On Tue, 29 Sep 2009 13:53:12 +0100, "Keith G"
wrote:


"Don Pearce" wrote in message
...
On Tue, 29 Sep 2009 09:19:41 +0100, Jim Lesurf
wrote:

In article , Trevor Wilson
wrote:

"Don Pearce" wrote in message
...


The damping should all be associated with the spring - which is the
stylus cantilever suspension. There should be no expectation of extra
damping associated with the arm bearing, which is ideally as free to
move as possible. Indeed damping of the arm bearing impedes arm
movement that is needed to prevent low frequency high-amplitude stylus
excursions.

In other words, what is being damped is the spring - mass system of
the cantilever and effective arm mass. The right thing to damp is the
spring involved in that resonant system. Ie, the damping must be in
the cartridge.

**Unfortunately when theory meets reality, things don't always go to
plan. In my long experience (30+ years) running dozens of different MC
and MM carts with dozens of arms (including most SME models), I have
found that arm damping is critical to decent performance with MC carts.
SME arms (knife edge bearing types) are amongst the worst choices for
MC carts. This arm is one of the best choices, IME:

http://www.dynavector.com/products/t.../e_507mk2.html

Even more unfortunately, a lack of damping in the stylus cantilever may
tend to produce a marked HF resonance. Damping of the arm won't fix that
as
the arm isn't really involved.

One of the points that people nowdays seem to overlook is the work Shure
and others put into having optimal cantilever damping for HF reasons.
People seem aware of the high compliance and, to a lesser extent, low tip
mass, but damping rarely seems to be considered.

The presumption seems to be that when you see an HF resonance with a MM it
must be purely 'electronic' in nature. This isn't really the case. When
experimenting with electronic loading you may simply be trying to trade
off
two quite different HF LP resonances - one electronic and the other
mechanical - to get an overall optimum. But so far as I know, this has
largely been ignored in recent decades. Preumably because of the
(incorrect) assumption that MC designs are immune.

Slainte,

Jim

How does the HF damping thing work? It seems to me that if you can
dissipate energy quickly enough for critical damping at HF, it will be
almost solid at the main LF resonance



The energy is dissipated in the tonearm, not the cartridge. See:

"A decade ago, high-compliance cartridges were the rage and these needed to
mate with very low mass tonearms. However, today's heavier, lower-compliance
phono cartridges (especially moving coils) have required tonearm
designers/manufacturers to reorient themselves in the direction of medium to
high-mass arms. Further, some of the currently available MC cartridges put
back a tremendous amount of energy into the arm. This reflected energy takes
the form of standing waves, which travel up and down the length of the
tonearm, potentially creating mis-tracking problems and/or frequency
dependent cancellation. A well designed tonearm will dissipate this energy,
rather than reflecting it back to the cartridge. The ability of the arm to
accomplish this will be dependent upon bearing design, internal damping and
rigidity."


From he

http://www.gcaudio.com/resources/how...cartridge.html

Then stop worrying about it....


Ok, got that. But in order to stop worrying about it, I would have to
have started. Interested is altogether different.

d