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Calibration instructions for Setback?

Started by SugarKeys, December 17, 2022, 12:11:16 AM

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I've built the Setback and am starting calibration.

It looks like the clock circuit is happy - my little pocket scope shows a nice clean square wave of about 11 V peak to peak coming off the MN3101.

The calibration instructions state "Starting conditions: Set all knobs and trimmers to 50%." Presumably this includes the Delay knob. But no twisting of the Clock trimmer gets me anywhere close to the stated 6.5 kHz target frequency.

By my reckoning, 4096 stages = 2048 pairs of stages, divided by 6.5 kHz gives 315 ms, which I would expect as an approximate value for the Delay knob at max - should the instructions perhaps read "Starting conditions: Set the Delay knob to maximum, and all other knobs and trimmers to 50%"?

With Delay at max, the Clock trimmer gives me about 5.5 kHz at full CCW and about 8 kHz at full CW. Which looks like a perfect range to dial in for step 3, when I'll dial it back to around 6 kHz or until I don't hear artifacts. With Delay at 50% I see around 25 kHz (82 ms) and at minimum I see around 50 kHz (4 ms).


If you're going the o-scope/frequency counter route, max out your delay knob to maximum delay time when measuring the frequency on your mn3101.  Then adjust the clock trimmer to 6.5 kHz.  The sweet spot for a single mn3005 delay is around 6.5 to 6.8 kHz.  That usually gives the most delay time with minimum clock noise.
The kind of guy who sticks a fork in his Dr. Pepper... If you know what I mean.


Thank you! So max it out, instead of setting it to 50%. I think the PDF instructions have a minor error, then.

Can't wait for my batch of MN3005's to arrive so I can finally finish the build  8)