P801 Power Amp

Alan, I was curious about the history of the IMD test and asked Microsoft's AI called Co-Pilot. It gave the answers below:

1741622612349.png

Essentially the test is to reveal amplifier non-linearities (e.g. due to bandwidth and slew rate limitations) at frequencies where they can be heard.
 
When I asked google Gemini AI, it gave the following answer:
1741623167033.png

Similar answers ... X is down so I can't use its Grok ai for answers. I find it to be the best overall.

You may want to move these answers to the Technical thread if that's more appropriate.
 
I was reading Bruno Putzey's article in Hometheater Magazine and he said the following:

" ... But how then do we verify that an amplifier can even handle signals above 10kHz? A single sine wave won’t cut it because all harmonics are outside the measuring range (and inaudible too). The amplifier could be grossly clipping, and we wouldn’t know.

The solution is to blast the amplifier to near-clipping with two sine waves right at the end of the audio band and to inspect the resulting spectrum. You’ll agree that this is just about the worst possible test signal that still technically qualifies as “audio”. Nothing like it ever occurs in real music, so it’s a proper stress test."

He later on says "Even for linear amplifiers, I consider this intermodulation (IMD) test more meaningful than a non-bandlimited THD test with 20kHz."

I think its a valid amplifier stress test as he said and should be part of standard amplifier testing.
 
SmartOne_2000 said:
I was reading Bruno Putzey's article in Hometheater Magazine and he said the following:

" ... But how then do we verify that an amplifier can even handle signals above 10kHz? A single sine wave won’t cut it because all harmonics are outside the measuring range (and inaudible too). The amplifier could be grossly clipping, and we wouldn’t know.

The solution is to blast the amplifier to near-clipping with two sine waves right at the end of the audio band and to inspect the resulting spectrum. You’ll agree that this is just about the worst possible test signal that still technically qualifies as “audio”. Nothing like it ever occurs in real music, so it’s a proper stress test."

He later on says "Even for linear amplifiers, I consider this intermodulation (IMD) test more meaningful than a non-bandlimited THD test with 20kHz."

I think its a valid amplifier stress test as he said and should be part of standard amplifier testing.
Click to expand...

Yes, for sure. I totally agree with the validity of IMD testing. Bruno is absolutely correct. However, you have missed the point. :)

It is useful, even essential information for an amplifier designer. As a designer you want to test at conditions that characterise the amps behaviour. Slew rate will be higher at higher output voltages and frequencies. You may modify the design to achieve certain objectives.

My point is, that as a consumer, what benefit is that information to you? This is very much like the dumb FTC test where you test an amp with sine waves at max power and high frequencies for extended periods.

Or SINAD measurements up to 96kHz bandwidth where 3/4 of that bandwidth is inaudible.

It's just something that will never happen in real world use, or you cant hear. It may well be iformation you need as a designer, but what is it telling you as a consumer?

So this is one time I actually agree with Amirs testing regime. He tests IMD at 5 watts and that's probably more power than will ever be required at 20kHz in real world use.

Also, why 50 watts? Why not 100 watts? You could argue to "properly" stress test an amp, it would have to be at its rated power. As every amp has different power output, you could then never make comparisons. What if its a tube amp that cant output 50 watts?

This sort of comes back to a point I have previously made. It's a contributory reason as to why measurement has a bad reputation amongst many audiophiles. As to why they think it has no relevance to sound quality. It's simply because many of these technical tests do indeed have a poor correlation to audible sound quality, yet are touted as important by some.

Measurements are very important and we strive to acheive the best possible performance, but they have to be put in context.

My point was simply that IMD testing you typically see (specifically the 19kHz+20kHz CCIF standard - there are other varieties) at high power levels isnt relevant to real world use.
 
I see your point as to its relevance to real-world music. But as a piece of audio equipment, the buyer would be best served knowing that their equipment was thoroughly tested at the extremes to ensure no design compromises or limitations were part of the amplifier. Probably that was an issue of great concern when the IMD test first came out in the 70s (?) or 80s (?) when the audio industry first transitioned from vacuum tubes to bipolar transistors. I see the IMD test as an electrical stress test that can potentially reveal badly designed amps from good ones.

To me this is akin to temperature testing a circuit board from -40C to +85C, over multiple cycles, knowing full well its nominal operating temperature will be between 40C - 50C in its proper environment for the foreseeable future.
 
Last edited:
If it performs OK at 5 watts, which is possibly the top limit for required power at 20kHz, then why would you consider it badly designed?

Its doing what it needs to.

This is the same specious argument where some insist you need to measure SINAD up to 96kHz. Whats important is whats happening below 20kHz as thats what you can actually hear.

Testing to extremes is the same specious argument that attempts to justify the FTC power tests. Tests that couldnt be less relevant to the consumer.
 
Alan March said:
If it performs OK at 5 watts, which is possibly the top limit for required power at 20kHz, then why would you consider it badly designed?

Its doing what it needs to.

This is the same specious argument where some insist you need to measure SINAD up to 96kHz. Whats important is whats happening below 20kHz as thats what you can actually hear.

Testing to extremes is the same specious argument that attempts to justify the FTC power tests. Tests that couldnt be less relevant to the consumer.
Click to expand...
Yeah, testing SINAD at 96kHz is nutty for sure and nothing about it is grounded in science. If something performs ok at 5W, I think it behooves the designer to test it at the rated power/distortion levels as well to make sure no surprises occur due to component reliability or compromised design issues within the amp. After all, its the performance at these power levels one is paying for as a consumer?:)

I believe that's how you and other designers spec their amps, right? For example, that an amplifier is rated at 100W per channel @ 0.01% THD+N and passes all standard time/frequency tests at 100W ... even though in reality we only reach 100W on infrequent musical peaks in the highest treble or the lowest bass regions (and possibly into lower impedance loads).

Thanks for the informative NFB referral from Bruno(y).

Also, curious to know what new products you coming up with next and when? A subwoofer would be nice! I watched one of your speaker demos on facebook and was impressed by the depth of the bass coming out of the speaker 🤟.
 
Alan, I was curious to know if you can audibly tell your amplifiers apart, assuming they are operated well within their specifications. If so, can you tell us what you hear? I am more concerned about the audible differences between P801 and the P481 mono blocks. I'm assuming you'd be testing them using your own speaker brands?
 
SmartOne_2000 said:
Alan, I was curious to know if you can audibly tell your amplifiers apart, assuming they are operated well within their specifications. If so, can you tell us what you hear? I am more concerned about the audible differences between P801 and the P481 mono blocks. I'm assuming you'd be testing them using your own speaker brands?
Click to expand...
In anticipation of Alan’s answer…
I can state that there is not a lot I hear as differences between various amps.
Some older amps maybe a bit sibilant, and some sound thick (tube amps)… but most SS gear these days just seems to work.
I have a pair of P501s, but haven’t listened to them per se… yet.

If you have some tough speakers in terms of loads, then it gets more challenging for the amp, and easier to hear differences.
So it is not like the amp has a sound independent of the speakers it is driving.

I would expect that the P801 could sound different with some high dynamic range music when the volume knob is cranked over hard, as you have some extra dB before clipping. But maybe not.

Depending on one’s listening habits it would generally be more amp than is needed in a lot of cases.
One would have to be pretty happy to turn the knob hard over clockwise, and not have grumpy neighbours too close by.

It also gets a bit tricky as some distortion is what people find pleasing in amplifiers.
Particularly 2nd and 3rd harmonics.
It is not like low noise amps are something that a lot of people like.

And low distortion speakers are also not something that a majority of people think are good.
So it is a perplexing thing.
 
Last edited:
SmartOne_2000 said:
Alan, I was curious to know if you can audibly tell your amplifiers apart, assuming they are operated well within their specifications. If so, can you tell us what you hear? I am more concerned about the audible differences between P801 and the P481 mono blocks. I'm assuming you'd be testing them using your own speaker brands?
Click to expand...
They are all very consistent in terms of basic tonality, ie there isn't much if any 'character" to the sound. "Straight wire with gain". You can tell differences in terms dynamics and drive capability.
 
Holmz said:
I would expect that the P801 could sound different with some high dynamic range music when the volume knob is cranked over hard, as you have some extra dB before clipping. But maybe not.

Depending on one’s listening habits it would generally be more amp than is needed in a lot of cases.
One would have to be pretty happy to turn the knob hard over clockwise, and not have grumpy neighbours too close by.

It also gets a bit tricky as some distortion is what people find pleasing in amplifiers.
Particularly 2nd and 3rd harmonics.
It is not like low noise amps are something that a lot of people like.

And low distortion speakers are also not something that a mojority of people think are good.
So it is a perplexing thing.
Click to expand...

It really depends on your speakers load and sensitivity. To get truly wide dynamics you need massive power. Every 3dB increase in volume, you need twice the power. Every 3dB decrease in speaker sensitivity, you need twice the power to reach the same volume.

Many amps out there run out of steam and start to sound strained. The P801 doesnt.

I dont really buy into the euphonic distortion argument. I have heard some high distortion amps and dacs. They sort of give the impression of a bit more warmth, but you soon realise this isn't what you are hearing. It's just a lack of clarity and detail. It's mistaken for "warmth".


"And low distortion speakers are also not something that a mojority of people think are good."

Can I ask how you concluded this? Its certainly not my experience.
 
Alan March said:
It really depends on your speakers load and sensitivity. To get truly wide dynamics you need massive power. Every 3dB increase in volume, you need twice the power. Every 3dB decrease in speaker sensitivity, you need twice the power to reach the same volume.

Many amps out there run out of steam and start to sound strained. The P801 doesnt.

I dont really buy into the euphonic distortion argument. I have heard some high distortion amps and dacs. They sort of give the impression of a bit more warmth, but you soon realise this isn't what you are hearing. It's just a lack of clarity and detail. It's mistaken for "warmth".
Click to expand...
^true^ - but it is a fact that many people buy into that.
So what I said was not a lie.

A small amount of 2nd and 3rd, is a lot better IMO, than noise.
An amp hissing like the local tiger snake or dugites is pretty grating to me..

Once you get to the P#01, Benchmark, etc. then the golden eared people often say that they are not “musical”.
That is a euphemism for distortion, but it is commonly used to justify a costly “effects box”.

Alan March said:
"And low distortion speakers are also not something that a majority of people think are good."

Can I ask how you concluded this? It’s certainly not my experience.
Click to expand...
Because most people objectively rate a speaker on frequency response.

It is hard to hear distortion until it gets pretty high.

The way I figured out that your’s were low distortion, is because it sounded somewhat quiet.
Having excess 2nd and 3rd harmonic, and even more so having higher order harmonics is something that the brain uses to determine SPL.

Historically, and most people with even a small fleck of grey beginning, just know that the way one knows it is subjectively loud, is when they turn it up and hear the distortions… and then they turn it back just a bit.

You obviously can run into more people that like higher end gear, so people that walk up are not the 99%.
That group is not “the norm”.

Or another way to put it, is there is nothing wrong with them. (Speakers),
It is often easier to find the faults in things.
The speakers are good even well past when the volume is “way past the OSHA recommended limits.”

If one listens to music in a quiet environment then a low distortion speaker and a low distortion amp, can take away some cues that people often like.
Maybe not everyone, but a lot of people.

Obviously I am not one of those people, but they do exist.
 
Holmz said:
^true^ - but it is a fact that many people buy into that.
So what I said was not a lie.

A small amount of 2nd and 3rd, is a lot better IMO, than noise.
An amp hissing like the local tiger snake or dugites is pretty grating to me..

Once you get to the P#01, Benchmark, etc. then the golden eared people often say that they are not “musical”.
That is a euphemism for distortion, but it is commonly used to justify a costly “effects box”.


Because most people objectively rate a speaker on frequency response.

It is hard to hear distortion until it gets pretty high.

The way I figured out that your’s were low distortion, is because it sounded somewhat quiet.
Having excess 2nd and 3rd harmonic, and even more so having higher order harmonics is something that the brain uses to determine SPL.

Historically, and most people with even a small fleck of grey beginning, just know that the way one knows it is subjectively loud, is when they turn it up and hear the distortions… and then they turn it back just a bit.

You obviously can run into more people that like higher end gear, so people that walk up are not the 99%.
That group is not “the norm”.

Or another way to put it, is there is nothing wrong with them. (Speakers),
It is often easier to find the faults in things.
The speakers are good even well past when the volume is “way past the OSHA recommended limits.”

If one listens to music in a quiet environment then a low distortion speaker and a low distortion amp, can take away some cues that people often like.
Maybe not everyone, but a lot of people.

Obviously I am not one of those people, but they do exist.
Click to expand...

You need to be careful when talking about "frequency response". The tonal balance of a speaker playing in a room is not soley dictated by the on axis frequency response. The room reflections, wall, floor and ceiling play a massive part.

As such the directivity characteristics of the speaker are crucial. The reflections must be similar in balance to the on axis. Also the wider the directivity the more overall bright the balance will be. In room measurements should always indicate a falling response with increasing frequency. Getting the gradient of slope right WRT the directivity is the critical factor.

Looking at just the on axis frequency response will tell you virtually nothing about how a speaker sounds playing in a room.

Again, I dont buy into the "euphonic distortion" concept. I have never found audible levels of distortion to sound good.
 
SmartOne_2000 said:
I guess you must not like listening tube (valve) amplifiers...
Click to expand...
Tube amps aren't necessarily high distortion. What is an issue is the fact that they have high output impedance.

This means that a varying load, as all speakers are, will cause the amp to vary its frequency response. Worse than this, that variation is dependant on the specific impedance characteristics of the speaker in question. I.e the amp will sound different on each and every speaker!
 
Alan March said:
Tube amps aren't necessarily high distortion. What is an issue is the fact that they have high output impedance.

This means that a varying load, as all speakers are, will cause the amp to vary its frequency response. Worse than this that the variation is dependant on the specific impedance characteristics of the speaker in question. I.e the amp will sound different on each and every speaker!
Click to expand...
Plus the fact that they have high even ordered harmonics many think makes them sound euphonic.
 
You must log in or register to reply here.
Back
Top