Page 18 CX335 Technical Manual
9.05
THD (Total harmonic distortion, Presets marked PR1 for the left channel and PR3 for the
right channel). No adjustment should be made to the THD presets without the use of an
accurate THD meter. Correct adjustment will leave the preset approximately central about
its track. A level of 0.015% distortion or lower can be expected (especially if the bottom
panel is still attached to the unit).
9.06
Apply +20dB input level. Rotate the Peak Level control counter clockwise whilst observing
the output level. Note that the Limit LED will start to illuminate at the onset of limiting (ie
as the control passes through the +20dB graticule). The output level should continuously
decrease as the control is slowly rotated, until a point were -6dB output level can be seen
when the control is fully counter clockwise. The Gain Reduction meter should be
illuminated up to the 20dB LED when this condition is applied.
9.07
COMPress, SOFT law & HARD law (Presets marked PR5, PR6, PR9 and PR7, PR8).
Because of the interactivity of the presets in this section, they have been grouped
together into one test. However, things are not as daunting as might be as presets PR6
and PR9 only apply to frequencies over 200Hz, (calibrate using 1KHz) and presets PR7
and PR8 apply to signal frequencies lower than 200Hz (calibrate using 100Hz or lower).
To commence these tests, the Hard and Slow switches must be released. Apply
maximum Compressor ratio and threshold (both clockwise).
Reduce the input level to -20dB. Observe the following readings at the output when the
test signal level is adjusted in 10dB increments and ensure the GR meter on the front
panel tracks accordingly:
INPUT LEVEL READ EXTERNAL VU
METER (APPROX)
VOLTS @ D8 ANODE
FOR HIGH
FREQUENCIES
VOLTS @ D11 ANODE
FOR LOW
FREQUENCIES
-20dB -20db 300mV 420mV
-10db -14dB 1.2 V 1.5 V
0db -10dB 2.9 V 3.1 V
+10db -10dB 5.0 V 5.0 V
+20db -10dB 7.25 V 7.0 V
The most important measurement using the above table should be the output level
remaining constant when +10dB and +20dB input level is applied. The table above shows
this level should give a reading -10dB. The amount of compression law can be adjusted
with preset PR5. Use preset PR6 to adjust the point at which compression 'levels off' with
high frequency input, and PR9 for low frequency input (-10dB in the above table).
Depress the Hard switch. Step the input signal level between -20dB and +20dB in four
10dB increments, whilst adjusting PR7 for high frequencies and PR8 for low frequencies
to show no output level change at all. Mis-alignment might cause 'fold-over', where the
output starts to decrease as input signal increases. The actual level will vary from unit to
unit but should be in the region of -21dB to -25dB. More importantly is that the constant
output level should be similar for both low and high frequencies.
With the Hard switch still depressed and a Ratio setting of 2:1 the following input and
output levels should be seen:
For an input of -20dB, read -20dB at the output.
For an input of 0dB, read -10dB at the output.
For an input of +20dB, read 0dB at the output.
(15 pages)
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