Circuit Description
The 6600R consists of two identical input circuits and two identical groups of three output
circuits. A jumper (H1) permits the two output channels to be both connected to one input
channel for use as a 1 input, 6 output monaural amplifier or as a 2 channel, 3 output per
channel stereo amplifier.
Since both input amplifiers are the same only the A channel will be described.
The differential input signal is applied to the inverting inputs of U3:A and U3:B. An
inverted version of the common mode signal (if any) is also applied to these inputs from
U7:A such as to cancel any common mode component at the outputs of U3:A and U3:B.
The outputs from U3:A and U3:B are then applied to the differential amplifier, U7:B.
Optimum common mode balance is achieved by adjusting RV6 at the output of U7:A.
The output from the differential amplifier passes via the gain control potentiometer, RV1,
to the variable gain amplifier, U6. U5:A inverts the second input to U6. U6 provides gain
adjustment under control of the front adjustment potentiometer, RV5, or via a remote
control voltage from the rear panel (output B4). The variable gain amplifiers in each
channel are controlled by the same control voltage from U15. The circuitry associated with
U15 scales the control voltage and also provides temperature compensation for U6. The
balance potentiometer, RV2, is not used with the "T" version of the SSM2018.
The output from U6 is connected to the first group of four output amplifiers and also to
the MONO/STEREO selector, H1. IC U4:A provides the un-inverted signal to the non-
inverting output drivers, while U4:B provides an inverted signal to the inverted output
drivers. The A channel drivers are contained in U1 and U12 while the B channel drivers
are contained in U2 and U13. IC U4:C and U4:D provide the input to the B channel
output drivers.
The input and gain stages are powered from ± 15 V supplies provide by VR1 and VR2.
Model 6600 Analog Audio DAs and Frame
6600-8
