Turntable Hum Problem

[alexandermusgrove]

Hey y'all,

Hoping some audiophile good samaritan can help me make sense of this, without having to spend ALL the $ and time on every troubleshooting step. I'm getting a hum. When I turn the volume up, it gets louder and bassier. When I turn the volume all the way down or unplug the turntable at the mixer, it goes away.

I built this setup over time and now in SF, so it's recently transplanted to a less helpful space:
Turntable = Denon DP-300F, replaced cartridge with Grado Prestige Blue
Preamp = Cambridge CP1... I do NOT have the turntable grounded to this, but I don't think that's the issue for reasons below.
These 2 items are plugged into a single 2-prong extension into an outlet on one side of the room.

From the Cambridge, I run about 20' good quality RCA to the stereo setup on THE OTHER SIDE of the room. If I unplug the RCA from the pre-amp, the hum gets way louder, but if I unplug the RCA from the mixer/receiver/speakers, the hum goes away. Perhaps it's cable interference/bad cable, but it's a pretty new cable, a pain in the ass where I ran it, and I wasn't having this problem before.

On the far side of the room:
Rolls Mini-Mix - this is kind of weak, but I couldn't think of a better way to easily have Alexa/Echo, TV, and turntable all on at all times.
Runs to Kanto Yumi speakers. If I cut out the Rolls, and just run the long RCA straight to speakers, still get hum.

This side (with TV, Mixer, Echo Dot, Yumi speakers) may have sketchy electronics in general, cuz old building, but that's just a theory.

Anyway, any ideas? Thanks in advance!!!

Thanks,
Alex

 

[jay32267]

"These 2 items are plugged into a single 2-prong extension into an outlet on one side of the room."

In my experience....this doesn't matter. The turntable has to be grounded. I have pretty much the same setup....turntable....amp.....2 prong plugs.....if I don't ground the turntable I get 60 Hz hum like crazy.

 

[alexandermusgrove]

"These 2 items are plugged into a single 2-prong extension into an outlet on one side of the room."

In my experience....this doesn't matter. The turntable has to be grounded. I have pretty much the same setup....turntable....amp.....2 prong plugs.....if I don't ground the turntable I get 60 Hz hum like crazy.

Thanks Jay! I'll try to ground it, not quite sure how but a little research should show me.

What weirded me out was that I still get the hum in the speakers even if I break the RCA connection from the turntable pre-amp to the speakers. Maybe it's just related to crappy electricity in the apartment, or maybe I have 2 different things both causing hum, thus making it harder to isolate.

Thanks for the tip. I'll do that and come back.

 

[jay32267]

I believe you may be getting that hum because it's open. This is not uncommon.

Of course there is always the possibility of something else going on.

How to ground the turntable: There are many ways to do this. Usually the turntable has a ground lead or terminal. If so great. Use this lead...or connect a wire to the terminal. The wire should be about 16-20 gauge....nothing special...just an insulated wire .

The other end needs to be connected to a ground. This can be a lot of things like the screw to the frame of a steel outlet....also many receivers and amps have a ground screw (but not two prong amps/receivers).....a water pipe can work too.

If there is no ground available on the turntable you need to connect that end to the chassis of the turntable somehow.

 

[alexandermusgrove]

Hey Jay, I haven't been home to test this yet, but thanks in advance that you're probably right and a lifesaver. One remaining head-scratcher... the Cambridge CP1 pre-amp has a turntable ground "thing" (see image: https/images-na.ssl-images-amazon.com/images/I/61giABmbx0L._SL1500_.jpg), which would seem to obviously serve this purpose. But the CP1 itself only has a 2-prong power supply, so I don't understand how the ground could even do anything. Am I misunderstanding something about electricity?

 

[jay32267]

The deal with that is....it's what's called a virtual ground...or it's called a floating reference....and in many cases...depending on the wiring...it can eliminate the need for an actual ground.

Have you tried it? It may actually work for you in your case.

....but there is nothing wrong with grounding the turntable to a real ground either....which is what I usually do...

...but now that I think back....I think I had a Radio Shack Realistic preamp hat was similar to what you have with two prings and a "ground" and I used it and recall it working.

 

[alexandermusgrove]

Ok, so I held a grounding wire between the pre-amp and the turntable arm, and it didn't change anything. I also then held the ground between turntable arm and the screw on a wall plate, which also didn't change anything. A few places have shown this turntable doesn't need a ground, although perhaps that should be taken with a grain of salt: http/www.avsforum.com/forum/173-2-channel-audio/1658993-denon-dp-300f-no-ground.html

But 2 more interesting facts I realized:

1. The turntable and pre-amp are plugged into the end of this extension cord. When the plugs are held close to the pre-amp, the hum is worse, and if I move them further away from the pre-amp, it's less loud.

2. There are some places that if I physically touch them with my hand, the hum gets louder. Touching the cartridge, louder. Touching the ground terminal on the pre-amp louder. Touching the volume knob on turntable's channel in the Rolls mixer, the hum gets louder.

It's a very low-pitched buzz by the way, in general. When it gets louder (like when I'm touching something), the pitch goes up and gets a little noisier as well.

Any other thoughts?

Thanks again for all the help!

 

[jay32267]

Other thoughts...

I could be that the turntable arm is not ground. There's no reason why it has to be....although I imagine in some cases it might be.

I don't know how much access you have to the turntable...but I would be trying to ground the chassis.

...and all the things you mentioned are pretty much symptoms of a bad ground.

It is 60 cycle hum. If you measured the frequency it would be 60 Hz.

It's also possible that you have an issue with the preamp itself or the turntable electronics....but the easiest thing to try at this point is to try and ground the chassis of the turntable....at least that's what I would do.