Re: What's a transient?

On Thu, 27 Apr 2006 00:20:29 +0100, Pooh Bear
<rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:

Iain Churches wrote:

"Don Pearce" <donald@xxxxxxxxxxxxx> wrote in message
news:444f35a2.2676390@xxxxxxxxxxxxxxxx
On 26 Apr 2006 01:51:34 -0700, "Bassling" <Bassling@xxxxxxxxxxxxx>
wrote:

It is interesting though that the ChipAmp/Gainclone people report the
same effect.
They often state that a smaller capacitor across the PSU increases the
speed of the amp.

That is another matter entirely. That is a matter of the capacitors
not having a decently low high frequency impedance, but it is nothing
to do with how much capacitance there is.

In fact, in a properly designed amplifier, this should really make no
difference.

d

Hi Don. Do you happen to know the typical rise time of a good SS
amp on a square wave?

Regards to all
Iain

It'll be determined by slew rate. A few microseconds typically.

Actually, slew rate and risetime are not closely related, as risetime
is a small-signal parameter, but slew rate is tied to the current
capacity of the early amplifier stages. An amp can quite readily
combine a risetime of less than a microsecond, with a slew rate of
less than 1 volt per miscrosecond. This is the classic 'slew rate
limiting' much discussed by Matti Otala in the '70s, but easily
avoided by any decent designer.

However applying a step input ( an out of band test signal like asquare wave
) is not really a valid test for an amplifer designed to reproduce only
audio frequencies.

A 5kHz square wave is quite a reasonable test of an audio amp's
stability into a difficult load, and only requires 55kHz power
bandwidth to give a nicely square output. This can be a stretch for
many valve amps, but should be standard fare for any decently designed
SS amp.
--

Stewart Pinkerton | Music is Art - Audio is Engineering
.

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