5
SECTION IV
SECTION IV
SECTION IV
SECTION IV
ADA
ADA
ADA
ADA----101/R
101/R
101/R
101/R
Circuit Description
Circuit Description
Circuit Description
Circuit Description
The ADA-101/R 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 one input, six output monaural
amplifier or as a two channel, three 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. 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. U4:C and U4:D provide the
input to the B channel output drivers.
The input and gain stages are powered from ±15V supplies provided by VR1 and
VR2.
The output drivers are powered directly from the ±21V supplies.
