In addition, there was an SQD2 Quadraphonic Decoder, designed
for use in the FC1. I have never seen
this unit, but I'm sure it is identical
to the SQD1, except for the cable connections.
The cable connections are different
from those used in the other machines
since a different Stereo Network (SN11)
is used in the FC1. It may have been
identical to the SQD1, with an extension
cable included. Field update kits were
available for both the FC1 and FC2 machines.
These kits probably included some sort
of graphics panel to set the machine
apart from the normal version. If anyone
has one of these, please send photos!
Only a few SPS2 jukeboxes were modified to use the quad adapter.
The SQD1 pictured above was used
in the SQS160 and later jukeboxes.
The SPS2 quad conversion actually
used a metal project box to house
the circuitry, which was riveted
shut and also riveted to the machine's
lower rear panel, just inside the
rear access panel. See the photos
below, which were provided by Jeff
Ziemer. In the right hand photo,
the gray cable with round, black
connector plugs into the side of
the decoder. The barrier strip on
the other end of the cable is used
to connect to the external speakers.
The black cable is used to connect
a PRVC to this machine, and has
nothing to do with the quad decoder.
What was inside the box, sealed
with tamperproof screws?
'Under the hood' of the SQD1
At the left is a schematic diagram
of the SQD1. As you can see,
it's simply three potentiometers,
connected between the amplifier
outputs and the speaker terminals.
The two connectors (the 3-pin
and the 5-pin plug into the
cabinet cable, and replace the
stereo network connections in
the normal machine. The machine's
internal speakers and the stereo
network are not used.
The red wire of the 3-pin connector
comes from the amplifier Left
Channel output connection; the
Blue wire of the 5-pin connector
comes from the amplifier Right
Channel output connector. In
the normal machine, these wires
connect directly to the Left
and Right channel woofer speakers,
respectively. The Wht/Red and
Wht/Blu connections (which are
part of the SQD1 input cable)
are not used in the SQD1, and
are perhaps a bit of subterfuge
on the part of Seeburg. In the
normal machine, they connect
to the Left and Right channel
horn tweeters, respectively.
How does it work?
This
is how it's connected to the speakers.
Note that the 'Lt Front' and 'Rt
Front' potentiometers are connected
in series with the front or main
speakers. They simply serve to control
the relative volume between the
front and rear speakers. The rear
speakers are connected across both
amplifier output channels, with
the 'Lt & Rt Rear' control connected
between the common connections of
the rear speakers and the amplifier
common output terminal. Connected
in this manner, the Rear speakers
will only output the difference
between the Left and Right amplifier
outputs. The 'Lt & Rt Rear'
potentiometer controls how much
of this 'difference' signal you
hear. With it set to 0 Ohms, all
you hear is the amplifier Left and
Right audio. With the control set
for maximum resistance, you get
the maximum effect. This simple
circuit was invented by David Hafler
(U.S. Patent #3,697,692), and was
licensed to the Dynaco Corporation
by him. In fact, he was the founder
of Dynaco and one of the main designers
of most of their amplifiers, renowned
in the 50s, 60s, and 70s for superb
high-end audio systems. This simple
circuit recovers the rear ambient
sounds such as audience coughs or
applause, which the recording microphones
generally pick up in opposite phase
to what is generated by the musicians.
Also picked up are echoes from the
recording location. All this adds
to the ambience or realistic sound
of many recordings. The effect will
vary from record to record, but
the operators simply set the controls
so that the average record sounded
okay, and left it at that. I'm not
sure you would hear much difference
in the typical place where you would
find the jukebox. It seems to me
you would have to listen in a pretty
quiet environment to pick up any
rear channel sounds. Home installations
would certainly sound much better
than the typical bar or restaurant.
Other Seeburg Quad efforts
As a follow-on to the Hafler Quad
system, there was an effort to incorporate
matrix-decoded quadraphonic sound
into the jukebox line. While I worked
in the Engineering Department, a
project was started to determine
what changes would be required to
incorporate matrix quad sound. Examples
of both SQ and QS decoders were
obtained, and a comparative listening
test was set up in our audio demonstration
room. I was not invited to any of
the sessions, since I was not a
high-powered executive, but I did
help in the setup and attended the
informal Engineering demo that occurred
prior to the big shot's session.
We Engineers were unanimous in thinking
that the Sansui QS Vario-Matrix
system was superior to the others,
except for CD-4. This latter system
was not seriously considered, due
to the major tooling effort required
on the part of both Seeburg (to
significantly reduce the tracking
force of the pickup arm) and Pickering,
the cartridge supplier (to totally
change the contours of the stylus,
and increase compliance substantially
to be able to handle 20 - 50 KHz
audio). For the matrix system, the
cost of the decoder, two more channels
of amplification, and the licensing
fee for whatever system was to be
used proved to be more than management
thought the operators would pay,
and this version of quad died, too.
Thanks to Ron Rich for providing
many of the details that went into
this article.
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