Sony TA-E88B - Equalizer Amplifier; Buffer Amplifier

resistance
rbb’.
(This
base
spread
resistance
is
one
of
the
critical
factors
which
have
to
be
considered
in
high
frequency
amplification).
The
detailed
diagram
is
shown
in
Fig.
5.
The
lower
the
rbb’
resistance,
the
less
the
noise
will
become.
This
may
be
achieved
by
connecting
transistors
in
parallel
—
n
transistors
connected
in
parallel
reduce
noise
by
1/v/n.
This
may
also
be
considered
as
parallel-connected
transistor
collectors
(noise
output
terminals),
resulting
in
the
averaging
out
of
noise
levels
and
phase
differences
of
the
noise
elements
in
each
transistor.
collector
Ie
base
rbb’
base spread
resistance re
emitter effective resistance
emitter
Fig. 5
head amp
Fig. 6
1-2.3,. Equalizer Amplifier
The
phono
equalizer
amplifier
stage
consists
of
Q201
through
Q214.
In
order
to
design
the
TA-E88/E88B
as
a
direct-coupled
de
amplifier,
this
stage
includes
the
following
features:
@
AnFET
in
the
first
stage
i
i
|
|
TA-E88 /E88B
®@
The
Miller.
effect
by
caused
internal
capacitance
between
drain
and
gate
of
FET
in
the
first
stage
results
in
deterioration
of
high
end.
frequency
response
due
to
high
input
impedance.
To
prevent
this,
the
drain
of
FET
in
the
first
stage
is
connect-
ed
to
the
source
of
the
following
low
input
im-
pedance
transistor
(Q202).
The
impedance
of
the
equalizer
components
(R228.
to.
R230)
is
kept
low
to
further
improve
the
S/N
ratio.
The
equalizer
amplifier
output
stage
employed
to
drive
these
components
con-
sists
of
a
-2-stage
emitter-follower
push-pull
circuit.
A
dual
transistor,
featuring
two
pairs
of
elements
mounted
on
a
single
wafer,
is.
used
to
improve
the
thermal
and
pair
characteristics
for
different-
ial
operation
of
Q201,
Q202
and
Q205.
1-2-4. Buffer Amplifier
The buffer amplifier (Q301 to Q312) up to the
equalizer amplifier has a gain of OdB. That is, there
is 100% negative feedback of the output voltige
rom the output terminal to the input negative
feedback terminal.
This amplifier is used to drive BALANCE control and
ATTENUATOR.
Frequency response deterioration will occur if high-
value resistors are used in the step attenuator. The
TA-E88/E88B employs low resistance resistors
(3kQ). This also resuits in decreased thermal nose.
A buffer amplifier is used to drive the low resistarce
BALANCE control and ATTENUATOR. This ampli-
fier uses a differential-cascode amplifier in the first
stage.
Fig. 8 shows the location of the FET.
variable resistor