Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/3/84; site teddy.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!teddy!rdp
From: rdp@teddy.UUCP
Newsgroups: net.audio
Subject: Re: Turntable Clamp & Turntable Controversy
Message-ID: <1024@teddy.UUCP>
Date: Fri, 26-Jul-85 15:50:32 EDT
Article-I.D.: teddy.1024
Posted: Fri Jul 26 15:50:32 1985
Date-Received: Sun, 28-Jul-85 05:16:58 EDT
References: <353@cmu-cs-cad.ARPA> <440@moncol.UUCP>
Reply-To: rdp@teddy.UUCP (Richard D. Pierce)
Organization: GenRad, Inc., Concord, Mass.
Lines: 64

In article <440@moncol.UUCP> ben@moncol.UUCP (Bennett Broder) writes:
>
>- A signal-to-noise ratio of 78db??  How does a turntable get a
>  signal-to-noise spec at all?  Since the only part of a turntable
>  that carries signals is the cable, I would assume that s/n ratio
>  could only be determined for a specific cartridge.
>
>Ben Broder
>..ihnp4!princeton!moncol!ben
>..vax135!petsd!moncol!ben

It is quite simple to imagine how a turntable can have a signal to noise
ratio.

Mechanical noise suorces such as rumble generate mechanical vibrations
in the platter, in a variety of directions. It is these vibrations,
when referenced to a standard velocity, that comprise the signal to
noise ratio of the turntable.

The most rigid spec for signal to noise is (if I remember my numbers)
is DIN spec 45.539, which measures rumble, with no weighting or filtering
referenced to a velocity of 5 cm/sec, which, in a typical moving magnet
cartridge produces about 5 mV. So a signal to noise ratio of 60 dB would
be equivalent to an average equivalent rumble veloctity of 50 microns per
second ( .001 x .05 m/sec), which would produce a signal voltage from 
such a cartridge of 5 uV. This is about an order of magnitude greater than
the typical noise output of good phono preamps, but the spectrum of the
rumble noise is weighted towards the deep bass, so there is not a direct
comparison possible.

Most Japanese (and most others) use a weighting filter before measuring
the noise, which significantly reduces the sensitivity of the measurement
below 500 Hz, where, of course, most of the rumble energy lies. It is
undoubtedly such a weighted figure that NAK touts above.

As a point of comparison, my own unweighted and weighted measuements for
venerable turntables follows, much from memory, so I might be off a bit
here and there. The measurements were made using a custom-made glass
"record" covered with a very thin layer of silicon oil to eliminate
possible "squeal" and other extraneous effects.

	Model		DIN 45.539	DIN A weighted

Thornens TD-125		48 db		61 db
Thorens TD-124		42 db		58 db
Lynn Sondek (new)	68 db		76 db
            (old)	58 db		64 db
Connoisseur BD-2 IV	61 db		75 db
Dual 701		52 db		71 db
Dual 601		52 db		68 db
Denon 600 (?)		63 db		72 db
LUX pd-121		56 db		68 db
Phillips GA-212		38 db		50 db
AR turntable		48 db		58 db

The last of these measurements were made in 1980, so I have no comparison
to modern equivalents.

You should note that differences on the order of 4 db or so might be
considered insignificant, primarily due to experimental variations. What is
shown is that there is not a clear cut advantage of one type over another,
just that bad turntables are noisy, good ones aren't.

Dick Pierce