VAC PA90 - Manual (Page 5)

5
INSTALLATION
Physical requirements:
1) Provide adequate ventilation - allow at least 3 inches above and 1/4 inch between VAC
chassis.
2) Do not place in a completely enclosed cabinet.
3) Do not stack other equipment on top of the VAC units.
4) Do not operate on carpet or any other surface that might block air flow.
5) The chassis of the PS90 will become hot in normal use.
6) Do not allow the chassis of the VAC components to touch any metal parts, such as the
frame of an equipment rack. This might create a parallel ground path that will degrade
the sound of your system.
Electrical connections (refer to Figure 2 to identify the connectors and leads referred to in these
directions.):
1) FOLLOW THESE DIRECTIONS CAREFULLY. FAILURE TO CONNECT THESE UNITS AS
DESCRIBED MAY RESULT IN INCORRECT OPERATION AND MAY POSE A DANGER OF
LETHAL SHOCK.
2) The PS90 Power Supply must be unplugged and turned completely off.
3) Connect the heavy gauge grounding cables between the ground terminal of the PS90
and the ground terminal of the PA90 Power Amplifier. The binding posts provided for
this purpose have a nut that can be completely removed, and so accommodates the
circular lug (ring tongue terminal) used on the ground cables. Remove the nut, place the
lug over the binding post shaft, replace the nut and tighten firmly (an 11 millimeter open
end wrench may be used). The ground cable ensures a ground return for the power
supply in the unlikely event that the two redundant ground paths in the power cable
between chassis should fail.
4) Connect the power cable provided into either socket marked "To Power Amplifier" on the
back of the PS90 Power Supply. Connect the other end of the power cable into the
socket marked "Power Supply In" on the PA90. NOTE THAT THE POWER CONNECTORS
ARE DIFFERENT ON EACH END OF THE CABLE, ARE KEYED, AND HAVE A KEYED
LOCKING COLLAR. You should feel a slight "snap" when the locking collar has been fully
turned. Never attach two PA90s to a single PS90.
5) Connect signal inputs to the power amplifiers. BALANCED (XLR INPUT) AMPLIFIERS
CAN ONLY WORK CORRECTLY WITH FULLY BALANCED INPUT SIGNALS - OTHERWISE
DAMAGE WILL OCCUR.
6) Connect loudspeakers between the appropriate pair of binding posts on the back of the
power amplifiers. The binding post nut accepts an 11 millimeter open end wrench. Be
careful not to over tighten. Note that the positive terminal is the same for all impedance
connections. For further information see Tips & Advice: A Word About Impedance
Matching.
7) Connect the PS90 to the power source indicated on the rear panel, either 120 volts AC
or 220 volts AC, 50 or 60 Hertz.
8) Follow the BIAS procedure described in this manual to set the idle current at 54
milliamperes per tube, checking the idle current at 1 minute, 30 minutes, 1 hour, and
2 hours. Also, read the section entitled INSTALLING NEW OUTPUT TUBES.
CAUTION FOR GROUNDED SPEAKER SYSTEMS OR COMMON GROUND SWITCHING
SYSTEMS. The PA90 chassis and "-2 ohm" output connector are at ground potential with
respect to the 120 volt AC source and the signal input shield. NEVER CONNECT ANY OUTPUT
TAP EXCEPT "-2" TO THE GROUNDED SIDE OF A GROUNDED LOAD, such as may be
encountered with some switch boxes and certain speakers. In such a system, the only output
impedance available from the PA90 is 2 ohms. Special modifications for grounded and
common loads are available. Contact VAC for details.