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Re: arsclist ELT, continued
From: "Art Shifrin" <goldens2@xxxxxxxxxxx>
Subject: arsclist ELT, continued
Date sent: Thu, 7 Jun 2001 17:24:09 -0400
Send reply to: ARSCLIST@xxxxxxxxxxxxxxxx
> Hi George,
> Thanks for the clarification on the size issue.
> About vertically cut grooves: it was explained to me that the system
> works by tracking and comparing the opposing groove walls from a
> nominally 45 degree angle: that the ELT system is predicated upon
> comparing the data reflected from the two grooves' walls.
If so, then
> how does it account for purely vertical mudoulations?
All stereo pickups are really two in principle perpendicular hill-and-
dale pickups (in practice they are not precisely perpendicular) at 45
degrees (45/45 as it is called, as opposed to what Blumlein
proposed: true vertical and true horizontal). The modulation of a
stereo record is really two hill-and-dale recordings simultaneously
(this is post-1957 - Cook used two completely separate horizontal
tracks, and London Decca experimented with a carrier wave
system). By wiring the coils in series in one way one obtains only
the resulting horizontal modulation - MONO, and by reversing the
connection to one of the coils in the series connection one obtains
only the resulting vertical modulation - again MONO.
Now, the ELP LT series works precisely the same, it is two
independent systems for the detection of hill-and-dale modulation
which are truly perpendicular and at 45 degrees to the horizontal,
and it is VELOCITY, not DEVIATION, mind you! The best
description of what is going on is still the basic FINIAL patent, US
patent no. 4,870,631, which you may download from the USPTO or
DELPHION. It is extremely complete, takes a couple of hours to
read with one finger on the drawings, but then you know a lot about
stereo signals. And, obviously about the working of the LT. Apart
from acquiring the FINIAL patents ELP have introduced
improvements and distortion correcting circuits, but the whole
signal chain is still analogue. So you end up with two channels of
stereo signal which you may combine any way you want - and also
get true vertical sensitivity for those hill-and-dale mono records that
had used a suitable cutting stylus.
> outputs of a phonographic cartridge are reverse phased, the resulting
> signal is derived from the stylus' emulations of the groove. IF I'm
> correctly recalling the explanation of their pickp method, then (at
> least as of last summer) it could not detect such vertical movements.
> If this is so, then reverse phasing the two outputs could not yield
> best possible S/N & distortion from vertical cut grooves.
I believe that my explanation holds water.