Electronics-World-1959-05

Over -all design of this stereo preamp
has attractive and neat appearance.
ELECTRONICS--
LAB TESTED
"Stereo Master"- a Hi -fi Control Center
A new hi -fi component that has
extremely low distortion. Both
lab and listening tests prove
quality sound reproduction.
ONE of the most recent additions to
Lafayette Radio's hi -fi component
line is its Model KT -600 stereo preamplifier.
It incorporates just about
all the features one could hope to find
on a single chassis. Evidently, considerable
time and effort has been
spent on its design, which was created
by Stuart Hegemann in conjunction
with Aaron Newman, chief engineer at
Lafayette Radio. Stuart Hegemann is
well -known and respected for his engineering
achievements in the hi -fi
field.
In addition to the usual controls
such as bass, treble, loudness, and
rumble and scratch filters, it has many
other features. The entire righthand
section, which includes the stereo function
switch, bridge control, and volume-
balance control, is identical to
Lafayette :s KT -315 stereo adapter
unit. Its complete operation was described
in last month's issue. Briefly,
though, the stereo function switch provides
for selection of normal stereo,
reverse channel, reverse phase, and reverse
phase and channel, in addition to
either channel through both speaker
systems or both channels together. It
includes a calibration position which is
unique in itself in that it permits proper
electrical balancing of the two
channels up to the inputs of the power
amplifier. It is used in conjunction
with a monophonic signal with both
channels being handled by the preamp
out -of- phase. Controls are adjusted
and when proper balance is attained, a
null occurs at the speaker outputs.
64
Top view shows printed circuit assembly and general arrangement of parts.
The "volume- balance" are individual
controls for each channel but incorporating
a clutch that can gang both together,
converting them to a single
level control.
The bridge control allows for combining
a portion of each channel into
the other channel to eliminate the socalled
"hole-in- the -middle" effect. In
its extreme position one can obtain
100e /r combination resulting in a mono-
phonic presentation through both
speakers.
The selector switch is used to permit
a choice of six separate inputs;
auxiliary, tape amplifier, tape head,
tuner, and either magnetic or ceramic
cartridge. Each channel has its own
selector switch, thereby providing the
flexibility of mixing any combination
of program material. Four dual concentric
-type input level controls are
also incorporated. The outer shaft is
used to adjust the inputs on one of the
channels and the inner shaft of the
control is used for the other channel.
Equalization is obtained by means of
four separate controls. two for each
channel. The turnover point is selected
by one and the roll -off by the other. A
choice of any combination thereby increases
the flexibility to the user.
A third channel output is provided
with a bridging control that would
permit any desired combination of A
and B channels. Not only can this output
be used as a third channel for
stereo, as another method of eliminating
the "hole -in- the -middle," but it can
serve as a monophonic channel for
playback in any other section of the
home.
Another unique feature that we have
not run across in any of our previous
tests on stereo units is the incorporation
of a "presence control." The function
of this control is to provide a
slight boost in the mid -frequency
range. Our tests showed a 6 db rise
at 2500 cps and then a return to the
ELECTRONICS WORLD