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The Barney Oliver Audio
A.
PHONO-P RE-AM P LIFIER
The phono pre-amplifier uses a combina
tion of series and shunt feedback to the
terminals to
of the proper value to produce,
self inductance of the
roll-off above 2120 Hz. If
inductance and R o the
is the input resistance to the pre-amp we
require that
This leads to the value of Rl
matic. As
Shure V-15
variation of high end response, the shunt feed
back is halved or doubled.
The series feedback is applied to the low end
of the
(normally the outer shields of coaxial
above
To avoid hum and RF pIckup It
recommended that an outer shield insulated
both inner shields be used. This shield should
connect the record
chassis.
A balanced differential
input to avoid drift and RF rectification. The
remainder of the
for power leveL The
B stage can supply a 600!J line or headphones
at line level (0
without
The low end bass boost of the RIAA charac
teristic below 500 Hz is provided by C12 and R3
R4
R5
R6 and R28. The low end cutoff is
+
+
+
provided
C2 and C3
RIO. This combination
and a fourth order maximally flat low-end
cutoff at about 16 to 20 Hz.
was used to make the projected
circuit zero in all directions
the conductors and by
shown. This minimizes the
to the power transformer and reduces
the hum below audibility.
hum, it's from
5
IR
UIT D
a resistive input
with the
the
'" 7 5 x 10- 6 seconds
in the sche-
Rl is
for the
To provide the . 1 6 dB
which places these ends
.
frame to the
is used at the
is similar to the power
distortion.
with C4, C5 and
doc external
you notice any
directly to the cartridge.)
TI
N V
CRt
TION S
Because the
)
10 K !J
cable
high end response for
Many of the components that may
RIA A
you, such as Q3 or CR8 or such as
is
are there to avoid tum on transients or
and
avoid emitter base breakdown. Everything has a
function, but invincible fatigue prevents me from
going into all the gory details.
B.
FI LTER BOARD
The filter board
cutoff below 16 Hz to
large useless cone exursions, and a control
lable high-end cutoff to suppress the
with
�O?
The board contains four
IS
of two cascaded emitter followers
very high
and low distortion.
The two
to the
Class
high pass filters that
below 16 Hz (example:
The output of these feed the mode selector switch.
The
drive for the dual precision volume control and
are coupled to the mode selector switch via active
low-pass filters.
of the
base currents of the input emitter
thereby enable the
and 21 to be set equal to zero. This eliminates
transients when the mode and filter switches are
switched.
Circuit
impedance is low (about
has no effect on the
up to 10 or 20 feet
a sharp low-end
or distorted program material.
and
with constant current supplies
and Q7) . This combination provides
very low outpu t im-
selector switch through active
rapidly in transmission
unity
amplif iers provid e
are three
by the input RC net-
poles
are provided to supply the
at terminals 5,
CRl,
the speakers
fre-
gain
are
C3,
Q5).
filters, two
zeros) by the
and
20
5-1
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