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The harmonic distortion of the 2707 is very low (Fig.4.2) mainly because
of the separate power supplies to preamplifier and output stages, and the
use of direct coupling.
The power output transistors (four NPNs Type 2N5302 and four PNPs
Type 2N4399) are each protected by a fast-acting 5 A fuse. Power transistor
failure resulting in a short circuit emitter-to-collector will blow the fuse and
light the yellow TRANSISTOR warning lamp. The amplifier design is such
that faulty output transistors do not affect the operation of the remaining
output transistors.
Peak current limiting circuitry is arranged to provide limiting of
instantaneous positive and negative output current peaks. The limiting value
can be adjusted independently for positive and negative peaks. It is set up to
limit at 40 A. Current limiting is indicated by the CLIPPING lamp.
34
RMS
Output
Current
0
- - 4 0 H
z
- - -
1 kH
z
- · - 10
kHz
0
10
11
12
13
14
15
16
17
18
19
20
21
Clipp ing Limited RMS Output Voltage
271 170
9
Fig.4.5. Clipping Limited Output
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