does it make sense to test how amps behave when they clip?

[March Audio]

Yes just in case that the probe 1:10 was not calibrated and trimmed with 1kHz calibrator square. I think it was the case and you probably hit the nail. Before ANY measurement with 1:10 probe switch position, calibration is necessary. We may have more than one scope ....... with the same probe used.

Checked that, square wave spot on. No idea what the issue was and can't replicate it.

 

[pma]

Checked that, aquare wave spot on. No idea what the issue was and can't replicate it.

Understood, fair enough. You will definitely find it later.

 

[RayDunzl]

Meanwhile, most power amplifiers have unregulated output voltages.

I'm an outlier again...

 

[Mnyb]

Are clipping indicators really fast enough ? wonder if not many of us live in the illusion that we have enough power anyway ?

 

[SIY]

Tube amp clipping generally has a VERY bad and highly audible side effect: blocking. Unless an amp is specifically designed to avoid this (e.g. Morgan Jones's Crystal Palace or my Red Light District), it can transform a brief and possibly inaudible overload into a distinctly unpleasant fuzzy choking sound. With tube amps, I test by using a sinewave stimulus that cyclically switches from just over clipping to well under clipping.

 

[March Audio]

A clip indicator is something I have previously considered implementing. The Hypex modules all have the functionality built in.

 

[Thomas savage]

Yes.

 

[solderdude]

it does

 

[AudioTodd]

Get a class D amp with a few hundred watts of power and then don't need to worry.

Or monoblock some AHB2s!!!

 

[restorer-john]

A clip indicator is something I have previously considered implementing. The Hypex modules all have the functionality built in.

Perhaps before you do that, experiment with the open collector clip indicator pin on the modules to ensure it does actually show the actual point of clipping or how far into clipping it triggers.

It may be pessimistic or optimistic, if you know what I mean.

A clip indicator may sell more powerful amplifiers for you, or may have the opposite effect.

 

[March Audio]

Perhaps before you do that, experiment with the open collector clip indicator pin on the modules to ensure it does actually show the actual point of clipping or how far into clipping it triggers.

It may be pessimistic or optimistic, if you know what I mean.

A clip indicator may sell more powerful amplifiers for you, or may have the opposite effect.

Knowing Hypex it will just be accurate

I don't see it will affect sales either way.

 

[amirm]

Basically, the entire thread is about what happens to amplifiers at the onset, or when driven past transient clipping events. As amplifier topologies and PSU topologies vary significantly and the various "protections" range from a simple fuse to a microcontroller monitoring everything, I don't think it is unreasonable to be looking hard at this, don't you?

It shows up in every power measurement I perform. You can see the shape of the overload. Sine waves in time domain on scopes are not as revealing due to pixel limitations and lack of dynamic range.

 

[pma]

It shows up in every power measurement I perform. You can see the shape of the overload. Sine waves in time domain on scopes are not as revealing due to pixel limitations and lack of dynamic range.

Seriously, how can I see the "shape of the overload" (?) from your power measurements? And the consequences of such inversion clipping?

 

[restorer-john]

It shows up in every power measurement I perform. You can see the shape of the overload. Sine waves in time domain on scopes are not as revealing due to pixel limitations and lack of dynamic range.

No "shape" of the overload or recovery "shows up" in any of your reviews. Maybe there is a "scope plot" on the AP CEA burst test you could push into overload and show the recovery?

Seriously, how can I see the "shape of the overload" (?) from your power measurements?

Short answer: you can't.

Here is how it was done in the late 1970s by HiFi choice in the UK- for every single amplifier they tested. Notice the "shape" of the overload? Overload recovery was tested at various spot frequencies (published 1KHz) with asymmetric (diode clipped) 20mS bursts every 100mS. Amplifier was driven to half rated power and each 10dB burst took it 7dB into overload.

Quad 405 power amplifier

Sansui AU-1100A integrated amplifier

Pioneer SA-9900 integrated amplifier

FA-600 integrated

Sony TA-3650 integrated amplifier

This was regarded as a typical overload situation and a very useful indicator of overall stability. Some amplifiers do very well, others do very poorly. Some recover instantly, others do not. I use somewhat similar approach, but use the EIA/IHF 1KHz toneburst with both symmetric and clipped with a 20dB range to take the amplifier 3dB into clipping, over and above rated power.

These signals are trivial to generate these days and are used with purely resistive loads of 4 and 8 ohms. They pose no risk of damage to amplifiers, regardless of their age or quality.

 

[Panelhead]

I think with fast overload recovery the need for very high power is reduced. A 50 watt solid state amp that can do this will work for most home audio.
My days of building an amp from Pavel’s circuits are behind me. I was modifying an amplifier built 10 years ago and had to use a magnifying glass to see the construction. I did not have a magnifying glass 10 years ago.
If I move on, an AHB2 would be my choice today. But would prefer to build.
I built a preamp circuit designed by PMA many years ago. Bipolar transistors, seems like it had degeneration. Worked great.

 

[restorer-john]

I was modifying an amplifier built 10 years ago and had to use a magnifying glass to see the construction. I did not have a magnifying glass 10 years ago.

Same for me. It's quite a rapid deterioration of what was perfect closeup eyesight. Now, by necessity, I have plenty of lighting and illuminated large, articulated magnifiers.

 

[SIY]

I think with fast overload recovery the need for very high power is reduced.

Completely agree. A clipping event has to be pretty large to hear IF the recovery is essentially instantaneous.

 

[Doodski]

I doubt that my Crown XLS 1502 ever clips. The -20 db lights blink occasionaly. It takes a big room before you can crank that amp up.

That's because everything is bigger in Texas(and Alberta) ;P

 

[Doodski]

The simple solution to this is to use over-powered amps which never clip. I really don't understand why there aren't more audiophiles taking this approach. Before the onset of clipping, almost all blind tests which have been conducted show that amps are more or less indistinguishable from each other. If there are differences, they are very subtle. But when amps clip, all bets are off: they start sounding different from each other, and do bad things to tweeters.

So why not just use amps which are very powerful?
(ah yes, maybe I know why, because then one wouldn't be able to use esoteric "puristic" technology, or put vanishingly low levels of THD on the spec sheet)

Simple solution. Use a active electronic equalizer and bi-amp, tri-amp or use as many amps as req'd Clipping is more difficult to detect but it sounds great. I've done it at home with about 600 watts total/ch at 8ohms rated power output. Works very well.

 

[Doodski]

Those plots are a long way into clipping, but they do show the amplifiers' behaviour when grossly over-driven. Very stable at 1KHz into hard clipping.

Whether that is a steady 1KHz tone or a 1KHz toneburst, I don't know. Tonebursts are good as they don't stress the amplifier too much and you can uncover some real sleepers in the dynamic department.

I've requested for amirm to do amplifier slew rate measurements with pics. That would be kewliO.