Is a 100 Watts a 100 Watts?

amplifiers, receivers and loudspeakers
Bob257
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Is a 100 Watts a 100 Watts?

Post by Bob257 » 22 Nov 2019 14:52

As a newbie, I have all kinds of questions which create even more questions! I've listed before that by next year I'd like to upgrade my amplifier. I currently use a Yamaha a-s801, rated at 100 watts/channel into 8 ohms, to drive a pair of Focal 1028be floor speakers. I was thinking of PS audio Stellar stack which would have two mono blocks producing 350 watts/channel into 8 ohms and also buy their phono pre amp and the Stellar gain cell dac. Recently I've been interested in the McIntosh MA252. It's also rated at 100 watts/channel. The Luxman 505 Mk II is another I've looked into and the McIntosh 5005 both of which are rated at 100 watts/channel. So what gives? Is there a difference between 100 watt amps? Will it be noticeable? Would I be better served with the PS audio and the extended head room? I usually listen at low to mid volume. I've heard so much good stuff about tubes, which is why the MA252 makes me curious. It has a tube input stage and solid state output, so a hybrid. What are your opinions??? The PS stack and phono preamp would be around $6500, the Luxman around $4500, the MA5005 around $5000 (?), and the MA252 around $3500.

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Re: Is a 100 Watts a 100 Watts?

Post by Pauw » 22 Nov 2019 16:41

I think the first move is to compare like with like...There are many ways of rating an amps power and quite a few involve Watts . The standard is Watts RMS per channel into 8 ohms. ( There are other measurements but we will not go into there here) .If you can obtain these figures for both amps you want to compare then this will give a fair comparison.

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Re: Is a 100 Watts a 100 Watts?

Post by Bob257 » 22 Nov 2019 18:01

Any suggestions as to where I can find that information?

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Re: Is a 100 Watts a 100 Watts?

Post by Pauw » 22 Nov 2019 19:16

It should be in the handbook for each piece of equipment.

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Re: Is a 100 Watts a 100 Watts?

Post by aardvarkash10 » 22 Nov 2019 21:11

Hi Bob.

You listen at low to mid volumes (your description). Your speakers are rated at 91.5db and 8 ohms with a dip to 3.5 ohms minimum - interestingly, no statement on maximum, but we can assume its not an easy speaker to drive. We can also assume the figures given are ideals and reality is they will measure different irl - expect 89db/6ohm/3ohm. This means your power stage is definitely going to be semiconductor based.

No idea how big your listening area is or the music types you enjoy.

Paul Joppa theorises a "rule" that makes a lot of sense - I've included its derivation by Paul below verbatim from a post in the Bottlehead forum.

"Simplistic summary:

1) Most ordinary solid-state amps put out more than enough power for most ordinary speakers.

2) SET amps need high efficiency speakers to attain the loudness most audiophiles want.

Over the years, I have tried to gather enough data to make those vague rules more specific. It is complicated (isn't everything?!) by the notion of headroom. Loudness is measured typically as a short-term average, over something like 1/4 second. But the instantaneous peak power, for example hitting a drum, or the initial impulse of a guitar or piano, is much greater. For well-recorded music, the initial impulses are about 25 times more power than the peak you see on the loudness meter. That's about 14dB headroom. So if you listen at a level that gives measured peaks of 82dB, you need an instantaneous peak of 96dB if you do not want to hear clipping distortion. I chose 82dB because that is typical of the level used by recording engineers. Movies typically need 6dB (four times as much, i.e. 102dB). The THX standard for movie theaters calls for peak levels of 102dB per channel, which is consistent with the recording engineer levels. Some 20 years ago, I gathered a bunch of speaker reviews from Stereophile, which give a minimum-power rating and the speaker sensitivity. I got the same number (102dB peaks) again. So I think that 102dB peaks is enough for most audiophiles, most of the time, and 96dB peaks are enough for the average audiophile. These numbers are somewhat affected by room acoustics (size and absorption), and more strongly affected by your personal preferences and choice of music.

Amplifier power is most usefully expressed in dB, which can be added to the speaker sensitivity to get the peak level. Here's a short table:

1 watt = 0dB
2 watts = 3dB
4 watts = 6dB
8 watts = 9dB
16 watts = 12dB
32 watts = 15dB
64 watts = 18dB

So for example an 86dB speaker needs 10 to 40 watts to obtain undistorted peaks of 96 to 102dB.

These rules are quite flexible, of course. I have two systems in my own home, the music system has 101dB speakers with 8-watt amplifiers (110dB peaks) and the movie system in another room has 89dB speaker with a 2-watt amp (92dB peaks). Both are quite satisfactory to us, for the sounds we listen to.

I know that is a lot to take in, and it's still over-simplified, but I hope that is at least some help"


Following Paul's rule, we start from a 102db peak listening level, subtract your speaker sensitivity (lets call that 90db to make the math real easy) and the balance is the power required to drive your speakers to the 102db theorised peak listening level = 16w.

Remember, your speakers are measured at 1m, the math changes with the size of your room and your distance from the speaker, but you are unlikely to be more than 3m (10 feet) from your speakers when actively listening and because of the reflective additive effect of walls, ceiling etc the increase in power required is not linear.

Power in an semiconductor amplifier is relatively cheap, so I wouldn't scrimp on it - for every doubling in distance from speakers, I would increase amplifier power by a factor of 1.5 - 2. So in a large room sitting 3m from the speaker, I would theorise an amp with 64w minimum (16 x 2 x 2).

In short, an amp rated at 100W rms into an 8-ohm load is going to work fine. Anything over 150W and you are just buying bragging rights.

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Re: Is a 100 Watts a 100 Watts?

Post by lenjack » 22 Nov 2019 23:10

Note that doubling the power increases the output by only 3dB.

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Re: Is a 100 Watts a 100 Watts?

Post by kalaur » 23 Nov 2019 11:10

Couple of things to add:
Bob257 wrote:
22 Nov 2019 14:52
Is there a difference between 100 watt amps?
Absolutely yes. Since there is no standard on how to measure amplifier power, you will see widely varying specs between amplifiers. There are many chip type amps, class D amps, and inferior quality amps that are rated to 100W. Can they touch 100W for an instantaneous moment while wall voltage was at its peak, with only one channel driven into a perfect load at 30% distortion? Maybe. Can they sustain 100W for more than a few seconds into both channels with an actual speaker load? Highly unlikely. Unfortunately there's usually not a clear way to tell if a manufacturers specs are legit or 'ILS' rated (if lightning strikes it). Usually big power requires big power supplies. If your 100W amp takes a 1 amp fuse, don't bet you'll ever see 100W out of it.

Bob257 wrote:
22 Nov 2019 14:52
Will it be noticeable?
Differences in amplifiers can certainly be audible, but not always. Sometimes you just cant hear it, sometimes the rest of your system doesn't lend to revealing the differences, sometimes they just sound really similar.

Bob257 wrote:
22 Nov 2019 14:52
Would I be better served with the PS audio and the extended head room? I usually listen at low to mid volume. I've heard so much good stuff about tubes, which is why the MA252 makes me curious. It has a tube input stage and solid state output, so a hybrid. What are your opinions??? The PS stack and phono preamp would be around $6500, the Luxman around $4500, the MA5005 around $5000 (?), and the MA252 around $3500.
IMO, no such thing as too much power, but 100W is probably plenty for most home listening with easy loads (speakers).
Tubes can be great, or a curse. Some people love them, some hate them. Just keep in mind that tubes do wear out or occasionally fail. Also keep in mind noise floor will generally be slightly higher with tubes. This can bother some folks, but for the most part the slight bit of noise is far below the volume of the music and only noticeable unless you're looking for it. I rather enjoy tubes, and use a tube phono and preamp with solid state power amps.

aardvarkash10 wrote:
22 Nov 2019 21:11
Power in an semiconductor amplifier is relatively cheap, so I wouldn't scrimp on it - for every doubling in distance from speakers, I would increase amplifier power by a factor of 1.5 - 2. So in a large room sitting 3m from the speaker, I would theorise an amp with 64w minimum (16 x 2 x 2).
Note that sound in air follows the inverse square law. Every doubling of distance is 6db less volume. That means 3x power to maintain volume at 2x distance.

aardvarkash10 wrote:
22 Nov 2019 21:11
In short, an amp rated at 100W rms into an 8-ohm load is going to work fine. Anything over 150W and you are just buying bragging rights.
The last part I could disagree with, but my amps can do 500+W into 8ohms, and 2200+W into 1ohm on tone burst ;-)

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Re: Is a 100 Watts a 100 Watts?

Post by Bob257 » 23 Nov 2019 14:25

Thanks for all the input. It sure is confusing! I have to admit that the Yamaha sounds pretty good to me, although I might not be a "good" listener. My turntable is the Rega P6 and I enjoy the vinyl. My CD player is the Marantz 6006 which sounds pretty good through the Focals and using the DAC in the Yamaha. I have to decide and research if it's worth the money to "upgrade". I've always lusted over McIntosh so maybe that's why I'm looking at them? I've also investigated the Parasound Hint6. Is there an end to the madness? Should I just stick with what I have for a while? help I'm going crazy!! LOL!

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Re: Is a 100 Watts a 100 Watts?

Post by Pauw » 23 Nov 2019 15:13

One piece of advice......there are two paths you can choose...

1.The upgrade path.....where you run after an ever smaller improvement and the money you spend doubles each time in a y =X2+C path until you find you have a very empty wallet

2. Remember what is important and enjoy the music with a good system


I will leave you to choose which provides satisfaction... :D

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Re: Is a 100 Watts a 100 Watts?

Post by rewfew » 23 Nov 2019 16:31

You have entered into the lure of upgrade promise where there is no guarantee to meet the expectations. That seems to drive a segment of the audio world with it's information apparatus. Some people invest enough time and money trading up or laterally to keep places like Audio Mart and Audiogon a viable business model. I've done my time with it without a great amount of financial involvement, (diy). It's an individual, amount of interest before 'that itch' is quenched. Seems like you have some nice speakers which at your listening level, the issue with power is not a overwhelming aspect of sound quality to be enriched with higher priced watts.

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Re: Is a 100 Watts a 100 Watts?

Post by lenjack » 23 Nov 2019 17:14

No matter how much power you have, most of the time, you will be listening at levels of 10 watts or less. In fact, if you only had a 10 watt amp or receiver, you'd be amazed at how loudly it would play.

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Re: Is a 100 Watts a 100 Watts?

Post by jdjohn » 24 Nov 2019 03:30

I assume the PSA monos are the M700 Class-D. I have an S300 with the SG Pre/DAC all powering a pair of JM Lab/Focal Mezzo Utopia...sounds great to me. The other amps you listed are (I think) class A or A/B. They will all sound slightly different based on topology and also the company's house sound.

Those are all fine choices, so will come down to personal preference. Home auditions are best, and with PSA's generous 30-day trial policy, you should give the M700s a try. I find the S300 to be very neutral and clean. Class A and A/B have a small amount of harmonic distortion, which can be quite pleasant, so again, personal preference.

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Re: Is a 100 Watts a 100 Watts?

Post by lenjack » 24 Nov 2019 03:53

Class A should have NO audible distortion. Even AB should not, if distortion is below .05%.

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Re: Is a 100 Watts a 100 Watts?

Post by jdjohn » 24 Nov 2019 04:19

I'm talking about harmonics, such as 2nd order, not THD. Of course tubes are more well-known for harmonics, but they are present in solid state as well. IME, well-designed class D virtually eliminates it.

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Re: Is a 100 Watts a 100 Watts?

Post by aardvarkash10 » 24 Nov 2019 04:25

jdjohn wrote:
24 Nov 2019 03:30
Class A and A/B have a small amount of harmonic distortion, which can be quite pleasant, so again, personal preference.
Hmmm. Interesting claim as a statement of fact.

A Class A amp is an amplifier (audio, video or indeed any signal type) that maintains the same current through its power stage at all levels of output. A Class A/B operates in Class A for lower outputs and then moves toward Class B as output increases, typically from about 33% output level.

Either can be designed to have any distortion spectra you like. Poorly designed amps can have distortion spectra you don't like. A "small amount" of 5th order distortion, if its the largest distortion harmonic, will set your teeth on edge. Conversely, a small amount of even-order harmonics will sound pleasing (generally), often described and "warm" or "rich".

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