Michael Squires wrote:
In article ,
Sidney Cammeresi wrote:
On a couple of records however, in passages of high amplitude, I am
hearing a clipped, grating, lower-volume, static-like noise. At first,

This could be several things.

(1) the cartridge could be mistracking - if increasing the tracking force
solves this then you've found the answer. You may also not have the
anti-skate, if any, set correctly.

It's very easy to mess up the alignment while moving a turntable, so
I'd seriously consider getting the stuff you need to check the alignment,
tracking force, etc., at home. A PDF files of the required protractor
is posted here regularly, and a tracking force scale isn't expensive.
I'm sure that you'll get recommendations for a modern LP for checking
tracking force and antiskate. I used to use CBS STR100 and an old
oscilloscope, but there must be easier methods...

Remember that catridge manufacturers often understate the required
tracking force, and what we were told when there were no CDs is that
low VTF with a lot of mistracking causes more wear than a higher VTF
with no mistracking.

It's also possible your tonearm is binding, i.e., the bearings have
problems or the wires are getting in the way. This was a very common
problem with the old AR-XA turntable.

(2) your cartridge may have very high output and is causing the preamp to
clip. This most commonly happens when you have a moving-magnet (high
output) cartridge and you've connected it to the moving-coil input
(although most preamps don't have moving-coil inputs).

Mike Squires
Grado/SME 3009II/Thorens TD125II

I agree with the above. Mistracking is the most likely reason for the
noise as described.

Regarding the possibility of clipping n the phono stage, the MF preamp
has an overload margin of 24dB above 2mV, or around 16x. This means that
the cartridge needs to give out 32mV before clipping. The Rega cartridge
claims an output of around 7mV on a nominal 5cm/sec recorded velocity.
This gives an overload capability in your system of 4.5x or 13dB which
is a little low, so clipping could be a possibility on heavily modulated
records. The only real way of telling is to put a 'scope on the output
and see if you get clipping. Alternatively, try a lower-output
cartridge, or try another preamp with lower sensitivity and equally good
or better overload margin. What you have, in my opinion, is an
unbalanced system of high output cartridge and over-sensitive preamp.

S.

S.



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