AR-XA grounding problem?

[Tommarc]

Which Rotel do you have?

Some receivers and amps have the grounds for the RCA jacks grounded differently. Some even are grounded to the Mains ground.
This could be the cause of your hum.
If possible you might want to disconnect the ground that is in the Existing RCA of the AR and run a separate GND from
where you disconnected the RCA GND ( under the plinth) to the Rotels GND conection and see if it gets any better.

Athanasios

Interesting...I may give that a try. Thanks!

 

[Tommarc]

Red is almost always right, white/grey is left.

Hey, while I have you on the horn.....I just read a thread about about an AR-XA restoration that mentioned re-capping (I have figured out that this means replacing capacitors!). I don't know what a capacitor is but it seems like a good idea (I read that they eventually lose their mojo). Do you know any specifics about this upgrade? Thx

 

[N8Nagel]

I did it to mine but it didn't make any difference. Unlike signal path caps which can make a beneficial difference (especially speaker crossover capacitors) the ones in an XA are just for motor function.

I was hoping that replacing mine might get rid of the motor "quiver" with the switch off but it didn't.

 

[Tommarc]

I did it to mine but it didn't make any difference. Unlike signal path caps which can make a beneficial difference (especially speaker crossover capacitors) the ones in an XA are just for motor function.

I was hoping that replacing mine might get rid of the motor "quiver" with the switch off but it didn't.

Thanks! I can cross that off my list.

 

[woodj]

Have you tried a set of cables without the extra ground?
Are both ends of the cable the same?

 

[marcmorin]

Have you tried a set of cables without the extra ground?
Are both ends of the cable the same?

the other ends of the cable are spade connectors plugged onto the wire tree

 

[WaynerN]

I did it to mine but it didn't make any difference. Unlike signal path caps which can make a beneficial difference (especially speaker crossover capacitors) the ones in an XA are just for motor function.

I was hoping that replacing mine might get rid of the motor "quiver" with the switch off but it didn't.

You will never get rid of the motor "quiver". The switch capacitor (usually something like .01uf) is across the poles of the on off switch. Because no capacitor is a "brick wall", there is voltage leakage, so the motor is still seeing some voltage and that gives it the quivering feeling.

Capacitors are frequency dependent, just like in speaker cross-overs. And like speaker cross-overs, they are not brick walls.

 

[marcmorin]

You will never get rid of the motor "quiver". The switch capacitor (usually something like .01uf) is across the poles of the on off switch. Because no capacitor is a "brick wall", there is voltage leakage, so the motor is still seeing some voltage and that gives it the quivering feeling.

Capacitors are frequency dependent, just like in speaker cross-overs. And like speaker cross-overs, they are not brick walls.

correct, about 60vac is still going to the motor. not enough field strength to move the motor.

 

[marcmorin]

One thing I forgot to ask, and it could cause an issue. How do you have the cart wired? AR headshell pattern is Red right hot, Black right ground. White left hot, Green left ground. on "SME" pattern Green is right ground. If your cart has color coded pins, ignore that and attach the right ground (black wire) to the green pin on the cart. The green wire to the blue pin on the cart.

 

[N8Nagel]

damn, that's a good one Marc, I forgot about that. I actually remember that now and that's a great catch. Guess I don't swap carts enough

 

[Tommarc]

One thing I forgot to ask, and it could cause an issue. How do you have the cart wired? AR headshell pattern is Red right hot, Black right ground. White left hot, Green left ground. on "SME" pattern Green is right ground. If your cart has color coded pins, ignore that and attach the right ground (black wire) to the green pin on the cart. The green wire to the blue pin on the cart.

Sorry for the lag time here. I think I'm OK in this regard (The instructions that came with the Shure were a help). Anyway, for whatever reason, the hum is almost negligible now, and I didn't really do anything except clean the RCAs with deoxit. Could that have made a difference?

 

[marcmorin]

Sorry for the lag time here. I think I'm OK in this regard (The instructions that came with the Shure were a help). Anyway, for whatever reason, the hum is almost negligible now, and I didn't really do anything except clean the RCAs with deoxit. Could that have made a difference?

yep, as will cleaning the inside of the headshell clips where they attach to the cart pins. a full open to ground will cause a real bad hum, a partial open to ground will cause some hum. dirt, corrosion is a "partial open"

 

[Tommarc]

yep, as will cleaning the inside of the headshell clips where they attach to the cart pins. a full open to ground will cause a real bad hum, a partial open to ground will cause some hum. dirt, corrosion is a "partial open"

Copy that. Thx!

 

[AdamAnt316]

Several years ago, I replaced the cable on my AR XB with a 6' length of Radio Shack interconnect cable which had RCA connectors whose metal shells you could unscrew. I peeled the old ground wire off of the original cable, and tried connecting it to the binding post on the back of my preamp as with a normal turntable, but this resulted in hum in the audio.

After discussing it with a friend, I replicated the old cable by running the ground wire along the left channel lead of the new cable, and soldered the ground lead inside the shell of the left RCA plug. This eliminated the hum; I'm not sure why it wasn't enough to just ground the wire to the chassis of the pre, but AR must've known what they were doing when they designed the cable that way.
-Adam

 

[inperson]

One thing I forgot to ask, and it could cause an issue. How do you have the cart wired? AR headshell pattern is Red right hot, Black right ground. White left hot, Green left ground. on "SME" pattern Green is right ground. If your cart has color coded pins, ignore that and attach the right ground (black wire) to the green pin on the cart. The green wire to the blue pin on the cart.

God Bless Marc. I just was hooking my AR to my old Fisher 400 and got a hum. I switched the green and blue wires after reading this and the hum is gone.

 

[Bicyclist]

He is still helping!

 

[Joeloscar]

One thing I forgot to ask, and it could cause an issue. How do you have the cart wired? AR headshell pattern is Red right hot, Black right ground. White left hot, Green left ground. on "SME" pattern Green is right ground. If your cart has color coded pins, ignore that and attach the right ground (black wire) to the green pin on the cart. The green wire to the blue pin on the cart.

7 years later and this is still helping. I had a bad hum on my AR and this solved it! Thanks.