Shure M625 Schematic

222 HARTREY AVE.. EVANSTON. IL. 60204 U.S.A.

AREA CODE 3121866-2200 . CABLE: SHUREMICRO

TWX: 910-231-0048 TELEX: 72-4381

DATA

SHEET

MODELS

and

M625AM VOICEGATE@

~625

Model

DESCRIPTION

The Models M625 and M625AM Voicegate are designed to reduce the effects of background noise in microphone installations by controlling the gain of each microphone input channel in response to the level of its input. When the input is below an adjustable trigger level, the gain of the microphone

channel is reduced; an increase above this trigger level quickly raises the gain to unity. The principal use of the Voicegate is in sound-reinforcement systems and multiple-microphone recording applications, such as conference rooms. In such cases, a Voicegate associated with each microphone will assure that only those microphones intentionally in use will contribute their outputs to the system. The gain of those channels with microphones sensing only background noise

(below the Voicegate trigger level) will be reduced,

thereby improving the signal-to-noise ratio for the overall system.

The Model M625 Voicegate is designed to operate

from a 108-132 volt,

50160 Hz power source.

One Voicegate is required for each microphone and

associated mixer input in the system. One ac-operated

M625 Voicegate will provide power for up to three

additional

M625AM Voicegates, which are identical to

the M625 but do not have self-contained power

supplies.

Features include:

Control circuit which is especially sensitive to voice

signals.

Internally selectable attenuation of background noise in steps of 6, 12, and 16 dB.

Fast attack time for quick response to initial sounds.

Wide, flat frequency response.

Front-panel sensitivity control for adjusting input

signal trigger level.

Hold time adjustable from under M second to over

minute by front panel control.

Gate switch to defeat Voicegate action when de-

sired.

Gate light emitting diode (LED) lamp to indicate

when input signal is above trigger level.

Power "On-Off" switch and pilot light (M625 only).

Female (input) and male (output) professional three-

pin audio connectors with low- or high-impedance

selector switches.

Low hum, noise and RF susceptibility.

Provisions for rack mounting in groups of one to

four on accessory 8.9 cm

power for three

M625AM Voicegates supplied by

(3% in.) rack panel with

one M625 unit.

Model

M625AM

Listing by Underwriters' Laboratories, Inc.; and by Canadian Standards Association as certified

(M625

only).

SPECIFICATIONS

Test Conditions (unless otherwise stated): Power switch ON. Lo-Imp. Mic. lnput through 150 ohms.

Hi-Imp. Mic. lnput through 33k ohms. Lo-Imp. Mic. Level Output terminated with Ik ohms. Hi-Imp. Mic. Level

powel +30 Vdc and

Out~ut terminated with 33k ohms.

Vdc (M625AM) or 120 Vac,

60 Hz (M625).

Gain

(input above trigger level or Gate switch OUT):

Output

Mic.

Input

Lo-Impedance Hi-Impedance

Lo-

Impedance

0.5 k 2

-23.0

Hi-

lmpedance

22.0

-0.5

Gain is 16 dB (may be changed internally to 12 or 6 dB) lower when input is below trigger level and Gate

switch is set to IN.

Frequency Response:

Flat

dB, 40 Hz to 20 kHz.

Hum and Noise, Maximum:

Equivalent lnput Hum and Noise, Lo-Imp. Mic., 150ohm source, 20 kHz noise bandwidth, 20 Hz lower

cutoff: 124 dB below 1 volt.

Equivalent lnput Noise, Lo-Imp. Mic., 150-ohm source, 20 kHz noise bandwidth, 300 Hz lower cutoff: 127 dB

below 1 volt.

lnput Trigger Level

Lo-Imp. lnput adjustable from -62

-96

dBV (16 p.V).

(at 1 kHz):

dBV (790 pV) to

Hi-Imp. lnput adjustable from -40 dBV (10 mV) to

-74

dBV (200 p.V).

Attack Time:

4 msec (typical)

Hold Time:

Adjustable from approximately 0.25 sec. to 45 sec.

Total Harmonic Distortion:

0.5% maximum THD at 2 kHz, at -10 dBV (320 mV) Hi-Imp. Mic. Level Output or -32 dBV (25 mV) Lo-Imp.

Mic. Level Output.

lnput Clipping Levels, Minimum:

Lo-Imp. Mic.: -28 dBV (40 mV) Hi-Imp. Mic.:

dBV (500 mV)

27A1087

1978,

(RJ)

Shure

Brothers

Inc

Printed

U.S.A.

107

(4-7/32 IN.)

FIGURE

OVERALL DIMENSIONS

Phase: Gate Switch:

Corresponding pins of Input and Output connectors are in phase.

Impedances:

Input Designed for Use With Actual Impedance

Lo-Impedance Balanced or unbalanced 25 to 680 ohms f25%

Hi-Impedance Unbalanced IOk to 50k ohm 130K ohms f 25%

Output Designed for Use With

LO-Impedance Balanced or unbalanced 25 to 600 150 ohms i15% Hi-Impedance Unbalanced

600 ohm microphones balanced

microphones unbalanced

Actual

Impedance

ohm microphone level circuits unbalanced microphone level circuits unbalanced

IOk to 50k ohm 2k ohms 215%

Temperature Range:

Operating: Storage:

-7OC to 57OC (20°F to 135OF)

-2g°C to 710C (-200F to 160°F)

Weight:

M625: 1.93 kg (4 Ib, 4 oz) M625AM: 1.48 kg (3 Ib, 4 oz)

Dimensions:

See Figure 1

Operating Voltage and Power:

Ac Operation:

M625: 108-132 volts, 50/60 Hz, 3 watts

Dc Operation:

30 volts

&20%, 5.5 mA, and 9 volts

+35%, 20 mA

with Gate lamp illuminated (M625AM and M625).

CONTROLS AND CONNECTORS Hold Time:

The Hold Time control sets the period of time that the Voicegate maintains unity gain after the input signal drops below the trigger level. At minimum (full

counterclockwise) position, it sets the hold period to

approximately

'/4

second; at maximum (full clockwise)

With the Gate switch set to the OUT position, the gain of the Voicegate remains constant at unity and the Gate lamp turns on. In the IN position, the Voicegate performs its normal gain control function and the Gate lamp flashes intermittently.

Power Switch and Pilot Light

The Power On-Off switch controls the ac power

applied to the M625 and the dc power supplied to all

M625AM units connected to the M625. The pilot light is illuminated when the ac power is connected to the M625 and the Power switch is in the ON position.

Microphone Input:

The microphone input is designed for low-impedance

(balanced or unbalanced) microphones with 25 to 600

ohms impedance or high-impedance (unbalanced) dynamic, ribbon, or condenser microphones. The unit is not recommended for use with crvstal or ceramic

microphones. The microphone impedance is selected by a slide switch above the Microphone lnput receptacle on the rear panel. The input receptacle is a professional three-pin audio connector (female).* See

Figure 2 for low- and high-impedance microphone

input plug connections.

NOTE:

some condenser microphones produce very

high output signals which may overload the input. Use of an attenuator (such as the Shure A15A In-Line Low-Impedance Microphone Attenuator) will improve this situation.

Microphone Level Output:

The microphone-level output is available at the receptacle labeled Mic. Level Output on the rear panel. It is a dual-impedance output, either low-impedance or high-impedance unbalanced, as selected by the switch above the receptacle. The low-impedance output will drive either a balanced or an unbalanced microphone

input.

position the hold time is approximately 45 seconds.

Sensitivity:

The Sensitivity control sets the level at which the

input signal triggers the control circuit to increase the

Voicegate gain to unity. With a high-impedance input,

the trigger level may be varied from approximately -40

MICROPHONE MIC. INPUT MICROPHONE MIC. INPUT

LOW IMPEDANCE (BALANCED LINE1

MICROPHONE INPUT PLUG CONNECTIONS

dBV (10 mV) with the Sensitivity control at 0 (fully counterclockwise) to -74

trol set to 10. Corresponding levels for the

pedance input are -62 dBV (790 pV) at 0 and dBV (16 pV) at 10. The Sensitivity control is adjusted by observing the Gate lamp. The Gate lamp will be illuminated when the input signal is above the control

circuit trigger voltage as adjusted by the Sensitivity

control, and will turn off quickly when the signal drops below this level. The Sensitivity control should be

dBV (200 pV) with the con-

low-im-

-96

MIC. OUTPUT

LOW

(BaANCED LINE) (UNBALANCED LINE

MICROPHONE

INPUT AND OUTPUT CONNECTIONS - FIGURE

adjusted so that the lamp is off when only background

noise is entering the microphone, and turns on reliably when actual speech is present.

Designed to mate with Cannon

(Q.G.)

series or equivalent connector.

IMPEDANCE

OUTPUT

(M625):

SHIELD

1-,----

HIGH

IMPEDANCE

MIC. OUTPUT

HIGH

LOW

PLUG

CONNECTIONS

series, Switchcraft

--,'

SHIELD

IMPEDANCE

)

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