"VU"-meter. movie inside

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ChrioN

Well-known member
Joined
Aug 31, 2005
Messages
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Location
Gothenburg, Earth
I just built a driver for a meter I got. Its like PRRs design ( http://www.electronaut.info/public/PRRMeterAmp_02.gif ) but with some changes.

Instead of using 1Mohm resistors I used 470Kohm, and all the capacitors were 0.1uF. I powered the circuit with a 24vdc wallwart. The opamp is a JRC4556. Oh, and I skipped the 3.6Kohm resistor i serie with the meter.

Now. The meter reacts very differently with different frequencies. When the volume is low, the needle only reacts to bass..

I filmed the meter while I putted a sinustone through it. You can see clearly that the needle goes down when a high frequency is put through it. The mic on the camera is a joke, I don't know what the frequencybandwith is, somewhere between 200hz-10khz.

the clip is roughly 2.2mb
http://hem.bredband.net/b237697/vu.avi
 
[quote author="ChrioN"]Now. The meter reacts very differently with different frequencies.[/quote]

That's VU meters for ya!

[quote author="ChrioN"]Can we conclude that most not true vu-meters are garbage?[/quote]

I farted this morning. It didn't smell. Can we conclude that most farts don't smell? :razz:

Peace,
Al.
 
[quote author="alk509"]I farted this morning. It didn't smell. Can we conclude that most farts don't smell?[/quote]

Aaaaaaaaaaaaaaaaaaaaaaahahahahahahahahahahaha
 
Looks to me like your meter needle was sticking. Is there a problem in the meter, perhaps? Did you test both meters? Did you test the meters without the circuit? You want to eliminate the variables.

PRR might be able to comment on the circuit you used.

You should not be having frequency variations in a meter, even cheap meters.

[quote author="ChrioN"]Can we conclude that most not true vu-meters are garbage?[/quote]

No, you cannot conclude that. The Sifam AL series (Audio Level) are not true vu meters, and they are very useful, many of us use them here. But if you mean most $5 meters, well maybe you are right. :grin: I haven't tried those.

However, even the best vu meters are not accurate in reality. Or rather, they are only accurate in a portion of their scale. PRR has posted about this eloquently here. VU meters are just rough indicators and guides, and when you take into account their inacuracies, etc. they can be useful IMO. But they are not accurate. This is one reason why non true vu-meters can still be useful. We don't expect total accuracy.

I would test your circuit with better meters, then you'll know if it's the circuit or the meter.
 
[quote author="tommypiper"]You should not be having frequency variations in a meter, even cheap meters.[/quote]

That runs contrary to my experience... I couldn't tell from the movie which deflections were caused by frequency changes and which by amplitude changes, but all meters definitely have their own wacky frequency response - it's the nature of the beast, with meter movements being basicaly an inductor inside a magnetic field. You may try to damp the movement a little with some resistance or something...

Peace,
Al.
 
What is your signal source? That's not an H-P 200AB, is it? Or any sort of Wein? All those things bobble badly when swept rapidly.

A few K in series with the movement helps swamp coil inductance.

With resistor, most junk meters should be pretty flat from the low freq where they jiggle a lot up to above 5KHz. That's ample for general speech/music monitoring. For line-up, get a proper VU meter, a good ACVM, or something with LEDs.
 

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