ATI L1000-1 User Manual

L1000

DUAL LINE AMPLIFIERS

OPERATION AND MAINTENANCE MANNUAL

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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.

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