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Old 1st May 2013, 07:35 PM   #1
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Question Are leds noisy ?

i have a hybrid amp with a bunch of leds i dont need , should i remove them or they dont harm the sound ?
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Old 1st May 2013, 07:44 PM   #2
djoffe is offline djoffe  United States
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It all depends where the LEDs are! Can you post a schematic?
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Old 1st May 2013, 07:46 PM   #3
knutn is offline knutn  Norway
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Take a look here:
Some noise measurements for LEDs and zener diodes
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Old 1st May 2013, 08:25 PM   #4
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sorry i dont have the schematic for this amp
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Old 2nd May 2013, 10:53 AM   #5
FoMoCo is offline FoMoCo  United States
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Some are. It can even vary for each individual part with the same number. LED's are not designed as voltage references. Other than for economy reasons, I can't see why they are used for that purpose. The TL431 isn't that expensive...
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Old 2nd May 2013, 11:03 AM   #6
AndrewT is offline AndrewT  Scotland
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But far noisier.
A LED combined with a BJT also has some temperature compensation.
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Old 2nd May 2013, 11:48 AM   #7
DF96 is online now DF96  England
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LEDs can be used for bias in quite low-level signal circuitry, I understand. Never done it myself, though.

However, I suspect the OP is asking about panel LED indicators or merely cosmetic LEDs. Perhaps he has read of the significant interference generated by LED lighting? In that case the problem is the SMPS circuitry used to power the LED from the mains supply. The LED itself generates no noise or interference to speak of.

If you can use an LED in the circuit without harm, then putting one on the front panel will do even less harm to the sound.
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Old 2nd May 2013, 12:06 PM   #8
Pano is offline Pano  United States
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Agreed. LEDs themselves are not noisy. But the power supplies that run large banks of them often are very, very, noisy.
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Old 2nd May 2013, 08:19 PM   #9
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Quote:
Originally Posted by FoMoCo View Post
LED's are not designed as voltage references. Other than for economy reasons, I can't see why they are used for that purpose. The TL431 isn't that expensive...
Except that the average LED is at least 50dB quieter everywhere... with single-figure dynamic impedance if run at optimal current; and is a passive, therefore utterly well-behaved part. And is dirty-cheap!
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Old 3rd May 2013, 10:23 AM   #10
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by martin clark View Post
Except that the average LED is at least 50dB quieter everywhere... with single-figure dynamic impedance if run at optimal current; and is a passive, therefore utterly well-behaved part. And is dirty-cheap!
Possibly true, depending on the LED. However, the 431 is more consistent across different current ranges. When bypassed properly, you'll never know the difference. And... You don't have to worry about selecting the optimal part.
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