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The meter LEDs are arranged in an 8x16 matrix, in rows and columns.
Each row of LEDs in the matrix has a 1/8 duty cycle ON time. The rows are multiplexed
at a fast rate so that the meters appear continuously illuminated. Via the serial port, the
DSP sends meter data values to the Z-180, which sends the appropriate LED control
words (8 bits at a time) to the data latches that drive the LEDs directly.
Component-Level Description
The meter LED matrix consists of ten 10-segment LED bargraph assemblies
(CR1-CR9, CR16) and one discrete LED (CR10). Row selector latches IC4, IC5,
IC6, and IC9 are controlled by the Z-180, and alternately sink current through the
LEDs selected by column selector latches IC1 and IC2, which are also controlled
by the Z-180. IC1 and IC2 drive the selected row of LEDs through current limit-
ing resistor packs RP1 and RP2.
Input Circuits
This circuitry interfaces the analog and digital audio to the DSP. The analog input stages
scale and buffer the input audio level to match it to the analog-to-digital (A/D) converter.
The A/D converts the analog input audio to digital audio. The digital input receiver ac-
cepts AES/EBU-format digital audio signals from the digital input connector, and trans-
mits them to the input sample rate converter (SRC). The digital audio from the A/D and
SRC is transmitted to the DSP.
1. Analog Input Stages
The RF-filtered left and right analog input signals are each applied to a resistor load and
a resistor pad. The load is enabled or disabled by a jumper that is positioned by hand.
The loaded and padded signal is applied to a floating-balanced amplifier that has an ad-
justable (digitally-controlled) gain. The gain is set by FET transistors and analog
switches. The state of the FETs and switches is set by the outputs of a latch. The control
circuits control the gain according to what the user specifies from the front panel con-
trols by writing data to the latch. The gain amplifier output feeds a circuit that scales,
balances, and DC-biases the signal. This circuit feeds an RC low-pass filter which ap-
plies the balanced signal to the analog-to-digital (A/D) converter.
Component-Level Description:
The left channel balanced audio input signal is applied to the filter/load/pad net-
work made up of L300, L301, L302, L303, R300-R305, R316, R317, C323 and
C326. J301 is a jumper that removes or inserts the optional 600Ω termination load
(R300) on the input signal. CR200-CR203 are protection diodes applied to the
padded input signal before it is applied to IC300, a differential amplifier. R306,
R307, R310-R313, FETs Q300-Q301, and quad analog switch IC307 make up the
circuit that sets the gain of IC300. The FETs, along with IC307, are used as
switches to change the resistive paths in the circuit. The state of the FET switches
is set by the outputs of digital latch IC303. The latch outputs feed IC306, a quad
comparator, which outputs 0V to turn on a FET and −15V to turn off a FET. The
control circuit writes directly to IC307 to control the state of the switches on
:
6-11
TECHNICAL DATA
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