Sierra Video 10 Series - Manual (Page 19)

SIERRA VIDEO
13
Audio Modules
Introduction
The 501026 is a high performance fully differential distribution amplifier designed for
demanding applications. Using surface mounted components to increase density, each
board is capable of driving 10 separated outputs with user adjustable gain range of –6 dB
to +18 dB. The unit can be purchased optimized for mono or stereo use, jumper selected
600 ohm or High impedance inputs, and with either 600 ohm or low impedance outputs,
better than 110 dB dynamic range and 5 Hz to 150 KHz frequency response there are
very few audio devices available today which matches the flexibility and specifications of
the 501026.
Note:
Mono modules use only the Right inputs and outputs on the 801017 frame.
501026 Audio DA
Circuit Description
The circuit consists of 2 parts a differential input stage and a differential output capable of
supplying high output currents.
U1A (U4A) and associated components make up the input stage. The circuit has –6 dB of
gain, > 40K ohm input impedance, > 60 dB common mode rejection. Each input can also
be configured using a jumper to be 600 ohm input impedance is desired. The frequency
response is set by 100 pf capacitors and 10K ohm resistors and the high end (150 KHz)
and a unique DC restoration feedback circuit U1B (U4B) which sets the low frequency –3
dB point at well under 10 Hz without passing the audio signal direction through a
capacitor.
U1C (U4C) is a high current driver stage with a coarse and fine gain adjustment
available. U1D (U4D) is a high current driver stage which is an inverted copy of the
output of U1C (U4C). These combine to form the fully differential output which is
connected to all 10 outputs through isolation resistors. In the low output impedance
version, these resistors are 10 ohm resulting in less than 0.09 dB gain error when driving
any number of loads each of which is > 2K ohm. In the 600 ohm version, these resistors
are 300 ohms resulting in the perfect impedance match for driving extremely long line
requiring telephone line 600 ohm terminations.
Chapter 4