Audio/Rf Block Diagram; Circuit Description; Audio Circuit Description; Audio Section - Shure SLX2 Service Manual

AUDIO/RF BLOCK DIAGRAM

Audio Input
(mic head)
IR
Photodetector
LCD
32.768
kHz
LCD
Driver
EPROM
Channel
Select,
Power Mute
LPF
AA Battery
Supply

CIRCUIT DESCRIPTION

AUDIO CIRCUIT DESCRIPTION

25A1090 (Rev.3)
User Gain
Pre-
Control Switch
emphasis
Tone Key
Microcontroller
Frequency
Synthesizer
control
RF Muting
RF
Pad
Amp
0-4 dB (Band
dependent)
+5V DC
Source
DC-DC
Converter

AUDIO SECTION

Audio enters the transmitter board through pin 4 of the mic-jack board connector (CON100).
Pin 2 of the connector provides 5 Vdc bias for the mic head. Pin 6 supplies the ground connec-
tion. The audio preamp (IC150-2) provides either 0 or 10 dB of gain (user switchable via
SW100). Capacitor C140 couples the signal into a pre-emphasis network formed by R140, R141,
and C141.
Next, the audio signal enters the patented Shure ARC™ processor. The main elements in this
section are the VCA (IC100-5) and the RMS Detector (IC100-4). The VCA, or Voltage Controlled
Amplifier, is a DC controlled amplifier. Following the VCA, the signal enters a 3-pole 17kHz low-
pass filter stage (IC100-2) that protects the RMS detector from energy above the audio band.
Next, the signal is coupled to the RMS detector (IC100-1), which converts it to a DC voltage. A
+1 dB increase at the input to the detector produces a +6 mV increase at its output. The detector
output is fed to the compression threshold stage (IC150-2). This stage provides the transition
from uncompressed to compressed signal. At low levels, the audio is uncompressed because
diode D169 is turned off. As the AC level increases, the output of IC150-2 decreases enough to
turn the diode on. As D190 conducts, the compression ratio changes from 1:1 to 5:1. Once D190
is turned fully on, the audio compression ratio remains fixed at 5:1. An additional diode in the bias
Deviation Trim
and Tone Key
2-pole,
Sum Amp
17kHz,
VCA
LPF
Limiter
RMS
Detector
Compressor
Audio Muting
RF
Pad
Amp
0-4 dB (Band
dependent)
4
VCO (Carrier
Range)
Loop
Filter
Frequency
Synthesizer
16
MHz