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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Volts Per Octave Calibrator
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elmegil



Joined: Mar 20, 2012
Posts: 2177
Location: Chicago
Audio files: 16

PostPosted: Thu Jan 10, 2013 10:15 pm    Post subject: Volts Per Octave Calibrator Reply with quote  Mark this post and the followings unread

When I built my V/Oct Calibrator, I added an LED from the clock output to ground through a 3.3K resistor. The idea being I wanted to see the pulse of the clock.

Normally, When I'm using it, I'm stepping manually, so I didn't notice until recently that with the LED lit, it was causing my output voltage to droop.

I'm powering this from a good +/- 15V supply, not from a battery. When I measure the current through that branch of the circuit, it's only drawing 2.5mA so I presume it must be a low current LED (was something I bought early on when I didn't know to pay attention, so I don't know definitively).

For now, I've just cut the LED line to ground, but I'm still scratching my head over why it should be behaving this way. Does it have to do with the whole zener + cap power supply arrangement?

This is the circuit: http://www.musicfromouterspace.com/analogsynth_new/VPO_CALIBRATOR/pdf/oscillator_calibrator_schem.pdf

Anyone have any idea?

Thanks....
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brock



Joined: May 26, 2011
Posts: 112
Location: Canada

PostPosted: Fri Jan 11, 2013 11:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

The addition of the LED is probably exceeding the current capablility of the zener regulator which is less than 6 mA from a 15V supply. You could reduce R2 to get more current but you will probably find you are introducing a step error on the DAC due to zener current fluctuation causing a voltage variation when the LED is on or off.
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