Circuit
Configuration
The
amplifier is electrically and physically in two sections, the pre-amplifier or
control unit and the power amplifier. The pre-amplifier is again in two
electrical sections. The first section is a feedback triple of high gain
transistors forming the disc amplifier. The output of the disc amplifier or one
of the high level inputs is selected and fed to an emitter follower circuit
which in turn feeds the tone control, filter snd output stages. Each power
amplifier has a low noise input transistor coupled to a high voltage
bootstrapped stage to convert the input EMF to a high amplitude EMF approx
equivalent too the required output voltage. The voltage amplifier is followed
by a bootstrapped medium power emitter follower stage working into a resistive
load. This circuit is followed by twin complementary pairs of output emitter
followers with emitter coupled drivers. The quiescent current is fairly high at
100 mA. This method has been found to produce a linear output even without
feedback thus only 30 dB or so of negative is used with a much greater attendant stability into
complex loudspeaker loads. The output stage is protected by reverse fast diodes across the output devices
and curent limiting cicuiry. Cartridge
fuses protect against over dissipstion
from a sustained short circuit.
Construction
and finish
The basic
chassis is a U section front panel joined to a U section rear panel with two
tray section side members and a lateral U section member also joining the two
side members. One side member caries the large main transformer, the lateral
member the power smoothing and loudspeaker coupling capacitors together with
the two bridge rectifiers, the front panel carries the pre-amplifier and the
rear panel the power amplifier. The pre-amplifier components except for the
controls which are mounted on the front panel are carried on a printed circuit
board supported on special nylon stand off pillars. The entire pre-amplifier is
screened in a two part cover formed from 22 gaue steel. All other steel parts
are formed from 18 or 16 gauge mild steel. The power amplifier circuits are
mounted on nylon stand off pillars carried by the rear panel and the power
transistors are mounted on four massive heatsinks carried outside the rear
panel and machined from from a special aluminium extrusion produced for JE
Sugden by Alcan Booth Aluminium. The heatsinks are anodized matt black and all
the ferrous metalwork is zinc plated and chromate passivated for maximum
corrosion resistance. The chassis is clad in the "trim" consisting of
a nextel finished strip behind the knobs and two aluminium trims which carry
the front lettering. These trims are acid etched and anodized and printed with
an epoxy ink. The top and sides trims are made from aluminium and finished in
Nextel - a very durable paint with a suede effect feel to it. The push button
knobs are of hard moulded black plastic and the rotary knobs are centre collet
fixing (for perfect positioning and for not coming loose) in a rather pleasing
matt black finish. The rear trims are aluminium faced with matt white PVC upon
which the connector details are printed using a scratch resistant vinyl solvent
ink. Non-staining soft plastic feet are fitted to the bottom.
Specification
Power Output
(from Loudspeaker Sockets):
8 Ω Loads
: 45 W RMS per channel (90 W from both
channels simultaneous operation)
16 Ω Loads
: 35 W RMS per channel
4 Ω Loads
: 50 W RMS per channel
Headphone
Output: 600, 300 and 8 Ω (from TRS jackk
socket on front panel, fed via an attenuator network from the loudspeaker
circuits)
Tape
Recorder Outputs: '
DIN 5 Pin :
200 mV / 100 k Ω
Harmonic
Distortion: less than 0,1% into 8 Ω at 1
kHz (just prior to clipping)
Output
Impedance: 0,2 Ω (in series with 10,000
µF)
Frequency
Response: 30 Hz - 20 kHz ±1 dB
Power
Response: 15 Hz - 35 kHz (at constant
input level the output is -3 dB relative to 45 W at 1 kHz)
Load
Stability: Unconditional (reactive loads
such as electrostatic loudspeakers will not cause malfunctioning of the power
amplifier section)
Input
Selection: Disc 2; Dosc 1; Radio; Tape
1; Tape 2
Input
Connections: by 5 pin DIN sockets on the
rear panel
Input
Sensitivity (ref. To 25 Watt output level, 8 Ω loads):
Disc : 2,5 mV/47 k Ω
Radio : 100 mV/180 k Ω
Tapes : 100mV/200 k Ω
Signal-to-Noise
Ratio:
Disc Input
: 75 dB
Aux, Radio,
Tape : 85 dB
Disc
Equalization: to BS1928 i.e. RIAA
Filter
Controls
Low : 70 Hz / 12 dB per octave
High : choice of 4, 7, 10 kHz / 18 dB or 6 dB per
octave
General
function
Mains Supply
Required: 110 - 120 - 220 - 230 - 240 V AC 50/60 Hz (set by
adjustment on transformer)
Dimensions
(W x H x D): 400 x 130 x 290 mm
(15,8" x 4,9" x 11,4")
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