8
THEORY OF OPERATION
Opti-Source™ Option Card
Sheet 2 of 2
Refer to the Opti-Source Source Option Card schematic diagram, sheet 2 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.
U300 detects signal presence on the CH1 A source, if S1 [sheet 1 at C2] is in the
AUTO selection mode. U300A [D8] amplifies the source, while U300B, C [D7] comprise a
peak detector whose output goes low when the absolute value of U300A's output
exceeds about 1 volt. U300D [D7] provides adjustable time delay and hysteresis for the
detector output, which goes high when source activity is detected. This signal, SW1 [D1],
passed through D312, moves the signal selector U200 [sheet 1 at C3] to the A source
position. U302C, D [D5] provide the final processing needed to make the ramped current
drive needed for the fade in circuit on Sheet 1. U302D and Q300 [D5] perform voltage to
current conversion. U301 [A8], U302A, B, [A5/6] and Q301 [A5] provide the same function
for CH2.
Signals DRC1 [C8] and DRC2 [B8], coming from the source selectors U200 and U201
[B/C3] on Sheet 1, are presented to S4 [C4] and S5 [B5], respectively, so that they can
pass through or bypass the dynamic range compressor (U400 [B/C3], U401B [C4],
U402C [B3]). IF S4, 5 are set to ENABLE, the selected source is passed through the
Dynamic Range Compressor. The DRC provides up to 25dB of gain to low level signals,
gradually dropping back to 0dB gain for high level signals. This improves the audibility of
low level passages of CD quality, wide dynamic range source material. U400 contains
both the level detectors and current in/current out gain cells needed to turn op amps
U401B, 402C into a compressor. The compressor output passes through S4 and a buffer
stage before being returned to the AmPlus™ 100. Op amps U401C, A [C1/2] watch both
the signal level out of the compressor and the voltage on the compressor release
capacitors and drive a bi-color LED, D402 [C1]. When the compressor is active, the LED
glows green and brightens as the signal level and compressor action rise. If the level out
of the compressor approached its linear limits, the LED changes to red to warn the installer
that the source gain has been set too high.
Identical circuits handle CH2.
