WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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• Phono Level controls for the right channel (R110) and the left channel (R120) = 1/2
clockwise rotation.
• Buffer amplifier gain settings for the Front Aux right channel (R164) and left channel
(R171) = 1/2 clockwise rotation.
• Gain control for the right channel (R156) and the left channel (R157) tone control circuits
= 2/3rds clockwise rotation.
After these preliminary steps have been successfully completed, operating levels should be
set, as detailed in the next section.
6.2.2 Setting Operating Levels
In order to achieve the best (lowest) noise performance from the preamplifier, it is necessary to
carefully set the operating points of the preamp stages. There are a number of variables involved.
The following steps are recommended prior to taking performance measurements. Be very careful
as hazardous voltages exist.
Note that a reference point is needed when setting the operating levels. In the steps that
follow, the Line input is assumed to be the reference point. However, the selection of available
source devices is wide and varied and as such it may be necessary to select a different reference
point, depending on the specifics of a given application. Operational experience is the best guide
here.
1) Confirm the front-panel settings detailed in the previous section. Connect an 8
Ω
load to
each speaker terminals. Connect an audio voltmeter to the right channel output terminals.
Connect an audio generator to the right channel Line Input jack on the back panel. Set the
Input switch to Line Input. Set the generator to produce 1 kHz at 1.0 V rms. Apply power to
the amplifier and allow a minute or so to warm up.
2) Advance the Volume control to the full clockwise position. Move the Balance control to the
full Right Channel position. Carefully adjust the right channel gain control on the
preamplifier PWB (R156) to produce 10 V rms output on the audio voltmeter. If an
oscilloscope is available, confirm that the amplifier is operating at just below clipping. With
a 1.0 V rms input, the typical position for R156 is fully clockwise.
3) Move the voltmeter to the left channel output, and move the generator to the left channel
Line input. Move the Balance control to the full Left Channel position. Carefully adjust the