ATI Audio DA2008 Руководство по эксплуатации и техническому обслуживанию - Страница 2
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DESCRIPTION
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 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 slew rate capability
of
13
volts/microsecond,
virtually
eliminating
slew
induced
Transient
Intermodulation Distortion. By contrast the old standard 741op 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
an input stage designed for excellent noise performance with a wide range of
source impedances thus eliminating the necessity for input step up transformers.
An output stage capable of driving 600 ohm loads directly to +22dBm with total
freedom from crossover distortion, high inherent linearity, 100dB 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 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
MICROAWPT" a minimum of 40dB of loop gain is available for 100: 1 distortion
reduction even at 20kHz. All program audio stages in the Distribution Amplifiers
use this unique device in its' dual version (NE5533).
INPUT
Input audio feeds a unity gain balanced differential high slew rate, Bi-FET input
buffer stage, which presents 30,000-ohm bridging impedance to the source. The
inputs are protected from over voltage inputs by clipping diodes. Dual bypass
capacitors protect the inputs against common mode RF pickup. Balanced
potentiometers (R15, R16) allow setting a precise null for common mode hum
inputs.
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