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Anyone compared high end Class D power amps?

Thetiminator said:
Yeh I’m not suggesting that Class D amps are better than A/B as a rule. More the performance you can get from a cheap class D amplifier (say £100-£500) surely is leagues ahead of anything A/B of similar cost. Mine are just stunning...
Click to expand...
Hi,
I checked the website for Temple Audio - the picture of the mono block and its performance characteristics indicate that the unit is possibly based on the Texas Instruments TPA3251 Class D amplifier chip, which costs £8.24 from Farnell UK.

The cost of the monoblock is stated to be £500 per pair which includes power supply. These are very good value for money in terms of performance and price for the end user.

You can get a class A/B amplifier which exceeds this performance by a fair margin more specifically at higher frequencies, for slightly more, which includes a pre-amp too and ESS DAC also - Audiolab 6000A. It may not have the same power capability, but it is more than adequate.

Class D is cheap, but it does have limitations at HF in terms of performance.

Regards,
Shadders.
 
No bubble bursting please. Studied a Naim Hi-Cap recently?

Anyway, my next Dac @ £2K is based on an obsolete chip that probably cost £6.50. Implementation seems key.
 
Shadders said:
Hi,
I checked the website for Temple Audio - the picture of the mono block and its performance characteristics indicate that the unit is possibly based on the Texas Instruments TPA3251 Class D amplifier chip, which costs £8.24 from Farnell UK.

The cost of the monoblock is stated to be £500 per pair which includes power supply. These are very good value for money in terms of performance and price for the end user.

You can get a class A/B amplifier which exceeds this performance by a fair margin more specifically at higher frequencies, for slightly more, which includes a pre-amp too and ESS DAC also - Audiolab 6000A. It may not have the same power capability, but it is more than adequate.

Class D is cheap, but it does have limitations at HF in terms of performance.

Regards,
Shadders.
Click to expand...
But only if you are a bat.
Bruno Putzeys discussing the Purifi design from the ASR review you linked to.
Quote,
‘Just checking in!

First off, mega thanks Amir for doing this review. And more generally for running this forum. It is enormously heartening to see someone working to collect actual data for a substantive technical discussion and comparison between products. It's even more heartening to see that indeed, substantive discussion ensues.

Amir mentioned I'd be saying something about the high-frequency IMD results. Let's start by explaining why I prefer to measure distortion strictly inside the audio band. There is an ongoing controversy about whether signals above 20kHz might or might not be audible, but what is not controversial is that signals below 20kHz are much, much more audible than signals above 20kHz. So if you are in a situation where you have to choose between optimizing performance below 20kHz or above 20kHz, you go for optimizing the bit that we are most likely to hear. Even high-res enthusiasts seem to have tacitly accepted this a long time ago. Remember DSD? A DSD AD/DA converter that, when measured over 20kHz, would easily clock a SINAD of 120dB would "degrade" to 50dB as soon as you upped the measurement bandwidth to 40kHz. But what you heard was of course 120dB, the rest was for the bats. Note the delicious irony. DSD was hawked on the grounds that you needed >20kHz bandwidth for high fidelity, while its skyrocketing supersonic noise floor was excused on the grounds that it was inaudible. As it is, DSD is perfectly listenable. I can find no more eloquent argument that the ear is not very sensitive above 20kHz than DSD...

Anyhow, this is why I like to test amplifiers with test signals that in themselves would be audible (i.e. fit below 20kHz) and also read the distortion and noise only in the band below 20kHz. Of course, I know perfectly well that if you then do a THD versus frequency sweep, any readings above 10kHz are meaningless because even the second harmonic will be outside the audio band. But as our sensitivity to those harmonics drops off rather quickly around 20kHz (as does the ability of most speakers to reproduce them), it's fair to conclude that they do not say much about sound. On the other hand, we can't just go ignoring any underlying non-linearity. We still need to test for misbehaviour at high frequencies. If you choose to limit measurement bandwidth to 20kHz you have to include something like the 19kHz + 20kHz test. I didn't invent that procedure btw, I got that from Bruce Hofer at AP who recommends it. In fact his version is even neater, he uses 19.5kHz and 18.5kHz, making sure that even order products sit at even multiples of 500Hz (from 1kHz upward) while odd products sit at odd multiples of 500Hz, from 17.5kHz down, potentially fitting 37 distinct IMD products inside the band. This refinement doesn't make much difference with the 1ET400 amp of course since there aren't that many IMD products poking up over the noise floor.

Given the choice between a sinewave test at 20kHz which only produces inaudible products and a two-tone test that produces all kinds of in-band distortion I go for the latter. By implication, we should be designing a control loop that maximises loop gain all the way up to 20kHz, but not beyond. Any control system obeys a law called the Bode Inequality. This is the closest we control theorists have to mass-energy conservation. In the case of a class D amplifier it implies that if you maximise loop gain over a largeish fraction of the switching frequency you'll have to take it down really fast afterwards. So that's why the wideband THD vs frequency plot goes up somewhat suddenly at the end. It's a compromise I'm knowingly making. Consider the alternative: I could instead pander to the bat-eared crowd and choose to minimise harmonic distortion components up to 40kHz, say. That would mean accepting a lot less loop gain below 20kHz and hence higher distortion in the audible frequency range. It's not a good tradeoff.

Anyhow, this should explain why the high-frequency IMD spectrum is so much cleaner than a wideband THD test would lead you to expect. But as I see it, the former is the one that is most likely to have a meaningful correlation to sound.

(While I'm at it I ought to point out that the idle noise is noise shaped. This is visible on the broadband noise plots where you can clearly see the rise after 20kHz. The extra outband noise is caused by the comparator and driver chips and ends up being noise shaped by the control loop. I only wanted to mention that because the wideband THD vs F plots are mostly swamped by this HF noise which bore some explaining.)

In vindication of that POV we've now seen more than one enthousiastic "subjective" reviews of the 1ET400A go up expressing delight that we have both great measurements and great sound (as if that were a contradiction). I'd like to state here that in our company, as listeners we are fanatic about sound and as engineers we are fanatic about measured results. The trick is to pick a set of measurements that have a modicum of relevance to psychoacoustics (in the case of amplifiers, accepting that hearing goes south beyond 20kHz and that music is more than sinewaves). Once we get the lab result that we expected, we go and listen carefully to make sure we're not missing anything. That's rarely the case so the next stage (playing great music and breaking open beers) tends to follow quickly afterwards.

Oops that's another page long post. I was wondering if I could ask for a favour. I have a proclivity to spending lots of time on very detailed answers but there's other work on my plate too. So what I'd like to do is sign off for something like a week and then sift through any items that come in during that period. So let's have all your questions and round about next weekend the two of us here will go through them.’

Cheers,

B.
Keith
 
Shadders said:
Hi,
I checked the website for Temple Audio - the picture of the mono block and its performance characteristics indicate that the unit is possibly based on the Texas Instruments TPA3251 Class D amplifier chip, which costs £8.24 from Farnell UK.

The cost of the monoblock is stated to be £500 per pair which includes power supply. These are very good value for money in terms of performance and price for the end user.

You can get a class A/B amplifier which exceeds this performance by a fair margin more specifically at higher frequencies, for slightly more, which includes a pre-amp too and ESS DAC also - Audiolab 6000A. It may not have the same power capability, but it is more than adequate.

Class D is cheap, but it does have limitations at HF in terms of performance.

Regards,
Shadders.
Click to expand...
This is an interesting thread, I’m currently using a IQAUdIO pi-digiamp on a RPi as I’m doing a rehash of things.

It’s amazing how prejudice can play such a part. I heard an audiolab 8000a many years ago and I wouldn’t now buy anything from audiolab. A better option for a simple, one box solution imo would be the Cyrus One HD. In fact I’m very tempted by it.
 
Purité Audio said:
"Even high-res enthusiasts seem to have tacitly accepted this a long time ago. Remember DSD? A DSD AD/DA converter that, when measured over 20kHz, would easily clock a SINAD of 120dB would "degrade" to 50dB as soon as you upped the measurement bandwidth to 40kHz. But what you heard was of course 120dB, the rest was for the bats. Note the delicious irony. DSD was hawked on the grounds that you needed >20kHz bandwidth for high fidelity, while its skyrocketing supersonic noise floor was excused on the grounds that it was inaudible. As it is, DSD is perfectly listenable. I can find no more eloquent argument that the ear is not very sensitive above 20kHz than DSD..."
Click to expand...

Appears to be ignoring the fact that many (most?) DSD DACs use a low-pass filter to suppress the HF noise, at least they did in the recent past. Have things changed?

Whether it's audible to the human ear or not, I'd rather my amplifier and speakers were not fed such unnecessary noise:
48056907407_26f64e3282_o.jpg
 
Purité Audio said:
But only if you are a bat.
Bruno Putzeys discussing the Purifi design from the ASR review you linked to.
.................
Cheers,

B.
Keith
Click to expand...
Hi Keith,
I am not saying that the noise persistently present on a class D output can be heard. What is possible, is that it can affect the loudspeaker crossover and tweeter, thus causing the characteristic sound that class D is clinical or transparent.

If the in-band (20Hz to 20kHz) distortion levels of both class A/B and class D is below the threshold of hearing, then why the reports of class D being transparent or clinical ? What is class D doing to present this, or what does class A/B add, to not present this ?

Or, is a class A/B amplifier being reported as clinical, sound the same as a class D with the same subjective impression ?

Regards,
Shadders.
 
I have Class A/B here, Class D and Benchmark’s hybrid design , there is no difference I can detect between them, in fact the only differences I have heard between low distortion solid state amplifiers is when the amplifier in question is incapable of driving the loudspeaker properly and ‘clips’.
Comparisons are probably best made, level matched with two identical systems switching quickly between them.
Keith
 
As I said before, a good amp is a good amp, no matter what class. It so happens that Class D is small, cheap to buy and run, generally high on the price/performance curve.

The Temple amps are not ‘clinical’ in the slightest and the Amptastic is positively euphonic (Tripath).
 
I agree 100% with Alex, my Temples are not in the slightest bit clinical or bright.
Compared to the best SS I have had like the Electrcompaniet Nemo’s, Musical Fidelity Titans (the best power amp I ever heard) and a couple of Boulders the Temples are a touch less natural and the soundstage is a touch flatter but they’re also £500!!
 
My Gato Amp is anything but clinical. The thing about Class D when done right - as opposed to virtually every other Class A or Class A/B amplifier I have owned - is the virtually total absence of mechanical noise. When the amp is on it is absolutely silent with no hum from the amp or hiss from the speakers.

Music appears from the blackest of backgrounds.
 
Robby said:
My Gato Amp is anything but clinical. The thing about Class D when done right - as opposed to virtually every other Class A or Class A/B amplifier I have owned - is the virtually total absence of mechanical noise. When the amp is on it is absolutely silent with no hum from the amp or hiss from the speakers.

Music appears from the blackest of backgrounds.
Click to expand...

That has nothing to do with it being class D.
 
Robby said:
Whatever it is to do with there is a total lack of mechanical noise from the couple of Class D amps I have tried against virtually every Class A or Class A/B I have owned.
Click to expand...

That's because they are powered by "hated" switch mode power supplies (SMPS) and there is no mains frequency transformer to buzz.
 
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