WhitakerAudio 60 W Stereo Power Amplifier, User And Assembly Manual

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60 W Stereo Power Amplifier
7 Performance Measurement
For performance measurements, the builder has three basic options:
• Run no further tests on the amplifier under the assumption that if built correctly it will
perform correctly. This may be a valid approach for an assembly line product where the
assembly process is well refined, but in the case of a custom-built audio device it is not
recommended.
• Perform tests at a typical operation level (e.g., 5 W output) and at the maximum rated
output of each channel (30 W). This is a reasonable approach and should yield valid
results under the assumption that if the amplifier can meet specifications at low power and
high power, then it can very likely meet specifications at other operating points.
• Perform comprehensive tests across a range of operating levels. This is the approach
detailed in the following section.
It is tempting, and quite acceptable, to put the 60 W stereo power amplifier into service upon
completion of the initial checkout steps detailed in Section 6. However, if the test equipment is
available, it is recommended that measurements be taken at various power output levels; e.g., 1
W, 5 W, 10 W, 15 W, 20 W, 25 W, and 30 W.
Measurements should be made on one channel at a time; the input terminals of the channel not
being measured are shorted. For the measurements, an 8 Ω 30 W noninductive resistor must be
connected to the output terminals of each channel. Target performance points for each channel are
given in Table 7.1. The values shown assume a bias voltage of –40 V dc and a B+ voltage of
approxi425 V dc. Note that the input voltages shown in the table will result in
approximately the desired power output. For simplicity, the input values have been rounded to a
convenient reference point for repeatability.
Table 7.1 Target Performance of Each Channel of the 60 W Stereo Power
Amplifier
Conditions Parameter Target Value Notes
Measurements taken at 1 W
power output
(2.8 V rms) Input voltage 0.15 V rms Volume control fully
clockwise
Frequency response ±1 dB, 10 Hz to 30 kHz
THD 0.4% Note 1
IMD (at 2.3 V rms output) 0.4% Note 2
Noise unweighted, (shorted
input terminals) –75 dB Volume control fully
clockwise