Cooper M1000 Operating And Maintenance Manual

audio.com

M1000

DUAL MICROPHONE AMPLIFIER

OPERATING AND MAINTENANCE MANUAL

audio.com

DESCRIPTION

This section is strictly written to boost the designer’s ego by letting him tell you of

some of the clever things we have done inside the MicroAmp. It may be skipped

by anyone having anything better to do.

For many years engineers (ourselves included) have been using operational

amplifier ICs in audio circuitry. These ICs, developed primarily for the

instrumentation market, had many shortcomings when used in high quality audio

applications. The lack of audio related specifications, crossover distortion, high

noise for low source impedances, limited output capability and limited gain

bandwidth product forced many compromises when used in high gain audio

systems. High ratio input transformers, output boost stages and multiple stage

designs were all used to compensate for op amp deficiencies and in turn added

additional response and distortion problems of their own.

Walter Jung in a definitive series of articles' analyzed and defined slew rate

induced distortion mechanisms, tested many commonly available ICs and

correlated various distortion tests with subjective (listening) criteria. A very

significant result of his efforts was the identification of an IC originally developed

for the European professional audio market which has almost ideal

characteristics for audio use and in particular provides a high rate capability of 13

volts /microsecond, virtually eliminating slew induced Transient Intermodulation

Distortion. By contrast the old standard 741-op amp has a slew rate of only

.6V/microsecond.

This op amp is now available from several U.S. Manufacturers in single and dual

versions and forms the basis for our MicroAmp designs. This chip incorporates a

low noise input stage designed for excellent noise performance even with low

source impedances thus eliminating the necessity for touchy 1:20 input step up

transformers in the M1000. High output capable of driving 600 ohm loads directly

to +22dBm with total freedom from crossover distortion, high inherent linearity,

100 dB open loop gain and 50Mhz gain bandwidth product make this an ideal

device for highest quality audio. The absence of Transient Intermodulation

Distortion may be detected in the smooth effortless high frequency output

capability, the absence of the harsh, raspy sound typical of IC amplifiers driven to

full output at high frequencies and the freedom from increasing harmonic

distortion vs. frequency. As used in the MicroAmp a minimum of 40 dB of loop

gain is available for 100:1 distortion reduction even at 20 kHz.

The high output swing capability allows the amplifier to use a simple, low

distortion, flat response 1:1 output transformer. ATI provides three models of

each MicroAmp; Transformer outputs (with faraday interwinding shields) for high

RF field environments, a balanced differential output stage version (bridge circuit)

for low RF environments where balanced output lines are required for hum

rejection in long runs and the minor performance degradations of an output

audio.com

transformer are not desirable and a simpler, lower cost single ended

(unbalanced) output stage version with full +22dBm, 600 ohm drive capability for

use in low RF environments for short line runs.

Inaudible crosstalk characteristics allow use of the M1000 for either Stereo or

Dual Monaural applications. A dual concentric gain control is provided to facilitate

either mode of operation. Only minimal coordination is requited to grasp both

concentric knobs simultaneously for stereo use.

Our power supply incorporates a couple of unique regulating devices called

zener diodes. In contrast to most fancy three terminal IC regulators, these

devices will live through line transients and simultaneously protect your

expensive circuitry.

INSTALLATION

Your MicroAmp may be desk mounted on its non-slip suction cup feet and left out

for everyone to see since it's so pretty. You can stack the amplifiers on top of

each other. We don't recommend stacking more than 30 high on a desk since it

is difficult to reach the top.

Rack mounting kits are available for your amplifier. P/N 20021-501 mounts a

single MicroAmp in 1-3/4" of vertical rack space. P/N 20024-501 mounts two

amps side-by-side in 1-3/4 inches.

MicroAmp mounting kit P/N 20090-501 allows a MicroAmp to be mounted under

a desktop or behind a cut out.

WIRING

Our insurance company insists on three wire grounded plugs. The third wire

ground can cause a ground loop with your station ground. If you are sure your

station ground will provide adequate protection to personnel in case of an AC line

short to the chassis, a 3 to 2 AC line adapter can be used to isolate the power

line ground. We recommend that the adapter be removed and the power line

ground reconnected prior to any service work requiring removal of the station

ground connection from the MicroAmp chassis.

The four inch copper strap which you are of course using for your station ground

is not going to fit around the #6 chassis ground screw on the MicroAmp rear

panel. Run strap to within a few inches of the chassis and jump to the chassis

ground with shield braid.

audio.com

Microphone inputs and outputs use XLR type connectors and require mating

plugs. The applicable input plugs are Switchcraft A3M or equivalent. The output

plugs are Switchcraft A3F or equivalent. Mike wiring is conventional, hi (in phase)

to pin 2, Lo (out of phase) to Pin 3, Shield to pin 1. Either 150 ohm or 50-ohm

microphones can be connected to the MicroAmp without modification.

The MicroAmp M1000 will accept microphone outputs up to 125 mVrms (-14dBm

available power/150 ohms) without distortion.

Output wiring is indicated on the rear panel label. HI outputs are in phase with

each other and with the input signal.

Transformer Output (M1000-1, L1000-1) may have either HI or LO outputs

grounded (but not both).

CAUTION: Balanced differential output (M1000-2, L1000-2) has active drivers for

both HI and LO outputs terminals. DO NOT GROUND either HI or LO terminals.

To drive an unbalanced (one side grounded) Load, connect it between HI and

GND terminals and let the LO terminal float. Two separate 600 ohm unbalanced

loads can be driven from each output without interaction by connecting one

between HI and GND and the other from LO to GND. The two loads thus driven

will be out of phase with each other. Individual grounds are provided for CH l/left

and CH 2/right outputs.

ADJUSTMENTS

The MicroAmp has sufficient gain and output capability to overdrive some

console inputs particularly those providing preamps for high-level input channels.

A -50dBm available power microphone output (2.5 mVrms) will provide +8dBm

output with the gain pot set to two o'clock position. 12 o'clock is approximately

OdBm and 10 o'clock is -10dBm output. Operation with the MicroAmp pot set

below 10 o'clock position degrades noise performance and a fixed attenuator pad

should be placed between the MicroAmp output and the Console input to allow

MicroAmp operation at around 2 o'clock.

MAINTENANCE NOTES

Power supply voltages are + and - 18 VDC nominal, dropping to +/16 VDC under

full output. Maximum allowable voltages are +/- 22 VDC (limited by IC). If zeners

are replaced, remove Al, A2, and A3 ICs and check output voltage before

plugging ICs back into the circuit. Remove power when inserting or removing

ICs.

audio.com

IC output DC voltages (no signal conditions) should measure 0 VDC +/- .5 VDC.

Significant deviation indicates IC or circuit problem. Measurable DC difference

between +/- amplifier inputs (other than due to meter loading) indicates IC failure.

Five to ten years hence, replace aluminum electrolytics in power supply.

Keep 250 W soldering guns out of the MicroAmp.

If hit by lightning, replace Al through A3.

MODIFICATIONS

230 VAC OPERATION

Your amp is wired for 115 VAC 50/60 Hz operations unless otherwise requested

at the time of ordering. It can be modified for 230 VAC use by removing the

Power transformer primary jumpers W1 and W3 and inserting a jumper in the W2

holes.

150-OHM OUTPUT IMPEDANCE

Transformer output M1000s are converted to drive 150 ohm audio lines by

removing jumpers W4 and W5 located adjacent to output transformers T3 and T2

respectively. Insert two new jumpers for each output transformer between the

original jumper terminals and the empty terminals immediately adjacent to and in

line with the original terminals in order to parallel the secondary windings.

Balanced differential output and single ended output will drive 150 ohm loads

without modification but will current limit before full supply swing is reached.

INPUT CENTER TAP

The center taps of the input transformer primary are available on the PC board

next to the transformers and are labeled CT. They may be grounded by adding

jumpers between each CT point and the adjacent empty holes.

INCREASED GAIN

Additional gain can be provided for low output boom mikes by raising feedback

resistors R21 and R40 (M1000-1, -3) from 220K to 680K ohms (10 dB increase).

The M1000-2 requires that R21 and R40 be increased to 330 K ohms and also

R45 and R49 be increased to 820 K ohms for a 10 dB gain increase.

audio.com

SPECIFICATION

GAIN 71dB minimum

MAXIMUM INPUT Microphone: -16dBm, 125mVrms

MAXIMUM OUTPUT +22dBm/600 ohms (M1000-1, -1P).

+24dBm/600 ohm (M1000-2, -2P)

NOISE OUTPUT 124dBm EIN with 150 ohm source and 20kHz

measurement bandwith. Yields 74dB S/N ratio

with -50dBm microphone input.

INPUT IMPEDANCE Microphone: 150 ohm source, 2500 ohm input

transformer isolated

DISTORTION .1% maximum THD at +20dBm output and

input levels from -52 to -18dBm, 30-20,000Hz.

SLEW RATE 13 Volts per microsecond for minimum TIM

CROSSTALK -70dB maximum at 10kHz.

HUM REJECTION 80dB for common mode hum.

PHANTOM POWER +48VDC at 4MA through 3,300 ohms and

center tapped input transformer. Switch

controlled.

POWER 115/230VAC +/- 10%, 47-63Hz, 10VA.

DIMENSIONS in. (mm) 8.5 (216) W x 1.75 (44.5) H x 7 (178)

D, 4lbs, ( .176Kg).

MOUNTING Suction feet for non-slip desk mounting. Rack

mount kits; 20021-501 mounts a single

centered unit, 20024-501 mounts two units

side by side.

CONNECTORS XLR type in and out

WARRANTY Limited, One Year Warranty

Cooper M1000 Operating And Maintenance Manual

Other documents