Magnetic Field or Earth Circuit

  wee eddie 04:02 11 Aug 2011
Locked

Nothing to do with Computers, a HiFi System Problem:

Over the last 2 years, or so, I have noticed a small Hum from my Turntable, a Thorens TD160 Mk2, but only when the needle is off the Record. Like Topsy, it has just growed and growed, until it is now quite noticeable when the needle is lifted.

The usual cause for such a problem is the needle being too close the a Transformer. In this case the Needle is 18" to 20" inches away from the pair of Transformers that this Amplifier has. Huge great things, it's possible that the shellac insulation is beginning to break down. Not really unsafe as the 5amp Fuse would blow before any real problem occurred.

The Question: Anyone know of anything that I can put between the two that will damp the resultant Magnetic Field?

The other possibility is that there is some sort of problem in the Earth Circuit, which is currently routed through the Amp. Maybe I should by-pass the Amp and go straight to, either the Mains, or a Copper Pipe.

  wiz-king 05:51 11 Aug 2011

Turn every thing off and then unplug each lead and give all the connectors a clean with a fine emery board or wire wool. Do the same with the cartridge - very carefully. My turntable also has a separate earth lead that is connected to one of the outer braided signal leads, if yours has clean that connection as well. If it uses a different mains socket to the main amp try plugging them into the same socket if possible.

Mu-metal is what you want from magnetic shielding but I don't know where it is available now days.

  bjh 09:26 11 Aug 2011

The earth should always be a common earth, so earthing one item to a copper pipe, and the others to the mains earth will a) produce more noise, and b) might damage the system! The record player being earthed via the amp should be fine, so long as the amp is suitably earthed. Best is for all items to share the same extension lead. Keep the earthing cables as far from all sources as possible, and do not coil them neatly behind the hi fi... for once, a random mess is best!

  Aitchbee 09:46 11 Aug 2011

Off the subject slightly - but are these USB turntables for converting vinyl albums to digital any good? HB

  interzone55 10:03 11 Aug 2011

My last AMP didn't have a Phono input, so I earthed the turntable to the phono pre-amp and for the first time I didn't have the low level hum you describe.

Now I've got a NAD amp with phono input and my Pro-Ject turntable is earthed to the amp so I full expect to get the humming again in a couple of years.

I think if I do get the buzzing again I'm going to earth the turntable to the radiator behind the settee to see if that clears it

  flycatcher1 10:25 11 Aug 2011

I remember a cartoon in "Hi-Fi News" eons ago.

Massive HiFi System and chap saying to companion. "Never mind the music - listen to the hum".

Thorens - happy, happy memories.

  Wilham 12:05 14 Aug 2011

When the stylus is raised it reduces damping of the arm at one end. This in turn makes the cartridge sensitive to the clicks/vibration of the mechanism,... behaving like a crude microphone.

To counteract this in a high quality Thorens 160 Mk2 I would expect there to be a mute switch driven by the lifting arm, and it to short the cartridge inputs as soon ss the stylus is safely clear of the record.

Test if mute switch works by lifting the arm very slowly. You won't hear the switch but you should detect a brief hum period before the mute. If no mute. lift the arm with the lever and move your hand near the raised cartridge/stylus. An increase in hum indicates the mute not working. I'd even touch the stylus with a feather.

Cause could be a damaged connection, or fine spring dropped off.

  wee eddie 15:45 14 Aug 2011

Wilham ~ I shall start looking. Nothing in the Multi-Lingual Handbook so I shall try on-line tomorrow.

Many thanks for the hint.

  Wilham 17:34 14 Aug 2011

wee eddie: I'm guessing the arm-operated mute was faulty when you first had the turntable. The hum would increase when drive bearing needed a touch of oil.

Is it easy to identify the make/model of the pickup arm?

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