Trying to understand the Naim Armagedon power supply, please help - diyAudio
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Old 14th January 2007, 03:29 AM   #1
pjpoes is offline pjpoes  United States
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Default Trying to understand the Naim Armagedon power supply, please help

Ok so I want to understand the Naim power supply. It uses an isolation transformer to isolate the motor from any noise in the line from the wall, correct. Then it uses a resistor to step down the voltage, and a .2uf capacitor for phase shift.

Other than the transformer, the typical power supply used in many AC Sync turntables right? Could a similar method be implimented on any AC Sync turntable simply by using a filtered power supply with isolation transformer. Would a possible way to upgrade the power supply be to replace the transformer with one that offers isolation and also reduces the voltage down to the needed one, say 12 volts, and have it be of a larger VA rating. Do they make transformers that both isolate and reduce voltage, would that be essentially a step down transformer?

Ok final question, do you think the quality of the phase shift capacitor would really make any difference, I know Naim used a different one, but is there really any difference between say the quality of the cap used in the naim and that used in the Linn Basik. I don't have a Linn, I have an Acoustic Solid now which uses a 12 volt AC Sync motor. They offer a very expensive microprocessor controller, and I was curious about implimenting a Naim style system with the A-S since it would probably not cost all that much.
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Old 14th January 2007, 01:01 PM   #2
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The Armageddon is designed for the 2-pole synchronous (airpax) motor. In principle you could use this approach for any 2-pole motor run at mains frequency, but you will need to recalculate the component values. If the Acoustic Solid uses a 3-pole motor it can't be done this simply I'm afraid.


By way of background - the Linn (Airpax) motor is nominally 110v, with a winding resistance around 4700ohms and 5H inductance per winding. You need these last two measurements for your target motor to get the phase shift correct. So, for the UK 'geddon, the transformer provides about 80v output, with 4K7-5K2 in series* to further drop the voltage (reduces vibration) and the 0.2uF cap. In the US, with your 60Hz mains, the cap is 0.18uF by the way. This gives the necessary 90degree phaseshift, more or less. Note that this motor draws very, very little current - only 10mA or so when running. Hence the cap quality doesn't matter, becasue impedances are very much higher than the caps' own ESR/ESL values.

Value of the series resistor is not critical - but higher reduces voltage at the motor, which in turn reduces vibration markedly and also torque. You cna take it up to about 6K5, meaning c. 60v at the motor, before the plattter needs a gentle push to start.

The transformer can be any regular part at appropriate voltage (110v primary, 12VAC secondary in your case). 'Isolation' only means that the phase shift network isn't directly connected to the mains supply, as it would be with the Linn 'Basik' supply.
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Old 14th January 2007, 05:38 PM   #3
pjpoes is offline pjpoes  United States
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Ok thanks for the input. So more than likely the capacitor built into the motor housing itself is good enough and not worth changing correct. I imagine they calculated the value correctly for US use, especially since I am getting correct speed.

It's a very high mass platter, weighs about 20lbs on its own, and though I know some feel that an upgraded power supply can't possibly make a difference, I respectfully disagree. Besides having very obvious problems arise when my thorens controller stopped working correctly, and being able to hear the problems the vibrating motor was causing, I was able to adjust it to see how more and less of that problem changed the sound.

On this table what I find is that the motor does vibrate, quite a bit more than I would have expected. Also the aluminum enclosure that the motor is housed in gets almost too hot to touch after a long listening session. I'm suprised by this to be honost. Also, the motor is quite noisy compared to the best I have heard, but that noise is inconciquential as listening positions.

I would love to experiment a little and try reducing the vibration and heat. Torque is really a null issue at the moment I think as its a string drive and is unable to start the platter easily anyway. It doesn't have the problems you describe of needing to start it by hand, but the slip that is available from the string suggests to me that possibly I could get away with lower torque no problem.

I don't believe its a 3 phase motor, wouldn't I have three wires going from the power supply to the motor then. I only ahve two, so I really think its a simple two phase AC motor with a capacitor used for phase shift. I haven't opened the motor housing yet, and plan to do that next.

What I have noticed and think I can even hear a little through the speakers, is the motor vibration is vibrating the table and I can feel it through every part. I can feel it through the arm even a little. The only area I don't feel it, which is a good sign, is when the string isn't attached I don't feel it in the platter, and I don't feel in the bearing even with the string attached. However I can hear it with a stethascope all over. Also, durring silent record tracks, I'm quite sure I can hear the noise through my speakers. Its not intrusive, and I have noticed this effect on lots of turntables before, but I would like to get rid of it if possible, without having to resort to a complicated and expensive motor drives.

Would the same DC component of wall voltage that causes transformers to hum also potentially cause worse motor vibration and noise. If so, would a filter designed like the PS Audio's, and various others, to reduce transformer hum, also then reduce the motor vibration. I believe there are some DIY designs for this, like the Jon Risch stuff. Thanks again for the input.
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