Welcome to the digital age! OK, so it's been here a while, but it seems that our beloved world of mobile audio has taken its sweet time to come around. There have been a few companies that have tried to break the digital barrier over the years (PPI in 1990 with the DCX series, Rockford's Symmetry, Orion Digital EQ) while others sat back and schemed, waiting for the perfect alignment of silicon chips and consumer awareness. Zapco introduced their reference DC (Digitally Controlled) series at the Consumer Electronics Show in January 2006, and now we get the chance to look deeper into the 6-channel DC650.6 digitally controlled amplifier.
The DC650.6 is a well-regulated 6-channel Class A/B amplifier rated at 4 x 50 watts plus 2 x 100 watts into 4 ohms and 4 x 90 watts plus 2 x 180 watts into 2 ohms. (I'm thinking this is a printing error. Channels five and six easily put out the 2 x 100 watts and 2 x 180 watts, but at lower impedances.) The brain of this amplifier is a very full-featured digital signal processor that includes crossover, equalization and time delay for all six channels. As do all reference series Zapco amplifiers, it makes use of their proprietary SymbiLink balanced input connectors. Except for the all-black finish, this one doesn't really look much like an amplifier. Fins run the length of the back, but the amp's really long and not very wide. The top cover rolls smoothly down to become the front panel, which has only enough surface area for the ample speaker and power connectors, the SymbiLink inputs and a set of USB and data ports. The cast-aluminum endplates reveal vents and ducts for the fan-cooled heatsink. Four aluminum pieces make up the chassis--the extruded base/heatsink, the 1/8"-thick top/front cover and the two cast endplates. Also on the front panel is a Low-Z switch and an indicator light, input clip light, output clip lights for each channel pair and power and protect indicator lights. Take the cover off and you find the inside doesn't look like an amplifier either. I can't really figure out what it does look like, maybe an industrial network router or something. Anyway, the main circuit board is barely 3" wide and runs the full length of the chassis. The "hang-off" devices stand up along the back edge of the circuit board, clamped to a fairly thick vertical fin on the heatsink extrusion. This fin forms the front wall of a cooling tunnel, with a small fan in the center that draws air in through the endplates, across the main circuit board, and then through the cooling tunnel and back out the endplate vents. At 3" deep, the circuit layout doesn't have much choice but to reflect the front panel connections.
The output devices for channels one through four occupy the circuit board behind the output connectors, taking up the left third of the amp. Just to the right are the input jacks and digital I/Os, which are reflected inside by minimal analog circuitry and four small, vertically mounted daughter boards that hold the digital stuff. To the right of that are the power connectors and mini-ANL fuse, which reflects the power supply immediately behind. The right end is filled up with channel five and six output connectors and the corresponding output circuitry. The power connectors are the 45-degree angled terminal blocks that accept 4-gauge cable on an upward angle, and the clamping screws are on the downward angle. B+ goes directly through the 80-amp mini-ANL fuse, past five 100-microfarad caps to the primary legs of two transformers. One transformer serves channels one through four while the second takes care of channels five and six. A single SG3525A controller switches both transformers at a little under 27kHz. A pair of 200-watt Mosfets drives each transformer for a theoretical 800-watt total capacity. Secondary voltage is rectified and fed through a toroidal inductor and past the sixteen 1,000-microfarad filtering capacitors to provide + and -26 volts (+ and -24 volts when the Low-Z switch is engaged) rails to the output devices. The two transformers are identical except for auxiliary winds on one that provides power for the op-amps and low-level circuits. That means that Zapco expects channels five and six to do the same total amount of work as channels one through four. That's good news for those of us who like a little bass.
The output devices for channels one through four are the good old TIP35c/36c bipolar transistors, one pair per channel, providing good sound quality and up to 250 watts per channel. Channels five and six use beefier bipolar pairs in the TO3p package size, each pair good for 300 watts.