IcePower slew rate

[Rikard Nilsson]

Anybody knows how good the IcePower slew rate is?
I can´t find any figures.

[Eva]

The concept of slew rate does not make sense for class D amplifiers, or even for modern linear audio amplifiers at all. It's mostly operational-amplifier related, where it still makes a lot of sense, particularly for non-audio applications, where waveforms can have sharp edges.

Audio people started to consider slew rates many years ago in the context of linear amplifiers that could not produce full output up to 20Khz, (or whatever upper frequency was required in each application, not only audio!). This was because some internal stage would clip before delivering enough current to charge the input capacitance of the next stage fast enough. This results in "triangulation" of the output waveform (when maximum slope is reached).

Nothing of this exists on class D, there are no linear power amplification stages and no triangulation is possible (at least not unless the designer did something really wrong, like using a too big output capacitance with a too low current limit, so unlikely).

Anyway, modern audio amplifiers, both class D and linear, can produce full output well above 20Khz, so they cannot distort the signal in the way the old "slow" ones could do, and by "slow" I mean stuff from LM741 age, 1970s, germanium, tubes with high capacitances (yes tubes!), etc.., so way way outdated!

[Javin5]

Eva, I fully agree. If an amp can produce full power at 20 kHz with low distortion (and full stability at actual speaker loads), that's already in excess of anything that will ever appear in real music signals.

Reminds me a little bit on the damping factor discussion, where totally meaningless numbers are claimed by not including the voice coil resistance.

Kurt

[Ouroboros]

I agree with Eva regarding 'slew-rate' in class-D amplifiers. Just consider: the output of the switching transistors (at the node before the output LP filter) is switching from rail-to-rail at a slew rate that is orders of magnitude higher than the rate-of-change of any audio output signal. This switching signal is then low-pass filtered by a passive filter that imposes a 2nd-order response, but cannot cause any slew-rate limiting in itself.

I don't know the details of the self-oscillating modulator used in IcePower amplifiers, and it is conceivable that the modulator stage (if not designed properly) could cause a slew-rate limit, but even if it did, it should be appreciably higher than any audio signal will require.

[Gyula]

a passive filter that imposes a 2nd-order response, but cannot cause any slew-rate limiting in itself

Just think about the step-responce of that filter. The time-constant of the poles' radius determines the slope.

[Ouroboros]

Yes, but it's NOT slew-rate limiting! The L-C filter is a linear circuit element. S-R limiting is caused by a non-linear limiting case.

[Pafi]

In this case I agree with Gyula. I think if slew rate is limited, then it's slew-rate limiting. And slew rate is limited indeed. Limitation comes from the supply voltage, but it exist. The saturated element is PW modulator (at 0% or 100%).

In some cases the power bandwidth can be significantly lower then small-signal bandwidth (because of the efficient feedback), so I think SR is a relevant parameter in ClassD also. But it's soooo low (compared to linear amps), that nobody dares to specify it. :-)

[Eva]

But where is the triangulation? The output from a class D amp fed with a sinewave is always sine shaped.

[Mr Evil]

Originally posted by Pafi
In this case I agree with Gyula. I think if slew rate is limited, then it's slew-rate limiting. And slew rate is limited indeed. Limitation comes from the supply voltage, but it exist. The saturated element is PW modulator (at 0% or 100%)...

The two are different! I've attached a sketch showing the difference. With a pulse input (top), a low-pass filter results in a curved output (middle), whereas a slew rate limit results in the edges being limited to a fixed slope (bottom).

[Pafi]

At linear amps the SR limit not neccessarily manifested in triangular waveform neither. This is just an idealisation. In reality maximal SR doesn't have to be constant! If there is a limit, then it's done. It can be a function of load impedance, supply voltage, instanteous output voltage, previous states, etc..., but if increasing input doesn't make it faster, then it's slew rate limit. At least I call it this way. (And semiconductor companies too, because otherwise they couldn't specify some of their OPAs.)