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AR-XA grounding problem?

Tommarc

Tommarc

New Member
I restored (cosmetically, anyway) my old AR-XA from college. I relied on Vinyl Nirvana's DIY section for guidance, which was a great help. I decided not to attempt to rewire anything, at least this time around.
I did replace the cartridge with a Shure m97x (I think that's the model).
When I plugged the RCA plugs into my much newer (circa 2000) Rotel amplifier, with a phono stage, there was a loud hum. The phono stage has a ground post and the RCA cable from my 2003 Music Hall TT has a separate ground wire that I attach to it. I notice however that the old RCA cable from the XA TT does not have a separate ground wire, but there appears to be one embedded alongside one of the two wires that the cable is made up of. Do I have to open up this cable, split out the ground wire (assuming that's what it is) and rewire the RCAs? Or, when I acquire the vintage receiver that I just bought on eBay, will the problem go away? I don't remember having to attach ground wires back in the day....
Any advice would be appreciated!
 
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meter it out... bet one of your RCAs is bad, or the ground wire itself. Or did you not hook up the ground to the receiver?

ground should have continuity to chassis, and the RCAs should have continuity to each of the 4 cartridge wires
 
The braided wire loom coming from the arm is the arm ground. it attaches to the subchassis ground strap, and the top plate ground strap, and then feeds down to the ground side RCA connector. you need to run continuity checks from that RCA ground to all ground points. Generally the arm ground fault lies where the braided wire passes through the top plate. an open in either arm wire will cause a severe hum also,
 
marcmorin said:
The braided wire loom coming from the arm is the arm ground. it attaches to the subchassis ground strap, and the top plate ground strap, and then feeds down to the ground side RCA connector. you need to run continuity checks from that RCA ground to all ground points. Generally the arm ground fault lies where the braided wire passes through the top plate. an open in either arm wire will cause a severe hum also,
Click to expand...
Does this mean I have to learn something about circuitry and how to use a multimeter?? (Gulp!) I will try. But what about the ground post on my phono stage? Are you saying it's not really necessary, i.e. the RCA connector with the embedded ground wire is sufficient?
 
N8Nagel said:
meter it out... bet one of your RCAs is bad, or the ground wire itself. Or did you not hook up the ground to the receiver?

ground should have continuity to chassis, and the RCAs should have continuity to each of the 4 cartridge wires
Click to expand...
Thanks. I'll check
 
Tommarc said:
Does this mean I have to learn something about circuitry and how to use a multimeter?? (Gulp!) I will try. But what about the ground post on my phono stage? Are you saying it's not really necessary, i.e. the RCA connector with the embedded ground wire is sufficient?
Click to expand...
yep, the ground post, and the ground side of the RCA input is the same. It's there for arms/tables that don't have a summed ground to one of the RCA cables.
Using a digital VOM is pretty easy. two pins, and read what the screen says.
 
marcmorin said:
yep, the ground post, and the ground side of the RCA input is the same. It's there for arms/tables that don't have a summed ground to one of the RCA cables.
Using a digital VOM is pretty easy. two pins, and read what the screen says.
Click to expand...
I see....thanks for this! I'll get one and give it a try! And I'm adding a photo of my restoration, FYIIMG_4309.JPG
 
Tommarc said:
I see....thanks for this! I'll get one and give it a try! And I'm adding a photo of my restoration, FYIView attachment 1003427
Click to expand...
I reckon it's been said here a thousand times, but since you're new, I'll say this: When Marc talks AR, listen.
He knows his way around these tables like nobody's business, and he is beyond helpful. This place is truly lucky to have him ramblin' around.:D

Nice looking table, btw.
I actually just pulled my XA out of storage to finally install new RCA cables on it a few weeks back. I haven't had much time to sit and listen to it since, but life seems a bit better when it's on the TT shelf ready for use.
 
Tommarc said:
I see....thanks for this! I'll get one and give it a try! And I'm adding a photo of my restoration, FYIView attachment 1003427
Click to expand...
marcmorin said:
yep, the ground post, and the ground side of the RCA input is the same. It's there for arms/tables that don't have a summed ground to one of the RCA cables.
Using a digital VOM is pretty easy. two pins, and read what the screen says.
Click to expand...
Hi again. To back up a bit, when I first tried plugging the RCAs into my amp, the moment I touched one of the plugs to the socket this produced a rather loud hum and I ceased immediately. After getting all the above good advice I got a multimeter, but before opening things up, I decided to try connecting the RCAs again - only this time I plugged both in and then powered on the amp. There was an audible hum, but nowhere near as loud as before. I cleaned the RCA terminals with isopropyl alcohol and that seemed to help (is that possible?). Anyway, I then checked with the multimeter all the points of continuity you suggested and they all appear fine, i.e. the meter beeped as it should. The current status is that there is a hum, but it is not noticeable, i.e. drowned out, when the system is playing music. My question is: should I leave well enough alone? Is this a gremlin that may not be worth the effort to try and find the source of? What else can I try? Thanks!
 
Is the hum audible with the volume set at a normal listening level but no LP playing? (I don't *think* a XA has muting contacts, so this should be a valid test.)

You've just learned something here..

1) RCA connectors make the center pin before the shield, and break the shield before the center pin.
2) As a result of the above, you should really not plug or unplug them with gear powered up.
3) If you absolutely *must*, you should put the input selector in a position other than the one you are connecting or disconnecting.

A loud hum when the center pin but not the shield is made is perfectly normal, and this is why I say you shouldn't connect RCAs "hot".

For cleaning, isopropanol is a good grime cutter but if you want to ensure good connections, get some Caig Deoxit, the little tiny super glue sized bottle of D100 is probably the least messy for RCAs, but you will also want to have some D5 aerosol and some Faderlube aerosol on hand for cleaning volume, balance, tone etc. pots and selector switches (you are going to keep listening to music for a while aren't you?) It's a little hard to find, but Guitar Center usually carries their products as does Amazon.

A little hum with everything properly connected is normal, but it should really not be audible at normal listening volume with no signal, you should have to crank the volume to hear it.
 
Also - I will check tonight but I was rereading your post and my memory is that there is a separate ground wire alongside the RCAs, this must have got snipped over the years if there isn't a little tail of wire to connect to the ground point of your Rotel. That may be the reason you still have an "audible" hum.
 
I wanted to check and make sure that my memory was correct, and it is - what appears to be a ground wire between the L and R coaxes in the stock grey XA cable assembly in fact *is* a ground wire.

I didn't get any pics because it is connected to a big Sansui receiver on a stand that isn't easily moveable, but I can if you really want to know what it looks like later.
 
N8Nagel said:
I wanted to check and make sure that my memory was correct, and it is - what appears to be a ground wire between the L and R coaxes in the stock grey XA cable assembly in fact *is* a ground wire.

I didn't get any pics because it is connected to a big Sansui receiver on a stand that isn't easily moveable, but I can if you really want to know what it looks like later.
Click to expand...
Got it. Here's a pic of my cable which appears to be intact. Marc Morin above says that is sufficient - I don;t need to run a separate wire to the ground post on my phono stage. Anyway thanks for your clarifications about what was happening (the pin and shield business)! Knowing that is a big help to me. I'm feeling better about it now - the hum I'm hearing may be normal.
Cheers!IMG_4317.JPG
 
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
 
Tommarc said:
Got it. Here's a pic of my cable which appears to be intact. Marc Morin above says that is sufficient - I don;t need to run a separate wire to the ground post on my phono stage. Anyway thanks for your clarifications about what was happening (the pin and shield business)! Knowing that is a big help to me. I'm feeling better about it now - the hum I'm hearing may be normal.
Cheers!View attachment 1007943
Click to expand...

Interesting. Mine looks just like that but the center wire is split out and connected to the post on my receiver. What you show should work as well as the shell of the RCA jacks should be connected to the chassis of your receiver/preamp internally so the two connections would be functionally/electrically identical. I will have to look closely next time I have it unhooked and see if there is any evidence of that wire having been connected to the L channel shield.
 
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