Calibration
There are eight trimmers on the ADR30 main board. It is essential to have access to an
oscilloscope to complete the full calibration routine.
All voltages should be measured with respect to a suitable 0V point. That is the ground lead of
your scope probe should be connected to 0V. 0V is most easily found at the anode of D4 on
the ADR30 main board (ie. the pin of D4 nearest the front of the board)
RANGE
This adjusts the range over which the voltage controlled oscillator that directly
controls the delay time operates. Set the ADR30's modulation depth pot to its minimum. Set
the delay time pot to its maximum. Wait a few minutes for the VCO circuitry to stabilise. The
temperature of Q3 will affect the VCO frequency and it heats itself when the frequency is high
so must be allowed to cool before making this adjustment.
Connect the scope probe to pin 1 of U1. There should be a square wave of 0V to 15V here.
Adjust RANGE so that the frequency is approximately 6.5kHz (+/-200Hz).
WIDTH
This adjusts the width of the pulse train that controls both sets of switched capacitor
anti-aliasing filters. Connect the scope probe to pin 6 of U3. There should be set of narrow
15V pulses at around 52kHz. Adjust the time base of the scope to 500ns/division so that you
can measure the width of the pulses. Adjust WIDTH so that the width of the pulse at 5V is
approximately 1.2us.
OFF2 & OFF1
These adjust the bias point of the respective BBD line's input signal. If this
voltage offset is set too high or too low then the output signal of that BBD will distort too
easily. The ideal point will be when the signal running through the BBD is at its maximum
without any degradation at the waveform peaks.
Set the range switch to short, and set the delay time pot to its central position. Input a 220Hz
triangle wave or sawtooth wave into the ADR30. Adjust the input level so that the red PEAK
LED is just lit.
Adjust OFF2 so that the waveform seen on your scope at pin 15 of U5 is not clipping at either
the top or bottom of the waveform. Clipping will be seen as an obvious flat lining to the top of
the waveform and a rounding out of the bottom of the waveform. The ideal position of the
OFF2 trimmer will be halfway between the two points that do show clipping. It is best to set
your scope's input mode to AC.
Set the range switch to long. The audio signal will now be going through both BBDs.
Adjust OFF1 so that the waveform seen at pin 15 of U5 is not clipping at either the top or
bottom of the waveform. Again, the ideal position of the OFF1 trimmer will be halfway
between the two points that do show clipping.
8
