How do you test vu meters and others?

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JRE Productions

Well-known member
Joined
Dec 10, 2004
Messages
255
Location
Chicago, IL USA
Several post say to test a VU with 750ma and a 3.2K resistor. And another recomened a 1ma test for SSL type meters.

I don't understand how to perform this test. What is needed? Maybe a quick expination or drawing would help me out..

Wow, I am sure this is simple, I just can't seem to figure it out.

Joe
 
Hey, I don't have a scientific reply to your question, but the vu meters I bought not long ago I tested by making a 1/4" cable that connected to the VU terminals on the other end and put either a 3.6k or 3.9k resistor (I doubt it really makes much diff, though one is the "standard" can't remember which) in series with the meter. then I plugged the cable into my patchbay where audio was coming out and the needle moved! Meter worked.
hopefully that helps you at least get started.
 
Thanks for replying. I think this is so simple the more techinical guys don't bother reading. But I got to learn somewhere!

Heres something I just tried after trying to decode a few "meter" posts here on the forum. I used the Diode tester on my Ohm meter. When I touched the probes to one of my edgewise meters I already own, the needle went about half way over. About center. And when I tested meters that I know are VU meters in the same way, the needle on most all of them went all the way over to the right quickly. I did have one vu meter that also moved to the right but did not peg the meter like the others did.

Not sure if this means anything or not. But the edgewise meter only moved about half as much with this test verses the VU's.

Can anyone comment on this test?

Joe
 
just the plus.


alwyas have at least a few ohms in series with the meter you are going to test so you don't smoke the shunt.

the clear edgewise meters are cool, becuase you can watch the shunt turn red and then fill the clear plastic meter cavity with smoke.

some meters have a rectifier bridge inside, some don't, so figure that part out first.
 
A real VU meter will possess three major characteristics... One is easy to measure, the other two are a little more work to measure.

1. With a 3.6K resistor connected in series with the meter, and 1.228V RMS at 1kHz applied across the resistor and meter, the pointer will deflect to 0 VU.

2. The meter movement and its built-in rectifier will present a load impedance of 3.9K to a 1kHz signal of level sufficient to drive the pointer to 0VU. (That's 0.775VRMS across the meter itself, 1.228VRMS across the meter and external series resistor combination).

3. The ballistics of the meter will possess certain standardized characteristics.

For more on VU specs, see:
http://groupdiy.twin-x.com/albums/userpics/10031/VU-1.png
http://groupdiy.twin-x.com/albums/userpics/10031/VU-2.png
http://groupdiy.twin-x.com/albums/userpics/10031/VUVIMeterBallistics.jpg

And here's a Usenet thread about testing a cheap "VU" meter to see how close it is to the real thing.

Thread
 
Thanks guys, that helps a lot.

Some of that was over my head, but great reading. So it seems that the 3600 ohms external, plus the 3900 ohms from the meter causes the 7500 ohms total when the meter is drive to 0db.

Thansks

Joe
 
Ok here's what happend:

I set up my HP signal generator at 1khz. I used my DMM to measure the output in AC volts. I set the signal generator so that the DMM read 1.22vac.

Using a 3.6K resistor in serial connection between the + of the generator and meter. The return was connected directly to the meter.

Meter 1: Went straight to Odb
Meter 2 was lower. If I removed the resistor it went to 0db (do some have the resistor built in?)
Meters 3/4: no movement with 1khz signal
Meter 5: no movement with 1khz

All meters move fine with the diode test on the DMM.

Results?

My guess is that meters 1 and 2 are true vu meters. Meters 3 and 4 are marked VU, but need outside components? Meter 5 is an edgewise, and I presume is a ma meter like the ones used in SSL.

Can anyone remark on these results?

Joe
 
1. Can't be certain yet if it's true VU but looking good so far.

2. Could be. That Calrad meter discussed in the Usenet thread has extra series resistance built-in and doesn't need an external resistor to read +4dBU. However, a true VU meter will always need that resistor. This one may be close-enough-to-VU-for-general-purpose-use like the Calrad, but this simple level test isn't conclusive.

3,4 and 5: Most likely just DC milliameters or microammeters with a VU-type scale
 
meters.jpg


THe meters are numbered from right to left. Starting with #1 being the large meter. 2 the middle unit and the pair on the left was labeled 3/4. 5 was a Edgewise is not pictured.


I also hooked each meter up to the resistor and to a 1/4" cable. I connected that to audio source on mixer. As seen above, the meters labeled 1 and 2 danced with the music. Meters 3,4 and 5 made no movement.
 
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