Could meter lights really interfere with SQ

Archguy

Official Roiurama Factory Rep
Sort of hard to believe. I love meters as much as the next guy, but really.

LUXMAN-METER-LIGHTS.jpg


https://www.whathifi.com/luxman/l-509x/review

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No, I can't afford this amp, and don't need it. But want it.
 
The likelihood the average person would hear the difference is probably negligible. On a sweet piece of kit like the Lux, the likelihood drops dramatically.
 
The only time the meter lights should affect the sound by being on or off would be if the power supply were marginal. The best example I can think of is the Dynaco PAS-2/3 preamp, where the incandescent bulb used for the power indicator is wired to the same transformer winding which supplies power to the tube filaments, and draws almost as much current as one of the tubes. I'm guessing the power supply in that Luxman isn't marginal. :)
-Adam
 
Really shouldn't be a problem if done right, but what are the chances of that happening? LEDs, especially when paired with switching power supplies, can raise all sorts of RFI if not shielded and filtered properly. I originally planned to add dial and meter lights (using a separate power supply board) to my ST120 custom build and decided against it specifically for that reason.
 
Several of my amplifiers have switchable meters. It's more about the distraction and movement than any actual improvement sonically by turning them off.

I often have my meters turned off, particularly on the big Sony TAN77es power amplifiers and some of the Yamahas with the red vertical bar meters.

On CD players, the top models have switchable displays, the theory being the noise from the multiplexing/scanning of the VFDs can affect performance. Back in the day, many reviewers tested displays on and off and I don't think I recall there ever being a measurable difference.
 
Most of the higher end amps have separate power supplies for the meters, lights and protection/relays right down to a separate transformer. I’d bet that lux is no different, so there should be no effect on sq.
 
Interesting how things change. My Luxman C-02 preamp uses LEDs as part of the internal circuit design. There was a reason for it I read about, but I can't remember what it was at the moment. Sounds good to me :)

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The effect could be real, in the sense that an engineer may have noticed a small spike in the distortion spectrum that could be eliminated by shutting down a non-essential circuit. It's likely to be about as audible as the difference in flavor of toast from a toaster operated on pure DC power.
 
Most of the higher end amps have separate power supplies for the meters, lights and protection/relays right down to a separate transformer.

Wow, I learn something new every day. Sort of posted this as a "Can you believe it" joke but as always you guys have serious stuff to teach me. I agree about the toast though :beatnik:
 
The answer is it really depends upon the output impedance of the source driving the VU meter, how much loading the VU meter does, and how it does the measuring.

This is more of an engineering question than an audibility issue, as the amount in question is incredibly tiny. But it does distort, so that likely answers the question.

Here's a short discussion:
http://sound.whsites.net/project128.htm

While some users may simply connect a VU meter directly across the output signal lines from the mixer, this approach will cause extra loading on the signal, which is non-linear. While the distortion introduced might not be high (it depends a lot on the output impedance of the mixer), it is definitely measurable. The extra load may also reduce headroom, because the output stages may clip earlier than expected due to the additional load. The meters shown above are quite sensitive (100uA DC full scale), but still cause over 0.3% distortion when connected to a 600 ohm source. Distortion is worst at around mid-scale - right where it will sit for much of the time with typical programme material. The nominal impedance for a "true" VU meter is 3,900 ohms - the resistor can be seen in Figure 2.
 
As soon as I heard the reviewers speel about " your good as long as you leave the tone controls alone " I knew the rest was pure nonsense ,even if the LEDs for an Amps meters we're built into an audible circuit for some reason we're talking MVs here ,when we need a doubling of wattage to hear a noticible increase in SPL common sense tells me that reviewer has began to believe his own hype , the engineers at Audioholics would have a feild day tearing that reviewers claims apart using state of the art testing equipment ,unless that reviewer is a polar bear there's no way switching meters on & off allowed him to hear audible changes in sound ,I personally won't own gear without tone & balance controls to make up for shoddy recordings and room accoustics .
 
The answer is it really depends upon the output impedance of the source driving the VU meter, how much loading the VU meter does, and how it does the measuring.

This is more of an engineering question than an audibility issue, as the amount in question is incredibly tiny. But it does distort, so that likely answers the question.

Here's a short discussion:
http://sound.whsites.net/project128.htm

While some users may simply connect a VU meter directly across the output signal lines from the mixer, this approach will cause extra loading on the signal, which is non-linear. While the distortion introduced might not be high (it depends a lot on the output impedance of the mixer), it is definitely measurable. The extra load may also reduce headroom, because the output stages may clip earlier than expected due to the additional load. The meters shown above are quite sensitive (100uA DC full scale), but still cause over 0.3% distortion when connected to a 600 ohm source. Distortion is worst at around mid-scale - right where it will sit for much of the time with typical programme material. The nominal impedance for a "true" VU meter is 3,900 ohms - the resistor can be seen in Figure 2.
It appears that what's being switched off is merely whatever illuminates the meters. The meters themselves presumably continue to work as before, just not being lit by anything. At least, that's what the blurb in the OP seems to imply.
-Adam
 
It appears that what's being switched off is merely whatever illuminates the meters. The meters themselves presumably continue to work as before, just not being lit by anything. At least, that's what the blurb in the OP seems to imply.

Ahhh, I thought it was switching off both the meter and the illumination source.

That claim notably does not appear in the marketing literature, which I just looked up, only in the review. Amazing what a reviewer can write, isn't it?
 
Generally, the power output meters on amplifiers are driven by active electronics, not passively derived. They place no load whatsoever on the output of a power amplifier and generally are run from completely separate supplies.

Here is a typical example:

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Here is another (same driver IC):

upload_2019-1-16_16-49-20.png

And an extremely sophisticated metering circuit on my Lux M03 with its own dedicated CPU to be able to display real time channel wattage readouts to two decimal points, all calculated taking impedance (switchable) into account, switchable range and various peak hold times. Also can be shut off if you want.

Very cool, but ultimately just another pretty light display.

upload_2019-1-16_16-54-21.png

None of these meters have any effect whatsoever on performance whether they are activated or not.
 
My guess is if the meter lights are operating correctly on most decent equipment, there will be no appreciable effect on sound quality. But if there is a malfunction in the circuit or lights, that could effect it.

If I could switch them off, I would try it both ways though just in case it does help. I don't hear any difference in sound quality in pure direct mode which turns off the VF display too on my Denon SACD player. It's probably just a marketing gimic.
 
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Marketing figured out that the LED lighting is PWM. Sounds like dirty switching digital stuff to the uninformed.

Since a lot of crap in the modern units is just that, people will probably believe it. HAven't read the thread - will do now.
 
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