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"Don Pearce" wrote


I don't follow the distinction. What has the NFB loop got to do with
this? What would you do with an amplifier that has no global NFB? Is
it not an amplifier at all as a result?


It's a passive network between the signal source and any active devices. In
my book that makes it signal conditioning, not amplification.

David.

New page on Squares waves and amplifier performance
 

On Mon, 11 Jan 2010 21:50:22 -0000, "David Looser"
wrote:

"Don Pearce" wrote


I don't follow the distinction. What has the NFB loop got to do with
this? What would you do with an amplifier that has no global NFB? Is
it not an amplifier at all as a result?


It's a passive network between the signal source and any active devices. In
my book that makes it signal conditioning, not amplification.


No, you are not going to get away with that little piece of tap
dancing. I never said it was amplification, I said it was a necessary
part of the amplifier. There are several places in any amplifier where
the signal gets attenuated slightly.

d

New page on Squares waves and amplifier performance
 

"Don Pearce" wrote

No, you are not going to get away with that little piece of tap
dancing.

My way of looking at this is no more "tap-dancing" than yours is, we are
simply looking at the same facts from a different perspective.

David.

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"Ian Iveson" wrote

In the meantime I suggest you check out how a cathode
follower works, and in particular how its output impedance
is defined.


Think of it like this. The valve can source current into the load
capacitance, but not sink current from it. So the only discharge path for
the charge stored in that capacitance is via the cathode resistor, and hence
the rate of drop of the cathode voltage cannot exceed that determined by the
time constant of those two components.

David.

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On Mon, 11 Jan 2010 22:31:09 -0000, "David Looser"
wrote:

"Don Pearce" wrote

No, you are not going to get away with that little piece of tap
dancing.

My way of looking at this is no more "tap-dancing" than yours is, we are
simply looking at the same facts from a different perspective.


Ok, here's a fact for you. You find this particular piece of circuitry
inside a box with the word "amplifier" on the front. And when the
amplifier designer is designing his amplifier, this is one of the bits
he designs in order to design it. Cut this any way you like, it is
part of an amplifier.

d

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"Ian Iveson" wrote in message
...
David Looser wrote:

Indeed, excessive bandwidth of the incoming signal.

Excessive slew rate. There really is no other adequate way of saying it.
Not excessive bandwidth, or amplitude, or combination of the two, but slew
rate, pure and simple. A signal of a particular frequency has a max slew
rate which depends on its amplitude, and vice versa, so neither frequency
nor amplitude alone define a slew rate. Although a particular combination
of frequency and amplitude defines a maximum slew rate, it isn't a unique
definition because it could be the same for any number of other
combinations and waveforms.

Absolutely, I'm not quibbling with that.

But as Jim showed a simple passive filter on the input to the amplifier
solves it.

Not if it's bad enough so that it can occur at audio frequencies, or
frequencies otherwise necessary for the satisfactory operation of the amp.
Then the cause of the limiting must be dealt with.


Well OK, if it's *that* bad!

David.

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"Don Pearce" wrote

Ok, here's a fact for you. You find this particular piece of circuitry
inside a box with the word "amplifier" on the front. And when the
amplifier designer is designing his amplifier, this is one of the bits
he designs in order to design it. Cut this any way you like, it is
part of an amplifier.


That's very much a "Hi-Fi separates" way of looking at things if I may say
so.

The theory behind this applies to more than Hi-Fi, more than audio. You
cannot say where and how band-limiting filtering may be applied in every
design. The filtering is there so that the slew-rate of the signal does not
cause problems to the amplifier; I take it we can agree on that? Arguing
about whether this filter is regarded as part of the amplifier, or not,
seems to me to be equivalent to arguing about how many angels can dance on
the head of a pin.

David.

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David Looser wrote:
"Trevor Wilson" wrote in message
...


DolbyT.

What's DolbyT?

**Dolby (trademark).


--
Trevor Wilson
www.rageaudio.com.au

New page on Squares waves and amplifier performance
 

"David Looser is an IDIOT "

It may have been "unheard of", but it existed all the same. Any amplifier,
with or without feedback, can exhibit slew-rate limiting if the bandwidth
is insufficient to cope with the rate of rise or fall of the input signal.


** This is just completely WRONG !!

Bandwidth and rise times are small signal parameters - but " slew rate
limiting " is a LARGE signal phenomenon.

All audio amplifiers have slew rate limits, usually quoted in V/uS - often
different rates apply for positive and negative going output voltages.

The usual cause is a current source internal to the amp's topology being
driven to its limit in trying to charge and discharge internal capacitances.


..... Phil

New page on Squares waves and amplifier performance
 

Don Pearce wrote:
On Mon, 11 Jan 2010 14:52:48 +1100, "Trevor Wilson"
wrote:

**Nonsense. It's all about phase shift.

Which of course speakers themselves don't have...

**Irrelevant and 'two wrongs rarely make a right'.

Or, to put it another way:

Just because one part of a sound reproduction chain is imperfect, that does
not suggest that we should deliberately compromise other components, when it
is a trivial exercise to make those components 'perfect' in the first place.


--
Trevor Wilson
www.rageaudio.com.au