to have one single Valhalla board and one motor unit that could be used world-wide.

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