What contributes most to a change in how an amplifier sounds?


Amplifiers include tubes (if not solid state), big transformers, lots of internal wiring, Power supply, cabinet, gain controls if you're lucky, connections for incoming and outgoing cables, Computer chips,  Control panels, semiconductor boards, design choices, age,  etc.

Of all this stuff, what contributes the most to a change in how an amplifier sounds?

 

 

emergingsoul

If you people would read the measurements section of Stereophile, you would see that I’m correct.

Look at the frequency response for the Moon 861. Remember, we are talking power amps here, so no preamp functions (e.g., loudness) enter into the discussion.

And the discussion:

The output impedance in stereo mode was extremely low, at 0.008 ohms at 20Hz and 1kHz, rising slightly to 0.03 ohms at 20kHz. As the two output stages are in series in mono mode, the output impedances were twice the stereo values. In both stereo and mono modes, the variation in the frequency response with our standard simulated loudspeaker (fig.1, gray trace) was negligible.

Now look at the BAT REX 500 frequency response:

And the discussion:

The REX 500 amplifier’s output impedance, including the series impedance of 6’ of spaced-pair cable, was relatively high, at 0.45 ohms at low and middle frequencies and 0.6 ohms at the top of the audioband. As a result, the variation in the frequency response with our standard simulated loudspeaker (fig.1, gray trace) was ±0.3dB.

So while the response is flat into a load resistor, it varies by ~+-0.3 dB into a real life speaker load. That’s enough of a difference to hear as a difference. And of course every speaker is going to have a different load, so the amp is going to have a different response for each speaker dependent on that load.

Know that a lot of amps show considerably more variation than this.

So the second graph is better with respect to the line that’s more wavy. Which means it’s more responsive with a more accurate delivery of Dynamics as the music demands. A lower level of Dynamics, flatter line, is expected when impedance is lower?

No the first graph is better as the power level, and hence volume, of the sound does not change with frequency.

In the second graph, the power goes up and speakers will get louder ~75 Hz and 1-2kHz and have a dip at ~5kHz so you would not attain a flat frequency response with that amp with that speaker load.

Note that the same "real life" speaker load is used for both amps.