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My criteria for a POTENTIALLY good sounding amp

I have been thinking for a long time about what design/measurements that are readily available to use as selection criteria for an amplifier.

I have distilled the ideas down into these guidelines. However, the final judgement is always in the listening, I am afterall and empirical scientist and don't rely on what people "know" to be good sound. Keep in mind that I have reached these guidelines by an empirical approach. When I heard an amp that sounded REALLY good I went and found as much info on the design and/or measurements as possible. After doing this for a long time I now have the following rules of thumb:

1) The amp must be Class A or high bias AB (around 15-20 watts A)
2) The amp must have little to no negative feedback or at least no global feedback
3) The amp must have a large, low impedance power supply
4) If the amp is tube output it must have LARGE output transformers that do not easily saturate, or be an OTL without much negative feedback
5) It should be simple in design, having only 2 or 3 total stages from input to output

6) The distortion should increase linearly (or nearly so) with power (also indicates a low feedback design)

7) The distortion should remain constant as a function of frequency, i.e. no rise at high frequencies as is often seen in SS and some tube amps and no rise in bass frequencies as is often seen in tube amps. This distortion is often far worse, harmonically, than the 1Khz typical measurent.

8) The damping factor should remain constant as a function of frequency

9) The harmonic distortion spectrum (usually taken at 1Khz) should be monotonic with a significant drop in level with increasing order and harmonics higher than about 5th should be down in the noise floor of the FFT.

10) Power supply ripple should be minimized so that distortion products do not produce intermodulation distortion products with the power supply harmonics. This results in a "dirty" noise floor.

11) IMD products should be low order like the harmonic distortion products.

If an amp meets most or all of these criteria then it probably has a good chance of being an excellent sounding amplifier. If it fails most then it will likely be mediocre at best and often quite "hifi" sounding rather than musical.

Again, this is an empirical observation and is open to reinterpretation if an amplifier that fails most of these criteria actually sounds really good to me. I haven't found it so far...

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Topic - My criteria for a POTENTIALLY good sounding amp - morricab 07:22:50 06/18/12 (154)
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