Cartridge Alignment Problem

Archived from groups: rec.audio.tech (More info?)

<rupesh@patre.com> wrote in message
news:1116727797.912650.207620@g43g2000cwa.googlegroups.com...
> Hi,
>
> I've recently bought a new Michell Gyro SE with Origin Live Silver
> tonearm and Reson Aciore cartridge. I have a problem with aligning the
> cartridge. I've used both the protractor that came with the Hi Fi News
> Test LP and the Turntable Basics (www.turntablebasics.com) protractor.
>
> Both protractors imply that for correct alignment there should be
> cartridge underhang and not overhang. This does not seem right to me.
> I've taken some photos to show you:
>
> http://www.patre.com/michell
> I'm pretty certain I've used both protractors correctly. Also can
> someone please tell me what order I should make the adjustments to my
> turntable ie tracking force, VTA adjustment etc.
> I look forward to hearing from you.

It's a long time since I bothered with this, but some overhang is
fundamental to the geometry of a simple pivoted arm. What radii are your
protractors designed to set "0" angular error to? I used 2.5" and 5" which
was near optimum for the LPs of the time, but cutting raddii may have
changed slightly over the years. This gave me an overhang of 0.6" on a long
arm set at 10" from turntable centre. Shorter arms require more overhang.


--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Archived from groups: rec.audio.tech (More info?)

rupesh@patre.com wrote:

> http://www.patre.com/michell

Looks fine to me. Now it's time to obsess over VTA...

Archived from groups: rec.audio.tech (More info?)

"Malcolm Stewart" <malcolm_stewart@megalith.freeserve.co.uk> writes in
rec.audio.tech<d6pf3b$shi$1@newsg1.svr.pol.co.uk>:

: Overhang is with reference to the pivot point of the stylus, not the
: mounting screws of the cartridge. Does this help?

Eh?
It's with reference to the stylus itself; the actual point of the stylus.

The "pivot point of the stylus" is an odd phrase, but would seem to imply the
pivot point of the cantilever holding the stylus, back in the cartridge body,
which would be very wrong. I'm not sure what you mean by it yourself.
--
RdM

Archived from groups: rec.audio.tech (More info?)

"RdM" <here@somewhere.net.zz> wrote in message
news:vnc391hau496qq4519chhcq7c0j8mjmdeb@4ax.com...
> "Malcolm Stewart" <malcolm_stewart@megalith.freeserve.co.uk> writes in
> rec.audio.tech<d6pf3b$shi$1@newsg1.svr.pol.co.uk>:
>
> : Overhang is with reference to the pivot point of the stylus, not the
> : mounting screws of the cartridge. Does this help?
>
> Eh?
> It's with reference to the stylus itself; the actual point of the stylus.

Correction accepted. Thanks - must have posted before thinking through what
I'd typed.

--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Archived from groups: rec.audio.tech (More info?)

A definition:

Rotate the arm such that the stylus tip, the turntable hub, and the arm
pivot are on the same straight line. "Overhang" implies that the
turntable hub is between the stylus tip and the arm pivot.

A point:

Don't be concerned if the final cartridge angle is not parallel to the
edges of the headshell. Very few arms actually have the correct angle
and even if they did, and are not mounted at exactly the distance from
the turntable hub used in the angle calculation, the ideal angle will
change.

A discussion:

The master record is cut such that the cutter is always cutting
parallel to a radius. You can think of the information being cut into a
"plane". A cartridge mounted on a pivoted arm cannot maintain alignment
with the original cutting plane at all points across the record. The
object of cartridge alignment is to minimize the audible damage caused
by this inevitable misalignment with the original cutting plane.

For such a simple concept, the math needed to get a grasp on "minimize
the audible damage" is a bit obscure and out of reach. Evidently, few
turntable designers have bothered to do the math or seek out the
definitive 1941 paper on the subject because the overwhelming majority
of turntables get the angle or dimensions wrong or specify an alignment
procedure that cannot guarantee the objective.

First, consider a straight arm with the stylus bar parallel to the arm
and the length of the arm allows the stylus tip to touch the center of
the turntable (the "hub" ). The angle between the stylus and the cutting
plane will be zero only at that center point and will be quite high at
the outside edge. This is not a particularly useful alignment because
we don't have any music to play at the center.

Obviously, we could help the situation by introducing an "offset angle"
that yields a zero point (perfect alignment with the cutting plane)
somewhere in the area that we actually play. Picking the optimum spot
then becomes the issue. One could pick the center of the played area,
thinking that we will "split the difference". Or, one could place the
zero point at the inner limit of play considering that, because the
musical wavelength is shorter near the center, misalignment causes more
audible damage near the center. [ As an exercise for the student, plot
the angular error for a straight arm at points between the inner and
outer playing radii -- you may decide a zero somewhere close to the
mid playing point might not be such a bad idea, or you may pick the
inner limit for your zero, but look what happens at the outer point if
you do. ]

Next, rather than keeping the pivot to hub distance such that the
stylus can touch the hub, introduce an overhang. [Students should plot
this] Yikes!! the magnitude of the error increases dramatically and
the error plot doesn't look as nice, but on reflection, the range (the
difference between minimum and maximum errors) decreases dramatically.
Now our task is to find the optimum combination of pivot to hub
distance, overhang, and offset angle. Remember, "optimum" is in terms
of audible damage caused by misalignment with the cutting plane.

Pivot to hub distance is self defining given that a longer arm will
always result in lower errors, but eventually the arm will be too long
to fit on our furniture or will be too massive for the cartridge. Pick
a practical arm length and optimize the overhang and offset.

This is where the messy math pops up and I won't go into it here.

The points that fall out of the math are that there are four zero
points on the surface of the record, two on each side of the record
hub. (Decide which side of the hub you want to play and ignore the
other two points) Once deciding on your minimum and maximum playing
radii, you can calculate the two zeros. While most records start very
close to the outer edge, the inner radii varies quite a lot from record
to record. There are arguments over what that inner radius should be
and there are a few different sets of zero points based on varying
assumptions. One could also consider different alignments for 10 inch
and 7 inch records.

From a user's standpoint the arm length has already been picked for you
and, to some extent, so has the arm pivot point (the arm mounting
location). Your job is to pick the optimum overhang and offset for your
situation when installing a cartridge. Note that you have two variables
(angle and length). If you remember anything about high school algebra,
you know that you need two equations if there are two unknowns. That's
why you must force cartridge alignment simultaneously at both zero
(usually called "null" ) points.

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