On Fri, 17 Mar 2006 09:52:29 +0000 (GMT), Jim Lesurf
wrote:

In article , Bill Taylor
wrote:
On Thu, 16 Mar 2006 23:23:34 -0000, "Serge Auckland"
wrote:


"Bill Taylor" wrote in message
...

(Compliance only needs to be more than about 10-12c.u. to track all
records)


Interesting theories. Can you tell me a bit more as to why a compliance
of 10-12cu is sufficient for all records? Interesting that in vinyl's
heyday, some cartridges were providing 30-40 cu. It could be a
marketing exercise rather than having a sound engineering reason for
it, but it would be useful to know why such high compliances are not
necessary.


According to J Walton in "Pickups - The Key to Hi Fi" (published 1968,
but the physics haven't changed): the maximum excursion on an LP is
about .005cm, "if compliance were the only factor involved a compliance
of 2 c.u. is quite sufficient to track the largest stereo amplitude of
.005 cm at 3 gm tracking weight". It's possible that a small number of
modern LPs have slightly higher excursions, and tracking weights are a
bit lower, so a slightly higher compliance is needed, but not that much
higher.

Afraid I don't have a copy of Walton. However I suspect the above may
either be an over-simplification on his part, or is out of context.

The quote does start with "if compliance were the only factor...."
which I thought did imply other considerations as well. I was just
about to leave for work when I posted that so I didn't have time for a
full precis, and I type slowly!. It was meant for illustration rather
than comprehensive analysis!

I may need to re-read some of the articles by Stan Kelley, but the above
looks to me as if is simply dealing with static compliance at LF. Thus the
physics may not have "changed", but may also not be as simple as the above
implies...

I also note that it quotes a playing 'weight' of 3g, which is high. A
small-radius tip could be expected to risk vinyl deformation even with an
unmodulated groove at such weights. Was he assuming a mono stylus which
would probably have been larger than a stereo one, and spherical?


Bear in mind that this was published in 1968 when 3 g was a typical
downforce for run of the mill cartridges. He was talking about stereo
cartridges, in this case of .5 thousands of an inch radius, and he
does say 3g is the maximum downforce before permanent groove damage
occurs.

If I look at Goddard's article in the 1963 "hi fi yearbook" he gives
a graph of the minimum acceptable compliance as a function of weight.

Simply to ensure contact this rises from 8 cu at 3g up to 20 cu at
1g playing weight. This ignores tip mass which will also contribute,
s you'd want a lower value to ensure avoiding mistracking. Also,
due to the finite compliance of the vinyl - which is more significant
with small contact profiles - you'd want a low compliance to minimise
vinyl deformation - and hence reduce distortion and wear.


Tip mass adds to the downforce neede to keep the stylus in contact
with the groove but I don't think you can trade off tip mass by
increasing compliance. According to Walton the demands of the tip mass
and mechanical resistance add to the downforce required by compliance,
so in this example he adds 2 gm to accomodate a 2mgm tip mass and 3 gm
to accomodate the mechanical damping appropriate to the tip mass and
compliance of the cartridge, giving a downforce requirement of 7-8 gm.
For a cartridge of 0.5 thou tip radius designed to operate with a 3gm
downforce he suggests a compliance of 5c.u. and a tip mass of 1 mgm.

The very high compliances of the 70s were very much a marketing
excercise.

They became so, but my recollection was that they grew for very good
reasons. Namely that unless the compliance was high and the mass was low,
the result was mistracking, high distortion, etc. (Also increased record
wear.) Personally, I'd regard a complaince as low as 10 cu would be too
low for comfort. I'd much prefer well over 20 cu.

A value as low as 2 cu would strike me as being unusuable for a modern
stylus profile - although the magazines rarely give any useful data
on this any more, so for all I know the profiles may be poor to
lower the pressure on the groove walls...

An advantage of high compliance and low tip mass is that you can have
a smaller contact area to improve the response and lower the distortion
level as well as keep down the wear on the LP.


Walton makes a very convincing case that the most significant cause of
groove damage is high stylus tip mass. He reckoned that a tip mass of
..6mgm or less would cause relatively low rates of wear. In 1968 this
was something of a stringent rquirement, I doubt that there were more
than one or two cartridges that could meet that requirement. (There
probably aren't that many around today.)

FWIW the best cartridge that I have owned was a Technics P205CMk4.
This tracked better than the Shures v15s that I've owned and has a
flatter FR. According to the makers spec it has a compliance of only
12c.u. but an effective tip mass of 0.11 mg, which agrees with Waltons
argument about the importance of low tip mass. I think that it is a
better cartridge than the V15-V, but my sample has got a collapsing
suspension and replacement styluses seem to be unavailable.

I can't comment on modern MCs. But my experience with some of the early
ones that were enthusiastically welcomed by 'reviewers' was that they
mistracked to an audible extent on many LPs, and this was the main
difference I noted when comparing them with something like a Shure V15.

That's my experience as well, but I haven't used any really pricy MCs.

I suspect the reviewers liked the way the mistracking and groove
deformation alterted transient peaks. It was noticable at the time
that the reviewers who liked the early MCs (e.g the Asak) also liked
'pop and rock' music, not classical music, and may have perhaps
liked the 'enhancement' on the transients of electric guitars and
drums... :-)

Also, recordings of pop music seem to be cut with lower peak
velocities than a classical releases, which makes cartridge tracking
ability less important.

Bill