Power Supply Resevoir Size

[AndrewT]

No.
Either the amplifier is clipping, or the amplifier is not clipping.

You are drawing a conclusion that is false.

[DF96]

For the amplifier not to clip the average music signal must be well below clipping, not just below. This is because of the large peak/mean ratio for real music and the slightly smaller ratio for well-recorded music.

[AndrewT]

I don't care what the music might do, the statement is
"the amp is not clipping the signal"

The conclusion that the amp
"must have some method to prevent clipping."
is not a valid.

[DF96]

That would depend on how clipping is avoided. Running near clipping for most of the time I take to mean that the average level is near clipping, as for most of the time music is near its average level. Maybe that is not what he meant, but that is what he said. If he meant to say that the music is at a much lower level, nowhere near clipping, then this tells us nothing about the PSU because it is not having to deliver very much current and there will be very little droop.

[Nico Ras]

Originally Posted by AndrewT

I don't care what the music might do, the statement is
"the amp is not clipping the signal"

Precisely!

The amp power supply may be modulated pretty severely but that does not necessarily imply that amp is driven into clipping.

Also music and pure sine waves would behave quite differently and that is what Frank is referring to. If it is a sine wave, the the powers supply modulation would be in sync with the signal and may affect the way it sounds but it would not be horrible.

However, if it is a complex signal the power supply will be modulated most by the highest power signal which would "mix" with all other signals and besides smearing due to inter-modulation artifacts these artifacts could also contain dissonance which is most fatiguing because it is sounds our brains do not like.

Exactly what this thread is trying to address.

[fas42]

Originally Posted by DF96

That would depend on how clipping is avoided. Running near clipping for most of the time I take to mean that the average level is near clipping, as for most of the time music is near its average level. Maybe that is not what he meant, but that is what he said. If he meant to say that the music is at a much lower level, nowhere near clipping, then this tells us nothing about the PSU because it is not having to deliver very much current and there will be very little droop.

There has been a misunderstanding of what I meant, I most certainly am not talking about average levels of the signal being near clipping, rather whether the peak level ever clips. I'm very much aware that music has dynamics , so when I say close to clipping I am referring to the piece of music as a whole; in the same way that a recording engineer will master a non-compressed CD so that the maximum level ever reached, at probably one point in the whole disk, is perhaps zero, one or two bits from the absolute maximum - the term used is to normalise the levels.

I have got my chip amps to overload, but this was thermal overload, the sound starts to chatter as the protection cuts in and out; interestingly, this is never on pop but rather operatic -- the soprano hits a big note and sustains it, a very pure, high level tone over a decent period was enough to start overcooking the chips ...

As regards drooping, it is, or was, endemic to amplifiers. Back when I was really into trying to understand what caused sound quality problems I made a point of experimenting with every system in a dealer's showroom that I came across, and they all displayed this characteristic. Irrespective of how massive the metalwork was, there would be a certain volume where the sound would start to collapse, not clip, which I interpreted as the power supply being overtaxed ...

Frank

[Kindhornman]

It would seem to me that what we need here is an absolute definition of clipping in this instance. I can understand when a power supply reaches the point where the sag in the rails is enough to change, or cut a waveform that the amplifier is trying to produce. A square wave that has rounded corners or a sine wave that has the tops cut off would make me think of clipping. On the other hand you could have a power supply so over-sized that you will never get into that condition but the amplifier is driven so hard it is out of the SOA and also is clipping in that the waveforms are distorted by thermal conditions. So who is going to define the actual term clipping as we are trying to use in this instance? I have always assumed that if you never reach the point where the loudest or sustained peaks do not become changed in any way that you are under the clipping level of the system. You have enough headroom to stay out of that condition.

[fas42]

Perhaps as good as any -- from the Rane dictionary: http://www.rane.com/par-c.html:

clipping Term used to describe the result of an amplifier running into power supply limitation. The maximum output voltage that any amplifier can produce is limited by its power supply. Attempting to output a voltage (or current) level that exceeds the power supply results in a flattoping effect on the signal, making it look cut off or "clipped." A clipped waveform exhibits extreme harmonic distortion, dominated by large amplitude odd-ordered harmonics making it sound harsh or dissonant. Hard clipping is the term used to describe extreme clipping of a signal, producing highly visible flattoped waveforms as viewed on an oscilloscope; soft clipping refers to moderate clipping that results in waveforms having softly-rounded edges, as opposed to the sharp edges of hard clipping.

I am talking otherwise of the power supply voltage rails being sufficiently modulated by the current demands to interfere with the correct functioning of the amplifier circuitry: the PSRR not being good enough, or the regulation or smoothing being insufficient, causing the SQ to deteriorate ...

Frank

[Kindhornman]

Thank you Frank for the definition. It appears that I had the correct idea about the term. Now I have a separate question. On an amplifier with a clipping light what exactly is the light indicating when it is triggered? I know it is called a clipping light but where in the circuit is the clipping indicator located and what is it actually measuring?

[fas42]

At least one take on an indicator, by that ever prolific chap, Rod Elliot, is here: Power Amp Clipping Indicator. It doesn't cover how it's often implemented in commercial units, but explains precisely how such a circuit should work ...

Frank