GAIN1
This adjusts the signal volume that comes out of BBD2 which is the BBD we are
listening to when the ADR30 is in short mode.
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.
Connect your scope probe to pin 7 of U16. Adjust GAIN1 so that the signal seen here is the
same amplitude (ie. the peak to peak voltage) irrespective of whether the front panel's Balance
control is either at one end or the other. In other words, adjusting GAIN1 makes the wet
signal to be the same size as the dry signal. You will notice that the wet signal is not quite the
same shape as the dry signal as it has had a long and tortuous journey to get here.
GAIN2
This should be done only after GAIN1 has been correctly set. Connect your scope
probe to pin 7 of U16. Adjust GAIN2 so that the signal seen here is the same amplitude (ie.
the peak to peak voltage) irrespective of the position of the range switch. In other words, you
should adjust GAIN2 so that there is no volume change when listening to the wet signal when
the range switch is changed.
BAL
This trimmer adjusts the amount of high frequency clock breakthrough into the audio
output of the final BBD. You want to set this so that the smallest amount of clock is getting
through to the output.
Set your scope's input to AC, the time base to 5uS per division and the scaling to 500mV per
division. Turn the input level down on the ADR30 so that no signal is passing through the
delay lines. Set the delay time control to its middle position. Connect your probe to the emitter
of Q7, which is the right hand pin when the ADR30's pots are facing you.
Adjust the BAL trimmer so that the waveform amplitude seen on the scope trace is minimised.
Set incorrectly you'll see a kind of spiky square wave. Set correctly the trace will reduce to
just a series of spikes.
FBK
This adjusts the maximum amount of feedback available from the feedback control knob.
This one is set to taste and it can be set to allow no self-oscillation at all or at the other end to
allow self-oscillation readily. I set mine so that self-oscillation only occurs when the feedback
pot is beyond the 3 o'clock mark.
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