Side by Side: Monitor Amplifiers
Sep 1, 2013 6:30 AM, By Chriss Scherer, editor
It's probably the most set-and-forget item in any studio: the monitor amplifier. And their reliability has become so good that they seldom fail, only adding to their forgotten status. Several brands are commonly found in the rack, including Crown, QSC, Yamaha, Ashly and Crest. But there are other options, too.
More and more, active monitors (with the amp built in) are being installed, but depending on the layout, it may be desirable to separate the amp and monitor.
There are two methods of cooling: active and passive. Active uses a fan to force air for cooling. This could contribute to room noise. Passive, convection cooling is the quietest, but the amp must be mounted to ensure it can dissipate the heat.
Power selection depends on use. A smaller amp has a lower output level (obviously), which can help keep overall facility levels down when multiple studios are in use. But if a smaller amp is pushed, clipped peaks could cause other problems and possibly even damage a monitor. The amp will also run hotter. Consider choosing the next larger amp power in the family if this is the case.
For this installment, we considered models that provide 50 to 100W, which is perfectly suited for a small studio for news, voice-overs and production. In some cases, there are other power levels within the same product family.
This family of amps is designed to provide more power and better performance at a lower overall cost per watt. The amp uses convection cooling for heat dissipation, so there's no added noise in a studio. It's 2RU and delivers 150W per channel at 4O, 90W per channel at 8O or 300W bridged into 8O. It's signal to noise ratio is >105dB, with a frequency response of 10Hz to 70kHz. Distortion is <0.02 percent at 4O, 20Hz - 20kHz. Other models in the series include the RA150 and RA500.
The SLA-1 studio linear amplifier is rated at 100W per channel into 8O, 130W per channel into 4O, or 250W bridged mono into 8O with a frequency response from 10Hz to 40kHz. Occupying 1RU, the SLA-1 uses a toroidal transformer design for reliability. Cooling is provided via SmartFan, an advanced, thermal-dependent, fan-assisted, convection-cooled system. Connections are made via XLR and 1/4" TRS balanced inputs and multi-way output binding posts. A tamper-proof cover is included. Total harmonic distortion is <0.05 percent. Also available is the SLA2.
DAS Audio PS-200
Housed in 1RU, the low-noise fans keep things cool, while the toroidal transformer saves weight. Rear-located switches that permit ground lift, operational mode selection (bridge, stereo or parallel) and input sensitivity selection. It delivers 70W into 8O, 100W into 4O and 200W bridged mono into 8O. Frequency response is 20Hz to 20kHz, and distortion is <0.05 percent. Connections are made via XLR and 1/4" TRS balanced inputs and output binding posts. Also available are the PS-400, PS-800, PS-1400, and PS-2800.
Dixon Systems SA-240
This 1RU stereo power amplifier provides 40W per channel into 8O. Inputs are XLR connectors through a filtered audio module. Outputs are biding posts. There is a front-panel headphone jack for monitoring. Distortion is rated at <0.02 percent at rated output. A custom, shielded toroidal power transformer reduces weight and provides ample power. The protection system will shutdown on a short and reset when power is removed.
Samson Servo 300
Large 10-segment, three-color level LED meters show levels of this 2RU amp. It has 1/4" balanced and RCA inputs, and five-way binding post and 1/4" speaker outputs. It features a four-stage power protection circuit to provide 100W/channel at 8O, 150W/channel at 4O and 300W mono bridged into 8O. Frequency response is 10Hz to 55kHz, and distortion is 0.04 percent. A toroidal transformer provides the system power, and it's kept cool via two variable speed fans. Also available are the Servo 120A, Servo 200 and Servo 600.
This 2RU steel chassis amp provides 100W per channel into 4O, 70W per channel into 8O, and 200W bridged mono into 8O. The MOSFET output stage is fault protected to allow the amp to forgive momentary output shorts. The unit is convention cooled so there is no fan noise, and it features a one-second delay time for power-on. Input connectors are 1/4" TRS and RCA. Output connectors are binding posts. Distortion is rated at <0.08 percent.
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