OFF1, OFF2, OFF3 & OFF4
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.
Input a triangle wave or smooth sounding tone into the SE330. You can use a keyboard and
hold down the A key to give you a constant 440Hz tone. Try not to make it too bright and
don't use a square wave. Adjust the input level so that the peak LED is just starting to glow
dimly. Turn down both modulation depth pots and set the balance pot to wet. Select
dimension mode.
Listen to the left output of the SE330 only and adjust OFF2 so that the sound is not distorting.
There will be a point at which the sound is not distorting noticeably while either side of it
sounds thinner and grubbier.
Now select quad mode. The sound from the left channel will be louder. Adjust OFF1 until the
sound is not distorting noticeably.
Listen to the right hand output only and select dimension mode again. Adjust OFF4 so that the
sound is not distorting.
Now select quad mode. Adjust OFF3 until the sound is not distorting noticeably.
NULL1, NULL2, NULL3 & NULL4
These adjust the amount of high frequency clock
breakthrough into the audio output. You want to set these so that the smallest amount of
clock is getting through to the output.
If you have no scope then just set this trimmer to its middle position. Although this sounds
pretty imprecise it's actually not too far from the perfect setting.
If you have access to a scope you can tweak it more exactly. Set your scope's time base to
5uS per division and the scaling to 200mV per division. Turn the input level down on the
SE330 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. This is the lower solder
pads of R13 for BBD1, R15 for BBD2, R17 for BBD3 and R19 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. Insert an audio input into the
SE330. The A440 note is a good one to use again. Set the triangle rate and triangle depth pot
to their middle settings. Set the sine wave pots to their minimum. Select the dimension mode
and turn the balance control to wet. Make sure the peak LED is not lit and listen to the left
output only. You should hear the pitch being modulated. Adjust T_FRQ so that you hear the
dee-dah sound repeating once a second.
If you have a 'scope, monitor the voltage at pin 1 of U3. Set the triangle rate pot to its
maximum value and adjust T_FRQ until you get a 50Hz triangle wave.
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