Symetrix 421m User Manual Download Page 15

Page: 15 / 22

421m

Specifications

Chapter 7

Connectors
Line Inputs 1/4" TRS jack and screw terminals,

20k Balanced Bridging

Mic Input

XLR-female, 10k Balanced Bridging

Outputs

XLR-male, screw terminals, 200 Ohm Source

Impedance, Differentially Balanced, +23 dBm maximum level

TS phone, Unbalanced, +18 dBm maximum level

Bypass

Relay controlled, hard-wire bypass in power off

and bypass conditions

Sidechain

TRS phone, Unbalanced Send and Receive,

1000 Ohm Source Impedance, 10k Input Impedance

Tip=Receive, Ring=Send

Downward Expander
Ratio

1:2

Threshold

-50VU (bypass) to -20VU (Auto Threshold)

Attack Time

1 ms

Release Time

Program dependant, 0.3 - 3.5 seconds

depending on amount and duration

AGC-Leveler
Ratio

1:1 to 4:1

Auto Release Threshold

-70 dBu to -30 dBu

Attack Time

approximately 1 ms

Release Time

Program dependant, 500 ms - 5 seconds

depending on amount and duration

Target Output
Range

+20 dB

Peak Limiter Ratio

10:1

Threshold

-15VU to +23VU (bypass)

Attack Time

1 ms for 90% gain reduction

Release Time

0.8 seconds

421m Architects and Engineers Specifications

The Automatic Gain Control (AGC) shall be a single channel model that reduces the dynamic range of wide range, wideband audio signals, providing
peak limiting, downward expansion and bandpass limiting filters. The AGC shall occupy one rack space (1U).
The AGC shall be capable of controlling audio signals ranging from -70 dBu to +24 dBu and reducing their range by an input/output ratio ranging
from 1:1 to 4:1. The input/output ratio shall be adjustable via a front-panel control. Fast/slow response speed switching shall be provided to
accommodate speech and music sources. A target output level control shall be provided to shift the level of the output signal over a nominal

20 dB

range. The release time of the AGC shall be controlled by the presence of input signal and the signal sensor shall be capable of discriminating between
music/speech and random noise or pure tones. The threshold level of the signal sensor shall be adjustable via a front panel control and the presence of
signals above the threshold setting shall be indicated via a green LED.
The AGC shall also contain an integral peak limiter having at least a 10:1 ratio and adjustable threshold level. A green LED indicator shall be provided to
indicate peak limiter activity. The peak limiter threshold shall determine the absolute maximum output amplitude of the AGC-Leveler regardless of other
conditions.
The AGC shall also contain an integral downward expander having a 1:2 expansion ratio with threshold and release time controls. Furthermore, the
downward expander shall be capable of operating automatically via the signal sensor circuitry. A green LED indicator shall be provided to indicate
downward expander circuit activity.
Bandpass limiting filters shall be provided having a lowpass characteristic of 24 dB/octave at 6 kHz and a highpass characteristic of 12 dB/octave at 125
Hz. Both filters shall be capable of being used individually or simultaneously.
The AGC shall provide identical peak responding input and output level meters. These meters shall be capable of responding to signals ranging from -
54 VU to +12 VU (-50 dBu to +16 dBu). An output clipping indicator shall be provided.
The AGC shall provide facilities for stereo-coupling two units via a shielded 5-pin DIN male-to-male cable. A front panel switch shall designate which unit
is the master and which unit is the slave.
The line level inputs shall be active balanced bridging designs terminated with 1/4" TRS female and screw terminals. The mic level input shall also be an
active balanced bridging design using a three pin XLR female (AES/IEC standard wiring). The input circuitry shall incorporate RFI filters. The outputs
shall be active balanced designs having equal source impedances and terminated with 3-pin XLR (AES/IEC standard wiring) and screw terminals. A
separate 1/4" TRS jack shall provide an unbalanced output.
The balanced line level inputs shall accom24 dBu signals without distortion, and the balanced outputs shall be capable of deli23
dBm into a 600-ohm load. The mic level input shall accom8dBu signals. There shall be separate gain trim controls for the mic and the line
inputs and the mic input shall provide 48v phantom power.
Overall frequency response shall be 20 Hz to 20 kHz,

1dB, measured at +4 dBm output. There shall be no more than 0.02% harmonic distortion,

measured under the following conditions: +4 dbu input, +4 dBm output, BYPASS switch out, 1000 Hz. Residual noise output shall be no greater than -
90 dBm, measured with a 20 kHz noise bandwidth.
When the unit is inoperative (either by loss of power, or via the BYPASS switch), the inputs and outputs shall be wired together. There shall be no
transients transmitted to the output terminals during either turn-on, turn-off, or bypass operation (unless something upstream generates transients).
Access to the AGC’s sidechain shall be provided via a single ˘" TRS female connector. The ring connection shall be the sidechain output and the tip
connection shall be the sidechain return.
The AGC shall be capable of operating by means of its own built-in power supply connected to 115V nominal ac (105 to 130V) 50/60 Hz (230V
nominal, 210 to 260V ac, 50 Hz where applicable). The AGC shall be listed by Underwriters Laboratories Inc. (UL) or other equivalent nationally
recognized safety testing agency.
The unit shall be a Symetrix Incorporated model 421m AGC-Leveler.

Mic Preamp
Gain Range

+15 dB to +45 dB

Impedance

10k Ohms

Max Input Level

+8 dBu

THD+Noise (gain control fully clockwise)

-85 dBu

Phantom Power

48V (

CMRR

>80 dB (10 Hz - 20 kHz)