Could meter lights really interfere with SQ

The low-power LEDs used for back-lighting in consumer gear are typically powered by continuous DC and are therefore noise-free. The relatively high-power LEDs used for typical household lighting are powered by pulsed DC and can be noisy. I suspect someone is confusing the latter with the former, or perhaps making the (not unreasonable) assumption that some consumers will confuse the latter with the former.
 
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

Probably as a voltage reference that's as simple as a zener diode, but has lower noise. At least, that's what was claimed for the AVM amp that came across my bench. LED operating voltages are relatively low, so they are likely to be used in multiples to add up to some voltage reference that's wanted in an audio circuit. The AVM, like your Luxman, was quite a sight with the cover off in the dark!
 
it is well known that a multi winding transformer has each section affecting another...if your lights blink with the music at even moderate volume levels, means the amp windings tried to 'borrow' from you.

dash and meter lighting can be a considerable draw....in fact, at lower volume levels it can be a larger draw than the mains.

alleviate that.
 
it is well known that a multi winding transformer has each section affecting another...if your lights blink with the music at even moderate volume levels, means the amp windings tried to 'borrow' from you.

dash and meter lighting can be a considerable draw....in fact, at lower volume levels it can be a larger draw than the mains.

alleviate that.
Example: Philips 22ah603 receiver shows this behavior.
 
it is well known that a multi winding transformer has each section affecting another...if your lights blink with the music at even moderate volume levels, means the amp windings tried to 'borrow' from you.

dash and meter lighting can be a considerable draw....in fact, at lower volume levels it can be a larger draw than the mains.

alleviate that.

True enough!

I bought a McIntosh C28 preamp new from my local authorized dealer back in 1971. By 1976 I had moved halfway across the country and by 1977 the C28 began to blink its panel lights with the music, starting at higher volumes but escalating to lower volumes after a few months. I wasn't thrilled with this preamp from the beginning, and this was just the excuse I needed to trade it in.

I should have bought a C22 instead of the C28 back in 1971, but I was young and naive back then. Live and learn.
 
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The middle transformer in the front row of three is for the meters, lights, soft start and protection circuit. It isn’t wired through the four larger audio supply trafos, instead having its own set of wiring wrapped into the mains AC cable.
 
Some folks install LED lights into their systems, not knowing what ill effects they may have on the power supply(s) to the rest of the system. I personally do not like the replacement LED lights in vintage equipment. They make them not look vintage anymore. Give me the good old incandescent pilot lamps!
 
Some folks install LED lights into their systems, not knowing what ill effects they may have on the power supply(s) to the rest of the system. I personally do not like the replacement LED lights in vintage equipment. They make them not look vintage anymore. Give me the good old incandescent pilot lamps!

No. No. No. Not possible. The transition to LEDs for lighting meters and dials cannot possibly have any deleterious effect upon the power supply. That is simply impossible from the physics standpoint. From an electrical engineering standpoint. Simply not possible. Such substitution will, in fact, reduce the load on the power supply by anywhere from 50 mA to 300 mA per bulb, depending upon the nature of the bulb. Since the bulb is typically driven from a low-voltage source, either a heater supply or logic supply, reducing that load will not increase the voltage so no "ill effects" could possibly accrue.

One might argue, in fact, that an incandescent bulb has more of an effect, albeit transient, briefly having a non-linear loading until the filament heats, and having a higher steady-state current draw. But that warmup effect, too, is negligible.

We are not talking about modulated LEDs to control brightness, such as is done with dimmers. Just simply swapping a bulb for an LED with a dropping resistor to illuminate a backlight. No audible difference can accrue from such a substitution. What you claim is simply impossible.

It is one thing to prefer the light from a bulb to an LED; aesthetics are a matter of personal taste. But to claim that the circuit will be degraded? No, no, no. Not possible.

What proofs can you offer for this purported effect?

I am reminded of Hume's commentary on the evidence required for extraordinary claims.

"The plain consequence is (and it is a general maxim worthy of our attention), That no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish: And even in that case there is a mutual destruction of arguments, and the superior only gives us an assurance suitable to that degree of force, which remains, after deducting the inferior. When any one tells me, that he saw a dead man restored to life, I immediately consider with myself, whether it be more probable, that this person should either deceive or be deceived, or that the fact, which he relates, should really have happened. I weigh the one miracle against the other; and according to the superiority, which I discover, I pronounce my decision, and always reject the greater miracle. If the falsehood of his testimony would be more miraculous, than the event which he relates; then, and not till then, can he pretend to command my belief or opinion."
Hume, David: An Enquiry Concerning Human Understanding, "Part 1", Chapter 10.13 (1748)

In the next chapter Hume cautions, "A wise man, therefore, proportions his belief to the evidence."

(Yes, I actually slogged through Hume and Kant while pursuing a philosophy double major in addition to an engineering degree. The epistemology occasionally proves useful in debunking pathological science and fanciful physics.)
 
Some folks install LED lights into their systems, not knowing what ill effects they may have on the power supply(s) to the rest of the system.
I know what ill effects they may have on the power supply(s) to the rest of the system: None.

Aesthetic considerations aside, replacing incandescent backlighting with LEDs is electrically completely harmless -- except in rare circuits where the incandescent bulbs were used a a series resistance or whatever -- and results in lower power consumption and heat emission compared to incandescent bulbs.
 
+1 for the above.

Reducing all that heat, beyond reducing the temperature inside the cabinet, also has the significant benefit of protecting the lettering on the dial or meter from heat-related degradation. I've seen many units with scorch marks on the dial or meter from bulbs.
 
In the next chapter Hume cautions, "A wise man, therefore, proportions his belief to the evidence."

Wow, mad props to you for quoting Hume! I'll counter with a bit of vintage Blake:

“When I tell the truth, it is not for the sake of convincing those who do not know it,
but for the sake of defending those that do.”
 
Well, one day Frank Van Alstine called me and he needed some changes done to one of the products. Turns out, the "on" LEDs was "F"ing up the transformer and causing DC offset (as I recall the problem) and causing hum.

Another time, I had an issue with one of my preamps. It was a strange noise in one of the channels. After a lengthy time on the bench, it was determined that it was a RESISTOR causing the noise. Frank had never, ever in his entire career come across a resistor problem like this before. Tales from the crypt.
 
Well, one day Frank Van Alstine called me and he needed some changes done to one of the products. Turns out, the "on" LEDs was "F"ing up the transformer and causing DC offset (as I recall the problem) and causing hum.

Uh, wait, what? What? WHAT?

Exactly how can an LED affect a power transformer? An LED draws a few milliAmps! So unless the LED had failed as a dead short no physical mechanism exists for the power supply to be affected. It just doesn't make any sense from any physical perspective.

Neither could an LED cause "DC offset" which is an mean displacement above zero. So the LED somehow lifted the baseline? Wait, what? How would that get into the rest of the circuit? This is a solid-state light bulb powered by some low-voltage winding.

Furthermore, "hum" is a noise issue. Hum typically means mains frequency or a low harmonic, such as 60 Hz or 120 Hz. A diode does not make noise like that. LEDs, in point of fact, have such low noise properties that audiophiles actually build circuits using LEDs as voltage regulators, as a Zener would be noisier. The carbon-composite resistors used for the rest of the gear will be many orders of magnitude noisier.

But, again, the LED in question is not used to set bias or for voltage regulation. It is to illuminate a dial or meter. So it CANNOT affect bias.


Weren't you an electrical engineer at AVA? How about some technical details here. Because this anecdote surely is 52 cards short of a full deck.

Another time, I had an issue with one of my preamps. It was a strange noise in one of the channels. After a lengthy time on the bench, it was determined that it was a RESISTOR causing the noise. Frank had never, ever in his entire career come across a resistor problem like this before. Tales from the crypt.

Ummm, unless that "RESISTOR" involves an LED used for illumination that's a red herring. We're not discussing resistors, we are discussing LEDs used for illumination.


Resistor noise, from carbon composite or carbon film, is well known and well understood. I have many times discussed the issue of why carbon-composite is a poor resistor technology. I've quoted Hafler's problems at Dynaco because the cracked-carbon resistors were noisy and even the legendary Stu Hegeman couldn't find it.

But, again, what exactly does this have to do with LEDs? Oh, right, nothing. Distraction.


Randomly changing components may cause correlated effects, as poor solder joints can be flexed during debugging. That may cause a problem to arise or vanish, but it does not mean that an illumination device is the cause.

It makes absolutely no sense that a glowing LED used to illuminate a meter or dial could cause any noise and thus requires a switch or other disconnection device.

I'll leave you with an observation from M. Le Comte Laplace (which I pulled from my quotes archive):
"De ce qui précède, nous devons généralement conclure que plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves. Car ceux qui l’attestent, pouvant ou tromper, ou avoir été trompés, ces deux causes sont d’autant plus probables, que la réalité du fait l’est moins en elle-même. C’est ce que l’on verra particulièrement, lorsque nous parlerons de la probabilité des témoignages."
M. Le Comte Laplace, Pierre-Simon: Essai Philosophique Sur Les Probabilités (Sixième Édition) (1840)

In case your French is worse than mine, I roughly translate that (the Google translation is execrable) as:
From the foregoing, we must generally conclude that the more extraordinary a fact is, the more it requires support by strong proofs. Because the attestor possibly is deceitful, or had been deceived, these two causes being all the more probable, since the reality of the fact will itself be lesser. This is what is particularly seen when one discusses the testimony's probability.

TL/DR: extraordinary facts require strong supporting proofs. The burden has not been met in this case and furthermore, I'd argue, cannot be met.
 
Apparently, the reviewer of the Luxman that the OP posted had a problem with noise he could hear when the meter lights were on...........the basis of this whole thread.
 
Apparently, the reviewer of the Luxman that the OP posted had a problem with noise he could hear when the meter lights were on...........the basis of this whole thread.

Wait, what? The reviewer made up nonsense to show off how sophisticated his ears are. Wow, never heard of that in an audio review. And that's your "evidence"? One reviewer's obviously fabricated claims? That isn't evidence. It isn't science. It isn't physics. It isn't credible. It's just audiophoolery. The reviewer likely kept that $11,000 amplifier for his personal use. That's the way the audio review game works. Sometimes the reviewers purchase a review unit at a steeply discounted price. But this should be disclosed. My point is that the reviewer has great incentive to make every unit sound spectacular with amazing features because otherwise the reviewer's supply of free (or discounted) gear dries up.

You also came back with supporting claims which I note you've dropped.

LEDs used as a non-modulated illumination devices in place of a bulb cannot cause the claimed effects. IMPOSSIBLE.
 
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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.

Thing is, you just don't have a good enough toaster to taste the difference. If you go back to a AC toaster after a while, you will certainly notice the difference.

Also, what toast are you using?
 
I doubt that the effect of adding an LED to a low powered existing circuit would have any sonic impact. However, if other circuitry is required to drive that LED...,

In my Yamaha RX-Z9 Manual:

PURE DIRECT allows you to enjoy the highest possible
fidelity from audio sources connected to the 2CH IN
PURE DIRECT or MULTI CH IN jacks. This function
bypasses all of this unit's decoders and digital circuitry to
provide uncompromised audio fidelity. It also turns off the
front panel display and the power to this unit's video
circuitry to eliminate noise.
 
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