Ptownkid
Well-known member
what is the diff between say, a meter that says volts and a meter that says vu....is it just the label?
panel meters?
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cannikin
Well-known member
Hey You Mods - Let's start a Meter Meta...
cannikin
Well-known member
I have a question too.
If you have a meter sitting with no labeling, how do you figure out what its rating is.
Example: I have a meter with a resistance of 17K.
(let me guess you use Ohm's Law I=E/R to find the Ampere Rating?)
If you have a meter sitting with no labeling, how do you figure out what its rating is.
Example: I have a meter with a resistance of 17K.
(let me guess you use Ohm's Law I=E/R to find the Ampere Rating?)
> what is the diff between say, a meter that says volts and a meter that says vu....
ALL ordinary needle meters are current meters.
If they show Volts, there is (or should be) a resistor in there somewhere to scale volts to amps.
All ordinary needle meters are DC meters.
A meter with a VU scale is a DC current meter plus a resistor plus a rectifier to convert audio AC into DC.
A True VU Meter has tightly specified sensitivity, ballistics, frequency response, and induced distortion. True VU Meters were never cheap.
Cheap DC Voltmeters are usually a 1 milliAmp current meter plus a resistor of 1KΩ per volt full scale. i.e. a 15VDC meter is often a 1mA meter plus a total of 15K resistance, probably 100Ω in the meter and a 14,900 (or 15K) semi-precision resistor.
Full-scale on a VU meter is 1.09VAC. Ignoring rectifier details, a 1mA meter will need about 1K of added resistance for a total of 1.09K resistance. If you put this across a 600Ω line it will cause a significant drop of level. VU meters are 200uA movements to give a total impedance around 5K, a small load on a 600Ω line.
If you use a silicon diode bridge rectifier, you will get almost no indication at nominal 1.09VAC level, because two silicon diodes take over 1V before they pass much current. Real VU Meters used copper-oxide rectifiers, which have other faults, but do have lower voltage drop than silicon or even germanium.
If you really need to read audio levels, get something sold as a VU-like meter: it should come with appropriate rectifier and resistor.
If you need to monitor speech/music levels, you really want a True VU Meter, which probably means stripping an old Ampex or other pro-gear. A second choice is the many semi-VU meters found in TEAC and similar tape decks and mixers. I can see the difference between a True VU and a TEAC meter, but the ballistics on the better TEAC meters is acceptable.
The alternative is to use some opamps to rectify and buffer any old meter. You can't do much about slow meters not twitching transients well, but you can do your rectification better than a True VU Meter.
Special case: limiter GR meters are mostly reading a DC signal. Sometimes they are fed from a source much less than 600Ω. While it was traditional to use a VU meter here, because we had them, any DC meter can probably be adapted, though it will probably twitch slower than a VU meter.
> If you have a meter sitting with no labeling, how do you figure out what its rating is. Example: I have a meter with a resistance of 17K. (let me guess you use Ohm's Law I=E/R to find the Ampere Rating?)
You only have one number, and you need two numbers to do anything with Mr Ohm's masterpiece.
Get a 9V battery and a 100K resistor. Put them in series with the meter. If it goes past full-scale, use a larger resistor, if it barely moves try a smaller resistor. Say that 9V and 100K moves the needle to about 9/10ths of full-scale: 9V/100K= 90uA. If 90uA moves the needle 9/10ths, then it seems likely to be a 100uA movement.
17K is a very odd impedance: too high for a current meter, not a round number for a voltmeter. It may be an AC meter, and your DVM is confused by the rectifier.
> Hey You Mods - Let's start a Meter Meta...
This is YOUR forum. You start a Meta. Ethan, Jakob, and I only put on the mod-hat when someone makes a mess that has to be mopped-up.
ALL ordinary needle meters are current meters.
If they show Volts, there is (or should be) a resistor in there somewhere to scale volts to amps.
All ordinary needle meters are DC meters.
A meter with a VU scale is a DC current meter plus a resistor plus a rectifier to convert audio AC into DC.
A True VU Meter has tightly specified sensitivity, ballistics, frequency response, and induced distortion. True VU Meters were never cheap.
Cheap DC Voltmeters are usually a 1 milliAmp current meter plus a resistor of 1KΩ per volt full scale. i.e. a 15VDC meter is often a 1mA meter plus a total of 15K resistance, probably 100Ω in the meter and a 14,900 (or 15K) semi-precision resistor.
Full-scale on a VU meter is 1.09VAC. Ignoring rectifier details, a 1mA meter will need about 1K of added resistance for a total of 1.09K resistance. If you put this across a 600Ω line it will cause a significant drop of level. VU meters are 200uA movements to give a total impedance around 5K, a small load on a 600Ω line.
If you use a silicon diode bridge rectifier, you will get almost no indication at nominal 1.09VAC level, because two silicon diodes take over 1V before they pass much current. Real VU Meters used copper-oxide rectifiers, which have other faults, but do have lower voltage drop than silicon or even germanium.
If you really need to read audio levels, get something sold as a VU-like meter: it should come with appropriate rectifier and resistor.
If you need to monitor speech/music levels, you really want a True VU Meter, which probably means stripping an old Ampex or other pro-gear. A second choice is the many semi-VU meters found in TEAC and similar tape decks and mixers. I can see the difference between a True VU and a TEAC meter, but the ballistics on the better TEAC meters is acceptable.
The alternative is to use some opamps to rectify and buffer any old meter. You can't do much about slow meters not twitching transients well, but you can do your rectification better than a True VU Meter.
Special case: limiter GR meters are mostly reading a DC signal. Sometimes they are fed from a source much less than 600Ω. While it was traditional to use a VU meter here, because we had them, any DC meter can probably be adapted, though it will probably twitch slower than a VU meter.
> If you have a meter sitting with no labeling, how do you figure out what its rating is. Example: I have a meter with a resistance of 17K. (let me guess you use Ohm's Law I=E/R to find the Ampere Rating?)
You only have one number, and you need two numbers to do anything with Mr Ohm's masterpiece.
Get a 9V battery and a 100K resistor. Put them in series with the meter. If it goes past full-scale, use a larger resistor, if it barely moves try a smaller resistor. Say that 9V and 100K moves the needle to about 9/10ths of full-scale: 9V/100K= 90uA. If 90uA moves the needle 9/10ths, then it seems likely to be a 100uA movement.
17K is a very odd impedance: too high for a current meter, not a round number for a voltmeter. It may be an AC meter, and your DVM is confused by the rectifier.
> Hey You Mods - Let's start a Meter Meta...
This is YOUR forum. You start a Meta. Ethan, Jakob, and I only put on the mod-hat when someone makes a mess that has to be mopped-up.
Ptownkid
Well-known member
Awesome explaination PRR, it's posts like this that make me love you. Purely plutonic of course,
or is it......? :grin:
or is it......? :grin:
bcarso
Well-known member
[quote author="Ptownkid"]Awesome explaination PRR, it's posts like this that make me love you. Purely plutonic of course,
or is it......? :grin:[/quote]
I think you meant to say Platonic. Plutonic is very different (see igneous, metamorphic, sedimentary...).
Of course you could be getting sedimental too...
or is it......? :grin:[/quote]
I think you meant to say Platonic. Plutonic is very different (see igneous, metamorphic, sedimentary...).
Of course you could be getting sedimental too...
Ptownkid
Well-known member
Right you are
mikep
Well-known member
[quote author="datape"]so is an LED based metering system better?[/quote]
In some cases an LED meter can be better. They are often cheaper, more reliable and more compact. They can have variable ballistics. you can implement a hold function easier than with a mechanical meter.
But a true moving coil VU meter is pretty much unbeatable for helping you judge RMS levels. Even a nice dourroughs Isn't as good, IMO.
[quote author="datape"]
how do we avoid the drop in level when you put the meter across a 600Ω line?[/quote]
you buffer it with an amplifier that has a high input impedance. this also keeps the VU rectifiers from distorting the signal on said 600 ohm line.
mike p
In some cases an LED meter can be better. They are often cheaper, more reliable and more compact. They can have variable ballistics. you can implement a hold function easier than with a mechanical meter.
But a true moving coil VU meter is pretty much unbeatable for helping you judge RMS levels. Even a nice dourroughs Isn't as good, IMO.
[quote author="datape"]
how do we avoid the drop in level when you put the meter across a 600Ω line?[/quote]
you buffer it with an amplifier that has a high input impedance. this also keeps the VU rectifiers from distorting the signal on said 600 ohm line.
mike p
AnalogPackrat
Well-known member
[quote author="bcarso"]
Of course you could be getting sedimental too...[/quote]
We all tend to get more sedimentary as we age...
Of course you could be getting sedimental too...[/quote]
We all tend to get more sedimentary as we age...
Flatpicker
Well-known member
[quote author="cannikin"]Hey You Mods - Let's start a Meter Meta...[/quote]Someone beat you to it: http://www.groupdiy.com/index.php?topic=2483
Larrchild
Well-known member
Maybe by Plutonic, he meant loving him from afar. :roll:
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