Hum in phono stage

[Bru23]

Hello

I have a quick question following the buzzingin the phono stage of my Luxman L-114AHum on both channels without deck connected
stronger on the left than on the right chanel
I shorted RCA on the Phono input and the hum disappeared.
How to interpret it?
Does that mean it comes from the phono preamp?

 

[Lavane]

That means there isn't anything wrong with it as long as your not hearing the noise with the turntable connected. Every one of my phono preamp will hum without a turntable connected, or with the jacks left open. Its normal for the open jacks to pickup noise. Many of the older stereo preamps would come with a set of shorting plugs if it had two phono inputs. If the second set of jacks doesnt have a turntable plugged into them, the shorting plugs were used. A phono preamp is amplifying a very small signal to line level, so they tend to be very sensitive to any noise that could be picked up by the power supply, etc.

 

[Bru23]

Thank you for your response Lavane,
the fact is that I also hear this noise with the turntable connected, and it is really loud, not like a "classic" phono noise.
And when I touch the carcass this noise disappears.
Do you think it comes from the preamp or rather from the power supply?

 

[Mike_S]

Sounds like a grounding issue. Maybe try another outlet, make sure the ground is secure and clean. If you have 2 prong plugs on the components swap the plugs around one at a time, the noise should change or go away.

 

[tourmax]

Ground issue.

 

[Lavane]

Ok, sorry, I read your first post wrong then. Yes it sounds like a grounding issue.
Does your turntable have a ground wire coming out the back? If so, connect it to the ground post on the phono preamp. There is also a ground lift switch on the back of the phono preamp, it a small switch that pretty much flush with the back of the chassis. Try flipping it and see if it gets better, or worse. Also if your turntable does have a ground wire, try it connected and disconnected to the phono preamp. Also the metal tube shields that came with this preamp should be used. Especially for the first two tubes from left to right. The preamp can be very microphonic and pickup noise if they aren't used.

 

[Bru23]

Hello,
in fact I thought there was a problem with this amp, so I looked for broken solders, and just by bringing a wooden stick near preamp the noise increased significantly, so I followed the advice and reversed the 2-pin power plug, the noise decreased, I unplugged my laptop, the noise disappeared....
Finally I reassembled the body of the amp (top and bottom) and everything was back to normal!
So it was simply the fact that the amp was bare.
Thank you all for your help, I learned again !

 

[jheu02]

That"s a good reminder for me, as i tend to test the gear I'm working on with covers off etc. When I hear what appears to be a ground issue, before going nuts trying to figure out where its coming from, put the covers back on and see if it diminishes. Same with the shorting plugs, so just received a bag of 20 from Amazon.

 

[Lavane]

That"s a good reminder for me, as i tend to test the gear I'm working on with covers off etc. When I hear what appears to be a ground issue, before going nuts trying to figure out where its coming from, put the covers back on and see if it diminishes. Same with the shorting plugs, so just received a bag of 20 from Amazon.

I recently bought a bag of shorting plugs from Amazon also. They do come in handy and tend to disappear for some reason.

 

[tourmax]

I recently bought a bag of shorting plugs from Amazon also. They do come in handy and tend to disappear for some reason.

Same. Although I’ve never heard any significant difference using them or not on the gear I’ve had.

They do look shiny though and confuse the friends that come over and seen them on the backs of my receivers.

And of course, its fun to BS them along a little bit about why they’re there and what they do. I always “fess up” though after a little chuckle has been had by all….I just keep pushing it to a more ridiculous level until I get a “aw, getouttahere, you’re pulling my leg!”

Fun is had by all.