Hum with a Decca... help!

Hi All,

I wasnt sure whether this should be posted here or not as I dont think its a problem with the valve gear, not sure...

I recently re-assembled my hifi after a couple of months of prolonged house move and room redecoration. However Ive been busy! I have sold my Goldring, had the Decca London retipped along with replacing the original Decca plastic mounting caddy with the metal variant, bought a new arm (Hadcock), replaced the solid state pre with a passive from Creek. So the system now is an LP12, Hadcock, Decca, WAD Phono II, Creek passive pre, 300b PP poweramp.

I set everything up last night. Excited as I had been without a music system for about 9 months. But oh dear problems.....hum. Quite a lot and also quite loud. After much cable moving rearranging plugging etc I couldnt remove it. At a realistic listening level its quite apparent, so the hifi is currently unuseable
I dont think the problem is amp or cable related but I could be wrong. If I short the cartridge pins out even with the volume turned to max there is only a slight hiss. I think it may be the cartridge. I seem to remember reading somewhere either in a magazine or on the web, that Deccas can produce hum under certain circumstances. 5 years ago with all my solid state gear all seemed to be ok.
Has anybody any ideas or experience with anything similar. I really would like to keep the Decca (because its a great cartridge!) but if it siimply isnt compatible then Ill have to move. But is it the cartridge and is there anything I can do to alleviate the hum or tests to prove one way or another?
Thanks for any help,
Matthew

[Stratmangler]

Is your arm earth ok ?

I only ask as I have found that the earthing on my modded RB250 (OL structural mod/Incognito rewire) is not as good as on my SME 3009.

Although the Incognito loom has a superior earthing arrangement to the stock Rega, I believe that it actually stops in the arm pillar, and does not contact directly with the arm tube. I did not do the rewire myself (I bought the arm and had it rewired by dealer before it left the shop).

I have found that there is a minor buzzing whenever I touch the arm, ie. when cueing up a record using the finger lift - my hands are very steady and I don't use the cueing mechanism.

The SME is electrically silent in operation.

Chris

[david counter]

Interesting problem with the Rega arm with the Incgnito rewire, I had this exact problem, extensive earthing didn't cure it, when I changed from a 1042 to a MC it went completly, very strange

Hi Chaps,

Checked all the arm earthing and all seems ok.
Even tried bridging different pieces of the arm etc back to the phono ground with a length of cable all to no avail.

Does the fact that shorting the cartridge tags, which removes the hum, rule out the amps as possible culprits?

Thanks,
Matthew

[Stratmangler]

I currently use a 1042 in the SME3009, and noise is not an issue.
When I was using the RB250 I was running a Reson Reca (ie a MUCH better version of the 1042 IMO), and it was then that I noticed the problem.

I have used the Reca in the SME using a friends' stylus (my stylus needs replacing, and that is why I'm using the 1042 for the moment) and noise is not an issue.

I'd assumed that the buzz encountered when cueing up a record was just down to earthing issues. Maybe there is some further reason why this occurs.

The buzzing stopped when letting go of the arm, so obviously was not a problem once the record had been cued up and playing.

Onto the Decca problem.
Have you tried another cartridge ?
Is the Decca particularly sensitive to electrical noise ?

I'm just suggesting that the Decca may possibly be the culprit.

Chris

[Rob042]

Just a thought from a fellow decca lover - are both the neg/return arm wires connected to the centre pin of the pod?

dont have any problems myself with the deccas I have used. at the mo is on a pttoo, alphason arm to wad phono....... . The cart was re-tipped by cartridge man but still have old plastic pob.

Rob

[Stratmangler]

Just remembered - had a similar problem with my amp/phono stage ages ago.

I discovered that my amp was designed with a floating signal ground (ie no mains earth).

The TT set up buzzed like a bag of angry wasps.

Wired up an earth cable straight to the amp chassis, and, hey presto, problem gone.

Check for earth continuity right through, and watch out for potential earth loops.

Chris

[Stratmangler]

Have you tried earthing the chassis on the Creek Passive ?

Chris

[David Mccallum]

Just a thought,do you have a separate phono stage?and if so is it close to a transformer. try moving them apart.

Hi,

Thanks for the replies.
I am going to check again tonight for earth continuity throughout the system and see if Ive missed anything. Should (in an ideal world) all earths be grounded to a single point or is a chain of earths between tt, phono, pre, power ok?

If that fails then it could well be the cartridge. The problem is that I dont have another old cartridge to try. All I need is the body a stylus isnt necessary. Anyway I`ll cross that bridge tommorow...

Thanks,
Matthew