Could a lower power amp actually be "better" ?

Kevin C Brown · 02-27-2004, 01:13 AM

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...

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.

Charles Gurganus · 02-27-2004, 08:19 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...

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.

Yogi · 02-27-2004, 11:50 AM

Were the amps in all your comparisions equally sensitive?

Mike Wilk · 02-27-2004, 12:59 PM

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.

YMMV

Felix_H · 02-27-2004, 02:30 PM

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

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Wayne A. Pflughaupt · 02-27-2004, 06:20 PM

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.

Regards,
Wayne A. Pflughaupt

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

Kevin C Brown · 02-28-2004, 01:41 AM

Felix- You must of remembered something from another thread.

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.

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

Bill Polley · 02-28-2004, 08:05 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).