Douk VU3 VU Meter Review (Updated Version)

[solderdude]

The 5V is for the LED's, the relays and remote control. It will also be used to power the meter circuit (incl. the peak LEDs).
The meter itself is probably at FSD with less than 1V and requires a few mA at most.
To damage the actual meter it would have to hit +10dB or more for a long time period. It would be really a daft design if it could not be used with amps >100W (it does not even say 4ohm or 8ohm which makes a huge difference) and the meter would break. It would be really, really easy to limit the input voltage to the meter circuit.

Of course it might be that when the meter is set at minimal sensitivity the meter would indicate '+5dB' but again... in 4 ohm or 8 ohm ?
100W in 4ohm is 50W in 8ohm (voltage wise and it measures voltage).

 

[KEFCarver]

That would be extremely unlikely. When it is the amplifier load (the small transformer) then that won't change much. Maybe it could even be worse even.
When it is the power relay (which aren't really suited as signal relay) then it is unlikely to change.

When you want to ONLY use the meters (just for the sake of seeing meters indicating nothing really) then you should connect the speaker directly to the amp (so NOT via the VU3) and connect the VU3 in parallel to the speaker.
There will be no increase of distortion in this case. This is assuming the (inaudible amount if increase in distortion when using a high SINAD power amp/system) is not caused by the load of the VU3.
Personally I suspect it is the relay that is the culprit of the (ONLY measurable) increase of distortion.

This would have to be measured though.



I bolded the important part.

I have tested two of these and they both had the same problem- the response is up 1dB at 20hz. I believe the problem relates to the VU circuit which uses transformers to couple the output to that circuit. I found the VU meters to be of little use to be honest, and required a lot of playing with the sensitivity control- I would use something more accurate than the built in VU's if I were doing an A/B test.

 

[Laniciffo]

The 'peak' led might just be the electronics over voltage warning.

 

[Laniciffo]

Just had a look at the user manual.
The 100 W limit really is a power limitation :

'1. It is better not to connect VU3 to amplifiers whose actual output power is greater than 100W, or else VU meter may be damaged. 100W refers to the actual power output from amplifier to the speaker. For example, your amplifier max can output up to 200W, but you only use it in the room and turn on the volume to about 20W. The actual power is 20W but not 200W'

 

[DualTriode]

I honestly also thought you where Joking... You know your hand held SPL meter has a transducer in it right?

I tell my wife that humor is at least half serious.

Oh yes, there is a transducer probably like this one.

https://www.digikey.com/htmldatasheets/production/102900/0/0/1/wm-61a-b-datasheet.pdf

 

[NoxMorbis]

The SINAD of an amp does not matter.

Most likely the extra contacts (2 extra plug/socket/clamp) + relay contacts are more than likely the culprit when routing the speakers through this (or any other) speaker switch box.
Not the device itself, nor the connection of the device through a wallwart nor it being powered or not.

Depending on several factors around the switchbox the 'extra' distortion products (way below any audible thresholds) the added distortion may become more visible in plots.
So a high SINAD amp will become a worse SINAD amp (in essence) and an amp with a low SINAD will also add the same amount of distortion but may be 'drowned' in that of the amp so not visible in plots.

So... when the goal is to see meters swing up and down there does not have to be ANY degradation at all, it is just a matter of not using the switchbox functionality in that case.
When the goal is to switch amplifiers and or speakers than any speaker switch box could add a similar amount of 'distortion'.

Regardless of the SINAD of the amp/system.
With a very high SINAD amp you can measure the differences in lab conditions, yet will remain inaudible.
With a very low SINAD amp you will not find the 'extra' distortion in the measurements and it will also be inaudible.

The key here is inaudible. Measurable is not the same as audible.

Nice explanation. So as far as audibility goes, this switch-box/VU meter is transparent (no audible difference)?

 

[ocinn]

The 100W limit is not only caused by the relay.

I was referring to running the meter in parallel with the speaker load, with nothing connected to the outputs of the meter. You'd lose all the switching capability, in exchange for no degradation by not having it not sit between the amp and speaker. There would be practically zero current passing thru the unit, save for the small residual amount caused by its own (likely sky-high) input resistance, no?

 

[solderdude]

I was referring to running the meter in parallel with the speaker load, with nothing connected to the outputs of the meter. You'd lose all the switching capability, in exchange for no degradation by not having it not sit between the amp and speaker. There would be practically zero current passing thru the unit, save for the small residual amount caused by its own (likely sky-high) input resistance, no?

Ah... well the 100W limit would still apply for the internal dummy load. That dummy load really cannot handle that power though but might survive 100W peaks in music.
I don't think many owners will use 2 amps with one speaker though and leave the not used amp running.
Douk calls this feature 'amplifier no load protection'. This is the component that will fail and make the device smoke.
For AB-ing 2 amps they would have to be on and running and the meter could then be used to check for level differences. Of course that meter could never resolve 0.1dB or even 0.5dB I reckon so even for that it is not really suited.
But yes, the '100W' (in what impedance) limit most likely is not an issue. That is... unless the meter, in the most insensitive setting would read +5dB at '100W' (who knows what impedance). That would not 'break' the device though. Nor would I believe you could harm the device with 300W peaks in a speaker unless those relays are really crappy.
The only thing that could really be 'damaged' would be the internal dummy load.

If the meter was set to 'most insensitive setting' it is still unknown what power (in what impedance) is indicated when the meter shows '0dB' nor what the max. voltage would be.
In that regard it is a totally pointless meter (not calibrated to any value) and basically only suited to watch 2 needles swaying to the music and maybe seeing peak-LEDs blinking.
Here too there is no way to tell what setting leads to what indication.
So not using the switch thing gives you 2 swaying needles not saying anything useful as the decay, attack, RMS values etc are unknown.

As a switch box it is a rather poor design with 4 relay contacts in series with each speaker while an amp with a speaker output relay only has 1 contact.
So no matter how we look at this box it is only eye-candy and while it has some functionality (and even remote function) the technical performance is nothing to write home about.

Nice explanation. So as far as audibility goes, this switch-box/VU meter is transparent (no audible difference)?

I don't think the added distortion will be audible.

Personally I would not use it as a switch box. 4 relay contacts + 4 extra binding posts is not going to 'improve' anything.
I would only use it to look at needles dancing to the music.

 

[NoxMorbis]

Personally I would not use it as a switch box. 4 relay contacts + 4 extra binding posts is not going to 'improve' anything.
I would only use it to look at needles dancing to the music.

Got it. Maybe if one wants dancing needles, this would be much better, and instead of plugging it inbetween anything, just run it in parallel from the amp itself, using a splitter, one side speakers, one side into the VU meter?

 

[ocinn]

Ah... well the 100W limit would still apply for the internal dummy load. That dummy load really cannot handle that power though but might survive 100W peaks in music.

Wait, why would douk use a dummy load that would ever draw 100w? They could put a 10kohm resistor in there and @ 50v of input would only draw a quarter watt. It also doesn't make sense from a financial point of view. Low ohm non-inductive 100w resistors aren't cheap in the grand scheme of things.

 

[solderdude]

That one is intended for line level and could induce groundloops into the RCA audio path.

For dancing needles I would recommend the VU3 and not run the speakers through it but in parallel to the speaker wires.

 

[solderdude]

Wait, why would douk use a dummy load that would ever draw 100w? They could put a 10kohm resistor in there and @ 50v of input would only draw a quarter watt. It also doesn't make sense from a financial point of view. Low ohm non-inductive 100w resistors aren't cheap in the grand scheme of things.

The idea Douk had is incorporating an 'amplifier no load protection'.
Some (tube) amps don't like it if they have no load. That's what the thick resistors are for. They will provide a load to the amp (in case the box is used to compare 2 amps) that is not connected to the speaker at that point. When no amp-B is connected the resistors simply do nothing.
I would guess they are about 5W (continuous) given the size, maybe slightly more, and could get quite hot (ceramic body).
With 100W peaks in music the average levels would probably be low enough not to break those resistors.

The whole point is the resistance value is not specified nor the continuous wattage.
@amirm (or an owner) could simply measure the value (might be between 10ohm and 15ohm ?) using a multimeter.... if it really is there which I think it is given the descriptions.

 

[kklarqvist]

There is off-course a definition of what a VU meter is calibrated — from Wikipedia "0 VU is equal to +4 dBu, or 1.228 volts RMS, a power of about 2.5 milliwatts when applied across a 600-ohm load." Modern speakers are not 600ohm —some used to be in the tube era pre-1970.

What would be more relevant today on the speaker side of the signal path? Maybe it would be better if they measured current since it is somewhat propositional to the cone displacement, wall power U*I, "inductive power"... or maybe just voltage (because it is so to implement with a simple voltage buffer?

Between stages, source-preamp, preamp-power-amp dBV (or voltage) is probably most relevant since input impedances are greater than 10k, and the relevance is to avoid overdrive, and distortion for recording, and get a sense of the signal level.

 

[solderdude]

Just had a look at the user manual.
The 100 W limit really is a power limitation :

'1. It is better not to connect VU3 to amplifiers whose actual output power is greater than 100W, or else VU meter may be damaged. 100W refers to the actual power output from amplifier to the speaker. For example, your amplifier max can output up to 200W, but you only use it in the room and turn on the volume to about 20W. The actual power is 20W but not 200W'

Meaningless words. 100W... in 8 ohm, 4 ohm, 2ohm, 16 ohm ?
What specifically gets damaged ?
The meter circuit would be really, really easy to protect from damage from any overvoltage.
The only thing that will be easily damaged are the 'dummy load' resistors which are part of the 'device'.

The manual is extremely unclear (Chinglish) in descriptions and the specs are equally worthless as the meters are indicative of 'power levels'.

It is not a measurement device, it is eyecandy, a toy, swinging needles for the sake of swinging needles built into a 'remote controlled AB switchbox' using relays intended to switch mains power circuits.

 

[NoxMorbis]

Meaningless words. 100W... in 8 ohm, 4 ohm, 2ohm, 16 ohm ?
What specifically gets damaged ?
The meter circuit would be really, really easy to protect from damage from any overvoltage.
The only thing that will be easily damaged are the 'dummy load' resistors which are part of the 'device'.

The manual is extremely unclear (Chinglish) in descriptions and the specs are equally worthless as the meters are indicative of 'power levels'.

It is not a measurement device, it is eyecandy, a toy, swinging needles for the sake of swinging needles built into a 'remote controlled AB switchbox' using relays intended to switch mains power circuits.

Sounds like what they have engineered a SINAD lowering box.

 

[danielbaen]

Well I have it to switch between 2 amplifiers.
What seemed strange to me is that it dimmed the light with the remote control but apparently I have read that it is the most normal ... as seen, I will have to buy a couple more speakers and connect them directly each to its amplifier....

 

[amirm]

@amirm (or an owner) could simply measure the value (might be between 10ohm and 15ohm ?) using a multimeter.... if it really is there which I think it is given the descriptions.

Measuring the speaker terminals, the active one is open load, the inactive one is 670 ohms.

On the amplifier terminal, active one is 670 ohm and inactive one reads 390 ohm.

So it seems they put a light load on the amp as to not have it seen an open load, but also not enough to cause a lot of power dissipation in the VU box.

 

[amirm]

Someone asked about remote control causing the display to dim??? I tried the few on my desk and none do anything. I can't think of what mechanism would cause it to do that anyway unless it had an undocumented IR support.

 

[amirm]

FYI I was wrong about lighting being a normal bulb. It is three surfacemount orange LEDs which are remarkable in the way they simulate the look of VU meters back when.

 

[solderdude]

Measuring the speaker terminals, the active one is open load, the inactive one is 670 ohms.

On the amplifier terminal, active one is 670 ohm and inactive one reads 390 ohm.

So it seems they put a light load on the amp as to not have it seen an open load, but also not enough to cause a lot of power dissipation in the VU box.

It looks as though the meter circuit loads the amp with 670 ohm. I would presume that is the (600 ohm ?) isolation transformer, maybe even a voltage divider + transformer.
That might be the 'power limiting' device here.

The 'no-load protection' appears to be a 390ohm resistor.
5W would be enough for that value (would dissipate 2W when 100W/8ohm is present).

390ohm might be a bit 'high' for being 'no-load protection' though.