The preamplifier has four sets of input connections, two sets of output connections,
an input selector, tape selector, and one level control.
It also has an AC line power connection. The preamplifier's voltage rating is
indicated on the rear. It will be either 240 volts, 120 volts, or 100 volts. A .5 amp
3AG slow blow fuse is provided with 100-120 volt units, and a .25 amp slow blow
fuse is provided with 220-240 volt units. The frequency rating of the power supply is
50 to 60 Hz. The preamplifier draws 30 watts and is designed to run continuously.
We have provided a standard AC power cord which fits into the line receptacle at
the rear. The preamplifier is equipped for operation with an earth ground provided
by the AC outlet. Do not defeat this ground. The chassis and circuit ground of the
preamplifier is connected to earth through a power thermistor, which gives a ground
connection for safety but helps avoid ground loops.
The input connections on the rear are one pair of XLR and four pairs of RCA
connectors with right and left channels indicated. If your signal source is balanced,
you will want to use the XLR input connectors. On these connectors, pin 1 is
grounded, pin 2 is the positive signal input, and pin 3 is the negative signal input.
The RCA input on the first input connects to pin 2 of the XLR connector.
For unbalanced operation on the first input, a shorting plug is provided between pins
1 and 3, shorting the negative input to ground, and providing the lowest possible
noise. Except for a small difference in noise, there is no significant difference in
performance between using the shorting plug or not.
The unbalanced input impedance of the preamplifier is a nominal 10 kOhms. In
balanced mode, the input impedance is higher, with a differential impedance of 20
kOhms.
Next to the inputs on the rear panel, the preamplifier offers tape outputs through
RCA connectors. Input 4 is deliberately not available through the tape output
connection. Input 4 is designated for use with a tape recorder if you have one, and
we have arranged that it will not place its output on the tape out, which will prevent
you from accidentally creating a feedback connection with your tape machine.
At the left hand side (viewed from the rear) of the rear panel, two male XLR
connectors and two RCA connectors are used for the main output. On the XLR, pin
1 is ground, pin 2 is positive, and pin 3 is negative. The RCA connector’s ground is
in parallel with pin 1 and the RCA hot is attached to pin 2. You may use either or
both of these connectors for balanced or unbalanced operation.
The circuitry of the preamplifier is such that it will drive any impedance without
distortion, however as the load impedance goes down, you will experience a
reduction in gain. The preamplifier will act as a maximum plus and minus 30 ma
current source into a dead short.
