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Could a lower power amp actually be "better" ?


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#1 of 49 OFFLINE   Kevin C Brown

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Posted February 26 2004 - 06:13 PM

I think I have *my* answer, but I was wondering what y'all thought:

1) Let's say I generically compare a 100W/ch amp vs 200W/ch. Now let's also say that I know that I will never ever use more than 100W. (I.e., room size, speaker impedances & efficiencies, how loud I like to listen etc.) Let's say that sure, I hit 80W/ch on transients watching a movie or listening to CD. So in the 100W/ch case, I'm using up to 80% bandwidth of a channel (for transients) at any given time. But for the 200W/ch case, I'm down to 40%. I never use higher than 40%, and typically, it's probably more like 10-20%. Isn't it better to use a greater percentage of an operating range of an amp? (A kludgy analogly is that I work in an industry where rule of thumb, is that you want to operate components within 15 - 85% range of their operating range for maximum acuracy and precision of whatever you're doing. RF generators, mass flow controllers, etc.)

2) Because of the higher gain a higher power amp needs, a higher power amp can actually have a higher noise floor at similar power outputs to the smaller amp. (Well, not getting close to the limits of the smaller amp's output, of course.)

I already know 2 is true, because I started with an Acurus 100x3 then went to the 200x3, and the noise floor did increase incrementally. I also had the same experience with a Nakamichi PA-5AII and a PA-7AII. 150W/ch and 225W/ch. More speaker hiss evident for the bigger amp. You could say that *maybe* the Acurus isn't that evolved a design and that shoot, hiss *shouldn't* increase for more power, but the Nak amps were based on Threshold designs by Nelson Pass.

Anyways, just curious what the HTF community thought... Posted Image

Oh yeah, and just to clarify, I'm not really thinking about comparing between two different manufacturer's. More within a manufacturer's line where the basic design is exactly the same, just that one amp is more powerful than the other.
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#2 of 49 OFFLINE   Charles Gurganus

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Posted February 27 2004 - 01:19 AM

Kevin so you are basically saying you think more powerful amps have more noise than their less powerful siblings? Of course you would have to volume match the hiss...Posted Image

So to test your theory, did you calibrate using the same source and at that calibrated volume, you heard more hiss with nothing playing from that source? (whew) That is the only valid way I could think of for testing this. If both amps require the same voltage and you calibrate both to a certain volume, I could see your point.

The thing is, my system is now dead quite even pushing biamping NHT VT2's with 400 wpc (sherbourn). I would actually think the harder you had to push the lower powered amp the more distortion/hiss would become apparent. While at that same level, the bigger amp would hardly be breaking a sweat.
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#3 of 49 OFFLINE   Yogi

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Posted February 27 2004 - 04:50 AM

Were the amps in all your comparisions equally sensitive?
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#4 of 49 OFFLINE   Mike Wilk

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Posted February 27 2004 - 05:59 AM

A higher power amp is less likely to go into distortion at the same SPL thus is less likely to damage the speakers. Also, remember amp power is not linear but logarithmic, that is 200 WPC is not twice the power of 100 WPC.

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#5 of 49 OFFLINE   Felix_H

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Posted February 27 2004 - 07:30 AM

Kevin, are thinking about getting a more powerful Bryston? :wink:

#6 of 49 OFFLINE   Wayne A. Pflughaupt

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Posted February 27 2004 - 11:20 AM

Quote:
Isn't it better to use a greater percentage of an operating range of an amp?
Kevin, I’ve been an audio nut for more than 20 years and I can’t say I’ve ever heard anyone – respected source or not – claim this is something of concern.

Quote:
Because of the higher gain a higher power amp needs, a higher power amp can actually have a higher noise floor at similar power outputs to the smaller amp.
First time I’ve heard this, too. And I wouldn’t believe it, except for your own experience which you’ve related.

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P.S. If you're thinking about putting a Bryston out at the curb, send it to me, care of General Delivery, Katy, TX. Posted Image

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#7 of 49 OFFLINE   Kevin C Brown

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Posted February 27 2004 - 06:41 PM

Felix- You must of remembered something from another thread. Posted Image

Charles- Not more noise during playing something, just kind of the noise floor at idle. (Which I guess would translate to absolute s/n. but that's not really what I'm trying to get at.)

I'm not really saying a less powerful amp would better performing than a higher power version, just that for a particular application, could it be a better fit?

Yogi- Yes: same (or very similar) design in each case, just lower or higher power versions thereof.

Actually, I have a 4b-st (250W/ch), but I haven't had any luck in finding a "matching" 200W/ch, 5 channel amp for 7.1.

So I just made a deal for a 5b-st and an 8b-st. (120W/ch, 3 chs plus 4 chs.) And I'm still somewhat trying to rationalize that. Mike- right on: the 250W 4b-st is only 3 dB "louder" than the other two. And, Bryston always includes actual power testing results with their amps, and that 120W/ch monoblock module always tests to around 150W/ch. (But the 4b-st I have tested to exactly 300W/ch!)

As far as hiss, I'm just talking about idle. Someone else told me they had this experience too. Not 10 feet away from the speaker at the listening position. Posted Image Ear right up against the speaker kind of thing.

Remember, one of my "assumptions" is that I will never overdrive the smaller amp, so distortion from that never comes into play. (I will watch for this though, the color of the Bryston LEDs will tell me if that happens.)

Wayne- Hard to explain what I'm trying to get across. A friend of mine (same guy as up above) mentioned something about trying to run a pre/pro (receiver) referenced to Avia at as close as possible to 0dB to try and use the benefit of all the bits in the bit length of the DACs. ("More" dynamic range.) And then I add my experience with the equipment I use at work. And someone mentioned on the Outlaw site about using the 7100 instead of the bigger 755 or 770, again, to specifically use a greater portion of the power band of the amp in typical useage. Just made me think and try to connect them all. One last try: I have a V8 Mustang, right? Once a month or so, I do 0 - 80 mph runs, going to redline in gears 1, 2, and 3. In other words, I want to specifically use as much of the power envelope of the car as I can (at that time). Sort of different in that I want to clean the fuel injectors, break anything that will break at my choosing of time and place rather than randomly. Any of that make sense? Maybe it doesn't apply to power amps? (But the hiss thing I have heard myself on two occasions, and it wouldn't surprise me with the Brystons too.) Kind of like would I expect any "better" performance by running in the mid-voltage/current range of the output devices rather than in the bottom 10-20% kind of thing. I don't know... :b
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#8 of 49 OFFLINE   Bill Polley

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Posted February 28 2004 - 01:05 AM

Kevin, I have the exact belief that you are asking. While more power is better if you need it for peaks due to speaker efficiencies, room size, etc., then by all means use the bigger amp. However...IF you will not reach the limits of the smaller amp, go with the smaller amp.

My thoughts are this: a 100 watt amp only plays 3db less than a 200 watt amp (not a big difference, as you know). If you don't need the extra 3 db of headroom, then playing the amp at, as you say, 85% of output is a plus. The S/N ratio of the amp will be at its best. Also, (and I know that this is not ALWAYS the case) a smaller amp many times needs a lower input value to reach 1 watt of output. This means that at the opposite end, your pre-amp is not amplifying its inputted signal as much. Where the S/N ratio for a power amp gets better as it plays towards the upper limits of its output, the opposite is GENERALLY true about a pre-amp.

If you run full range speakers with deep bass, I can see how you need 200 or even 400 watts of power. If the speakers are inefficient, even more may be needed. For me...I run 85X5 in a 11X16 room. My speakers are fairly efficient Axiom M80s, and I run a powered SVS to take care of the deep bass. I have never come close to needing more power.

Keep in mind this is REAL power. My 85X5 is a Parasound that outputs just over 90X5 all channels driven. It is not a receiver rated at 100 wpc that really struggles to put out 45 wpc with all channels driven. Not to mention my speakers are 4 ohm, and my amp puts out an honest 135X5 into 4 ohms (all channels driven).
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#9 of 49 OFFLINE   John-Tompkins

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Posted February 28 2004 - 02:16 AM

Kevin,

Technically I wouldnt venture an answer for you but I have read more then one review that stated that the reviewer actually thought the 3bst sounded better then the 4bst, now Im not saying this is the case at all but it may go to your point somehow or another (Ive had both amps but not at the same time). The 9bst I have now is the quietest amp Ive ever owned (ear to the speaker and I hear absolutly nothing). One other thing that may not apply to your question but I'll mention anyways.. I have very inefficient speakers (85db) and listen at very high volumes, I thought for sure that I would get the clipping lights on the 9bst to come on often.. but Ive only had the clip light turn orange one time and that was on the center channel only during Jurassic park at extremly loud volume.

#10 of 49 OFFLINE   Kevin C Brown

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Posted February 28 2004 - 10:06 AM

Bill- You perfectly expressed what I was thinking but couldn't get out in words. Posted Image

JT- Right on. Even though I have 200W/ch now with Acurus, a small part of my brain still wonders if 120W (150W in reality) from the Brystons will be enough. Even though I know it will. Funny thing too: I am most concerned about the center channel during movies. Thanks.
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#11 of 49 OFFLINE   Michael R Price

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Posted February 28 2004 - 10:16 AM

Well, a higher power amp probably has higher gain so any noise on the input will be stronger in the output. That's kind of like how sensitive speakers tend to hiss more. Most amps are designed so it takes between 1 to 2 volts on the input to get full power into 8 ohms. It also means it's generally not a good idea to hook a CD player without volume control directly into a solid state amplifier. Posted Image

I would say, a lower power amp could be better since you can get better sound quality for any given price. (Example: small Class A amp.) But in most systems the power ability matters enough that a 100, 200 or even 500 watt amp would be worthwhile. I have found that even when neither amp is driven into distortion, the larger amp *sounds* more powerful, dynamic, etc. My viewpoint however is skewed because I have never compared on my system with good commercial amplifiers... only things I built plus my old 100 watt amp.

#12 of 49 OFFLINE   Robert AG

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Posted February 28 2004 - 03:47 PM

I copied this from another forum. I don't know if it's true, but it sounds logical at least:

Basically, the more efficient your speakers are, the less gain you want from your power amplifier. A more powerful amplifier has more gain than a less powerful one, and the inherent noise from the amplifier is raised. A less efficient speaker will not make this noise as obvious as a very efficient speaker will, and horns are very efficient.

Also, the less of the available power your use from a class A/B power amplifier, the closer you are to the point where the "upper" and "lower" transistors hand over the signal. The area of this transistion can contain small amounts of what is known as crossover distortion, and this is made more audible by efficient speakers. A less powerful amplifier that is driven harder has less of it's signal residing in this crossover region. A powerful amplifier that is barely diriven spends most of it's time in this crossover region. The resulting sound can be harsher and grainier.

The best solution with speakers that are very efficient is a class "A" amplifier that has no crossover distrotion potential at all since a single output device or devices reproduce the entire signal. Vacuum tube class "A/B" power amplifiers are better than class "A/B" solid state amplifiers in regard to crossover distrotion because there is far more overlap between the upper and lower halves of the signal between the output tubes. The ulitmate solution is class "A" tube amplification for very efficient speakers, but this can be an expensive path.

#13 of 49 OFFLINE   Felix_H

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Posted February 28 2004 - 04:01 PM

Hi Kevin,

I think the answers could go either way depending on how you look at it.

Quote:
Isn't it better to use a greater percentage of an operating range of an amp?


Yes: you are thus maximizing/utilizing the amplifier's ability.

No: performance is limited if you reach (or come close to) high volumes for long periods of time. ie. Thus the need for a more powerful amplifier.


Your example of your Mustang is a good one.
You could own a base Honda Civic (or other 4 banger :wink: )and use it as your daily drive to and from work. You may drive the car 50km/hr (or mph) which may use 60-70% engine power and occasionally you may need to gas the car in traffic thus working the engine up to 80-90%.
You could also drive a Mustang/Corvette Posted Image to and from work while only utilizing 40-50% of the engines power going 50 mph. You may then feel the need for speed and red-line the car for a few gears with minimal incremental power usage.

I know this analogy may not be totally correct. :b

Bottom line: Will you drive your Mustang most of the time like a granny? However, with a Mustang, you can have fun as compared to a stock Civic.

Kevin, I guess you are trying to justify from going the 4BST route to the 5B/8B combo.

Do you ever feel your Acurus is ever out of steam when you watch your movies?

I would say if you dont plan or need to use all the power of the 4B ST @ 300 watts, stick with the 5B/8B as they would be rated around 150-160 watts/channel.

In a small room, I would get the 5B/8B combo. Otherwise you could keep your 4B and look for a PowerPac 250 or get a 6B.

Am I repeating myself over and over? Posted Image

Am I making sense at all? Posted Image

#14 of 49 OFFLINE   Kevin C Brown

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Posted February 28 2004 - 08:35 PM

Quote:
Kevin, I guess you are trying to justify from going the 4BST route to the 5B/8B combo.

Bingo! I even asked Bryston once why they didn't do a 5 ch 200W/ch amp. They said too big if it was all monoblocks. So I said, well I still bet Bryston could do a kick ass 5 ch, 200W/ch amp with only 1 or 2 transformers. They said they could and they have (!), but it didn't meet their internal ideas of quality performance, so thet stuck with the 120W monoblock modules.

Robert- Good info too. Good info all around.
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#15 of 49 OFFLINE   Michael R Price

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Posted February 29 2004 - 01:42 AM

"A powerful amplifier that is barely diriven spends most of it's time in this crossover region."

Fortunately, good quality powerful amplifiers have as much or more bias current than their smaller counterparts. So that really isn't true. I would think of a good high-powered amplifier as having its operating range extended farther upwards, but not reduced at the other end. Of course, this probably doesn't hold true for lower quality equipment. I wonder if a cheap PA amp sounds better at 100 watts.

"Vacuum tube class "A/B" power amplifiers are better than class "A/B" solid state amplifiers in regard to crossover distrotion because there is far more overlap between the upper and lower halves of the signal between the output tubes."

This is not really true since the bias point of a class AB solid state amplifier is totally up to the designer and it can be adjusted to almost anything. The tubes do have different turn-off characteristics, but not necessarily less crossover distortion. Instead the switching noise might be less "abrupt" and consist of lower order harmonics. Also, since tube amps have less gain, there usually isn't as much feedback to reduce those distortions.

#16 of 49 OFFLINE   Robert AG

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Posted February 29 2004 - 02:45 AM

>>>Fortunately, good quality powerful amplifiers have as much or more bias current than their smaller counterparts. So that really isn't true. I would think of a good high-powered amplifier as having its operating range extended farther upwards, but not reduced at the other end. Of course, this probably doesn't hold true for lower quality equipment. I wonder if a cheap PA amp sounds better at 100 watts.

"Vacuum tube class "A/B" power amplifiers are better than class "A/B" solid state amplifiers in regard to crossover distrotion because there is far more overlap between the upper and lower halves of the signal between the output tubes."

This is not really true since the bias point of a class AB solid state amplifier is totally up to the designer and it can be adjusted to almost anything. The tubes do have different turn-off characteristics, but not necessarily less crossover distortion. Instead the switching noise might be less "abrupt" and consist of lower order harmonics. Also, since tube amps have less gain, there usually isn't as much feedback to reduce those distortions. <<<

Supposedly the information I quoted was from someone who designs power amplifiers professionally. I would tend to believe him unless you happen to be a designer too and know something he doesn't know.

#17 of 49 OFFLINE   Michael R Price

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Posted February 29 2004 - 03:17 AM

Robert, of course I wouldn't want to contradict them! It just seemed strange given that class AB tube amplifiers are governed by similar rules as solid state, and properly designed amplifiers are set to eliminate the crossover distortion as much as possible even at low levels. See http://www.aikenamps...rDistortion.htm and also maybe Douglas Self's page section 5.3: http://www.dself.dsl...ipa/dipa.htm#5. Can you elaborate a little bit on what you said or direct me to the original post where that's from?

#18 of 49 OFFLINE   JohnSer

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Posted February 29 2004 - 04:44 AM

Kevin, if the only thing that changed in the system was the amps, and you had the volume at the exact same position, you are hearing the difference in db gains and +- any noise from the amps themselves. If you want to compare the noise floor of each amp, plug some grounded input connectors into the amp inputs. I suspect what you heard was mostly the hiss/noise of the pre/pro, with two different db gains.

Amps from the same mfg and same model series can differ considerably in design. Many times, the higher power one will have a better voltage gain stage as well as higher current output stage. But, not always so. More compromises might have been made on one or the other to meet a certain price point. You mention just one possibility, going from a dual mono, to a common power supply.

I think the answer to your question is that it "could" sound better with the lower wattage amp, but it is certainly not the rule.

#19 of 49 OFFLINE   Kevin C Brown

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Posted February 29 2004 - 09:51 AM

Quote:
I suspect what you heard was mostly the hiss/noise of the pre/pro, with two different db gains.

Pre/pro was off, actually. Just the amp was powered.

Yes, even though the design *appears* to be the same, there could be other differences between the low power version and the higher power version.
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#20 of 49 OFFLINE   RobertR

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Posted February 29 2004 - 11:37 AM

Quote:
Because of the higher gain a higher power amp needs, a higher power amp can actually have a higher noise floor at similar power outputs to the smaller amp. (Well, not getting close to the limits of the smaller amp's output, of course.)


I don't think that's true. Someone can correct me if I'm wrong, but from what I've read, an amp simply has a certain inherent noise level, a level which is measured in volts. The S/N ratio for a given output is then the ratio of the signal voltage to the noise voltage. Note that the S/N ratio will vary depending on the output it's measured at, which is why you see it specified for a given output. So if the two amp are putting the same voltage into the speakers, it's simply a matter of which has the lower noise floor. Does a more powerful amp have a higher inherent noise floor?


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