Stillwater Designs, now better known as Kicker, is an "All American" company that's been around a long time. Back in the day, they originated the "kicker" box before anyone else even thought about it - that's probably why people still refer to them as "kicker" boxes. In the early 1990s the company started building amplifiers and has since quietly grown into a large force in the market. This time we take a look at the latest stage in the evolution of the Kicker amplifier, the ZX350.4.
DescriptionKicker rates the 4-channel ZX350.4 amplifier at 60 watts per channel into 4 ohms, 90 watts into 2 ohms and 2 x 175 watts bridged into 4 ohms. The amplifier is an unregulated Class A/B design with both RCA and speaker-level inputs, and crossover and bass boost for each pair of channels. Visually, the amplifier retains its family resemblance to Kicker amps from the past several years. It has predominantly a textured black finish with a trio of rubber-capped knobs for each channel on the top plate. Swooping "V" contours in the top sheet metal frame the Kicker badge, and a red strip of silicon rubber lines the top plate on both sides.
The ZX series is an "upside-down" style amplifier. The main chassis is an aluminum extrusion that forms the bottom and sides of the amp. A cover plate made of stamped steel with the design and vents embossed in it covers the top of the amplifier. Adorning this piece are two badges (one for the logo and the other for the model number) and the control knobs for the gain, crossover and bass boost. The cover plate fits into two red silicone-rubber extrusions along each side of the heatsink. The molded plastic endcaps hold it in place.
The power/ground/remote terminal, two 20-amp fuses and the power/protect indicator light are all found on the left endcap, while the speaker connectors, RCA and hi-level inputs, fader and crossover switches are on the right endcap. Crossover frequency, gain controls and bass boost level controls are located toward the right-hand side of the cover plate.
The circuit layout inside is pretty much what you'd expect from looking at the outside. The power supply and the amplification/output section each occupy half of the main board, with an empty 1" strip running right down the middle as a buffer between them. There are other ways of controlling noise from the power supply, but it looks like isolation is important to the engineers at Kicker. The preamp section is nicely contained on a daughter board suspended above the output end of the main board. Both circuit boards are double-sided, but the preamp board uses mostly surface-mount parts while the main board uses all through-hole parts.
Starting with the power supply, power and ground is accepted through two large brass blocks. These two blocks will accept up to 4-gauge cable, although the manual recommends 8-gauge for this one as it is the smallest 4-channel in the series. B+ runs through a pair of 20-amp fuses and a small inductor. It then goes past three 2,200F capacitors for primary filtering and on to two pairs of high-speed, 49-amp switching Mosfets. A TL494 pwm controller drives the switching through the toroidal transformer at about 36kHz, achieving rails of + and - 30VDC. Secondary filtering consists of four 3,300F capacitors to stabilize the rails.