EM84 based VUmeter "lines" don't go to zero - diyAudio
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Old 17th August 2006, 07:23 PM   #1
Danko is offline Danko  Hungary
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Default EM84 based VUmeter "lines" don't go to zero


I have built this circuit:
The problem is, when there's no input signal to the circuit, then there are still lines on the tube.
The lines are a little bit longer than they:

What could be the problem? Could somebody help me? :-)
Best regards, Danko
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Old 18th August 2006, 02:50 PM   #2
EC8010 is offline EC8010  United Kingdom
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Do remember that "magic eye" tubes are not precision devices. What you're seeing is quite normal...
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 18th August 2006, 03:16 PM   #3
jane is offline jane  Norway
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Is there any difference if you ground the grid of the magic eyes (e.g. short the 1M2 grid-leak)? If yes, you might try to decrease the value of the grid-leak.

Just my 0.2dB
Life is hard - Then you die.
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Old 18th August 2006, 03:27 PM   #4
anatech is offline anatech  Canada
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Hi Jane,
Just my 0.2dB
I like that!

EC8010 is right Danko. They were only ever meant for rough signal indication. Good luck on your project! It will look really neat.

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Old 18th August 2006, 10:32 PM   #5
coresta is offline coresta  France
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Hi! the NIXIE IN13 or 14 bargraphs look more linear . I've been testing one and linearity is my 0,5 dB
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Old 19th August 2006, 11:04 AM   #6
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On my magic eye vu-meter, i simply biase the tube as a grounded cathode, for the fully closed voltage. Works a treat and it's simple! Just about 3 resistors and you're done.
"There's something organic about a happy cloud of electrons" - Neutron Bob
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Old 20th August 2006, 10:29 AM   #7
Danko is offline Danko  Hungary
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Thanks for everyones response!!

If I short the 1.2M resistor, then the signal doesn't get to the tube, so that's not a solution.

I tried to insert a trimm.pot between the cathode and the GND. But when I started to increase the trim.pot's resistance, then lines started to grow longer.

When I turn off the amplifier, the lines are getting longer, when the B+ is decreasing.

Maybe the B+ isn't high enough in my amplifier? Under steady state, when all the tubes are warmed up, the B+ is 320V.
Best regards, Danko
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