I
I
The
622
Equalizer
should be packed
so
that
there
is at
least
1-1/2"
of
packing
material
protecting every point. A
plastic wrap around
the chassis will
protect the
finish.
Cushioning material
such as Air-Cap, Bubble-Pak,
foam "popcorn",
or fibre
blankets are acceptable. Folded
newspaper is
not suitable.
Blanket-type materials
should be tightly wrapped around the 622 Equalizer
and taped in
place to prevent
the
unit from
shifting out
of its
packing
and contacting
the walls
of the carton.
The
carton should be packed evenly and fully with
the packing material filling
all
voids such
that the unit cannot shift in the carton.
Test for
this by closing but
not
sealing
the carton and shaking vigorously.
If
the unit
can
be felt
or
heard
to move,
use
more packing.
The carton
should be well-sealed
with
3"
reinforced
sealing tape applied
across the
top and bottom of the carton in an
"H"
pattern. Narrower
or parcel-post
type
tapes will
not stand the stresses applied to commercial
shipments.
The package
should
be
marked
with
the name
of the shipper, and the words
in
red: DELICATE INSTRUMENT, FRAGILE!
Even
so, the freight
people will
throw
the box
around as if it were
filled with
junk. The survival
of the unit
depends
almost solely on the
care
taken in packing!
3:
CIRCUIT
General: Except
for
the power supply, the
left and right channels
of the 622
are
DESCRIPTION
independent
and identical.
In
the
following
discussion, the
LEFT
CHANNEL
will
be
described.
The
circuitry is divisible into seven major blocks. These
are:
1)
input buffer and "active transformer"
2)
high
frequency equalizer
(HF)
3)
mid-high
frequency equalizer
(MHF)
4)
mid-low
frequency equalizer
(MLF)
5)
low
frequency equalizer
(LF)
with
discrete current-booster
output stage
6)
overload indicator
7)
power
supply
These
will
be
described in
order.
Input Buffer
The signal enters
the 622 in balanced form.
CIA,
CIB shunt
RF
from
the input
leads to
the
chassis.
These
capacitors
are
not effective at
VHF
and
higher
frequencies; therefore, ferrite beads have been placed around the input and output
leads to suppress such high
frequency
RF.
It
should be noted
that this
degree of
RF-proofing
is moderate but adequate for
a
vast
majority of
installations. However,
installation next to a high-power transmitter
may still cause problems.
Additional
RF
suppression,
careful examination
of
the grounding
scheme, and
other
considerations familiar
to
the
broadcast engineer may have to be used in
conjunction with the
622's
built-in
RF
suppression.
The
filtered signal
is applied
to 1C
I,
a
low-noise FET-input
opamp
configured
as
a
differential amplifier with
a
gain of 0.5. When both non-inverting and inverting
inputs are driven by
a
source impedance which
is
small with respect to I00K (such
as
600 ohms
or less), the
amplifier
is essentially insensitive to signal components
that appear equally on the non-inverting
and inverting inputs (such as hum),
and
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