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MMD > Archives > July 2000 > 2000.07.17 > 09Prev  Next


Playing Vertically-Modulated Phonograph Disks
By Dave Vincent

For 78 single listening, I can recommend the Lenco (also sold as
Benjamin/Lenco) variable-speed turntables.  I have had one for over
twenty years and it has performed with absolutely no trouble and very
little rumble, despite having a design that one would think might be
rumble-prone.  Since it has continuously variable speed from about 16
to something approaching 90 rpm, it should be able to play 'most any 78
disks, including "high-speed 78s" like Pathe.  I would hope that these
turntables might still be available in good used condition somewhere on
one of the Internet auctions.

Incidentally, if anyone is trying to play vertically-modulated 78s
(Pathe, Edison) with a modern (well, more-modern, anyway) stereo
cartridge, there is a "trick" that they can use to improve the
playback.   If the cartridge leads are reversed on one channel only
from their normal stereo playback position, the results will be much
more pleasing than if the leads were left in their normal position.

The stereophonic grooves are cut and the stereo cartridge is wired such
that pure vertical movement (such as that carrying the information in a
vertically-modulated record) produces out-of-phase signals at the
outputs of the cartridge.  This was done to reduce pop and click noise
from scratches on the record surface, since such scratches tend to
produce a vertical movement of the stylus.

Unfortunately, this also produces nearly zero signal when playing one
of those "hill-and-dale" records in monophonic mode, where the two
out-of-phase channels are added together in the preamplifier before
being sent to the power amplifier stage.  Changing the cartridge wiring
defeats this noise-canceling feature of the stereophonic recording
process, but restores the information of a "hill-and-dale" 78 by
putting the two outputs back in phase.

I keep a spare head shell and cartridge for my turntable wired in just
such an "improper" manner solely for listening to Edison discs.

Dave Vincent


(Message sent Mon 17 Jul 2000, 23:57:11 GMT, from time zone GMT-0400.)

Key Words in Subject:  Disks, Phonograph, Playing, Vertically-Modulated

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