Power Amplifiers

Halcro MC70 Seven-Channel Power Amplifier

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Introduction

Halcro is an Australian manufacturer of high-end electronic components. Until very recently, it was owned by Minelab Electronics, makers of land-mine detection equipment. If you figured that people who make land-mine detectors, which require extremely accurate and reliable performance (because lives literally depend on it), would design and produce incredible audiophile products, you'd be right. Halcro's Reference line of amplifiers has been widely praised for their accuracy.

The subject of this review is the Halcro Logic MC70 seven-channel power amplifier. Halcro Logic is the home theater line of Halcro products. The MC series amplifiers come in two, three, five and seven channel configurations (designated the MC20, MC30, MC50, and MC70). The MC70 lists for $7,000, but compared to the Halcro Reference DM88 monoblocks, which will set you back more than $40,000 per pair, the MC70 is quite the bargain. So what kind of amp do you get for a kilobuck per channel?

Specifications

  • Design: Class D (Switching)
  • Power: 200 Watts RMS x 7 into 8 Ohms, 350 Watts into 4 Ohms
  • MFR: 5 Hz - 45 kHz, -3 dB
  • THD+N: 0.007% at 1 kHz upt to 350 Watts into 4 Ohms
  • Input Impedance: 10 kOhms
  • Inputs: XLR and RCA
  • Dimensions: 7" H x 17" W x 16" D
  • Weight: 55 Pounds
  • MSRP: $7,000 USA
  • Halcro

The Design

The MC70 is a Class D, switching amplifier design. Class D does not mean digital, although the waveform produced by a class D amp shares one characteristic with a true digital design in that the signal is produced by turning a switch on or off. In the more traditional Class A/B design, an output device is carrying at least some amount of current at all times, which is inefficient and results in dissipation, generating heat. A Class D amp converts the input signal into a series of pulses, so the output device is either "on" or "off." The pulse signal operates at a much higher frequency than the original signal (such as 500 kHz). The length of time that the signal is "on" results in a triangular waveform, from which the amplitude and frequency of the original signal can be derived.

So far, so good. But switching amplifiers tend to produce high levels of distortion, due to timing errors in the on/off switching which mathematically generate distortion in the form of phase shift (this occurs even with "perfect electronic components," according to Halcro). The distortion is typically dealt with via various types of negative feedback systems. Because this distortion increases at higher frequencies, switching amplifiers are most often used only in subwoofers, where the lower frequencies and higher tolerances for distortion mitigate the problem.

Halcro created a technology called Lyrus, which uses patented distortion canceling circuitry to eliminate the phase shift caused by timing errors. The Lyrus circuit sends a compensating timing signal to the clock which adjusts when the output signal switches, and that eliminates the phase errors. Halcro claims that the Lyrus amplifiers produce 1/5 to 1/10th the distortion of well-designed competitive products at higher amplitude, with performance on par with other Class A, A/B or B amplifiers.

Assuming that you can design around the distortion-inducing phase shift, there are obvious benefits from the efficiency of a Class D design, include drastically reduced heat from the unit and significantly lighter weight than similar powered amps using traditional Class A/B designs. Halcro claims that the MC 70 is 94% efficient at full load (350 watts at 4 ohms), throwing off less than 22 watts of heat. The Halcro weighs in at a svelte 55 pounds, and lacks any obvious external heat sinks or fins. The top cover grill is well ventilated, but I never felt it get even slightly warm.

The Halcro can be ordered in two, three, five and seven channel configurations, each one having its own separate slot modules. If one channel becomes defective, the offending module can be replaced.

halcro-mc70-amplifier-module.jpg

In fact, the MC70 includes something called HRAS, Halcro Reliability Assurance Service. Using software installed on your PC, the Halcro is monitored through an Ethernet connection to your computer. In the event one or more channels develops a fault, HRAS will automatically send an e-mail to either Halcro or your local dealer, who will contact you to arrange replacing the defective channel. Kind of like HAL from 2001: A Space Odyssey telling you that your AE35 unit is about to fail, but without the sinister overtimes.

The aesthetics of the amp follow a minimalist design. The front panel contains only a power button (standby/on) and seven blue LED's, one for each channel, which glow in a turquoise (almost McIntosh) blue to tell you that the amp channel is working properly. The amp channel light will turn red if the module is overheating, or flash red if it is receiving too much current. The LED's are rather bright, and not dimmable, so you'll want to hide the Halcro in an equipment closet if lights bother you.