Where do the other watts go? Need basic understanding please

[johnah5]

I have 93 db speakers. So at 1 watt I get 93db of SPL/DB sound.

So 2 watts = 96 db etc etc

My current amp is SPL S1200. Specs state 300 wpc. If I only need to get 2 to 4 watts to the speaker where do all the other watts on the amp go?
Why are they needed vs 15 watt amp?

Thank you. I love learning

jh

 

[Doodski]

My current amp is SPL S1200. Specs state 300 wpc. If I only need to get 2 to 4 watts to the speaker where do all the other watts on the amp go?

That's a good question and the answer goes pretty deep or can be fairly simple. In the simple explanation the amp is idling away ready for a voltage input to be amplified. The amplifier has a certain amount of gain(amplification) and depending on the source input voltage the gain will cause a small amount of voltage to be output from the amp circuitry or if the voltage at the input goes higher then the gain causes a bigger output voltage and current at the amp output. Typical gain numbers are in the order of ~14dB to 16db for a headphone amp and I think if memory serves me correct for a home audio amp 29'ish dB gain is not out of the ordinary. The amplifier is always ready to amplify/apply gain to a incoming signal/voltage and it is a matter of how large the input signal/voltage is to determine how much the output voltage and current is.

I state voltage and current in my explanation near the ending parts because a amplifier amplifies the voltage in most of the amp's circuitry and then right before the speaker output there is a unity gain stage that only amplifies the current so that the speaker can operate with enough current.

 

[johnah5]

Thank you. That helps. So my pass labs XA25 had 25WPC and 20db gain and was a power house. The SPL which is an A/B amp has 300wpc so I wonder does amp typology cause this difference or do companies just want to build a higher output amp for less effcient speakers? J

 

[Chrispy]

What was the sensitivity of your older amp? What was the input level?

 

[Doodski]

Thank you. That helps. So my pass labs XA25 had 25WPC and 20db gain and was a power house. The SPL which is an A/B amp has 300wpc so I wonder does amp typology cause this difference or do companies just want to build a higher output amp for less effcient speakers? J

They build higher power amps with increased voltage output and increased current output too not only for power hongry speakers but for handling of the dynamic range of the source audio. Music is made of dynamic transient waveforms and the bigger and badder that a amp can be the better it will be at handling difficult speaker loads. Some speakers are very easy to drive and are efficient and accurate and other designs rely on high power levels and high current too. That's why it's important to match the amp with the speakers to ensure not synergy but to ensure basic electrical compatibility.

 

[Ken Tajalli]

Just to add an observation .
Not all amps are linear all the way up to their max. output levels.
Some amps do better, some don't .
I built an amp of only 6W output per channel and it was pretty linear up to almost 6.
I have had some amps that were linear only a quarter of way!
It is not a bad idea to have an amp with some headroom , as to avoid pushing it too hard.

 

[pseudoid]

There are a few different amplifier designs that are the primary basis of most audio amplifiers.
These are called "classes" and we have ClassA, ClassB, ClassAB, ClassD and a Class'G'.
These classes (of amplification) are based on 2 basic designs: LinearPowerSupplies and (or) SwitchModePowerSupplies.
Some intermix of these two (classes/designs) make for less or more efficient usage of input power.
Gets a bit deeper but if you want to really dig deep, these should suffice for you to forage!

 

[Mr. Widget]

It is not a bad idea to have an amp with some headroom , as to avoid pushing it too hard.

Definitely, but it is best to match the amp and load. For example, there are mega watt amps that have fairly high noise and distortion in the low milliwatts... putting one of those on 105dB or higher horn speakers is not a good idea.

Regarding headroom, I like at least a factor of 10... so I would treat a 6 watt amp as a 600mW amp. This is fine with highly sensitive speakers. With medium or low sensitivity speakers you will likely be running into some 2nd order harmonic distortion which may or may not be bothersome.

 

[Chrispy]

There are a few different amplifier designs that are the primary basis of most audio amplifiers.
These are called "classes" and we have ClassA, ClassB, ClassAB, ClassD and a Class'G'.
These classes (of amplification) are based on 2 basic designs: LinearPowerSupplies and (or) SwitchModePowerSupplies.
Some intermix of these two (classes/designs) make for less or more efficient usage of input power.
Gets a bit deeper but if you want to really dig deep, these should suffice for you to forage!

Then again doodski has somewhat his own definition of linearity rather than what is generally referred to.

 

[DonH56]

I have 93 db speakers. So at 1 watt I get 93db of SPL/DB sound.

So 2 watts = 96 db etc etc

My current amp is SPL S1200. Specs state 300 wpc. If I only need to get 2 to 4 watts to the speaker where do all the other watts on the amp go?
Why are they needed vs 15 watt amp?

Thank you. I love learning

jh

Ah, simple questions with complicated answers...

1. If you are only using a few watts, the amp is not producing the rest, so they are not there. Where does the electricity go when you turn off the light? Answer: nowhere, it is just not used. If you only need 4 W, the amp does not produce any more than that. The 300 W rating is what it can deliver, not something it does even when not needed. But there are some other considerations.
2. There is idle power, the standing power the amp needs just to "stay alive". That can be less than a watt to several watts or (much) more depending on the type of amplifier. So even if the amp is only putting out 4 W, it may be using 10 W just to keep bias circuits, low-level amplifier stages, and output stages operating.
3. Music has a peak-to-average ratio of about 50:1 (17 dB) and movies can be 100:1 or more. Think a very quiet passage to a very loud passage, or whispers to gun shots, plus there are transient peaks from things like drums (and guns) that require peaks well above your average level. So at 1 W you may need 50 W or more to avoid ever clipping on dynamic music or movies. That is why people get bigger amps than they need for just the average listening level. Of course, some go way overboard...

HTH - Don

 

[Doodski]

Then again doodski has somewhat his own definition of linearity rather than what is generally referred to.

I usually use linearity two ways. The first is the linearity of a linear transistor load line and the second is the input signal of amp versus the output signal that makes the input signal basically the same as the output but the output being larger of course; that's another definition of linearity.

 

[Chrispy]

I use linearity two ways. The first is the linearity of a linear transistor load line and the second is the input signal of amp versus the output signal that makes the input signal basically the same as the output but the output being larger of course; that's another definition of linearity.

I just think you need to expand on it when you mention "linearity"

 

[pseudoid]

Then again doodski has somewhat his own definition of linearity rather than what is generally referred to.

Do you offer the fish or the fish hook? I prefer the latter!

 

[Chrispy]

Do you offer the fish or the fish hook? I prefer the latter!

LOL

 

[Doodski]

I just think you need to expand on it when you mention "linearity"

Yeah, they are both formally defined as linearity but it gets confusing for me at times too...lol. I'll try and delineate them futuristically.

 

[Doodski]

Do you offer the fish or the fish hook? I prefer the latter!

I prefer the hook as I tied fishing flies for 12 years and thoroughly enjoyed tying every one of them. I suck big time at fly fishing though.

 

[Chrispy]

Yeah, they are both formally defined as linearity but it gets confusing for me at times too...lol. I'll try and delineate them futuristically.

LOL I just remember running into a defintion of yours when it was like....whut?

 

[NiagaraPete]

Headroom / dynamic range.

 

[pseudoid]

...where do all the other watts on the amp go?

I certainly was NOT going to get into how some becomes heat, or other parts are kicked back to the utility, or power factor and not touching noise and emi...
@johnah5 sounds like he already knows the Ohm's Law and can jump around the logarithmic scale readily, so why should we bloviate?

 

[Ken Tajalli]

I certainly was NOT going to get into how some becomes heat, or other parts are kicked back to the utility, or power factor and not touching noise and emi...
@johnah5 sounds like he already knows the Ohm's Law and can jump around the logarithmic scale readily, so why should we bloviate?

Since the question was so basic, I doubt the OP was as knowledgeable as you state.
Not knowing is no shame, not wanting to know, is.
And Yes, on a Class A amp, the extra watts do get wasted into heat.
On Class A/B, not so much.
On Class D, almost none.
Just in case the OP was wondering.