7
THEORY OF OPERATION
Opti-Source™ Option Card
Introduction
Refer to the Opti-Source Source Option Card schematic diagram, sheet 1 of 2 for the
following information.
Note: The designators inside the brackets “[ ]” are the schematic grid coordinates which
are provided in order to make it easier to locate components on the schematic sheet
indicated in the description.
This card accepts a pair of line level sources at its CH1 and CH2 "B" inputs. It allows
automatic or manual selection of the A (supplied by the AmPlus™ 100) or B sources,
passes them optionally through a dynamic range compressor, and returns the signal to the
AmPlus signal path.
Sheet 1 of 2
The CH1 and CH2 "B" Inputs at J1 [C8] accept line level sources. U1A, B [B/C8] are
unity gain, differential input amplifiers, with inputs well protected against RF and ESD.
With S3 [B6] in the 2 CH position, each op amp sends its output through a TRIM
potentiometer (R1 [C7], and R2 [B6]) into a fade in circuit. When S3 is in the MONO
position, the CH1 B input is steered forward to both CH1 and CH2 paths, in mono.
U1C, D and U102A, B [B/C6] constitute a two channel fade in circuit. When S1, 2
[B/C2] are in the AUTO selection mode, circuits on Sheet 2 detect when the sources
connected to the A inputs at J1 on the rear of the AmPlus 100 amplifier become active.
When A is active, it will override the selection of the B input, turning B off and A on. When
A becomes inactive, the fade in circuit slowly fades the B signal back up to full volume
and switches from A to B. When S1, 2 are in the manual selection mode, switches external
to the AmPlus 100 force selection of the A or B sources, independently for CH1 and CH2,
if desired. The fade in circuit incorporates a transconductance amplifier in the feedback
path of a non-inverting op amp stage. As long as the currents IABC1 [D1] and IABC2
[A1] into U102 [C6] and [B6] are essentially off, there is only the negative feedback
provided by R115 [C6] and R121 [B6], and the stage gains are normal. When IABC
ramps up, U102 turns on and provides additional negative feedback, reducing the stage
gain by 20 or 30dB, fading the B input.
U200 [C3] and U201 [B3] are selector switches for the CH1 and CH2 A, B signals. The
CH1 selector, U200, can select among sources A left (CH1), B left (CH1), A mono
(CH1+CH2), and B mono (CH1+CH2). U201 behaves similarly for CH2. J3, A/B
REMOTE Connector [C1], accommodates two SPST normally open selector switches
(located on the Zone 2 Remote Volume Controls) that can be placed near the system
operator to allow manual selection between A and B sources.