Vera Audio Class-D Amp Build Quality

[MakeMineVinyl]

Regarding distortion / noise measurements on class D amps, it is common practice to use an AES-17 low pass filter before the measurement device to filter out the out of band hash. No class D amp I've seen would meet their spec otherwise.

 

[boXem]

I bet that if something is to go wrong in a modern class D amp, it'll be in the switching power supply since that's the part that gets the hottest in the amp, notably the output coils, which in turn get too hot and damage the output filter capacitors, which may not be properly rated for the temperatures they'll experience in actual product use. Heat is the enemy of all electronics.

Class D amps are not class D because of their power supply.

 

[boXem]

Regarding distortion / noise measurements on class D amps, it is common practice to use an AES-17 low pass filter before the measurement device to filter out the out of band hash. No class D amp I've seen would meet their spec otherwise.

https://www.audiosciencereview.com/...easurements-of-purifi-1et400a-amplifier.7984/

There is a subjective aspect to measurements that doesn't come across in the graphs. When I run these tests with switching amplifiers, I often watch the analyzer struggle to get reliable reading, or there are jumps and glitches in measurements. None of that was here. The amplifier basically acted like a traditional class AB amplifier. Indeed, I measured it with and without my AES-17 40 kHz filter and the analyzer was happy both ways. This is when I know there is quality engineering that has gone into design of this amplifier.

As a side comment, you are tagged as a manufacturer. You and I are supposed to stay away from the threads from other manufacturers, especially to criticize their products

 

[David_M]

Class D amps are not class D because of their power supply.

Yes, I know that. Thanks anyways!

 

[MakeMineVinyl]

https://www.audiosciencereview.com/...easurements-of-purifi-1et400a-amplifier.7984/


As a side comment, you are tagged as a manufacturer. You and I are supposed to stay away from the threads from other manufacturers, especially to criticize their products

How on earth is mentioning that AES-17 filters are normally used when measuring class D amplifiers a criticism of anything? Its just a statement of usual practice.

 

[Feyire]

@Armand, will you also be making a bridged Purifi 1ET7040A?

 

[Bjorn]

@Armand, will you also be making a bridged Purifi 1ET7040A?

Not likely. The 1ET7040A only offers a good increase of power with very low impedance loads. I believe there output numbers on the Rougue site are with 1% THD. With 0.1% THD they are 200W in 8 Ohm, 400W in 4 Ohm and 750W in 2 Ohm. So there's basically only a major difference with bridging and 2 Ohm loads compared to the VA P150/600 RS amplifier.

The noise and distortion is also somewhat higher with the 1ET7040A module.

 

[Feyire]

Right, so given these charts you provided previously, there would be a case for bridging x2 1ET7040A modules for additional power in stereo mode from < 3.4 Ohms and in bridged mode there would be a benefit from < 6.4 Ohms. But yeah, bridging the 1ET400A modules is the combination of best power and associated measured performance.

 

[Armand]

I made an estimate of how a couple of bridged 1ET7040A modules would perform.

Peak power will be at 2,75 Ohms. This is based on the THD curves from Purifi at about 0,1% THD. It can vary slightly depending on the voltage of the power supply, but will not be very much above this.

For very low impedance speakers the 1ET7040A is a monster, but bridged 1ET400A also puts out clean power of continous 1kW at 4 Ohms. That is really enough for the majority of users.

 

[Bjorn]

View attachment 147908
View attachment 147907

Right, so given these charts you provided previously, there would be a case for bridging x2 1ET7040A modules for additional power in stereo mode from < 3.4 Ohms and in bridged mode there would be a benefit from < 6.4 Ohms. But yeah, bridging the 1ET400A modules is the combination of best power and associated measured performance.

Take not that the charts you showed are for the P400/1000 amplifier that uses Ncore NC500 modules.

Below you can see the output power of the P150/600 RS amplifier with the Purifi 1ET400A modules.

 

[Bjorn]

The Vera Audio P400/1000 can be ordered as a 120V version now. Just need to specify this when ordering.

We have sent a P400/1000 to to Prosoundtraning and it will forwarded to Amir for review here afterwards. This unit (in silver finish) will be possible to buy at a rebate and will be announced in the "Desperate Dealers Forum" section later.

A review at ASR of the P150/600 RS will come later.

 

[pma]

Take not that the charts you showed are for the P400/1000 amplifier that uses Ncore NC500 modules.

Below you can see the output power of the P150/600 RS amplifier with the Purifi 1ET400A modules.

View attachment 147974

For how long period of time would it give say 875W/5ohm sine power before thermal protection shuts it down?

 

[Armand]

For how long period of time would it give say 875W/5ohm sine power before thermal protection shuts it down?

With 875W continous sine wave into 5 Ohms I guess the P150 will give up after 2-3 minutes or thereabouts. The front LED will issue a warning with yellow light when the temperature is close to shutdown. If the temperature continues to increase, the amplifier will shut down and the button on the front will be disabled for 30 seconds.

The fans on the P400/1000 enables it to manage 1kW of continous power for hours. At the cost of increased fan speed of course.

 

[pma]

It is very important to understand what we are looking at here. In my experience many people do not understand what 0,035% THD+N at 20kHz actually mean. For some reason they think that the (barely audible) 20kHz tone is somewhat distorted and will "sound" different, but that is not the case. The reason for that is that the distortion occurs at frequencies above 40kHz and will be completely inaudible unless you are a bat.

First, thank you for your reply re continuous power.
Because of so many threads in the forum, I have noticed this thread no sooner than now. I appreciate your effort re thermal management of the OEM modules.

Concerning your debate with @restorer-john , your 20 kHz THD+N results are noise dominated for obvious reason of noise shaping with high ultrasonic noise content. That is inherent to the circuit design and differs from linear amplifiers. To see the high frequency nonlinearity, THD (free from N) would say more. Or you might show full scale CCIF IMD 19+20kHz, which also covers high frequency nonlinearity with all distortion components inside the audio band.
To argue with audibility/inaudibility is pointless in this case, especially if you want to stay strictly on engineering side as declared in your statement

We do not believe in snake oil theories or old audiophile myths and there is nothing mystical going on here. Just hardcore engineering using the best components available today.
Our goal is a lot of power, compact design, a clean look with no visible screws or seams, low noise, high CMRR and low THD+N. We are confident this is a well engineered product that will last for many years.
We also want to be transparent and privide ALL measurements and technical information about the product.

 

[Bjorn]

To argue with audibility/inaudibility is pointless in this case, especially if you want to stay strictly on engineering side as declared in your statement

I highly disagree with that. We're talking about an audio product, so it makes perfectly sense to discuss what's within the audible range. We don't spend time discussing driver or speaker performance way outside what's audible and neither is there any good reason to do this with an amplifier.

If you're looking to theorize around what's not audible to the human ear, this is not the thread for that as I don't see that would benefit any customers.

 

[pma]

If you're looking to theorize around what's not audible to the human ear, this is not the thread for that as I don't see that would benefit any customers.

On contrary, my view was more or less supporting you, I tried to separate noise and distortion. Maybe your more technically oriented colleague will reply. I am not theorizing and I have stayed firmly in technical terms.
To continue:
1) have you made any study that would support the assumption that ultrasonic noise does not degrade tweeter linearity at acoustical side,
2) will you post full swing CCIF IMD 19+20kHz to verify good linearity at high frequencies.

 

[restorer-john]

I highly disagree with that. We're talking about an audio product, so it makes perfectly sense to discuss what's within the audible range.

At the end of the day, we are measuring harmonic or other distortions stimulated within the accepted audio range of 20Hz-20kHz.

You would surely have to accept that a device that produces distortion harmonics from stimulii within the audible range is inferior to a device that does not. Where those harmonics fall is utterly irrelevant.

No different to a flashlight that produces a perfect brilliant daylight colour temperature light, only to also emit invisible ultra violet light which damages human skin cells, discolours clothing and breaks down plastic. I remember MR16 12v halogen reflector bulbs. The most wonderful invention ever- not. Until they started fading clothing and furniture due to the huge UV (invisible) output. Then we got glass filters. Still didn't stop the problem.

I had 96 MR16s in one of my retail shops. I had to rotate the stock so quickly to prevent clothing, packaging etc, becoming faded, from out of band, invisible (to humans) light.

I want my audio gear to produce only the stimulii it is fed with and nothing else, be it inaudible or not.

 

[Armand]

On contrary, my view was more or less supporting you, I tried to separate noise and distortion. Maybe your more technically oriented colleague will reply. I am not theorizing and I have stayed firmly in technical terms.
To continue:
1) have you made any study that would support the assumption that ultrasonic noise does not degrade tweeter linearity at acoustical side,
2) will you post full swing CCIF IMD 19+20kHz to verify good linearity at high frequencies.

I have done the 19-20kHz test, but only at 5W average power. We can see thet the in band distortion is at maximum -115dB at 1kHz. This is at (or close to) the limits of my analyzer. No high frequency noise.
Will do a full power test later.

I can do a THD measurtement also, but it will be the same as THD+N if the bandwidth is less than 40kHz. At 80kHz the noise shaping might come into consideration. I can check it for the fun of it.

Regarding the tweeter issue we have not tested if it heats up. But when the amplitude of the remaints is only 0,3V at 500kHz that equals only 0,01W not taking into account the inductance of the tweeter itself.
The amplitude is also symmetrical around zero so any offset is not a problem either.

Found a measurement of THD+N with bandwitdth up to 40kHz. The test tone is 15kHz.
370W continous power both channels at 15kHz with total of -108dB THD including N.

In other words, we have 41,4 volts RMS of clean 15kHz signal, and the total sum of noise and THD up to 40kHz is 108dB below the signal.
Not too bad?
NOTE! The "jumps" in the measurement is my mesasuring gear changing range. Better measuring gear would measure this down to at least -112dB

 

[Armand]

At the end of the day, we are measuring harmonic or other distortions stimulated within the accepted audio range of 20Hz-20kHz.

You would surely have to accept that a device that produces distortion harmonics from stimulii within the audible range is inferior to a device that does not. Where those harmonics fall is utterly irrelevant.

No different to a flashlight that produces a perfect brilliant daylight colour temperature light, only to also emit invisible ultra violet light which damages human skin cells, discolours clothing and breaks down plastic. I remember MR16 12v halogen reflector bulbs. The most wonderful invention ever- not. Until they started fading clothing and furniture due to the huge UV (invisible) output. Then we got glass filters. Still didn't stop the problem.

I had 96 MR16s in one of my retail shops. I had to rotate the stock so quickly to prevent clothing, packaging etc, becoming faded, from out of band, invisible (to humans) light.

I want my audio gear to produce only the stimulii it is fed with and nothing else, be it inaudible or not.

It seems you have understood that even if the the second harmonic of a 10kHz signal falls outside the hearing range it will show up on the graphs at 10kHz.
See below picture from Amirs test that many people misunderstand. They interpret this in a way that they think there is "distortion" at 10kHz (where I have drawn a line). This is not the case. The 10kHz signal is clean. All it shows is that there is "something" in the 90kHz bandwith that is not supposed to be there when the amplifier amplifies a 10kHz signal. We do not know if this distortion is at 20kHz ,60kHz ot 90kHz. Most probably it is not noise either because then THD+N would be higher at lower frequencies also.
To fully characterize an amplifer a FFT of a single 10kHz signal must be shown also. If the main contribution af the harmonic distortion is third order, this will fall outside the hearing range at 6666Hz, and if you look closely it is there it start to rise.

To claim that it is "utterly irrelevant" where the harmonics end up is just a confusing statement for me. Do you at all all understand what is going on? Do you know math? Do you really, really think that you can hear a 30kHz signal at 1,4mV (0,0000005W) when the tweeters are pumping out 28 volt and 200W power?
Come on...

 

[pma]

I am sure that John does not speak about audibility, he rather speaks about technical accuracy.

BTW, is this a sine wave or something else? And we are sure it does not matter?