What is the meaning of 30W amplifier?

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Discussion Overview

The discussion revolves around the meaning and implications of a 30W amplifier specification, particularly in relation to load impedance and output voltage. Participants explore technical details, potential misunderstandings, and the marketing of amplifier power ratings.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants suggest that the 30W rating typically corresponds to a specific load impedance, which should be specified in the amplifier's documentation.
  • One participant calculates that connecting a 30 ohm load could lead to significant power draw, potentially causing the amplifier to clip.
  • There is a discussion about the maximum output voltage, with references to 70.7 volts and its implications for amplifier performance.
  • Some participants express uncertainty about the appropriateness of using a 30 ohm load, with one clarifying that their actual load is 12 ohms.
  • Concerns are raised about the reliability of power ratings, with claims that manufacturers often overstate the true power output of amplifiers.
  • One participant mentions that the amplifier's true power may be significantly lower than advertised, suggesting realistic expectations of 7 to 12 watts.
  • There is a mention of the potential for distortion and the importance of understanding the amplifier's specifications, including RMS power versus peak power.
  • Participants discuss the implications of using the amplifier without a load, particularly for class D amplifiers.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the interpretation of the 30W specification, the implications of load impedance, and the reliability of power ratings. The discussion remains unresolved with no consensus reached.

Contextual Notes

Limitations include missing specifications for the amplifier in question, assumptions about load impedance, and the variability in power ratings across different amplifier models.

Who May Find This Useful

Individuals interested in audio equipment, amplifier specifications, and those seeking to understand the implications of power ratings in audio systems may find this discussion relevant.

Nikhil N
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When I have gone through spec of amplifier, I saw 30W for output. Is it mean that even if I am connecting a load of less impedance, say 30ohm, will I get 30V output voltage across the load?
 
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Probably not. Usually that is the power at a particular impedance -- which should be given as well, somewhere in the specs.
And 30 W can mean 30 W peak with the (rms) continuous power out considerably less.
[edit] why don't you post the specs (or a link) so we know what we are talking about
 
You're maximum output voltage is 70.7 volts.
With a peak sine wave signal, 30ohm load may draw ((70.7)^2)/2/30 = 83W, so your 30W amplifier would clip severely. But if you turn the volume down to 42V peak, you would be all set.
 
Last edited:
.Scott said:
You're maximum output voltage is 70.7 volts.

Where did that come from?
 
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Are you sure that's 30 ohms? Cuz that's a lot

Maybe a guitar amp?
 
Last edited:
jim hardy said:
Where did that come from?
It's a standard for some sound systems - although perhaps not if it's just 30W.
It's actually a maximum of 70.7Vrms. It puts the maximum DC at 100V.
If it's not a 70.7 volt system, it probably doesn't really "clip". Instead, it just gets muddy - or pops a breaker.
 
Oh ok a pa
 
.Scott said:
It's a standard for some sound systems - although perhaps not if it's just 30W.
It's actually a maximum of 70.7Vrms. It puts the maximum DC at 100V.
If it's not a 70.7 volt system, it probably doesn't really "clip". Instead, it just gets muddy - or pops a breaker.

Andy SV said:
Oh ok a pa

yeah ... very different to a home stereo which will be either 4 Ohm or 8 OhmWe really need the OP @Nikhil N to come back and clarify what he is talking about so that we all don't have to make wild guessesDave
 
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Andy SV said:
Are you sure that's 30 ohms? Cuz that's a lot

Maybe a guitar amp?
Its just for calculation I took as 30ohm, Actually I have load of 12ohm
 
  • #10
davenn said:
yeah ... very different to a home stereo which will be either 4 Ohm or 8 OhmWe really need the OP @Nikhil N to come back and clarify what he is talking about so that we all don't have to make wild guessesDave
This is the amplifier I am using. I was using it last few days, but it is not working nowadays. So I am looking for a new amplifier to buy which suits for my experiment. Is there any problem, if we have switched on the amplifier without load? I read some where, for class D we should not turn on without load.
http://www.amazon.com/dp/B011ECOCHY/?tag=pfamazon01-20
 
  • #12
Nikhil N said:
When I have gone through spec of amplifier, I saw 30W for output. Is it mean that even if I am connecting a load of less impedance, say 30ohm, will I get 30V output voltage across the load?
Good thing you finally posted the specs.
Did you miss the 4-8 ##\Omega## ?
Did you mention 30 ##\Omega## because you have such speakers at hand ?
Did you also see the working voltage is 12 V, 2 A ? That is 24 W at 100% efficiency ... as the sum of two channels:rolleyes:
I wonder if someone can guestimate the rms power into 4 ##\Omega## ? and 30 ?

I think you'd need pretty efficient speakers if you want to use this thing on a motorbike - but then again, I'm not a subject expert.
 
  • #13
Why not repair and upgrade the old amp it's got to be cheaper than a new one
 
  • #14
Lepai ? They're only about twenty bucks US

Their true power is a fraction of what's advertised, Google will find test reports that show true power is overstated by about 4X.
To OP's original question,

What is the meaning of 30W amplifier?

The meaning is it should deliver thirty watts into its load.

Marketeers of audio stuff know how to lie with statistics
real useable power is called "RMS" which is not exactly taking the average but very similar.

For a very brief instant an amplifier can deliver watts nearly equal to (its supply voltage squared ) divided by (resistance of its load) ..
That is called 'Peak Instantaneous Power" and it's a pure marketing ploy "of dubious integrity", to borrow a phrase from Janis Ian...
It can deliver that power for only milliseconds not continuously.
Note the Lepai with supply voltage of nominal 12 volts and a load of four ohms might claim "peak instantaneous power" of perhaps almost 122 / 4 = 36 watts , and they do claim 30.
I'd expect realistically seven to twelve.

Manufacturers can include an internal booster power supply to give the amplifier higher voltage, which is how those preposterous car "Boomer " amps work, but don't expect that in your ten dollar Lepai.

Here's an article to peruse, written by engineers for anyone who wants to learn.
http://www.ti.com/lit/an/slea047a/slea047a.pdf

old jim
 
Last edited:
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  • #15
Hay thank you for posting that I consider my understanding of audio equipment to still need some corners knocked off and this should help
 
  • #16
jim hardy said:
Lepai ? They're only about twenty bucks US

Their true power is a fraction of what's advertised, Google will find test reports that show true power is overstated by about 4X.
To OP's original question,
The meaning is it should deliver thirty watts into its load.

Marketeers of audio stuff know how to lie with statistics
real useable power is called "RMS" which is not exactly taking the average but very similar.

For a very brief instant an amplifier can deliver watts nearly equal to (its supply voltage squared ) divided by (resistance of its load) ..
That is called 'Peak Instantaneous Power" and it's a pure marketing ploy "of dubious integrity", to borrow a phrase from Janis Ian...
It can deliver that power for only milliseconds not continuously.
Note the Lepai with supply voltage of nominal 12 volts and a load of four ohms might claim "peak instantaneous power" of perhaps almost 122 / 4 = 36 watts , and they do claim 30.
I'd expect realistically seven to twelve.

Manufacturers can include an internal booster power supply to give the amplifier higher voltage, which is how those preposterous car "Boomer " amps work, but don't expect that in your ten dollar Lepai.

Here's an article to peruse, written by engineers for anyone who wants to learn.
http://www.ti.com/lit/an/slea047a/slea047a.pdf

old jim
Thanks for this detailed replay.
 
  • #17
It's difficult to find what's inside that Lepai amplifier.

One source said it's heart is an LA4625 IC

datasheet at https://www.onsemi.com/pub/Collateral/LA4625-D.PDF includes these graphs
Lepai_LPA6.jpg


it's an honest ten watts if you don't mind some distortion. Just a few percent won't be objectionable...

It's not class D though.

old jim
 

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