Real World Gear: Change For The Better (Part 2)
The emergence of multi-channel amplifiers
AB International
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John Murray Take: All use standard class A/B output topology with conventional transformer power supplies. No 70-volt units are offered but all are 2-ohm capable. Both 4-channel and 6-channel units are available, from 200 to 600 watts per channel at four ohms. Each pair of channels shares one power supply - a level of redundancy equaling that of 2-channel amplifiers. |
The 6-channel units have a permanent low-pass filter (LPF) on channel 6, defining them primarily for 5.1 home theater applications. These can be adapted for live sound use as long as you’re content with LPF fixed frequency.
Ashly Audio
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J.M. Take: Offers a low-impedance and 70-volt model in both 4-channel and 6-channel units. The 70-volt units do not have isolation transformers, neither internally nor externally as options. The Tri-Path amp modules provide a spread-spectrum switching output stages using the MOS-FET transistors. |
This results in a 56-pound package for the 250-watt by 6-channel models. I’ve always liked the sound quality of Ashly’s MOS-FET output stage. MOS-FET clipping produces even harmonics, like tube amp clipping (what some would call a “warm” sound), thus sounding better with bad gain structure than class A/B amps that produce odd-harmonic clipping. If you insist on running your amps with the inputs on 11, this is a series to consider.
Biamp
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J.M. Take: Two 8-channel models, at 50 and 150 watts per channel, respectively, are offered. Both have optional internal toroidal isolation transformers. This is a unique feature among the products covered here. |
Biamp also offer a clean, low-cost remote input level control option that is perfect for the permanent-install application. The intended market for these models is commercial fixed installations, where conservative reliability is the prime concern and limited dynamic range is not an issue.
CAMCO
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J.M Take: Distributed in the U.S. by NEXO, CAMCO offers a single 4-channel model. The Vortex Quadro 3 has produces 750-watts per channel and employs class H outputs and a switching power supply. |
At 27 pounds, this is quite light for the power derived. These units are just starting to get a toehold in the U.S., and preliminary reports have been quite positive.
Chevin Research
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J.M. Take: A very good reputation for sound quality, the specs for the two 4-channel units are quite good. The Q6 offers four identical channels with up to 1000 watts per channel, weighing in at 34 pounds. The QB1000/600 is comprised of two biamping pairs and weighs in at 44 pounds. |
No reason is readily made available on the web site as to why this unit should be heavier with less power output, nor is there any discussion of the output topology of these units in the sketchy information. All units use switching power supplies.
Crest Audio
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J.M. Take: The company’s sole entry for multi-channel amps, the Pro 10004 is a 4-channel, 1225 watts per channel monster that will deliver 1400 watts into 2-ohm loads. The design is solid, with class H power plants and a pair of conventional power supplies. The 4-rack-space unit has built-in limiters, and at 137 pounds, no matter where it lives, it has nothing to fear from tornados. |
We just learned that Crest will soon be debuting two new units, the 4-channel CM2204 and the 8-channel CM2208, which will deliver 220 watts per channel to any load from 4 ohms to 70 volts. A cool feature is an auto-detect for the load that will deliver full power without need of connecting to particular terminals or to switch anything. Very interesting!
Crown Audio
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J.M. Take: Interestingly, of the three multi-channel models offered, two of them have standard inboard 70-volt capability. The sole low-Z model, the 4-channel Xs4300, is in the company’s entry-level line. |
Clearly, Crown focuses its multi-channel efforts toward the commercial application market, and does it well. Both the CTs4200 and CTs8200 are 4- and 8-channel models with built-in 70-volt capability in addition to 4- and 8-ohm operation. Both have switching supplies and an A/B+B output topology and are both remote VCA and IQ module capable. No optional isolation transformers are offered and 70-volt operation automatically engages a 100 Hz high-pass filter.
Dynacord
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J.M. Take: With listed power ratings at 4 ohms only, the Xa-2600 is a 4-channel unit intended for stereo biamplification, and employs class A/B outputs and a conventional power supply. It is somewhat Dynacord-speaker-specific, which might limit compatibility with non-Dynacord speakers. Weight is a somewhat “hefty” 66 pounds. |
Lab Gruppen
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J.M. Take: Known for outstanding sound quality in the switching supply category, Lab Gruppen’s sole multi-channel unit, the fP2400Q, is a 4-channel model that is 2-ohm capable at 500 watts. |
This high-tech unit sports class D/B outputs, built-in limiters and excellent specifications. I see big things from Lab Gruppen as the line expands. (For more about Lab Gruppen amplifiers, see Live Sound October 2002 issue.)
MC2 Audio
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J.M. Take: The company’s sole multi-channel amp, the T4-250, sports 4 channels providing 250 watts at 4 ohms. No option for 70-volt output, but there are built-in limiters. Both the outputs and power supply are conventional and, at 40 pounds, it might be time for the “next generation”. |
Miles Technology
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J.M. Take: The MPR-450 has been used successfully in a wide range of commercial applications. The unit offers single 6-channels, at 75 watts per channel. Outputs are class A/B and the power plant is conventional. |
A particularly unique feature is the power supply’s ability to route more power to channels with a higher demand, and away from channels that aren’t working as hard.
Peavey Architectural Acoustics
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J.M. Take: The ICS 4200 is a 4-channel unit with 200 watts per channel at 4 ohms. The output and power supply are conventional as is the weight at 40 pounds. |
Outputs are switchable in pairs for 70-volt operation. No isolation transformers are available. Due to the 80 Hz low frequency limit, this unit is recommended primarily for commercial ceiling speaker applications.
PowerSoft
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J.M. Take: This Italian company gets the award for most high-tech amplifier. (They also have a cool web site!) Hands down, PowerSoft takes the size- and power-to-weight ratio honors with 4 channels at 1000 watts in a 1U, 21-pound package. |
One model, also at 1 RU and 21 pounds, delivers 4 X 1250 watts into 1-ohm loads. Are they for real? Can their products be reliable? (For more about PowerSoft amplifiers, see Live Sound June 2003 issue.)
QSC Audio
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J.M. Take: A U.S. market leader in 2-channel amps, QSC doesn’t take a back seat in multi-channel amps either. They offer three 4-channel and two 8-channel models, including 70-volt versions of each, with optional isolation transformers. |
All have an A/B+B output topology and switching power supplies, and include switchable high-pass filters and limiters. And, all can be remotely PC-controlled by QSControl.
Rane
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J.M. Take: Two models available, with 6 channels and 3 channels, respectively. The 3-channel version, the MA 3, offers optional internal transformers and a switchable 80 Hz high-pass filter. |
The 6-channel MA 6s has built-in limiters and optional external isolation transformers. Both units employ conventional output stages and power supplies. Rane has been building rock-solid multi-channel amps since the ‘80s.
Stewart
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J.M. Take: The DA-70-4 is a half-rack space, 4-channel amplifier with the company’s DTM output stage and a switching power supply. It supplies 70 watts per channel at 4 ohms and gets the award for the both the smallest and the lightest, weighing in at a scant 3.4 pounds. This is so small it seems a little scary to me. |
It’s mainly applicable for commercial applications due to its limited dynamic range specification, which, as was the case with many manufacturers in this overview, is inappropriately labeled signal-to-noise (S/N) ratio.
December 2003 Live Sound International