The U.S. Audio DA-2 is a dual channel line-level distribution amplifier with four outputs per channel. All inputs and outputs are active electr onically balanced circuits accessed through XLR connectors. The input section and all critical gain sectio ns of the DA-2 use the same IC chips as top professional mixing boards. The inputs are instrumentation grade differential amplifiers tuned for a high amount of Common Mode Rejection (CMR). The CMR of the DA-2 is greater than 90dB, 20 to 20KHz. The DA-2 has tunable input impedance, factory-set by a resistor at 1 Meg ohms, which allows many units to be connected together with their inputs paralleled. If lower input impedance is desired it can be easily accomplish ed by an internal resistor change. Output volume pots control the level of the rear panel output XLRs over a gain range of -60 to +18dB. This feature allows the DA-2 outputs to easily compensate for variations in input levels. Unity gain on the DA-2 is approximately at the 9 O’clock position and 14dB of gain is approximately at the 3 O’clock position. 60dB of attenuation in the “off’ position allows the DA-2 to adequately “turn off” line level sig nals.
Maximum signal level through the DA-2 at clipping is +28dBm balanced and +22dBm unbalanced. The same figures apply to both the input and the output, and individual clip LEDs are provided which illuminate at 3dB below actual clipping. Green LED s are provided for each channel, which verify input signal levels above -14dB balanced and -20dB unbalanced. With THD+n typically less than .004% throughout the entire audio spectrum, and a unity gain signal to noise ratio greater than 85dB with 22dB of headroom, the DA-2 is well suited for use in all
audio distribution applications. Along with great audio quality, the DA-2 features a high degree of isolation between channels, as well as i mmunity to RF and electromagnetic radiation.
The DA-2 headphone monitoring section consists of a channel select switch, a volume control and a 1/4” TRS headphone jack. The headphone circuit is a mono type which drives both left and right stereo earpieces in any headphones with 20 ohms or greater impedance. The volume control has a gain range of -60 to +18dB to accommodate a wide range of aud io levels. The select switch allows listening to either the channel 1 or channel 2 inputs.
The combine switch is a unique feature th at serves two functions. First, it allows the DA-2 to operate as two independent 1 in to 4 out distribution amps or as a single 1 in to 8 out amp when in combine mode. Secondly, in combine mode the two inputs are actively mono summed, allowing the DA-2 to provide a mono feed from left and right stereo signals. Either input may be used to feed the eight outputs when the combine switch is activated.
The DA-2 utilizes a dual primary power transformer that is configured with internal jumpers for 120 VAC 60Hz or 230 VAC 50Hz operations. There is an internal fuse on the hot side of the AC cord and the power switch makes and breaks both the hot and neutral legs of the AC cord. A ground lift switch is provided which disconnects the audio circuit ground from the AC chassis ground when engaged.
