Noise pickup with phono stage RCA cables

[Thorin]

I need some help diagnosing a pulsing buzzing nose that's being generated when RCA cables are attached to a stereo amp. I've tried several sets of RCA's on a mid-fi preamp/amp setup as well as an old Sherwood receiver. Both do the same as attached video. TT is not even attached, it's just RCA into the phono stage. In the other case it was RCA into the phono preamp. No other inputs behave like this. I've used different speakers in each test too. Also turned off all power in the house except the circuit I was testing on. I don't even know what to call this interference, it's a lower frequency feedback buzzing that increases with volume. I can't be the only guy that's ever had this issue. Please help.

 

[Speedskater]

Do the RCA jacks on the preamp/amp have plastic insulating rings?

 

[Thorin]

Do the RCA jacks on the preamp/amp have plastic insulating rings?

Some do , some don't. I've tried many out of frustration. Did you listen to the noise? Ever heard that before?

 

[restorer-john]

Both do the same as attached video.

What attached video?

 

[restorer-john]

You plug anything into a phono input not terminated by a cartridge and you will get noise- that's normal.

 

[DVDdoug]

No other inputs behave like this.

The phono preamp has about 60dB of gain (1000x) at low frequencies (RIAA EQ means more gain at low frequencies). That gain amplifies any noise pick-up and the high input impedance also makes it sensitive to noise.

I don't even know what to call this interference, it's a lower frequency feedback buzzing that increases with volume.

It's usually power line hum (50 or 60Hz) from the power lines all-around you. If it's rectified you get double the frequency and more harmonics and it becomes more of a buzz than a hum.

 

[Blumlein 88]

Just amplifying restorer-john's comment, and DVDdoug, with the high gain of a phono stage you have to have the cables connected at both ends. The cartridge on the TT will keep a lowish impedance into the phono gain stage so it doesn't pick up hum so easily. And there is no attached video visible.

 

[Ruhled]

You might try just shorting the end of the phono input cable leads if you can't connect the turntable and see what your results is. I suspect it will be much better if not gone.

 

[Thorin]

I see now video uploads aren't allowed, so here's a link.

https://wistia.com/medias/5kt9dw0ky8

Great info about the rca's needing to be connected, but that takes me back to my original problem that it also does this when connected to my Fluance RT82. I even bought a cheap Audio Technica from Walmart to verify.

Also does it when running through a Pro-ject phonobox into a Schitt Freya+/Cambridge 851w/Klipsch Forte2 system on a dedicated circuit.

So it's not the TT, not the RCA's, not the phono stage, not the stereo, not the speakers.

I haven't swapped out speaker wire yet, but I will.

Could it be dirty AC?

 

[raindance]

You can rule out dirty AC... It's grounding between the turntable and preamp.

 

[fpitas]

Could it be dirty AC?

Dirty AC is the audiophile equivalent of blaming the dog. And various manufacturers will sell you expensive filters that sometimes don't even filter well. I agree with raindance, it sounds like a grounding problem.

 

[Thorin]

I've watched a lot of videos, and never seen/heard a grounding sound like what I have. Typically it's a steady hum. Is this something any of you have experienced?

I'm struggling with the fact that I can reproduce it with different two turntables and two phono stages. I'm not sure if the cheap Audio Technica I grabbed from Walmart is a good test though. It's mostly plastic, and there is no separate ground wire or even an attachment location for one. It uses a 1/8" stereo jack to RCA cable instead of straight RCA's. Maybe I need to buy another Fluance and take advantage of their 30 day free return policy to troubleshoot this.

 

[Thorin]

Dirty AC is the audiophile equivalent of blaming the dog

Ha. Good analogy. I always thought this too until my current situation.

 

[raindance]

The noise in your video is NORMAL. How about another video showing the noise with a cartridge connected?

 

[raindance]

And changing the speaker cable is like blaming the neighbor's cat.

 

[egellings]

The phono preamp has about 60dB of gain (1000x) at low frequencies (RIAA EQ means more gain at low frequencies). That gain amplifies any noise pick-up and the high input impedance also makes it sensitive to noise.

It's usually power line hum (50 or 60Hz) from the power lines all-around you. If it's rectified you get double the frequency and more harmonics and it becomes more of a buzz than a hum.

60dB is quite a bit of gain for a magnetic (not moving coil) cartridge, where about 40dB is commonly used. If the gain is selectable, I'd reduce it by 20dB in your setup.

 

[Thorin]

And changing the speaker cable is like blaming the neighbor's cat.

It's called desperation.

 

[Thorin]

How about another video showing the noise with a cartridge connected?

Here is an updated video with TT connected (and different speaker wire... ).

https://wistia.com/medias/vo8py7n9hv

So this is just a crappie old amp I had in my barn for a while. I can't adjust gain. Nor could I with the Pro-ject Phonobox as far as I know.

 

[raindance]

That's a little different! Seems to be pulsating. How long is the phono cable? Is the turntable plugged in?

Do you hear this with a line level source, like a cd player, with your ear closer to the speaker.

I may have to eat my words though, as it sure sounds like interference of some kind.

 

[Thorin]

Seems to be pulsating. How long is the phono cable? Is the turntable plugged in?

Do you hear this with a line level source, like a cd player, with your ear closer to the speaker.

It is pulsating. It's a 3 ft cable. The TT is plugged in.
I do not hear it on any line level inputs, l even at max volume with my ear to the speaker.
Remember it does this with all the other circuit breakers off, and only the receiver plugged in.
Weird.

Thanks everyone for your ideas. Don't give up on me!