Hum

[by the way]

I have a late 50's RCA record player that has slight hum in speakers. It gets louder when I touch the tone arm and then totally goes away if I only touch the amplifier and nothing else. The hum does get louder when increasing volume. When I recapped the amp, I did install a three prong power plug. I connected the ground wire from the plug to chassis ground on the amp. Did I create a ground loop and maybe should go back to a two prong plug?

 

[Catmanboo]

Maybe check tonearm/ cartridge wiring. Possible shielding problem there. Ensure shield (probably braided outer layer of tonearm wires) connects to chassis ground. Speculation here....

 

[cademan]

I try to not out guess the engineers. Remove the ground and see what happens? Also, is this a series string hot chassis record player?

 

[by the way]

I try to not out guess the engineers. Remove the ground and see what happens? Also, is this a series string hot chassis record player?

Yes. When I check continuity on the ground from the tonearm there is continuity to the chassis of the amplifier.

 

[Bill S]

Dinah Moe?

 

[mbz]

I check continuity on the ground from the tonearm there is continuity to the chassis of the amplifier

Measure resistance between tone arm and chassis. 1 ohm can result in hums. First short probes to get probe resistance, then measure. 0.5ohms or so above probe resistance should be investigated, eg, dirty/oxidized connections?

 

[Catmanboo]

Try using 2 prong plug. Check for hum by plugging 2 pronger into the outlet . Still hum? Reverse plug. No hum then? Fixed. Still hum? Further action warranted.

 

[mbz]

then totally goes away if I only touch the amplifier and nothing else

Reads like you have a bad ground connection, by touching the amp, you provide a GND path.
Try to find all ground points/connections to chassis, ideally only one point(eg, star GND) but early amps had multiple GNDs (even my Sansui AU-505!)
Again measure resistance between GND points, expect less than 0.5ohms above probe resistance. Clean GND points. Gently tug GND and other wires
with something non-conductive (chopstick?) and investigate any changes. Hopefully the GND wires will be black in colour to make things easily recognized.

 

[rothwellaudio]

Did I create a ground loop and maybe should go back to a two prong plug?

If the record player is a standalone unit with nothing else connected to it, you can't create a ground loop. You need two pieces of grounded equipment to form the loop.
Also, touching stuff doesn't affect ground loop hum.
That's two reasons why you haven't got a ground loop.
The problem is something else.

 

[highend64]

Is this a hum (60 cycles only) or a buzz (60 cycles with harmonics)?

 

[by the way]

Ok. Thank you. It is a stand alone.

 

[rothwellaudio]

Ok. Thank you. It is a stand alone.
View attachment 2738218 View attachment 2738219

Adding a three prong power plug can't have created a ground loop in your case.
Perhaps I should have elaborated on this:

You need two pieces of grounded equipment to form the loop.

The loop is formed when two pieces of grounded equipment are connected together through the interconnecting cable and through mains ground.
Anyway, that's a nice looking vintage piece and you don't need to worry about having created a ground loop.
Still got to find the cause of the hum though.

 

[by the way]

Adding a three prong power plug can't have created a ground loop in your case.
Perhaps I should have elaborated on this:

The loop is formed when two pieces of grounded equipment are connected together through the interconnecting cable and through mains ground.
Anyway, that's a nice looking vintage piece and you don't need to worry about having created a ground loop.
Still got to find the cause of the hum though.

Thank you. I appreciate the help. I’m really starting to believe it’s the tonearm wire I installed a couple years ago during restoration. Maybe starting to fail at tonearm pivot. I wish someone could offer ideas on how to make a shielded tonearm wire for these. The one I bought doesn’t have a very good shielding on it anyway.

 

[gadget73]

shouldn't need shielded tonearm cable. I've dealt with plenty of record changers with plastic arms and nothing more than twisted wires running up the length and they didn't hum.

 

[by the way]

Ok. That is the type of tonearm wire installed.
I just swapped identical turntables with one of my other RCA’s. The hum follows the problematic turntable.

 

[Catmanboo]

Ok. That is the type of tonearm wire installed.
I just swapped identical turntables with one of my other RCA’s. The hum follows the problematic turntable.

Smells of a signal wire shield issue or similar. It should be ideally be at the same potential as the motor board/ mounting plate.That narrows the suspects. Keep pluggin' away. You'll stumble onto something obvious, I predict.

 

[titanstats]

I have a late 50's RCA record player that has slight hum in speakers. It gets louder when I touch the tone arm and then totally goes away if I only touch the amplifier and nothing else. The hum does get louder when increasing volume. When I recapped the amp, I did install a three prong power plug. I connected the ground wire from the plug to chassis ground on the amp. Did I create a ground loop and maybe should go back to a two prong plug?

>>Did I create a ground loop and maybe should go back to a two prong plug?
Yes on both accounts.

 

[rothwellaudio]

>>Did I create a ground loop and maybe should go back to a two prong plug?
Yes on both accounts.

How have you come to that conclusion? Where is the loop? Please elaborate.

 

[by the way]

How have you come to that conclusion? Where is the loop? Please elaborate.

After everything I’ve been through on this, it has turned out that the new cartridge I installed was bad/harmonic. Replaced it with an extra cartridge I had and problem solved. Definitely overlooked that possibility.

 

[Catmanboo]

After everything I’ve been through on this, it has turned out that the new cartridge I installed was bad/harmonic. Replaced it with an extra cartridge I had and problem solved. Definitely overlooked that possibility.

Gotta love the simple fix. Who'd have thought that was the cause?? Glad you found it & can now put it back in commission.