Adjust OFF3 so that the waveform seen at pin 1 of U42 is not clipping at either the top or
bottom of the waveform.
Adjust OFF4 so that the waveform seen at pin 1 of U50 is not clipping at either the top or
bottom of the waveform.
NULL1, NULL2, NULL3 & NULL4
These adjust the amount of high frequency clock
breakthrough into the audio output of each BBD. You want to set these so that the smallest
amount of clock is getting through to the output.
Set your scope's time base to 5uS per division and the scaling to 200mV per division. Turn the
input level down on the SRE330 so that no signal is passing through the delay lines. We need
to monitor the voltage at the input to the first low pass filter for each of the four BBD circuits.
These are the solder pads nearest to the front of the unit of R159 for BBD1, R187 for BBD2,
R206 for BBD3 and R236 for BBD4.
Adjust the relevant NULL 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. Do this for all four BBD lines.
T_FRQ
This sets the frequency range of the triangle LFOs.
Set TYPE to MULTI and the triangle rate pot to its maximum value. Set your scope's time
base to 5mS per division and the scaling to 2V per division.
Monitor the voltage at pin 1 of U8. Adjust T_FRQ until you get a 50Hz triangle wave.
T_LVL
This sets the maximum output level of both triangle wave LFOs.
Set TYPE to MULTI, and the triangle rate and depth pots to their maximum. Set your scope's
time base to 5mS per division and the scaling to 2V per division. Then monitor the voltage on
pin 1 of U13 and adjust T_LVL until you get a 10V peak to peak signal.
S_FRQ
This sets the frequency range of the sine wave LFOs.
Set TYPE to MULTI and the sine rate pot to its maximum value. Set your scope's time base
to 5mS per division and the scaling to 2V per division.
Monitor the voltage at pin 1 of U20. Adjust S_FRQ until you get a 50Hz triangle wave.
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