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ARXA motor capacitor

H

HiFiHarv

Active Member
Can someone please tell me what the proper type, value, and voltage rating I should use for this cap? I teplaced it before back in the late 70s, so am not sure whether or not whats in there is correct, or maybe these days there is a better choice. Hoping this will eliminate a ground buzz that stops when i unplug the table. If that does not sound right to you, please feel free to comment on that as well. Thanks for any advice on this.
 
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Is the ground wire of the sub-chassis grounded to the "ground" terminal lug (where the tonearm wire shield is terminated)?
 
WaynerN said:
Is the ground wire of the sub-chassis grounded to the "ground" terminal lug (where the tonearm wire shield is terminated)?
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Hoping he has checked all that.........oddly enough, I've had caps way out of spec that caused all different kinds of weird noise.
An ES-1 I had here sounded like somebody trapped a cat inside........
 
Wayner, the sub chassis, top plate, and arm are all tied together and grounded via a seperate line to the preamp chassis. Been running quiet like this for decades into various systems. Nothing has changed recently and all of a sudden, this noise. I know this could be caused by a lot of things, but it is suspicious that it stops when the table is unplugged and then plugged back in. Next day, the noise is back, and again stops with un plugging and plugging back in. I thought reversing the plug had fixed the problem, but next day it was back, and thats when I discovered that it was inplugging that cured the noise.
 
Oh, that could be the cap on the switch.......

As this cap starts to fail (or change value due to age) it will pass thru more current to the motor, but not enough to make it run. The cap on the switch is there to take out on and off inrush from the switch. If it wasn't there, you would hear a loud "pop" every time you moved the switch. Because the switch cap may be letting thru more current (in the off position) the motor is vibrating (in the off position). This vibration is going thru the belt, to the platter and eventually into the tonearm and then microscopically vibrating the cartridge, producing the faint hum.

To semi-prove that idea, remove the outer platter so that you can touch the motor or the belt with your fingers and see if you can't feel some vibrations thru these parts with the table turned off.

This is a mechanically induced hum, because of an electrical failure.......

I think that cap is .022uf, 600v. Not 100% sure (would have to tear my table apart to find out) and I'm busy having a couple of beers and spinning records right now.......
 
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Yes wayner, it is the cap on the switch. As far as i know, thats the only cap on the XA. Unless, of course you might have one of the XAs with the universal power supply inside. Enjoy your listening and beer, thanks so much for commenting
 
WaynerN said:
I think that cap is .022uf, 600v. Not 100% sure (would have to tear my table apart to find out) and I'm busy having a couple of beers and spinning records right now.......
Click to expand...

that is the correct value........but still remember, that the current going through the motor still has to pass the run cap too
 
HiFiHarv said:
Yes wayner, it is the cap on the switch. As far as i know, thats the only cap on the XA. Unless, of course you might have one of the XAs with the universal power supply inside. Enjoy your listening and beer, thanks so much for commenting
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is this a two motor table?
 
So marc, can I assume you are refering to the switch capacitor as wayner describes, or something else? Thank you for that info. Im assuming that is a film cap, correct?
 
HiFiHarv said:
So marc, can I assume you are refering to the switch capacitor as wayner describes, or something else? Thank you for that info. Im assuming that is a film cap, correct?
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if this is a single motor table, there are two caps. the .022uf across the switch and a .1uf on the motor. The two motor tables have 1 cap only, at the switch. You can use a film cap, the originals are not.
 
Just noticed you referred to a run cap. I swear I dont remember seeing anything but a single cap on either of my Xas.
 
I guess Im wrong then. So, the originals were ceramic? Thought I remembered an original pyramid, or black cat that I replaced before. Teason I replaced that csp was thst the tsble would run even with switch off. By the way, both my XAs have always vibrated away when turned off. Thought that was normal. No?
 
Sorry for the mispellings. Using tiny celphone right now. Thanks for clearing up the question of the caps values
 
Fwiw, these are single motor XAs. And, when I say they vibrate when off, I mean they do so audibly and it stops when turned on.
 
These tables exhibit absolutely no sense of speed instability by the way, they sound great. Neither one is using the original AR arm.
 
The switch capacitor is not a brick wall. It passes a small amount of current between the on and off contacts. (remember that capacitors are frequency dependent). This small leakage will cause the motor to be slightly energized. With the switch in the off position and the motor turned by hand, you can "feel" the pole positions and feel some vibrations associated with this. When the switch cap ages and changes value, even more current gets passed it and causes the motor to vibrate even more than normal. This vibration energy will eventually end up in the arm, vibrate the cartridge (and thus the cantilever) and thru the sympathetic 60 hz mechanical energy will produce 60hz hum (as electrical energy), via the moving magnet and coils of the cartridge. The cantilever is mechanically vibrating in free air, inducing an electrical signal as it vibrates in front of the coils. So the trail is an electrical failure creates a mechanical energy which in turn creates an electrical hum.

(beer o'clock is over)
 
Thanks wayner for your insight. I always believed that once turned on and the platter is spinning, the vibration was gone and not creeping into the music we hear. You think thats wrong? Are you suggesting it is distorting the reproduction, regardless of what we think we are hearing? Sure doesnt sound so. Tonight was different. Noise would not go away from unplugging the table. So, I disconnected the AR and plugged in my Well Tempered table. Noise gone. Releived that it is apparently not an issue with the preamp. Thinking the failing AR cap(s ) have now failed. Its an easy fix. Well see what happens after replacement. Very busy at work right now, so might be a week or so. Work really gets in the way of what matters in life. Great to have multiple tables on hand though.
 
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