72
cross-over located on board #3. This is set in software so that discrepancies between the cross-over
sections can not occur. Since these cross-over designs are phase linear, using one or more of them has
little or no effect on the overall group delay to the audio signal. Thus, maintaining good sonic
integrity to the system.
FEEDBACK PROCESSING OPTION
On circuit boards #3 and #6, the lower two bands can be set to operate as feed-back processors
instead of the stock feed-forward setup. Some processing applications call for an added density to the
quality of the signal. This is usually at the expense of some quality or clarity. This option is easily
accomplished by the changing of jumpers located on the #3 and #6 circuit boards. Setting of these
jumpers should be done on a subjective basis. Generally changing the limiter options will provide
more dramatic effect to the audio signal. Once changed, it may require re-adjustment of the system to
achieve the desired sound.
The output of the jumpers feed the processor sections. U209 and U210 comprise the digital dynamic
level adjusting section. Single bit digital data appears at U209 to affect any level changes needed.
U215, U216, and associated components (R220-R222, C204-C206) form gentle third order filters to
perform critical reconstruction of the audio signal.
U211 - U214 are used as mixing controls to mix the relative audio bands with each other. For board
#3, these act as both EQ and individual band drivers for the following limiter sections. For board #6,
these act as the final spectral mix for the following clipper/filter section.
Both the #3 and #6 boards provide two forms of output for the audio signal. U217A/B provides both a
summing and balancing function so that wideband balanced audio can be provided. This is used for
the balanced output on patch-point #2 to feed any ancillary processing equipment. On board #6, the
summed unbalanced output of U217B provides the output signal to the following clipper/filter. The
individual buffered outputs are used on board #3 to drive the individual following limiters of board #6
when the system is used in the normal stock configuration.
Clipper/ NRSC Low Pass Filter
Circuit Board #8
Input audio appears at pins 7 and 5 respectively for the left and right channels. U601 is used as an
adjustable voltage divider to provide drive/attenuation for the clipper section. It is setup to p/-
5dB of clipping. U602, R530, R531, C519, and C520 form the pre-emphasis options for the system.
Through the usage of jumpers J1 and J2, the modified 75 µs NRSC pre-emphasis boost is created.
The output of the pre-emphasis section feeds the “MR GIBBS MODULE”. Here is where the
magic
takes place! Within this module, loudness clipping and distortion control are performed. Without
writing a detailed technical thesis on overshoots and specific physical phenomenon, just understand
and accept that here is where the system is trying to fool the ear into accepting more distortion than it
would normally notice.
