A question on amp matching

You know the difference between a 400 watt amp and a 200 watt amp is only 3db. Just use the power output as a guide not as an absolute.

What speakers are you trying to drive? The impedance plot and efficiency of your speakers will shed some light on what amps might sound correct.

I would not enjoy the sound of a modest ARV receiver driving, for example, Focal Kanta 3's. On paper it might look like it should work, but the 8 Ohm nominal and 91 db efficiency rating is not the full story on these speakers and what you need to make them sound right.

+1 @nwres

@pryso - it would be much easier for us to help if we knew which speaker, or better yet which speaker and amp paring was disappointing.

If you want to figure it out yourself, you’ll have to be able to read/understand the impedance/phase vs frequency plot and efficiency of your speakers.

There are a lot of differences in amplifiers besides watts. I remember using a Naim 200, with 60 watts I think and it sounded a bit thin and anemic.  I switched to a Naim 250 with only 10 watts more, but it sounded twice as powerful because of the bigger and regulated power supply. So there’s that. You really need to go beyond wattage in your search, IMO.  As stated above, the way an amp handles difficult loads can make all the difference. It depends a lot on the speakers you are using. 

I always find it frustrating when someone posts a question, receives multiple replies, then fails to respond to any of them.  That seems disrespectful to those who took time to try and help out.

So thanks for the replies.  The general answer seems to be gain is useful to know but not nearly as important as power rating.  Of course other design elements can be important as well, so it is not one thing.

And again, I was looking for general advice, not asking about specifics for one model.  Anyway, a big part of the disappointing audition was a hook up mistake, nothing to do with characteristics of the amp involved.

Yes, power is a more important spec than gain. Here's a way to understand power amp gain in practical terms: let's say you have two amps, both rated at 100 watts power but one has 22db gain and the other has 27db. If you were to play music through each amp in turn, at a moderate level so that you are nowhere near their maximum power output, and you kept the volume control on the preamp at the same level, the amp with 27db gain would play 5db louder. Amps with lower gain can sometimes be better because you can use a wider range of the volume knob. With a high gain amp you might rarely get the volume knob much above 9 or 10 o'clock. A minor issue but something to consider.

Power is a measure of an amp's ability to do the work of moving the speaker cones. More power is usually better because you can play louder before the amp begins to produce noticeable distortion. As russ69 points out, due to how the ear works, doubling power output only makes the music slightly louder (3db). In order to make sound twice as loud before distortion you would have to increase the power by 10x. So to get twice as loud as a 100W amp you'd have to go to 1,000watts (assuming the speaker could handle it). More power is often better because you rarely push the amp close to its distortion, also known as headroom. For most people with average sensitivity speakers 100 to 300 watts is usually sufficient.

Thanks for replying @hertzhead.  I knew about doubling power for a 3 dB increase in loudness, and the 10x increase in power to double output level, but lacked a clear understanding of listed gain.  So this was very helpful.

Among all the other specs, how important is gain in addition to power output at a rated speaker impedance?

Usually, the gain specification of a power amplifier is the voltage gain in dB, which evaluates the amplifier’s amplification capability in terms of the output/input voltage ratio.

For example, the Bryston 14B³ has selectable voltage gain with 23dB (low) and 29dB (high) settings. The preamplifier requires an output voltage of 2.5V (high gain setting) or 5V (low gain setting) to drive the amplifier to its rated power of 600W@8Ω.

In other words, the gain specification of the power amplifier determines the preamplifier output voltage requirements.

I hope I’ve answered your question.