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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
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Posted: Sat Apr 30, 2022 10:01 am Post subject:
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hm, just a guess...
only counting in the offset
the minus 4 Volt going in to 101d coming out as plus 2V
then these
2V and -4V coming out of 101a as 2V, right?
so the LED would be always on with no CV applied,
i guess |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Thu May 05, 2022 12:04 pm Post subject:
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gabbagabi wrote: | hm, just a guess...
only counting in the offset
the minus 4 Volt going in to 101d coming out as plus 2V
then these
2V and -4V coming out of 101a as 2V, right?
so the LED would be always on with no CV applied,
i guess |
yes, I think that is indeed correct, with no CV and the pan pot (PAN #1) at the center position.
with a supply voltage of -/+15V and R3 = R4 = 27K the output of 101a can be varied from -1V to +5V
by adjusting the pan pot. This is with T101 set to -4V so once properly calibrated itwill be slightly different.
It would be a good location to get a voltage to drive an LED but it requires some extra components to get it
working properly. Driving an LED so that it corresponds nicely with a varying voltage is a bit tricky.
The best way might be by using PWM but that get's a bit complicated for a single LED. Another way to do it
is with an opamp configured as a current source, or with a transistor. But all methods would need some extra
components and proper testing since it also depends on the used LED and the response you want. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Fri May 06, 2022 1:44 pm Post subject:
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I think I'm going to have to pull my build of this from my rack, and tack on some flying test wires.
I'm using the subcircuit in another module, and would like some kind of visual indicator |
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gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
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Posted: Sat May 07, 2022 11:33 pm Post subject:
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What comes quickly to my mind,
The difference between 101a and 101d is zero with no CV applied
With CV the difference will rise
Could be antiparallel LEDs + resistor between the two outputs a solution? |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Mon May 09, 2022 11:21 am Post subject:
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gabbagabi wrote: | What comes quickly to my mind,
The difference between 101a and 101d is zero with no CV applied
With CV the difference will rise
Could be antiparallel LEDs + resistor between the two outputs a solution? |
good thinking and worth trying. The forward voltage of the LEDs might create a large dark section
and it may affect the outputs of the opamps, it actually creates somewhat of a feedback path for U101a.
But it would be a nice and simple solution. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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