ATI L1000-1 User Manual

Download

L1000

DUAL LINE AMPLIFIERS

OPERATION AND MAINTENANCE MANNUAL

audio.com

DESCRIPTION

The IC’s that were 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 symmetrical high slew 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 designs. This chip incorporates a low noise input stage designed for excellent noise performance even with low source impedances and eliminates the necessity for touchy high ratio 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, 100dB open loop gain and 50 MHz gain bandwidth product make this an ideal device for highest quality audio. The absence of Transient Intermodulation Distortion may be detected by 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 amplifiers, a minimum of 40dB of loop gain is available for 100: 1 distortion reduction even at 20kHz.

The high output swing capability allows the amplifier to use a simple, low distortion, flat response, 1 - 1 output transformer. ATI provides two models of each; Transformer balanced outputs (with faraday interwinding shields) for high RF field environments, and an active balanced output version (bridge circuit) for low RF environments where balanced output lines are required for hum rejection.

Inaudible crosstalk characteristics allow use for either stereo or dual monaural applications. Dual gain controls are provided to facilitate either mode of operation.

audio.com

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 circuitry.

INSTALLATION

MOUNTING

Your amplifier may be desk mounted on its non-slip suction cup feet or you can stack the amplifiers on top of each other. Rack mount system 21075-501 mounts two units in one rack

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 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 rear panel. Run strap to within a few inches of the chassis and jump to the chassis ground with shield braid.

Line inputs are connected to the rear screw terminal strip following the rear label designations. G1 is the CH1/Left Ground, G2 is the CH2/Right ground. If grounding input and output shields at the MICRO"P, use the proper ground for each channel.

The L1000 will accept input audio to +24dBm bridging (12.5 Vrms). Inputs are protected by clamping diodes for signal swings exceeding ±41 Vp-P.

Output wiring is indicated on the rear panel label. H1 outputs are in phase with each other and with the input signal.

Transformer Output MSCROAMPS (L1000-1) may have either HI or LO outputs grounded (but not both).

audio.com

ADJUSTMENTS

The amplifier has sufficient gain and output capability to overdrive some console inputs, particularly those providing preamps for high-level input channels. A -1 0dBm line input will provide +8dBm output from the amplifier with the gain pot to approximately 2 o'clock. 12 o'clock is approximately 0dBm output and 10 o'clock is -10dBm output (unity gain).

The common mode adjustment pots R1 6 and R35 are factory set to an 80dB null at 60Hz If disturbed, they can be readjusted by applying a common mode 60Hz input to HI & LO input together referenced to ground and renulling R16 for CH 1/L and R35 for CH 2/R. The null drops to 40dB at 20kHz due to slightly unequal; roll offs in the input RF bypass capacitors.

MAINTENANCE NOTES

Power supply voltages are +/- 18VDC nominal, dropping to +/- 16VDC under full output. 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.

IC output DC voltages (no signal conditions) should measure OVDC +/- .5VDC. Significant deviation indicates IC or circuit problem. Measurable DC difference between +/- amplifier inputs (other than due to meter loading) indicates IC failure.

MODIFICATIONS - 230 VAC OPERATIONS

Your L1000 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.

audio.com

PERFORMANCE SPECIFICATIONS

OUTPUT CLIPPING LEVEL +22dBm /600 ohms

DISTORTION @ +20dBrn output and input levels to +24dBm

FREQUENCY RESPONSE +/-.25dB, 50 to 20,000 Hz -1 dB at 20 Hz

.2% maximum THD, 30 to 20,000 Hz

INPUT IMPEDANCE Balanced differential inputs, 30,000 ohm

bridging

EQUIVALENT INPUT NOISE 3.5 Microvolts 20kHz measurement bandwidth 600 ohm source impedance

HUM REJECTION 80dB for common mode hum

INPUT OVERLOAD +24dBrn bridging 600 ohms

GAIN 34dB, front panel adjustable

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

SIZE 8-1/2" W x 1-3/4" H x 7" D, 2-1/2 lbs.

MOUNTING Suction feet for non-slip desk mounting. Rack

mount system 21075-501 mounts two units in one rack

audio.com

ATI L1000-1 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual