ATI Audio DA206 - Manual (Page 2)

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DESCRIPTION
The DA206 and DA412 Analog Audio Distribution Amplifiers provide two (DA206)
or four (DA412) 1X3 distribution amplifier channels with balanced inputs and
outputs. A master gain adjustment for each channel controls all three outputs
together to adjust for varying inputs, while individual trimmers for each output
allow adjustment over a 20dB range to accommodate -10dbu semi-pro up to
+8dBm line levels.
Another of the DA206 and DA412 Distribution Amplifiers many claims to fame is
the use of XLR type input and output connectors. XLRs are easy to use but make
paralleling inputs for 1X6 or 1X12 operation difficult. However, if you look under
the hood (remove the top cover) you will find some convenient jumper plugs that
allow you to parallel inputs A and B (P4 & P5), B and C (P6 & P7), C and D (P10
& P11), individually or simultaneously. If you are making a stereo 1X6 DA, drive
inputs A and C with Left and Right signals and jumper inputs A to B and C to D.
You can use the empty input connectors to loop-thru to the other dozen ATI
distribution amps that we hope you are using.
A rugged NE5532 IC forms the quiet, clean, gain selectable, 20Kohm
instrumentation amplifier input stage with good common mode hum rejection. An
internal gain selection jumper plug for each input (P2, P3, P8, P9) lets you
optimize for nominal inputs at -20dBu, -10dBu or +4dBu. Inputs up to +24dBu will
not clip in the +4dBu position and input signals exceeding +24dBu will clip
cleanly with no hang-up or phase reversal.
An LF347N quad bi-fet opamp forms the three variable gain output adjustment
stages. These variable gain stages use a unique circuit arrangement that allows
us to provide a smooth, logarithmic gain control for each output using an
inexpensive (but good) linear cermet potentiometer. Since we actually reduce the
stage gain for low outputs rather than taking the more conventional approach of
reducing the input level to a fixed gain amplifier, you can use the DA at low
output levels with very little noise penalty. You can use the DA to match console
medium level inputs (-20dBu) or to drive semi-pro IHF inputs without requiring
outboard attenuator pads.
SSM2142 active balanced output drivers sense the voltage on their high and low
output lines and will shut off drive to a grounded output line while doubling the
drive on the other. This capability allows you to connect the outputs to balanced
or unbalanced loads without regard to whether or which side of the output is
grounded. Maximum output at clipping is +22dBm into balanced loads; however,
even though the gain is the same under either condition, clipping output is
reduced by 6dB when driving an unbalanced load since the full output swing
capability of only one driver of the two is available.
Your DA206 or DA412 operates from a bipolar 15VDC regulated power supply.
The power supply is designed for minimum susceptibility to power line transients
and conducted RFI using ferrite beads, double bypassing and a non-concentric
wound semi-toroidal transformer.