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How much power?

I am curious, Ken; in your journeys through amp design forays and assistance in adoption of FTC standards (I love the as if struck by lightning) what particular segments (what and how many frequencies) were specified to be (power rated) and what weight was each measurement given?
 
charles 1973 said:
For all intents and purposes the "Continuous power output: 20W/20W rms at 0.3% THD"
is the most legitimate. To be totally legit it should include the bandwidth (from 40 - 20,000 Hz for example), an impedance (typically 8 ohms), and would be driving both channels simultaneously. It should all be included in the power spec. Bandwidth as a separate spec may not be the same.

Peak power in a stereo amp is Very Important. The IHF spec is a peak rating, but unfortunately it is only measured over 10 - 20 Ms. Short term peak power sustained for 200 Ms would be more useful, but is seldom mentioned. It is the peak power of one amp that makes it sound much more powerful than it's RMS rating would suggest. Large power supplies and plenty of heat sinking relative to its output in a class A/B amp are an indicator of such reserves.

It should be enough to drive those PSB T5's to satisfying SPL's without clipping for the most part. If your trying to impress your friends with how loud those speakers will go, then you might want 50 - 100 wpc. Myself, I seldom use more that 10 wpc with speakers of comparable sensitivity, and they play plenty loud then.

A word of caution: If you are using the tone controls to add bass or treble, back them off to neutral before running the amp near full power. Adding 6 db's of bass would require about 80 wpc instead of 20. Loudness is best used at lower volumes, and should be turned off at higher volume. Often loudness is linked to the volume control, so as we approach full power, the loudness compensation is reduced to 0. But I wouldn't test it.
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Thanks. As it turns out I am using this system in a very small room, and being 56 I seldom need to show off how loud my stuff can get!!! This system is at its best at low volume with the loudness on. I just wish I could get that same sound with a little more volume is all.
Now I'm going to try and run a different turntable through it in the aux in with a pre amp between the table and the amp. I suspect the Dual 1211 that is built into this Sony plays a large role in the volume issue.
 
Welll... If yer liking the sounds of the amp... at low levels.. revealing of the amps design is that.
Then perhaps Speakers with efficiencies in at least the low 90's would be the clever /easiest choice?
 
ken kantor said:
Yes, I understand the history of amp ratings. (I designed power amps for a number of years and contributed to the FTC standard that is currently in use.) The stringent adoption of RMS was a clear over-reaction to "When struck by lightning," power claims of the past. It brings with it several problems and weaknesses. Any power spec that ignores the signal characteristic of what it is purporting to measure is doomed to failure. An anal allegiance to RMS rating yields amps that are over-priced, inefficient and potentially sonically compromised, and the RMS power of an amp tells the user relatively little about how loud the amp can play.

I wouldn't say that the cure was >worse< than the disease, but close!

-k
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What would be the best measurement to go by, then?
 
"What would be the best measurement to go by, then?"
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I agree with ken kantor about the RMS spec being an over reaction to the the IHF peak power claims used in the past. NAD and Harmon Kardon also agree and were pushing for a standard to measure much longer (200 Ms vs 10-20 Ms) short term power than IHF specifies. Unfortunately there is currently no such measurement.

These two companies (and perhaps others) understand that it is short term peak power that is important for music, and they have designed some amps with this in mind. But this leaves them at a disadvantage when it comes to marketing claims that are so important to the UN-educated consumer, which makes up the bulk of the sales of many of their products, so they too have little choice but to play the RMS power game if they want a piece of that market.

One spec that might help is the FTC power rating for an amp into both 4 and 8 ohms combined with the IHF peak power. NOT the 4 and 8 ohm IHF peak power ratings alone. But this spec is seldom found in home stereo amps. If the 4 ohm FTC power rating is about 1.7x higher than the 8 ohm rating, this would suggest that at least it has plenty of current reserves (some amps, especially more recent ones actually reduce power at 4 ohms), and a high IHF rating may suggest that the amps voltage rails are set higher than an amp with low IHF ratings.


"I am using this system in a very small room, and being 56 I seldom need to show off how loud my stuff can get!!! This system is at its best at low volume with the loudness on. I just wish I could get that same sound with a little more volume is all."
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If this is the case it may be a matter of the systems tone that changes, as it should when loudness is used. At higher volumes with the loudness off you could try experimenting with the tone controls, or blending the loudness function with the tone controls to achieve the desired results at higher volumes.

One of the drawbacks of most loudness controls is that they are calibrated for speakers at with no accommodations for differences in a speakers bass response and sensitivity, and room acoustics. I give Yamaha and Kenwood credit for designing the loudness function on some of their amps with either variable, or several fixed levels of compensation. All amps should have this feature IMO.

A different TT, and phono preamp will likely change the sound of your system, Hopefully for the better.
 
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I am going way off on a tangent.

Most speakers are rated now days at 1 meter listening distance at 1 watt. So if have a speaker with 90 db sensitivity at 1 watt and you listen at approximately 10 feet the sound you will hear is around 80 db from one speaker. 83 db from two speakers ideally. But normally somewhere in between. Now the average person listens with average rms levels of 85 db so thats around 2 watts a channel. The issue then becomes peaks. Average pop recordings they are around 6 to 8 db . So lets say 8 to 12 watts per channel. So you are OK. Now Jazz recordings and classical recording can be much more dynamic and that is where the problem arrises. Of course you can always turn the volume down a bit and still be with in your power envelope. But if you like to live on the wild side a bit or your speakers are less efficient, then you will find your self in a real pickle, because you either have the wrong speakers or in sufficient power for those speakers.

Here's another monkey wrench you are going to have to deal with. In order for something to sound twice as loud to the human earn it takes 10 times the power. Another wrench is most folks with untrained ears have to hear a change of over 3 db to notice a slight difference and that requires twice the power. Now you may be perfectly happy as things stand now, but if your not just a small change of power say from 20 to 40 watts isn't going to be very full filling. You need at least 6 db difference or 4 times the power, 80 watts, in order to reproduce those peaks in music. Now obtaining a very common 100 watt reciever now days is not a big issue either pre-owned or new. The question then becomes can the speakers handle that kind of power. If you find more efficient speakers then you really don't need more power and you are ahead of the game. But more efficent speakers are normally, but not always larger. Which can be an issue.

So I will say we all hope you are happy. What ever you do don't listen to some else's speaker system. If its worse you will be sorry for the other person and happy for your self. But if his system sounds better to you with your favorite recordings you will never forget it and it will drive you to want to improve your system. Thats where all the rules about power needed and speaker sensitivity come into play.

We have just been talking about quantity of sound today. Then there is the quality of the sound and that is even a larger can of worms to be dealt with. Not here and not today. All I can say is read read read. This is a good place to start as there are many paths up the mountain to better sound and we talk about all of them.
 
hopeless said:
How do you know? I upgraded from 250 to 100. Numbers don't really tell much of a story.
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They do if they are the right numbers.
You probably upgraded by going down in power because of a better power supply in the lower watt amp or the replaced amp had audible noise or distortion or was load dependent.
 
UncleAng said:
This is the spec that counts.
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Well, about that...it's good that bandwidth is shown, keeps out the big cheaters. If you can't drive bandwidth into an 8 ohm resistor, you've got problems. We would still not know what power output or distortion would be into a speaker load. Distortion is a bit bogus anyway, your speakers have many times the distortion of your amplifier.

It all breaks down to synergy.
 
Retro_Pete said:
They do if they are the right numbers.
You probably upgraded by going down in power because of a better power supply in the lower watt amp or the replaced amp had audible noise or distortion or was load dependent.
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Both amplifiers have very beefy power supplies, beefy output sections, and roughly the same weight. They are not slouches, both are highly regarded. My speakers are quite easy to drive. The big one looks much better on paper.
 
hopeless said:
Both amplifiers have very beefy power supplies, beefy output sections, and roughly the same weight. They are not slouches, both are highly regarded. My speakers are quite easy to drive. The big one looks much better on paper.
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And by upgraded you mean exactly how? Which amplifiers?
 
UncleAng said:
This is the spec that counts.
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20x20 wpc rms @ .3% THD .. ???

??? But measured over what frequency response range ??? fixed at 1000hz ??
Is that the distortion spec for only 1000hz when the amp is providing 20wpc continuous in to 1000hz ..
It might actually be only 7wpc rms n to 20-20,000hz @ more like 1% distortion ..

Those specs are from the day when meaningless specs were common and overstating the amps capabilities was what it was all about ..
( and still is today since specs seem to be returning to this same type of garbage spec )

The rms spec is meaningless if it isn't measured over a stated range (minimallly the audible 20-20,000hz range) at a max rate of distortion over that range ..
Measuring it at only 1000hz (the easiest to reproduce frequency) was a common dodge ...
 
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opnly bafld said:
"both are highly regarded"
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I don't think a lot of people look down on Bryston and Electrocompaniet. The point is that the brand is irrelevant in this discussion, unless you are looking for a way to get snotty. The point is, on paper there should be a difference, in the other direction.
 
hopeless said:
How do you know? I upgraded from 250 to 100. Numbers don't really tell much of a story.
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Since 1969, 100W RMS to 130W RMS always worked just fine for me and performed and sounded great. 100W RMS is powerful enough - it works. 130W RMS is just perfect!

But you really need to do your homework and know the amp you are buying. Then there is no gamble as to what you will be hearing.

Another old-timer indication - pick the amp up! If it weighs a TON ... that's a good start! :) Heavy Transformers.

:beerchug:
 
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bluesky said:
Since 1969, 100W RMS to 130W RMS always worked just fine for me and performed and sounded great. 100W RMS is powerful enough - it works. 130W RMS is just perfect!

But you really need to do your homework and know the amp you are buying. Then there is no gamble as to what you will be hearing.

Another old-timer indication - pick the amp up! If it weighs a TON ... that's a good start! :) Heavy Transformers.

:beerchug:
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I don't have many below 40 lbs
 
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