Bandwidth Limitations Of Class D Amps??

If you look at Stereophile published bench measurements for Class D switching amps (say Bel Canto ref1000m for example) versus traditional class A/B (non switching amps), I think you'll see examples of what Kijanki referred to.

I would expect the switching frequency used/possible given the current state of the technology to be the technical limitation with switching amps. With current technology, effects appear to be measurable within upper limits of human hearing, ie 20Khz.

All amps have limitations. But with non-switching amps, the limitations are due to other design factors. Still, I believe many are capable of measuring flatter to well beyond 20Khz.

Of course what is measured may or may not be an indication of what is actually heard, especially when it relates to the extremes of what humans are able to hear. The upper limits of what humans can hear is probably still the weak point for Class D switching amps. How weak or how much it matters is debatable I suppose, much like what is the effects of CD redbook sampling parameters. Newer CLass D amps using newer technology might push switching frequency up higher than what was possible even just a few years ago. Have not seen measurements on those yet so not sure if the is the case (yet).

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Bombaywalla, Kijanki's post was a couple of days ago on 3-15-13. His entire post is below:

03-15-13: Kijanki
Some people argue that class D, as good as it is for the money, cannot really compete with best traditional SS amp. I can see that, especially with still limited bandwidth, but most of the weight is in the power supply that can be definitely class D (SMPS) since it is only holding steady voltage (much easier task than driving complex load with music signal). Rowland does it so why not the others? I think it is for three reasons:

1. Design itself is much more difficult than just
transformer+rectifier+capacitors
2. SMPS have bad rap from crude cheap computer applications
3. Audiophiles still believe that it has to be heavy to
sound good.

Third point is very important - why to design complicated light power supply when market believes that heavy=quality.
Kijanki (System | Threads | Answers | This Thread)

The Thread This Post Appeared In Is In This Link
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Realize that switching frequency spec of a switching amp would seem to set a clear theoretical limit to what is possible with that design in terms of frequency response. But alone it does not determine sound quality, even as measured. It may determine an absolute limit in theory, but the reality is many factors affect amp performance, switching amp or not. Specs are informative but alone do not tell the whole story. Only our ears can do that and each story will probably be a bit different as a result, especially when it is differences in the fine details of what is heard that is in question.

Most Class D amplifier designs require a filter at the output to remove the high frequency switching noise that is present in the signal. Various designs use different types of filters with varying cutoff frequencies. I doubt that any are designed to remove frequencies under 20KHz, but Class D amps are generally more frequency limited at the high end than conventional output stages can be. Whether this is audible can be a subjective question. Some engineers feel that in order to avoid introducing any phase shift to the audible high frequencies requires an amp to have a flat bandwidth response extending to many multiples beyond the audible frequency limit.

My Gilmore Raptors are -3db at 60khz
Alan