The way mine was wired (*), and assuming that yours is not likely to
be very different. Mine was a very old model, though, bought c1974,
and if yours is not of the same vintage hopefully things will have
improved. Nevertheless, I wouldn't bank on it, my impression being
that less, not more, care is taken over decks these days. I think the
manufacturers tend to think: "This is never going to have comparable
output to a good CD deck, so we'll make it cheap and cheerful!" That
means a ceramic cartridge and not much attention given to things like
hum suppression. I hope for your sake that I'm wrong, but time will
soon tell.
* The wiring mistakes were as follows ...
:-( The deck was made of metal, yet originally supplied with a
two-core, that is unearthed, mains cable. Very early on in its life,
I changed the mains lead for a three-core one with the earth attached
to the deck metal. Not only was this a lot safer in theory, in
practice it also meant that when dismounting a record I didn't get
electric shocks from static having built up from the normal action of
the stylus in the groove. When I first did this, I was using a
properly earthed amp, so didn't notice any increase in hum, IIRC quite
the reverse in fact, but by the time a couple of years ago when I was
doing the digitisation, I was using an amp with a two-core mains lead,
that is, although it had an earth point for a deck, it itself was not
earthed, and the deck now gave a big hum.
:-( When analysing this hum, the next thing I noticed was that the
arm and cartridge holder were grounded to the deck metal. Just
cutting, or in my case unsoldering, the cartridge holder earth
underneath the deck and instead taking it out the back to the earth
point on the amp made quite a bit of difference, but didn't get rid of
the hum entirely.
:-( Then I realised, and proved it with a resistance meter, that
the tone arm was not electrically insulated from the deck metal, which
meant that even after the above link had been fixed, the wiring to the
cartridge still picked up hum from being surrounded by the metal tube
of the tone arm. What follows is definitely not something to be
recommended, but it being a very, very old and already beat up deck
with zilch second-hand value, for example the lid hinges had broken
within a couple of years of purchase, I didn't mind hazarding breaking
it altogether, and so completely dismantled the tone arm, replacing
the wiring with the smallest stereo coaxial wiring I could find, so
that the outer sheath being grounded protected the signal wires
within, and this completely fixed the hum. However such cable is a
lot less flexible than the original very thin and delicate wiring that
is commonly used to wire between the terminals of the cartridge and
the outputs at the back, so this introduced tracking problems which
took a lot of trial and error to fix, which is why it's not something
to be generally recommended.
So if yours has a hum, my advice would be to repatriate it immediately
as not being "fit for purpose".
On Mon, 16 Feb 2015 14:49:38 +0000, Sumatriptan
wrote:
Thanks for the info. Any reason for thinking that the problem may be
common to all Dual models?
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Dual 505
Linear Mode
