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Author Topic: Power Amp Quality  (Read 18821 times)

Tim Padrick

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Re: Power Amp Quality
« Reply #20 on: March 24, 2015, 02:48:16 am »

Just because we can't measure it doesn't mean we can't hear it.

Being a Glaswegian, Stuart's likely listened to a bunch of Linn (not Roger) and other stuff, and knows how to listen comparatively.  What say ye, Stuart?
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Ivan Beaver

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Re: Power Amp Quality
« Reply #21 on: March 24, 2015, 07:26:56 am »

Just because we can't measure it doesn't mean we can't hear it.


I hear that "excuse" all the time.  But all that means is that they aren't using the correct tool to measure.

Most people think a 1/3rd oct RTA is the only tool to measure audio with.

Sure you can hear all kinds of things that don't show up on an RTA.

But if you use the correct tool-we can measure things that you cannot possibly hear.

You just need a different/correct tool.
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Jim McKeveny

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Re: Power Amp Quality
« Reply #22 on: March 24, 2015, 07:58:07 am »

I hear that "excuse" all the time.  But all that means is that they aren't using the correct tool to measure.

Most people think a 1/3rd oct RTA is the only tool to measure audio with.

Sure you can hear all kinds of things that don't show up on an RTA.

But if you use the correct tool-we can measure things that you cannot possibly hear.

You just need a different/correct tool.

...And quite possibly the correct tool/technique hasn't been developed yet.

There have been a number of "moonshot/open checkbook" attempts at creating a digital grand piano. To my ears I cannot perceive a difference, but pianists can regularly identify which is which via performance or playback.

Maybe we are in the X-Ray Era of audio analysis, awaiting the introduction of the MRI.
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Jim McKeveny

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Re: Power Amp Quality
« Reply #23 on: March 24, 2015, 08:08:50 am »

I hear that "excuse" all the time.  But all that means is that they aren't using the correct tool to measure.

Most people think a 1/3rd oct RTA is the only tool to measure audio with.

Sure you can hear all kinds of things that don't show up on an RTA.

But if you use the correct tool-we can measure things that you cannot possibly hear.

You just need a different/correct tool.

...And quite possibly the correct tool/technique hasn't been developed yet.

There have been a number of "moonshot/open checkbook" attempts at creating a digital grand piano. To my ears I cannot perceive a difference, but pianists can regularly identify which is which via performance or playback.

Maybe we are in the X-Ray Era of audio analysis, awaiting the introduction of the MRI.
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Peter Morris

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Re: Power Amp Quality
« Reply #24 on: March 24, 2015, 08:28:14 am »

When operated within their linear region (not clipped, over heated, or driven into too low impedance) amps are generally amps (even a Behringer). Where there is generally a difference is at higher power points and difficult conditions. Even then the difference is not as much about sound quality as working, vs. not.

Amp path linearity is not close to the weakest link for sound reproduction, microphones and loudspeakers are far less linear and harder to do well.

JR

The problem is, that's where many amps are operated in our industry.  So the difference shows more often than it should  :-\
« Last Edit: March 24, 2015, 08:31:04 am by Peter Morris »
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Steve Payne

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Re: Power Amp Quality
« Reply #25 on: March 24, 2015, 08:53:32 am »

The problem is, that's where many amps are operated in our industry.  So the difference shows more often than it should  :-\

Some things just stick with you.  From an exchange at the first SynAudCon Concert Sound Workshop, Orange County, CA, late 80s:

Attendee: So what's wrong with brand M loudspeakers?
Mick Whelan:  Brand M is ok until you run them on the fling.
Attendee:  What's on the fling?
Mick Whelan:  It's how we run them.

 8)
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John Roberts {JR}

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Re: Power Amp Quality
« Reply #26 on: March 24, 2015, 10:05:28 am »

Just because we can't measure it doesn't mean we can't hear it.

Being a Glaswegian, Stuart's likely listened to a bunch of Linn (not Roger) and other stuff, and knows how to listen comparatively.  What say ye, Stuart?
How do you prove that? If you can't measure it, either you don't know where to look, or there is no "it" to measure.

I have the normal engineer's problem in that I could measure differences that I could not hear. Back in the '70s I modified some of my bench test equipment to perform more revealing tests. Nowadays my exotic IM tests are built into AP test sets as one of the standard options.

In my experience human perception is far more variable, and this variability does not add more resolution or sensitivity, just different results based on different influencing factors. Proper tests are made double blind to mitigate these external influences that alter perception.   

Of course I won't argue about what people say they hear, what people prove they can hear has been well studied.

JR
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John Roberts {JR}

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Re: Power Amp Quality
« Reply #27 on: March 24, 2015, 10:17:09 am »

The problem is, that's where many amps are operated in our industry.  So the difference shows more often than it should  :-\
No doubt, but that is not really the amp's fault. Customers were operating CS amps down to 2 ohms for many years before Peavey opened up the current limiting to support 2 ohm operation. VI limiting to protect bipolar power stages against secondary breakdown could be tripped by unusual loads, but any failure of the amp to deliver full output would trigger clip-limiting and neck back the voltage gain until that overload situation stopped.

If your amplifier limiter lights are flashing, that is not linear operation. Amp designers make amps that will keep working despite how customers abuse them. If the amps shut down every time they were abused, there would be a lot of unhappy customers. 

JR
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Jim McKeveny

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Re: Power Amp Quality
« Reply #28 on: March 24, 2015, 10:56:41 am »




In my experience human perception is far more variable, and this variability does not add more resolution or sensitivity, just different results based on different influencing factors.

JR

Agreed.

This doesn't mean we have reached end-times in amp measurement, however.

...But perhaps we are spending too much effort chasing a diminishing return.
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John Roberts {JR}

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Re: Power Amp Quality
« Reply #29 on: March 24, 2015, 11:21:30 am »

Agreed.

This doesn't mean we have reached end-times in amp measurement, however.

...But perhaps we are spending too much effort chasing a diminishing return.
Amps are not completely commodities, but closer than they ever were. Only the most demanding applications require specialty amps. (I have expressed my opinions about the cons associated with a standard duty cycle spec... Amp designers would effectively design to look good for that spec, for better "and" worse.)

For decades there has been a debate between "Golden Ears" and "Meter Readers", both convinced that the others were wrong. I have seen test equipment evolve over the decades to do an even better job of characterizing circuit performance. In my judgement there are no significant unresolved gaps in our ability to measure and characterize an audio path. There was a classic example of a respected amp designer who challenged an audiophile magazine that he could mimic the sound of some tweaky audiophile amp, with his conventional bipolar amp by tweaking the transfer function. Long story short the amp designer won that bet to the satisfaction of the magazines resident Golden Ear.

======

I opined on the subject back in the '80s that "we need to not only manage the measurable metrics, but strive to understand the perceptual cues that customers use to shape their perceptions." I have had a number of spirited private communications with another console designer about the subtle details in console design that shape customer perceptions above and beyond spec sheet measurements (control laws and pot tapers, center frequencies and Q of EQ, etc, etc).

Even at Peavey which was not a high-touch brand, we invested in full custom gain pot tapers to meet customer expectations about how the gain pot "should" work.

JR
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Re: Power Amp Quality
« Reply #29 on: March 24, 2015, 11:21:30 am »


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