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Which of these factors are most decisive when choosing a good amplifier?

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DarkPop_92

New Member
Which of these factors are most decisive when choosing a good amplifier, knowing that the speakers are a dominant part of the choice (If it were possible a brief summary) ?
- Power Output
- Frequency Response
- Total Harmonic Distortion (THD)
- Signal-to-Noise Ratio (SNR)
- Input Sensitivity and Impedance
- Damping Factor
- Power Consumption
 
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Depends upon the speakers, to a great extent.

Ability to deliver power into lower impedances is usually indicative of amplifier quality. Always important, and critical with lower-impedance speakers.

Absolute power output is not, in and of itself, important. How much you need depends upon speaker sensitivity, and impedance.

Generally, THD below .5% is fine. Hard to find an amp these days with anything worse than this. Signal to noise of 90dB or better is good. The greater the sensitivity of your speakers, the more important this becomes.

Range of frequency response should be 20Hz to 20kHz, or better. More important (much more) is linearity of the response.
 
Transformer is part of the power supply. The quality of the power supply is indicated by power output into lower impedance loads vs higher impedance loads.
 
If I should build an amp, I pick the Power tranny first and then build a power supply around it. That's the way I was taught. The power supply is the part that comes after the PT in my mind but who cares, we can differ.
 
Of all those mentioned though I would lean to the largest signal to noise ratio. Distortion will compromise a signal to noise ratio and vice versa. So if the manufacturer is being honest then having an amp with 1 % distortion only has a signal to noise ratio of 40 db. Damping factor is another one to consider. A low damping factor means the amps frequency response can be easily effected by the speakers varying load impedance making its published frequency response meaningless. Thats why tube guys are always switching amps trying to get the sound they want from their tube amps with poor output transformers. Mcintosh has improved their auto-formers today but the 2000 series amps were as bad as tube amps when it came to being colored by the speakers load impedance. I use Mcintosh direct couple amps for that very reason to this very day .

Now if you like tube pre-amps then unless they have SS output buffers driving moderate to low input impedances on modern SS amps is a real issue. There are exceptions of course like the Fisher CX 400 as I recall which was a tube pre-amp designed to drive low impedance professional amps and processors.

QSC who builds professional amps and is one of Crowns chief competitors did some serious research and found as long as their amps were driven tinto clipping that the power that was required to reproduce live music was only 1/8 the power necessary when performing continous power performance checks. Now modern over compressed digital music might reguire you to use occasion peaks og 25 % of the rated draw from your AC output receptacles. Remember this that in most cases it takes 200% amp rating for a few minutes in order for a circuit breaker to trip. Any time a motor such as in your vacuum cleaner or HVAC system has to start up it requires 5 times the steady sate current consumption given for the motor. Your circuit breakers are designed to allow this to happen. My stereo power amps are rated to pull 6.5 amps a full power output each. But as I seldom use more than 25 % of their rated power for peaks and most of the time less than 10 % I don't worry about taxing my electrical system. Normal listening is around 1 % draw.
 
DarkPop_92 said:
Which of these factors are most decisive when choosing a good amplifier, knowing that the speakers are a dominant part of the choice (If it were possible a brief summary) ?
- Power Output
- Frequency Response
- Total Harmonic Distortion (THD)
- Signal-to-Noise Ratio (SNR)
- Input Sensitivity and Impedance
- Damping Factor
- Power Consumption
Click to expand...

The cost is my first and highest Factor. All other factors fall into place around what I can afford for that setup.
 
DarkPop_92 said:
Which of these factors are most decisive when choosing a good amplifier, knowing that the speakers are a dominant part of the choice (If it were possible a brief summary) ?
- Power Output
- Frequency Response
- Total Harmonic Distortion (THD)
- Signal-to-Noise Ratio (SNR)
- Input Sensitivity and Impedance
- Damping Factor
- Power Consumption
Click to expand...
You say a "good" amplifier with the speakers being the dominant force in the decision.

With most any "good" amp, FR, THD, SNR, and damping factor will all be ~flat and inaudible. So it comes down to does the amp have the power/current to drive the speaker load to an acceptable level and will the sensitivity of the amp's input work with the preamp's output to give an acceptable volume.
 
For me since I have difficult to drive speakers, it's rated power at 8 ohms versus rated power at 4 ohms. I've found it a great indicator of transformer power. Ideally an amp should double power from 8 ohms to 4 ohm load. Not all can, but the closer it gets, the better. The transformer or preferably transformers are the heart of an amp. Some manufacturers will try to bandaid a less powerful transformer with lots of capacitance, but comparing rated power at 8 and 4 and maybe even 2 ohms will always suss them out. In my opinion a little too much emphasis on distortion. Most quality amps will have a distortion below audible threshold, an acceptable SNR, and decent damping factor. I think you'd have to try to find an amp that has specs bad enough to cause audible distortion, at least in the solid state realm.
 
What ratio between the power at 4 ohm and that at 8 ohm would qualify as good? Of course, a ratio of 2 would be ideal, but if you can't achieve that, then how much lower can it be while still being deemed acceptable?
For instance, I was looking at a Rotel RB-1582 MkII. The rated power output at 8 ohms is 200W, and at 4 ohms is 323W. A ratio of 1.6. I guess that sounds pretty bad, doesn't it? :confused:
 
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As above ...
But you didn't include how it sounds which is hugely important ..

And for the reasons everyone else mentioned comparing the power consumption specs can tell you a lot ..
If one of your considerations is consuming considerably more wattage it's likely the more powerful amp regardless of the often inflated power spec.
 
Vlad Soare said:
What ratio between the power at 4 ohm and that at 8 ohm would qualify as good? Of course, a ratio of 2 would be ideal, but if you can't achieve that, then how much lower can it be while still being deemed acceptable?
For instance, I was looking at a Rotel RB-1582 MkII. The rated power output at 8 ohms is 200W, and at 4 ohms is 323W. A ratio of 1.6. I guess that sounds pretty bad, doesn't it? :confused:
Click to expand...

Seems quite good to me. 1.4:1 or better puts you in pretty good company. And yes, 2:1 is not possible in the real world without either understating the 8 ohm output, overstating the 4 ohm output, or both.
 
Dan13105 said:
For me since I have difficult to drive speakers, it's rated power at 8 ohms versus rated power at 4 ohms. I've found it a great indicator of transformer power. Ideally an amp should double power from 8 ohms to 4 ohm load. Not all can, but the closer it gets, the better. The transformer or preferably transformers are the heart of an amp. Some manufacturers will try to bandaid a less powerful transformer with lots of capacitance, but comparing rated power at 8 and 4 and maybe even 2 ohms will always suss them out. In my opinion a little too much emphasis on distortion. Most quality amps will have a distortion below audible threshold, an acceptable SNR, and decent damping factor. I think you'd have to try to find an amp that has specs bad enough to cause audible distortion, at least in the solid state realm.
Click to expand...

Seems to me that there's quite a bit more involved than just the transformer.
 
Vlad Soare said:
What ratio between the power at 4 ohm and that at 8 ohm would qualify as good? Of course, a ratio of 2 would be ideal, but if you can't achieve that, then how much lower can it be while still being deemed acceptable?
For instance, I was looking at a Rotel RB-1582 MkII. The rated power output at 8 ohms is 200W, and at 4 ohms is 323W. A ratio of 1.6. I guess that sounds pretty bad, doesn't it? :confused:
Click to expand...
Not at all. It still wouldn't be my first choice for my difficult to drive speakers, but it seems fine. That was more so aimed at amps that only go from say 100W at 8 ohms to 110W at 4 ohms. That to me indicates either a weak power supply, or insufficient cooling.
 
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