turntable hum

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T-bone Sanchez

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Ive got my mates dual 505.4 at the moment due to a repair it needed and the removal of those captive leads. I know the deck isnt the last work in quality but Im still surprised by the level of hum it produces. Ive re-terminated the earthing wire and cleaned everything but its still bugging me. Any idea? The offending item appears the be the chassis earth which is totally seperate from the catridge wires.
 
if it has an mm cartridge, sometimes the motor induces hum into that and its difficult to find. see if it varies by moving the arm near and away to the centre. if it changes it will be the mm generator.
only solution for this is to try an mc, and see if there is any difference
 
Another good one is to see if the hum changes as you touch various parts of the unit.

you need to undo every last grounding connection and clean them ...
 
The noise changes when I touch the actual earth spade that connects to an earthing post. To begin with it was okay, the hum was only audible when I turned the dial past 1 o'clock. However, I caught the earthing wire and that was it, it hummed for england (or germany I spose). If I tap the spade it makes loud popping noises. The chassis earth is in no way connected to the arm wires and I know its not the phono pre or psu.
 
Lt Cdr Data said:
if it has an mm cartridge, sometimes the motor induces hum into that and its difficult to find. see if it varies by moving the arm near and away to the centre. if it changes it will be the mm generator.
only solution for this is to try an mc, and see if there is any difference
Click to expand...

I know from T-Bone's last post that it doesn't appear that this is the problem, but just wanted to point out that motor induced hum is not something that affects MM carts universally, just those which are poorly shielded (Grados, strictly speaking Moving Iron I know, are notorious for it for example). So if it were the problem a different MM cart might well solve the problem, you wouldn't necessarily need to go MC (nor would many MCs actually work too well with the low mass arm on the Dual).

Now I'm no expert on it as, I've never experienced a serious hum problem (guess I've been lucky as I gather they can be a pig to track down sometimes), but I found this which may help:

Phono Hum Troubleshooting

The Van den Hul Faq also has some hints on the subject:

Van den Hul faq

Good luck.
 
Now your going to have to check the grounding points very carfully.... everything needs to be clean good metal to metal surfaces. Take a multimeter and check all the wire for continuity and resistance check across the connections. Have a look at the routing of the cables. Its a bugger I've been there it will be something small you might not even notice you have changed anything and the hum will go away. Mine did and I never was exactly certain what I did to cure it.
 
Well I started again last night. First thing that struck me was that the chassis ground is right next to the motor, so that got moved. Second, the tone arm wires and phono lead (now sockets) are connected by quite a crude pcb which is covered by a half-hearted shield so this needed attention. The general construction isnt partiularly great to be honest. I moved the psu for the phono away and cleaned everything including the cartridge connectors.

I've managed to rid about 90% of all noise, its only at the very top-end (and most def non-neighbour friendly) levels that something becomes audible. Im leaving it at that, hi-fi is starting to drive me mad. Its alot better than it was so job done.

New hobby ideas??
 
I get mild hum on my NAD533 - it's one of the cartridge tags as it gets louder if I touch it. What's the safest way of "squishing" the tag to make a better connection?
 
I told you it was a pain !!

well done sounds like your down to the same level of hum as the rest of us mere mortals
 
Its certainly alot better. The strange thing, as this is the first time Ive had a tt to try (the thorens isnt ready yet) I didnt really have a good idea how they really performed. In so many ways my sony transport/nos combo beats the dual on every individual aspect of music reproduction, however I found myself wanting to play vinyl all night long and I cant explain why.
 
T-bone Sanchez said:
Its certainly alot better. The strange thing, as this is the first time Ive had a tt to try (the thorens isnt ready yet) I didnt really have a good idea how they really performed. In so many ways my sony transport/nos combo beats the dual on every individual aspect of music reproduction, however I found myself wanting to play vinyl all night long and I cant explain why.
Click to expand...

Its The Bug!! Its bitten.
 
I fear it has, oh dear. Luckily the 160 aint too far away. My dad will make the plinth when he gets back of his hols, Ive ordered a sheet of carbon fibre to make an arm board and the phono pre and psu are all done and dusted.
 

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