DACS Model 411 Modular Automated Audio Mixer

	The 411, shown from the front. The 40x2 LCD, power switch, power LED, and link LED are visible. The 411 is built into a 3RU X 19" rack-mount case.
	Inside of the Model 411. In the rear left, the four 8-input balanced/unbalanced analog input boards can be seen. In the rear right, the two analog output boards can be seen - the top is an 8-output unbalanced 1/4" output, the bottom is an 8-output balanced XLR output. In the center near the front are four mix engine cards. The architecture supported up to 16 cards to obtain full 32x16 mixing capabilities. On the left front, the pBus interface card can be seen. The 68HC11 microcontroller board sat under the pBus interface card, but it had been removed prior to this photo. Vertically mounted on the right side of the chassis is the linear +/- 7VDC, +/- 14VDC, and +5VDC power supply. To the left of that supply is an off-the-shelf +12V/+5V switching power supply, which had to be added at the last minute because of the current draw of the bus combiner module, which sits under the mix engine cards.
	8-input analog audio input board. Accepts balanced or unbalanced line-level signals. Unstuffed parts were for input gain adjust circuit which had design problems. NE5532 op-amps were used throughout the system. There are four of these boards in the Model 411 mixer.
	32x1/16x2/8x4 mix engine card. Reconfigurable with bus combiner module. The Analog Devices SSM2163 SPI-controlled 8x2 mixer ICs were the core of the system. The logic at the top was the decode circuitry for the pBus interface. The card was designed to support parallel SPI such that independent, simultaneous communication with all four chips was possible. The row of connectors on the bottom are for the audio bus connections which are carried on ribbon cables with IDC connectors. There are four of these boards in the prototype Model 411 mixer, but the architecture supports up to 16.
	Audio bus combiner board. This board combined audio input and output buses so that a DACS system with fewer than the maximum 16 mix engine cards could be reconfigured. With all 16 mix engine cards, the system would always function as a full 32x16 mixer. However, because it was cost prohibitive to produce 16 mix engine cards (each mix engine card cost over $100) a reconfigurable bus scheme was designed. This allowed the system to function as a 32x4, 16x8, or 8x16 with 4 mix engine cards in the system.
	Unbalanced 8-output audio board. Provided eight tip-sleeve unbalanced line-level outputs from the system.
	Balanced 8-output audio board. Provided eight XLR balanced audio outputs from the system. It is worthwhile to note that both the balanced and unbalanced PC boards are identical - it was designed to allow parts stuffing to determine the configuration.
	Hand-wired linear power supply. Provided +/- 7V for the mix engine cards, +/- 14V for audio rails on the input and output boards, and +5V for digital logic on the mix engine and input cards.