Setup
The amplifier has three sets of connections and one switch: The first connection and switch is
the AC line power system. The amplifier's voltage and current rating are indicated on the
bottom. It will be either 240 volts, 120 volts, or 100 volts, all with a 6 amp 3AG type fuse. The
frequency rating of the AC line source is 50 to 60 Hz.
Your amplifier is provided with a standard AC power cord which fits into the line receptacle
located just below the power switch. The amplifier is equipped for operation with an earth
ground provided by the AC outlet. Do not defeat this ground. The chassis of the amplifier is
connected directly to this earth ground, and the audio circuit ground is connected to the
chassis and earth through a power thermistor, which gives a ground safety connection but
helps avoid ground loops. While the amplifier is equipped with an AC inrush suppresser, the
turn-on AC draw will peak (half cycle) at roughly 50 amps on a 120 volt system and 25 amps
on a 240 volt system. The fuse on the amplifier is a 3AG fast blow type rated at 6 amps. It is
in series with the AC power line.
The second connection is at the input. If your signal source is balanced, you may use the
XLR input connector. On this connector, pin 1 is grounded, pin 2 is the positive signal input,
and pin 3 is the negative signal input. To run balanced input, remove the copper shorting
jumper between pins 1 and 3 on the XLR connector. Save the jumper.
If your signal source is unbalanced, input will occur through the RCA input. In unbalanced
use, the copper shorting jumper can be used between pins 1 and 3 on the XLR which
terminates the pin 3 negative input to ground. When running unbalanced input, use of this
plug will increase the amplifier’s gain to 26 dB in the event that you need or prefer higher gain
than the standard 20 dB figure. If you don’t need that extra gain, our own preference is to not
use the shorting plug.
If you insert the copper shorting jumper, and the amplifier stops operating, you will find that it
is not in pins 1 and 3.
The unbalanced input impedance of the amplifier is a nominal 10 Kohm. In balanced mode,
the input impedance is higher, with a differential impedance of about 25 Kohm. Common
mode input impedance is matched at 20 Kohm per input.
The third connection is the amplifier output connection. Connect the 5-way output connectors
to loudspeaker plus and ground, using the cable of your choice. Do not drive the amplifier
into a direct short. If distortion or fuse blowing accompany an attempt to operate the amplifier,
please disconnect the loudspeaker first and check for a shorted circuit. As the amplifier does
not use a current limiting protection circuit, quite a large amount of power can flow from the
amplifier, and might damage the output stage.
At rated power, the amplifier draws approximately 300 watts from the wall, and during idle
operation most of this energy will appear as heat on the heat sinks. Good ventilation is vital to
the proper operation of the amplifier. It has been adjusted for optimal performance at room
temperature, but will work well between 50 and 90 degrees Fahrenheit (10 to 33 Celsius).
You should leave at least six inches clearance on the sides and top. The amplifier should not
be placed in a closed cabinet which does not have forced air ventilation.
