I'm always interested in testing a quality product, especially when it comes from a legendary designer in our industry. And that's just what we have this month, a new Signature Edition amplifier from the folks at Arc Audio, from the fertile mind of car audio guru Robert Zeff.
I consider Mr. Zeff to be one of the pioneers in this industry and definitely someone we can all learn something from. Since I have been a fan of his products for more years than I'd care to count, I was very interested to see what his new amp would have to teach me. I was not disappointed.
The Arc Audio 4200SE is a medium-sized 4-channel amplifier, measuring approximately 19 1/2" x 8" x 2 1/2". The power connections are on one end and the signal connections, on the other. This arrangement allows for maximum isolation of noise by keeping the noisy power and ground cables as far away from the signal and speaker conductors as possible. Throughout the amplifier were similar thoughtful details, dedicated to the minimization of noise and maximizing the sonic performance. The amp is relatively plain looking, finished in a low-sheen black and brushed aluminum, but it is nicely put together, with panel-mount RCAs and very good fit and finish. The Arc Audio emblem on top illuminates when the amp is turned on: in blue if everything is working correctly, and in red if there is a problem. The manual even explains how to remove the illuminated logo and custom paint it to match your install, and then how to sand off the paint to make it light up again when you're done! The logo's illuminating background can also be changed to over 200 shades of color using a sequence of events using the remote bass control knob. Nice!
The top-mounted controls are hidden under a brushed aluminum panel, which is removed by taking out four small Phillips-head machine screws. Lifting off the panel, (complete with Mr. Zeff's signature laser etched onto the brushed aluminum) you find a great assortment of switches and knobs. In fact, there are no less than 28 separate controls, enough to satisfy even the most avid tweaker.
This is one of the few amps in recent memory that uses individual gain controls for each channel, something I feel is missing on many "would be" high-end amps. Sure, one control is easier to set up, but having the extra control of independent pots allows you to finesse the installation and provide a little compensation for things like speaker proximity. You can't do this stuff with a balance control without affecting all the other channels, not to mention that in many cases a single pot is not always well matched left to right throughout its range of adjustment. Chalk up another point for the legendary Zeff attention to detail, and his understanding of the application for the product he's designing. Here's a guy who clearly does not take the train to work... I'd bet a lot of money he drives a car with an audio system in it, and like the rest of us enthusiasts, he "gets it."
The 4200SE has some of the most comprehensive crossover capabilities in any amp at any price. Each pair of channels has the usual highpass and lowpass settings, but the range of adjustment is from 30 to 550Hz, which is wider than most, plus there is a x10 switch allowing for those frequencies to be multiplied by 10. In other words, you could set either crossover anywhere between 30 and 5,500Hz!
And, the preamp section control doesn't end there. The crossover slopes can be set individually for 12dB or 24dB per octave slopes, or even set to a bandpass setting with a different slope on each end if you prefer! I've seen some digital crossovers that were not this flexible and well thought out.
Additionally, there are controls for bass boost level and frequency, allowing up to 18dB of boost, ranging from about 20 to 80Hz. Then there are special signal steering switches for using the amp in bridged mode that allow the user to select whether the left or right signal is used when stereo bridging, or the sum of the two for subwoofer applications. Still other controls allow the remote level control to adjust the level of all four channels, or just the rear channels so it can be used as a subwoofer volume control with an adjustment range of approximately 60dB. There is also a pair of RCA outputs for routing the rear signal to a subwoofer amplifier.
The controls and configuration of the amp are extremely flexible, allowing for virtually any conceivable installation requirement, and were obviously designed by someone who "gets it" when it comes to high-performance car audio.
Circuit Design
Taking a look inside the Arc Audio 4200SE, I found a very nicely laid out PCB and a lot of very good quality parts. Surface-mount parts make up the majority of the parts count on the PCB, and this is a good thing for a couple of reasons. First, surface-mount parts allow greater flexibility with PCB layout because of their small size, and secondly, because their values are laser trimmed, most SMT parts have a value tolerance of 0 percent. That kind of tolerance ensures the engineers' design will work as intended, even when mass-produced.
The power supply uses six of the expected Mosfet switchers, these being large case TOP-3 die size devices. There are five 3,300F caps in the power supply, for a total storage ability of 16,500F. Also worth noting is a second, fairly large toroid that acts as a filter to remove much of the normal switching "hash" that is a normal component of a switching power supply.
A quick check with my trusty Tektronics DSO showed the supply switching at about 38.5kHz, and the output of the filter indeed had much less noise and trash on it. Providing a cleaner supply of power to the output stage should result in a cleaner signal... another detail that says "no compromise" and one that many brands do not include for cost or space reasons. With each of these Mosfets able to handle up to 75 amps of current, the power supply will easily be able to meet the demands of the output stage.
It's a typical Class A/B amp, using a triple Darlington arrangement with high-speed (20MHz) bi-polar transistors for the output section (more on this later). The PCB is a top-quality fiberglass 4-layer board that is well laid out, with good attention to details that improve signal to noise, and reliability. There are a few good lessons in PCB layout here, for those who'd care to learn them. Solder joints were consistently good and I saw no evidence of post-production "kluges" or temporary fixes that are common in new models.