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Douk VU3 Review (VU Meters)

tomchr

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The problem with meters on outputs of amps is that they can only measure the output voltage.
When they must say something about the power (and have a scale stating power) one would also have to measure current without resorting to a low resistance in series so a current probe.
With both current and voltage one can create a 'power' scale independent of the speaker impedance.

Creating a meter that really says something thus isn't as easy as a meter jumping up and down and really saying nothing. The latter is what most want... bling.

For that... just buy this Douk thing and connect the meter in parallel to the speakers and be done with it.
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
 
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amirm

amirm

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If all you want is bling, why not just turn on the visualizations in your media player?
The problem with this is the pipeline latency from player to the output of the system/DAC. There is enough delay that I find that annoying relative to music beats. Then again these VU meters are not very fast so maybe it is workable. I love my RME DAC visualizations since they have such a low latency. This becomes even more important with respect to spectrum analyzer where to identify where some frequency comes in.
 

Doodski

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If only there where dedicated EQ with LEDs display... Hmmmz Technics SH-8055
technics.jpg
 

Doodski

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How noisy was that equalizer though? The few I played with years ago had significant noise.
Some of those oldies add a little hiss to the output. I don't remember this one being horribly bad or noticeable. As a plus it has pink noise and should have a microphone too.
 

tomchr

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How about displaying the average and peak voltage on some 7-segment LED displays? Could even be in amber yellow, Amir's favourite colour. Maybe have it update twice a second or something.

Tom
 

restorer-john

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How noisy was that equalizer though? The few I played with years ago had significant noise.

It seems most of the people here on ASR who want meters, only want them for the pretty light/movement display.

An eq with a couple of VFD spectrum analyzers can just be fed via tape out or Y from the source. You don't have use the eq outs if you just want the dancing lights display. So no hiss problem.
 

restorer-john

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How about displaying the average and peak voltage on some 7-segment LED displays? Could even be in amber yellow, Amir's favourite colour. Maybe have it update twice a second or something.

Switchable nominal 4, 6 or 8 R with peak hold times of zero, 1 and 3 seconds. Range switch to make the most of the display.

My Luxman M-03 has such a meter. VFDs, (bespoke) microprocessor controlled. No latency, it will accurately display millisecond transients. Sure, it's voltage derived, but a fabulous meter.

Why not use a current transformer like your little project for I sensing?
 

Doodski

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Vu or LED power meters- I like to know how fast I'm driving my amp- like the reviews.

How about displaying the average and peak voltage on some 7-segment LED displays? Could even be in amber yellow, Amir's favourite colour. Maybe have it update twice a second or something.

Tom
Dual scales c/w RMS Watts and Volts peak individually selectable for each meter. :D
 

tomchr

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Switchable nominal 4, 6 or 8 R with peak hold times of zero, 1 and 3 seconds. Range switch to make the most of the display.

Why not use a current transformer like your little project for I sensing?
Is the display even readable with zero hold time?

A current transformer did occur to me. That may be an option. The transformer bandwidth seems to be dependant on the sensed current, which is probably not ideal.
Triad_CST-1030__Amplitude_Deviation_vs_Current_Zload_102_ohm_Ref._1_kHz_-_Annotated.png

Dual scales c/w RMS Watts and Volts peak individually selectable for each meter. :D
Me thinketh you've been partaking in the medicinal herbs. Not that there's anything wrong with that... :)

A simple solution for an LED bar graph meter would be to print two scales on the front panel. One for 8 Ω and one for 4 Ω. Saves a switch.

Tom
 

restorer-john

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GarooowlZZzzzz . Luxman M-03... I don't suppose you have a C-03 too?
1918728-a23cf240-luxman-m03-and-c03.jpg

I did have, but sold it years ago. It was disappointing and not up to Lux's standards at the time (Alpine).

The M-03 is a powerhouse, produces over 350W/ch at 4R. It's one of my favourite power amps, sounds better than the Denon POA-1500 and the POA-2800 and anything Yamaha in my collection.
 

Doodski

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Luxman M-03 @ +/-81VDC rails and uses nice Sanken outputs on a decent heat sink.
100_1735.jpg

100_1737.jpg
 

restorer-john

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A current transformer did occur to me. That may be an option. The transformer bandwidth seems to be dependant on the sensed current, which is probably not ideal.

Maybe three switchable ranges with individual compensation at the LF end to bring them into line. Maybe even a switchable LPF for people to see if there's any content out of band cooking their tweeters?
 
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