Calibration
There are eighteen trimmers on the SRE330. It will be useful to have access to an oscilloscope
and a frequency counter for the complete calibration routine.
All voltages should be measured with respect to a suitable 0V point. That is the black lead of
your meter should be connected to 0V. 0V is most easily found at the anode of D14 on the
SRE330 main board which is the end that is nearest to the power header.
Set the SRE330 so that the two modulation depth pots are at their minimum value.
CLK1
This sets the delay time of BBD line number 1.
Measure the signal at pin 6 of U32. Adjust CLK1 so that the frequency of the square wave is
approximately 75kHz.
CLK2
This sets the delay time of BBD line number 2.
Measure the signal at pin 6 of U38. Adjust CLK2 so that the frequency of the square wave is
approximately 75kHz.
CLK3
This sets the delay time of BBD line number 3.
Measure the signal at pin 6 of U43. Adjust CLK3 so that the frequency of the square wave is
approximately 75kHz.
CLK4
This sets the delay time of BBD line number 4.
Measure the signal at pin 6 of U51. Adjust CLK4 so that the frequency of the square wave is
approximately 75kHz.
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. The ideal point will be when the signal running through the BBD is at its
maximum without any degradation at the waveform peaks.
Input a 220Hz triangle wave or smooth sounding tone into the SRE330. Adjust the input level
so that the red PEAK LED is just lit. Turn down both modulation depth pots.
Adjust OFF1 so that the waveform seen at pin 1 of U31 is not clipping at either the top or
bottom of the waveform.
Adjust OFF2 so that the waveform seen at pin 1 of U37 is not clipping at either the top or
bottom of the waveform.
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