ATI Technologies DA1000 Manuale operativo e di manutenzione - Pagina 2
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DESCRIPTION
The 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 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 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 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,
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 input buffer stage (Al), which
presents 30,000-ohm bridging impedance to the source. The inputs are protected from
over voltage inputs by clipping diodes (CR4-CR7). Dual bypass capacitors (C7, C29 and
C8, C39) protect the inputs against common mode RFI pickup. A balance potentiometer
(R9) allows setting a precise null for common mode hum inputs.
SIGNAL PRESENT INDICATOR
The second half of Al monitors the voltage at the output of the input buffer IC. The green
Signal Present LED on the front panel will light for audio inputs over -30dBm. The LED
will normally flicker with applied program material to tell you that all is well. (Happiness
is a green LED).
Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [email protected] │ www.atiaudio.com