WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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20 W Stereo Integrated Audio Amplifier
– Using extreme caution, measure the following voltages (+/–10 percent is typical). These
measurements should be taken after the amplifier has warmed up (about 1 minute or
more):
• Terminal #1 on the left channel PWB barrier strip TB4 = +345 V dc. This is the B+ supply
voltage for the power output stages.
• Terminal #3 on the left channel PWB barrier strip TB4 = –30 V dc. This is the bias supply
voltage for the power output stages.
• Terminal V+ on the preamplifier PWB = +24 V dc. This is the V+ power supply for the
preamplifier stages.
– Switch the front panel Input control to Phonograph. Rotate the volume control to
maximum level. Some hum or noise should be heard from the right and left channel
speakers. Touch the center pin of the Phonograph input jacks on the back panel with a
small screwdriver. A loud hum should be heard as each channel is contacted. Switch the
front panel Input control to Line and then to Auxiliary. No hum or noise should be heard
in these positions.
6.2.1 Functional Tests
The purpose of the following functional tests is to confirm that the amplifier circuits are working
as expected. Detailed measurements will be taken later.
6.2.1.1 Default Settings
Remove all power from the amplifier and set controls to the following default positions.
1) Set the front panel controls as follows:
• Volume control set to approximately 12 o’clock position
• Input switch to Line Input
• Bass to center position
• Treble to center position
• Balance to center position
• Speaker switch to On
2) Set the gain adjust potentiometers on the preamplifier module as follows: