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Douk VU3 Review (VU Meters)

AdamG247

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Not that it measures power…
But it says right in the face “Peak Power Level” ? Just kidding so don’t take this seriously.
 

Madjalapeno

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We need a picture for heaven's sake!!! :)

I gave you the important pictures already - how it performs ;)

Here is the bare board, the Neurochrome input selector and a video showing how it compares to the display on the MOTU M2. This looks a mess, because I was only testing to see if it was worth pursuing further, or just wasting my time. It also has the ugly meter in the video.

IMG_4234.jpeg


Even though it says AC12-18V input, it's working fine with 12V DC. The three variable resistors are to adjust brightness and each meters sensitivity.

IMG_4235.jpeg


 

solderdude

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The LM78M12 on that board, to operate properly, needs at least 1.2V above the output voltage (12V) and the rectifier will eat up 1V as well so min. 14.2Vdc is needed, lets say 15Vdc or 12VAC.

It will work at 12V but not exactly as intended.
 
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Madjalapeno

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The LM78M12 on that board, to operate properly, needs at least 1.2V above the output voltage (12V) and the rectifier will eat up 1V as well so min. 14.2Vdc is needed, lets say 15Vdc or 12VAC.

It will work at 12V but not exactly as intended.
And that is why I love reading this site. Thank you. The input selector will work on 8-25V, so not a problem.
 

solderdude

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The meter PCB can operate from 15Vdc to 25Vdc, so any DC voltage between these values will power both PCB's just fine.
 

rdenney

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Spot on. Making an instrument that measures meaningful parameters is a challenge. You want it cheap and good? It won't be fast then. I'm thinking delivery in about 100 years from now. I'll procrastinate until 99.9 years from now... :)

If all you want is bling, why not just turn on the visualizations in your media player? They provide as much information as the dancing needles do.

I had the exact same thoughts regarding the power measurement. You need V*I for that. You can certainly sense the current, but for the lowest impact on the system, you want the sense resistor to be small. This means you now have a tiny signal that needs to be amplified. Someone might use a BTL output amp with the meter, so you need a sense amp that can provide a precision measurement of a few mV across a resistor that bounces around within a ±100 V voltage range. That's a challenge in and of itself.

Then you need to multiply V and I to get the power. Feed that into a logarithmic amp to get the output in dBW. Analog multipliers do exist and log amps can be made by adding a transistor in the feedback path of an opamp. But will they actually be accurate enough to provide a valid reading? You'll need a peak detector. That part at least is easy. And you'll need to present the result on a graph of sorts (LED bar or moving coil meter).

One could turn it into a software project by throwing a micro controller at it.

That said, if one was willing to accept that the meter didn't read out power but rather voltage and maybe also that it wasn't terribly accurate, there are some options. One could simply have two scales: One for 4 Ω and one for 8 Ω (ignoring that the impedance of a speaker will be neither and also that it won't be constant with frequency).

If one wanted to measure the INPUT voltage and have it indicated in dBu (= 0 dBm ref. 600 Ω) the solution space expands greatly. In fact, grab any DIY electronics magazine from the 1980s and you'll likely find a circuit that'll make some LEDs blink to the music, possibly even with some indication in dB. LM3915 and LM3916 were popular ICs for this. They've long since been discontinued.

Tom
I recommend taking a look at the Crown OC-150 documentation that was linked upthread. It provides an interesting feature: A hold circuit that electronically measures a true RMS peak and holds the meter at that level for some user-set time. This could be used usefully, in conjunction with an LED peak indicator.

Another way is to use a row of LED's, which is so very '80's but it would work. With a calibration capability, one could calibrate it so that the peak LED lit just as the clip indicator lit. The amp I'm buying has a clip indicator output on the Hypex module, and I will be implementing that.

And then I wonder about repurposing old VOM's, some of which had really nice meter movements. How about a pair of Simpson meters with a new scale? Just reading voltage, or calibrated to a clip indicator, would do the job, probably.

Rick "the old Simposn VOM's might be way too expensive, but maybe not a pair of Micronta VOM's" Denney
 

MakeMineVinyl

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I recommend taking a look at the Crown OC-150 documentation that was linked upthread. It provides an interesting feature: A hold circuit that electronically measures a true RMS peak and holds the meter at that level for some user-set time. This could be used usefully, in conjunction with an LED peak indicator.

Another way is to use a row of LED's, which is so very '80's but it would work. With a calibration capability, one could calibrate it so that the peak LED lit just as the clip indicator lit. The amp I'm buying has a clip indicator output on the Hypex module, and I will be implementing that.

And then I wonder about repurposing old VOM's, some of which had really nice meter movements. How about a pair of Simpson meters with a new scale? Just reading voltage, or calibrated to a clip indicator, would do the job, probably.

Rick "the old Simposn VOM's might be way too expensive, but maybe not a pair of Micronta VOM's" Denney
Aren't the meter movements on those old VOMs way too slow for VU meter duty? I seem to remember from my high school electronics lab days that they took their time to settle down. I also remember Missy, who was fun, and not slow. :cool:
 

rdenney

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Aren't the meter movements on those old VOMs way too slow for VU meter duty? I seem to remember from my high school electronics lab days that they took their time to settle down. I also remember Missy, who was fun, and not slow. :cool:
With a peak hold circuit ala Crown, it wouldn't need to be fast. But you are probably right--I suspect they are damped but I don't know how. They sure do look nice, though.

I'm thinking a line-level VU meter would also work. Instead of VU, call it dBFS, and calibrate 0 dB to the clip indicator (that would require some care--ha!). But now it's injected into the low level signal, so it would need a very high impedance to avoid affecting the signal.

Rick "who has a Heathkit RF monitor in the radio pile somewhere--it used both a meter and a scope ala that Pioneer unit linked upthread" Denney
 

Madjalapeno

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Aren't the meter movements on those old VOMs way too slow for VU meter duty? I seem to remember from my high school electronics lab days that they took their time to settle down. I also remember Missy, who was fun, and not slow. :cool:

well if anyone has an old AVO meter, I'd be happy to try it

avo8-top.jpg
 

Madjalapeno

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Yeah, that's what I need to do. Set this up next to my amp:

Trio-uV-meter.JPEG


Rick "riiiiight” Denney

And listen to some very gentle music.
 

MakeMineVinyl

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With a peak hold circuit ala Crown, it wouldn't need to be fast. But you are probably right--I suspect they are damped but I don't know how. They sure do look nice, though.

I'm thinking a line-level VU meter would also work. Instead of VU, call it dBFS, and calibrate 0 dB to the clip indicator (that would require some care--ha!). But now it's injected into the low level signal, so it would need a very high impedance to avoid affecting the signal.

Rick "who has a Heathkit RF monitor in the radio pile somewhere--it used both a meter and a scope ala that Pioneer unit linked upthread" Denney
I could probably whip up a microcontroller program to make a very nice peak level meter. :)
 

Moulin

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Many of us want VU meters without having to pay through the nose.

I'd be on board with this.



JSmith
Me too. As a side note: can’t this thing just be plugged into tape out without ruining the SQ of the system?
 

Moulin

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I could entertain the thought of designing a DIY VU meter, though. Would LED indication of peak and average power be OK?

Tom
Hi Tom, if you mean bar meters I would decline, I’m a fan of old school needle meters and am v interested in adding a pair to my setup
 
OP
amirm

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Me too. As a side note: can’t this thing just be plugged into tape out without ruining the SQ of the system?
If you can be sure that the tape out is fully buffered and not a pass through connection.
 

pseudoid

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Set this up next to my amp:
Try setting up the "amp next to" your VU meter, instead...
Snag_1d824a12.png

...ONLY because parallax is even a bigger issue if there is no mirror where the graticules reside.:rolleyes:
 
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