Threshold cas 2 brochure

Page 2

pulley. The base of the unit has no
suspension as such (except for the
Audio-Technica feet), but it works
because the material it is made from
is so dense that it resists resonances.
The only other aspect of the
mechanics that need be considered
is the spindle bearing. It must have
4 or 5 drops of oil to function cor-
rectly. The bearing is made such
that the oil fills up the space be-
tween the spindle and the bearing
sleeve walls. Without the oil, the
platter will wobble slightly about its
spindle.

We have only one major reserva-
tion about the unit: the platter. In-
stead of being a full 12 inches, it is
only 10 inches in diameter. The
maker uses the Osawa platter mat
because it is stiff enough to support
the one inch worth of record that
hangs over the platter. Our nega-
tive reaction to this is probably more
psychological than tangible;
however, we still wish the unit had a

12 inch platter. The extra support
could only help.

The AC-4 is available by itself or
with a tone arm or with a tone arm
and a cartridge. (Call or write HCM
for details.) If you buy the table
with an arm and cartridge, HCM
will mount the tone arm in its proper
location and align the cartridge for
proper geometry. (Even if you just
buy the table and an arm, HCM will
align the whole thing if you send
your cartridge.) A combination of
the HCM AC-4 'table and a Grace
707Mkll tone arm, for example, sells
for $299. The HCM will never win
any beauty contests or technical
awards, but at those kinds of prices,
it sounds like a good deal to us!

Made by: HCM Audio, P. O. Box
2029, Chico, CA 95927, (916) 343-
0558 / Associated components: 1,
3, 6, 24, 7, 8, 9, 12,14,17,19 / Listen-
ing room: B / Price: $169.

Threshold GAS-2

All distortions produced by a
transistor? are due to changing gain
characteristics as the voltage and
current across the device fluctuate
in response to the audio signal. If
you accept that statement as true,
then you will understand the basis
on which all of Thresholds ampli-
fiers have been designed. That is, if
voltage and current across the gain
transistors could somehow be held
constant, the amplifier would be dis-
tortionless. In the case of the GAS-2,
the second generation fully cascode
power amplifier, Threshold takes a
swipe at one of those two distortion
causing situations by using a tech-
nique that suppresses voltage varia-

0r any type of gain device: tube. tun-inter. or whatnot.

tions across the gain transistors.
That technique is, of course, called
cascoding. We see no point in at-
tempting a technical discussion of
this technique since many of you are
probably not interested in the tech-
nical aspects, and even if you are,
there is material available from
other sources that provides a tho-
rough explanation of this topic. (See
the article by Nelson Pass in the
March 1978 issue of Audio maga-
zine. Literature on the subject is also
available from Threshold.) In the
simplest terms, cascading is a
method of using an extra transistor
to insulate the gain transistor (or
transistors) from voltage fluc-
tuations. Those distortions that
would normally be caused by

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