(2)
Placement of the Preamplifier
·
The 7PX3.5 should be placed well away from
components which generate strong magnetic fields, such as power amplifiers or motors.
Because the strength of a magnetic field diminishes quite rapidly as you move away from the
source, you should encounter little difficulty in properly locating the 7PX3.5 outside of hum
inducing magnetic fields.
Applying Power*
·
The external power supply provides filtered DC of dual polarity to the
7PX3.5 mainframe via a high quality screw-lock connector. An IEC 320 AC connector supplies
AC to the AC/DC converter. Before applying power, check the voltage indication on the
external power supply to be sure that it is correct for your AC power. (Units wired for
220/240V operation can be changed to 120V operation with the voltage selector switch inside
the power supply. The appropriate fuse must be installed if the operating voltage is changed.)
Connect the DC screw-lock connector to the receptacle on the rear of the preamplifier, then
connect the AC power cord to the receptacle of the power entry module on the rear panel of
the AC/DC converter and turn on the AC power switch on the module. The LED in the AC/DC
converter will glow green when it is on.
NOTE: WHEN FIRST CONNECTING THE EXTERNAL POWER SUPPLY, ALWAYS CONNECT THE DC
SCREW-LOCK CONNECTOR FIRST! (GREEN LED OFF). WHEN DISCONNECTING THE EXTERNAL POWER
SUPPLY, ALWAYS DISCONNECT THE AC POWER FIRST! WHEN TEMPORARILY TURNING POWER OFF
TO THE PREAMP, ALWAYS USE THE AC POWER SWITCH ON THE REAR PANEL OF THE AC/DC
CONVERTER.
*NOTE:
PREAMPLIFIER VERSIONS 3.5 AND HIGHER REQUIRE POWER SUPPLY MODEL XPS7B
WHICH HAS A HIGHER OUTPUT VOLTAGE THAN MODEL XPS7A. DO NOT USE THE MODEL XPS7B
POWER SUPPLY ON PREAMPLIFIER VERSIONS EARLIER THAN 3.5 AS THE HIGHER VOLTAGE MAY
TRIGGER THE OVERVOLTAGE CIRCUIT AND CAUSE THE INPUT FUSES IN THE POWER SUPPLY TO
BLOW.
The 7PX3.5 has been designed for continuous operation from standard AC Power. Although
turning the unit on and off with each use will not unduly harm it, we recommend that it be
left continuously on when used on a day-to-day basis. This will prolong the lives of the
electrolytic capacitors in the power supply, minimize thermal cycling of the components, and
maintain the DC servos at zero volts. (see section on DC servos.) Power consumption is
approximately 10 watts.
Turn-on Delay
·
The 7PX3.5 is equipped with a circuit which prevents DC pulses from
reaching the outputs during turn-on and turn-off. Operation is as follows: When the AC Power
switch is first switched on, the main outputs are clamped to the ground for approximately 45
seconds to allow internal DC operating voltages to stabilize. During this delay period, the
LED indicator light will glow
Red
. After the delay, the LED will remain
Red
until the mute
button is depressed once. This will disengage the muting FETs and the main outputs will be
active. If the preamp is switched off, or if there is a power interruption during listening, the
LED will immediately switch to red and the outputs will again be clamped to ground.
Restoration of AC power will reset the 30 second delay. As this delay circuit actually senses
the level of internal DC operating voltages, it cannot be fooled into false or unnecessary
delay. Thus, a brief power interruption such as those caused by power substation switching
will mute the 7PX3.5 only if it is of sufficient duration to deplete the primary DC storage
capacitors. However, if AC line voltage is too low to maintain proper DC regulation, the mute
circuit will remain activated.
