Model
A5
-12 Operation & Service Manual
A5-12 Manual A5 21 January 2005
Page 8
The input amplifier is very similar to an output amplifier module, except variable
gain is provided. The gain control is VR1, which varies the transconductance of
TR6 and TR7. C12 provides high frequency compensation. The 50
Ω
output
impedance of the input amplifier provides a good match to the passive splitter,
PS1.
The main board is supplied from a 24V DC supply. An off board regulator
provides 18V. R41 and R42 set the voltage of the 18V supply.
U3 is the 12V regulator. U1 provides the 2.5V bias supply for the input amplifier
and all the output amplifiers.
The output fail circuit comprises RN1, D1 to D6, and TR11. If any of the output
present transistors in the output amplifiers are off, TR11 will turn on.
