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From: Patent Tactics, George Brock-Nannestad

oh, is it difficult to use a precise terminology! I do not think that
Goran Finnberg and I disagree over very much, we simply use
different words. Anyway, to clarify:

Goran:

> George Brock-Nannestad wrote:
>
> > Since 1957 most stereo  cartridges have
> > relied on having one set of coils sensitive in a slanted direction 45
> > degrees to the right and another set of coils  sensitive 45 degrees to the
> > left of vertical. The stereo information in  such stereo records are cut for
> > those directions, termed right and  left channel.
>
> For a signal containing left OR right ONLY then weŽd see the above
> mentioned 45 degree movement.

----- I did not say 45 degree movement, only sensitivity. Actually the
combined sensitivity of the two sets of coils corresponds to a sort of
butterfly pattern, with maxima in the 45/45 directions.

>
> So in fact weŽd expect to see movement from all directions inbetween 45
> degree slant to side by side depending on the stereo width only.

----- I totally agree


>
> So, in fact, a stereo pickup will be able to move in all directions from
> lateral to vertical and everything in between.

----- again I agree, the stylus has to be able to move in all
directions, and that why it is important that its compliance is the
same in all directions. In fact, the stylus movement is basically of
the same shape that you can see on your phasor screen.

George wrote:
>
> > Blumlein's own design was
> > for vertical and horizontal  (lateral).

(and then Goran quotes British Patent Specification 394,325

>
> So in fact any movement from purely lateral to purely verical or
> anything inbetween not only 45 degrees as implied by you could be had by
> the 45 degree mounting arrangement of the driving coils when fed by
> varying signals whose PHASE content is different between the two
> channels which will produce different VECTOR forces on the cutting
> stylus.
>
----- when I said "Blumlein's own", I meant that which he
implemented for his experiments. His cutterhead was vertical
combined with lateral. That was used in his famous "walking and
talking" demonstrations.

> > You can obtain one type of signal
> > from the other type by  so-called  matrixing, in which you add and subtract
> > the signals  suitably. For 45/45, I obtain lateral mono from a stereo output
> > by  summing the signals from the coil sets, and I obtain vertical mono  by
> > taking the signal in the reverse from one of the coil sets and  summing
> > (series connection is summing).
>
> For the moving magnet pickup cartridge its essential to provide the
> correct electrical loading impedance which is set to nominally 47 kohms
> loading shunted by 100 to 500 pF of capacitive loading to get the
> manufacturer specified frequency response.
>
> Any change from this means a non flat frequency response and should be
> avoided if quality results is to be had from the disk to be transferred.
>
> The correct way to do this is to use a phono preamplifier with the
> correct replay equalisation for the disk to be replayed and do the
> matrixing by mono the left and right signals, L plus R equal to Mono or
> lateral sensing, or inverting the polarity of one channel and then
> summing, L minus R equal to difference sensing, S, or vertical sensing
> only.
>
> This way will not compromise quality.

----- point well taken! What you are saying is that combining the
signals in the headshell is not correct unless the input impedance
constituting the load on the pickup is adjusted at the same time.
Here I have been guilty a lot of times.
>
George wrote:
> > Now, the channel separation of a stereo cartridge is rarely more  than 20 dB
> > over a wide frequency range. For this reason there is no  way to obtain a
> > pure vertical or a pure horizontal signal by summing  as described, not even
> > with a balancing control.

Goran responded:
>
> The channel separation of a stereo cartridge has nothing to do with its
> ability to provide pure lateral sensing or vertical sensing.
>
> This is a matter of the phase response between the two channels only and
> if they are perfectly alike then pure vertical or a pure horizontal
> sensing will be perfect.

----- ah, but they are not perfectly alike in a manufacturer's world,
and that is why you will not get a perfect null if you have a lateral
record and a amplifier summing set up for vertical.
>
> Stereo separation by itself can be arbitrarily set by using M/S
> techniques to slightly widen the separation to any figure wished for.
> But that has nothing whatsoever to do with vertical/lateral sensing as
> such.

----- I agree. As an aside: the most impressive demonstration of
increased stereo separation I have heard in a room from an
analogue source was the use of ordinary left-right speakers in front
and side speakers connected in series (and correctly polarised!), to
the *hot* terminals of the amplifiers used. That effectively increases
the difference signal heard. Bang & Olufsen used that in the early
1970s (was it called Ambiophony?)

George wrote:
> > The only way to obtain that is to use a mono pickup.
Goran replied:
> ThatŽs one way to do it.
> Albeit a very good way to do it.
> Another way is to simply mono, L plus R, a stereo cartridge.
>
> This will net you a 3 dB increase in S/N compared to any other way
----- this I do not understand
 and
> rid you of boatloads of distortion and rumble and subsonic shit from
> warped disks free without the need to filter it out.

----- again, I do not understand this argument, provided the rumble,
etc. is of a vertical nature

George wrote:
> > And here Ortofon have a genial  solution: they have revived a
> > cartridge from 1949, it is dynamic  (moving coil), and it has a high vertical
> > compliance.

.....................

>
> > That will give  pure lateral mono, except for pinch effect, which
> > is reduced if you  use an elliptical stylus that is oriented as the cutting
> > stylus was
>
> Pinch effect does NOT excist in mono only pickups. In stereo pickups you
> get rid of pinch effect by mono the signal or L plus R.

----- here I disagree: pinch effect was one of the curses of early
mono reproduction, because it wore the records down due to lack
of vertical compliance of the early, heavy pickups and soundboxes.
That was also the reason why "trailing needles" were prescribed for
early instantaneous recordings.  Pinch effect refers to the fact that
you cut with a chisel-like stylus as opposed to embossing by a
round stylus. In the resulting groove the width measured across the
groove (perpendicular to the curve) at any point with a high velocity
(a steep angle with respect to the zero "line") will be narrower, and
the angle you encounter "between" groove flanks will be
consideralbly less than 90 degrees. This pushes the stylus up twice
in a period, and so has double the frequency. An elliptical stylus
will suffer less. In an embossed record an elliptical stylus sinks for
a similar reason. If the stylus is incapable to follow this vertical
movement, then the groove flanks suffer. Pinch effect wear and
needle chatter is avoided in any pickup having a high vertical
compliance. The Ortofon Mono Pickup known as the C-head (the
A-head had a lower *lateral* compliance) has a high vertical
compliance, but no vertical output, obviously. In the image of the
butterfly pattern used above, think of the two lateral wings being of
a very, very low height, so that any deviation from true lateral gives
virtually no output. This is considerably lower than what you will
have if your stereo pickup coils, core pieces, and capacities are not
perfectly balanced, which is also the prerequiste for a good stereo
separation.


Goran wrote:
> BTW, the use of an elliptical stylus will negate scanning losses, treble
> loss, in the inner grooves near the center of the disk where the linear
> velocity is much lower compared to the start of the disk since the
> scanning radius of such a tip will better follow the much smaller
> curvature of the treble frequencies.

----- that is not true of Dynagroove encoded RCA records. They
used a tracing simulator that pre-distorted the grooves to give a
good result with spherical styli. This means that the result will be
worse when an elliptical stylus is used. I have heard this extremely
clearly on an ELP turntable which has the smallest elliptical
footprint I know.

George wrote:
>  -  vertical tracking angle has to fit as well as any rotation of
> > the  original cutting stylus in its holder. If you want to use several kinds
> > of stylus on this cartridge it is going to be expensive.

Goran agreed:
> Yes, since you need several such costly cartridges for each stylus size
> you wish to use since the stylus cannot be removed from the cartridge
> body and changed to a different one as can be done with a moving magnet
> cartridge.

Boy, was this a lengthy exchange!!

Kind regards,


George