Purifi 1ET400A new range of class D amp modules

[firedog]

On 05/09/2019 at 3:28 PM, AudioGeek said:

Broadly speaking - whats the price difference between hypex and purifi modules?

 

 

Nord audio in the UK is now  selling purifi amps. Pricing is similar (actually slightly less)  to their NC 1200 amps. No idea if this is some kind of introductory pricing or not. 

Edited September 7, 2019 by firedog

[March Audio]

1 hour ago, firedog said:

Nord audio in the UK is now  selling purifi amps. Pricing is similar (actually slightly less)  to their NC 1200 amps. No idea if this is some kind of introductory pricing or not. 

 

My understanding is they have a small number of pre main production modules.

[Addicted to music]

4 hours ago, pete_mac said:

Indeed... many an output transistor has sacrificed its life to save a fuse!

Understand if it’s a single pair used but.....10A fast action fuses.....

share it across 10 devices incase of a short that equates to 1A per device.... each device is rated at 15A.... 30A max, all current share using a Re per device...

i will bet the fuse will go 1st....  

 

Edited September 7, 2019 by Addicted to music

[March Audio]

3 hours ago, Addicted to music said:

Understand if it’s a single pair used but.....10A fast action fuses.....

share it across 10 devices incase of a short that equates to 1A per device.... each device is rated at 15A.... 30A max, all current share using a Re per device...

i will bet the fuse will go 1st....  

 

 

Are you saying the fuses are in the signal path?  So high current peaks through a nice non linear resistance? 

 

I used to maintain some very high power amps used for driving large vibration shakers.  Similar thing, many output transistors (literally dozens) with a fast blow fuse each.  Transistors used to go short on a fairly regular basis, the current was never well enough balanced.   NOT saying this will happen with this amp, don't know the circuit. 

Edited September 7, 2019 by March Audio

[Addicted to music]

5 hours ago, March Audio said:

 

Are you saying the fuses are in the signal path?  So high current peaks through a nice non linear resistance? 

 

Yes,

this is what’s being deployed.  How many other amps have protection for short circuit..... i can bet not many, even the speaker protection that I built monitors DC offset and voltage rails, but was never designed to detect shorts.

 

 

5 hours ago, March Audio said:

 

Transistors used to go short on a fairly regular basis, the current was never well enough balanced.   

Transistors  must be critical matched,  if you want any multiple output devices to share the load,  this involves setting up a jig to ensure you have the right HFE and VBE. 

Look at  the ME, Classe or Dan D’Agostino power amps etc  and countless many others and they will tell you how important it is that this is accurately done right to almost perfect where in some case matched to within 0.01%  

   2ndly your emitter/collector resistor depending on the device used (common collector or common emitter ) must also be critically matched.   If a transistor fails you just can’t replace it blindly without knowing these values.. this is why you will see output devices blowing at random, and you hear that after a repair it’s still not right and still blowing devices, that’s because a different hfe (multiplier ) was used... Trevor who is a ME authorised ME repairer who use to post here, use to home in how important it is to get ME designed to work properly, he use to bang on about why you need to critically matched the output devices with the resistor...You hear in these neck of the woods that unauthorised repairs will do a repair and the owner of that ME amp is still having issues.

if you’re going to design a driver for reliability that doesn’t require critical matching then use Lateral Mosfets, they have a negative temp coefficient, short them out with full power and they will survive, as long as you don’t exceed the input Vgs and your fine, Lateral Mosfets are indestructible due to their temp characteristics however they’re  not a choice for amplifiers as you want the output impedance as low as possible.  

 

When there is an issue Roger Sanders sends a whole amplifier pcb that’s already populated, bias already set up and all you need to do is swap the faulty one out.   I’ve never seen Onsemi devices to blow on this design.   What I have seen and heard is that owners report where one channel goes hot on the heat Sink,  that’s because there are batches of know thermaltrak devices  that wonder in value due to the active thermistor used on the die,  once reported to Roger Sanders he’ll send you a new amplifier pcb that’s fully populated.   Some times it’s better to keep things simple....

 

 

As ive posted b4, a member here posted that they keep blowing the fuse when he does a freq sweep.  Gets to around 15-17k.  When someone pulled the freq and phase plot for the speaker he was doing the freq sweep with, it’s a wonder why, the impedance at that point where the member reports blowing the 10A fast action fuse at 15-17k is where it dips below 1- 0.6 ohms..   

Edited September 7, 2019 by Addicted to music

[ghost4man]

It's seems Class D is getting better. 

 

https://www.audioholics.com/amplifier-reviews/legacy-iv7-600-watt-7ch-amplifier#specCollapse

[georgehifi]

1 hour ago, ghost4man said:

It's seems Class D is getting better. 

Unless using GaN technology to it's fullest, the old technology still has two "achilles heels" it can't get rid of, no matter what sideway design steps it takes, switching frequency with it's output filter creating phase shifts down into the audio band, and dead time.

GaN technology vastly improves on both these, if used to its fullest as Technics have done with the SE-R1.

 

Cheers George 

[ghost4man]

On 05/09/2019 at 8:12 AM, March Audio said:

 Im sure the differences stretch beyond there but neither company will let out the fine detail of the secret sauce

 

Bruno has some interesting things to say about GaN, it has advantages and disadvantages.

 

https://audiophilestyle.com/ca/bits-and-bytes/purifi-audio-and-the-audiophile-style-readers-qa-with-lars-risbo-bruno-putzeys-r815/

Alan, 

 

I read the article. It does indeed but the technology is advancing at a hectic rate so the reliability issues which afflicts all technologies is something that you would expect to improve as well. 

 

There's no doubt that Class D has come a long way in the last ten years. GaN implementation is just another part of that evolution. 

 

To say that it has been perfected would be incorrect. 

[Addicted to music]

1 hour ago, georgehifi said:

Unless using GaN technology to it's fullest, the old technology still has two "achilles heels" it can't get rid of, no matter what sideway design steps it takes, switching frequency with it's output filter creating phase shifts down into the audio band, and dead time.

GaN technology vastly improves on both these, if used to its fullest as Technics have done with the SE-R1.

 

Cheers George 

If you had $30K AUS  to spend.  Would you chose this over a conventional amp?   

[georgehifi]

1 hour ago, Addicted to music said:

If you had $30K AUS  to spend.  Would you chose this over a conventional amp?

If I were very well off, and $30k was like $1-2K is to me now, yes I would get the Technics SE-R1 and sell my inefficient, hot, power guzzling high bias ME850's.

Or the next GaN one that comes along using it to its fullest capability, the 1.5mHz switching frequency available, (does need a little heatsinking though)

 

Cheers George

Edited September 7, 2019 by georgehifi

[ghost4man]

1 hour ago, Addicted to music said:

If you had $30K AUS  to spend.  Would you chose this over a conventional amp?   

I don't think you have to mate. 

 

As previously stated you can get the Orchard Audio BOSC monoblocs with GaN implementation for under 2k at least to try. 

[March Audio]

12 hours ago, Addicted to music said:

Yes,

this is what’s being deployed.  How many other amps have protection for short circuit..... i can bet not many, even the speaker protection that I built monitors DC offset and voltage rails, but was never designed to detect shorts.

..   

 

Probably more than you imagine.  Hypex ncore and the Purifi modules monitor the output current (non intrusive) amongst other parameters. 

 

I just don't like the idea of having a (relatively) high non linear resistance in the output. 

 

 

Edited September 8, 2019 by March Audio

[georgehifi]

2 minutes ago, ghost4man said:

As previously stated you can get the Orchard Audio BOSC monoblocs with GaN implementation for under 2k at least to try. 

They haven't used all GaN Tecnology has to offer, and the power supplies are very questionable

 

Cheers George

Edited September 7, 2019 by georgehifi

[March Audio]

1 hour ago, ghost4man said:

Alan, 

 

I read the article. It does indeed but the technology is advancing at a hectic rate so the reliability issues which afflicts all technologies is something that you would expect to improve as well. 

 

There's no doubt that Class D has come a long way in the last ten years. GaN implementation is just another part of that evolution. 

 

To say that it has been perfected would be incorrect. 

 

Not sure anyone has said it's been perfected

[March Audio]

3 hours ago, georgehifi said:

Unless using GaN technology to it's fullest, the old technology still has two "achilles heels" it can't get rid of, no matter what sideway design steps it takes, switching frequency with it's output filter creating phase shifts down into the audio band, and dead time.

GaN technology vastly improves on both these, if used to its fullest as Technics have done with the SE-R1.

 

Cheers George 

The Purifi has no phase shift in the audio band.  Have a read of the article linked to above. 

 

Mind you, if phase shifts are a concern whatever you do don't look at what your speakers are doing to phase

 

Re dead time gan doesn't necessarily reduce the problem if you want to maintain efficiency. 

 

From the article 

 

But the main thing that sticks in my throat here is output capacitance. Our good old FDP42, which is from 2002 mind you, has an output capacitance at 100V of 70pF whereas the EPC device puts in a whopping half nanofarad (or 250 puff after scaling). That means your idle losses will go up, or you will have to increase dead time to allow the output inductor to recover the extra stored energy at its leisure. And isn’t it just idle losses that more or less determine real-life power consumption in full? 

 

Edited September 8, 2019 by March Audio

[georgehifi]

3 hours ago, March Audio said:

The Purifi has no phase shift in the audio band. 

Ok, then what is the switching frequency? the only way it could have "no phase shift in the audio band" is if it has a switching frequency over 1.5mHz like the $30k Technics SE-R1 has courtesy of GaN Technology, and accordingly then the low order output filter is "also set" much higher, this way it has no phase shift effects down to as many Class-D 's have 5khz, at sometimes up to "50 degrees", and why nearly every detractor of Class-D has the same complaint, upper mids/highs don't sound right, never complaints about the bass. 

 

And please show a 10khz square wave without any of the A.P. test filter involved below.

Audio Precision's auxiliary AUX-0025 passive low-pass filter, which eliminates noise above 200kHz.

 

 

Edited September 8, 2019 by georgehifi

[March Audio]

4 hours ago, georgehifi said:

Ok, then what is the switching frequency? the only way it could have "no phase shift in the audio band" is if it has a switching frequency over 1.5mHz like the $30k Technics SE-R1 has courtesy of GaN Technology, and accordingly then the low order output filter is "also set" much higher, this way it has no phase shift effects down to as many Class-D 's have 5khz, at sometimes up to "50 degrees", and why nearly every detractor of Class-D has the same complaint, upper mids/highs don't sound right, never complaints about the bass. 

 

And please show a 10khz square wave without any of the A.P. test filter involved below.

Audio Precision's auxiliary AUX-0025 passive low-pass filter, which eliminates noise above 200kHz.

 

 

500kHz.

 

Your assertion regarding the switching frequency Im afraid is not correct.

 

I have measured the Hypex NC252 module  (450kHz switching frequency) phase shift at 19 deg at 20kHz.  The 1ET is better, has a flatter FR beyond 20kHz.

 

Yes Ice  are not very good in this respect.  As with everything not all class D is created equal, but dont assume any particular characteristic is a fundamental result of the technology.

 

Square waves are not an indication of very much.  Any band limited system will not produce a perfect square wave.  A square wave need infinite bandwidth to do so.

 

JFI this is the Hypex NC400

 

 

As I mentioned above, if phase was such a big subjective issue you would have massive problems with speakers.

 

Or, what do think the valve amp we looked at earlier in the thread is doing to phase?  If that FR is changing so is the phase.

 

 

 

Edited September 8, 2019 by March Audio

[georgehifi]

So that's your answer?  500kHz. is the Purifi switching frequency? What low order passive output filter is on the speaker terminals inside? If none then "yes" you have no phase shift in the audio band, but you have massive tweeter frying switching noise in your case 500kHz coming out of the speaker terminals.

If yes to the output filter, well then let me tell you, you have phase shift down to what I said, and that will also be confirmed when you present a 10kHz square wave as I outlined above if you dare without the A.P. high order, very low power, test filter. 

Edited September 8, 2019 by georgehifi

[March Audio]

29 minutes ago, georgehifi said:

So that's your answer?  500kHz. is the Purifi switching frequency? What low order passive output filter is on the speaker terminals inside? If none then "yes" you have no phase shift in the audio band, but you have massive tweeter frying switching noise in your case 500kHz coming out of the speaker terminals.

If yes to the output filter, well then let me tell you, you have phase shift down what I said, and that will also be confirmed when you present a 10kHz square wave as I outlined above if you dare without the A.P. high order, very low power, test filter. 

 

George can you please spend the time to read the article I linked in previous posts.

 

 

 

To quote the designer Bruno Putzeys

 

@Sagittarius: Class D has achieved very low levels of distortion, but is it possible for class D amplifiers to continue their evolution into something close to a straight wire with gain, i.e. minimal phase shift in the audio band? (A similar question from maty).

 

Bruno:  The 1ET400 module has the frequency and phase response of a 2^nd order Butterworth filter cornering at 60kHz. If you look at the phase shift of that, it’s very nearly “linear phase” in the audio band. To take some rough numbers, it if you have a circuit that has a 0.2 degree phase shift at 200Hz, 2 degrees at 2kHz and 20 degrees at 20kHz, that’s the same as saying it has “0.001 degree per Hertz” phase shift. That’s another way of saying that the whole signal is simply delayed by 2.8 microseconds. If you plot phase shift on a linear frequency scale that’s immediately obvious because you get a straight line. Of course a simple delay doesn’t change the sound. It’s literally the same as starting your music a few microseconds later.

 

Lars:  My dad used to say that if you left a CD in its case without playing it back, it’d just sit there accumulating massive amounts of phase shift as time went by.

 

Bruno:  What that matters to sound is how much phase shift differs from a pure delay. Anyone who’s ever done phase measurements on speakers will remember that you have to remove the time-of-flight delay from the data, for instance by marking the leading edge of the impulse response. Otherwise the linear phase shift corresponding to the distance between the speaker and the mic completely clouds the picture. In the case of the 1ET400 module it’s just under 1 degree at 20kHz. There never was a phase shift problem in class D, it’s simply a trick of the light that happens when you plot the phase response on a log scale without removing the fixed delay. 

 

 

The "tweeter frying switching frequency" is total nonsense and if you take the time to do some simple calculations you will see why.

 

 

 

Edited September 8, 2019 by March Audio

[Addicted to music]

5 hours ago, March Audio said:

 

Probably more than you imagine.  Hypex ncore and the Purifi modules monitor the output current (non intrusive) amongst other parameters. 

 

I just don't like the idea of having a (relatively) high non linear resistance in the output. 

Since you have to module in your hands,  would you put your faith in the technology and short the output to see it it works.? 

Edited September 8, 2019 by Addicted to music

[March Audio]

1 minute ago, Addicted to music said:

Since you since you have to module in your hand would you put your faith in the technology and short the output to see it it works..

 

I havent actually done it with the Purify but I certainly have with Hypex modules.  They just shut down.  They have a "hiccup" mode where if the max output current is exceeded for more than a set period it shuts down.  They have a microcontroller on board which does monitoring.

 

From Hypex NC1200

 

 

 

 

Purify is even more sophisticated

 

 

[georgehifi]

1 hour ago, March Audio said:

George can you please spend the time to read the article I linked in previous posts.

 

You said you have zero phase shift, now Burno says there's 20 degrees phase shift at 20khz. If it uses 500khz switching frequency there's either a lot more phase shift or there's  a lot of switching noise on the speaker outputs, you can't have it both ways.

That's why Technics with GaN Tech raised the switching frequency to 1.5mhz!!!! so the output filter can do its job properly without any phase shift into the audio band.

 

Post your own 10khz squarewave, without the A.P. test filter, you do have a scope and sig gen  don't you?

Edited September 8, 2019 by georgehifi

[ghost4man]

36 minutes ago, georgehifi said:

 

You said you have zero phase shift, now Burno says there's 20 degrees phase shift at 20khz. If it uses 500khz switching frequency there's either a lot more phase shift or there's  a lot of switching noise on the speaker outputs, you can't have it both ways.

That's why Technics with GaN Tech raised the switching frequency to 1.5mhz!!!! so the output filter can do its job properly without any phase shift into the audio band.

 

Post your own 10khz squarewave, without the A.P. test filter, you do have a scope and sig gen  don't you?

George, 

 

I don't quite get what Alan is saying about there being no phase shift. If I'm wrong or taking things out of context then please advise but I can't see the accuracy in stating that there is no phase shift. This is what I'm reading as coming from Bruno

 

Otherwise the linear phase shift corresponding to the distance between the speaker and the mic completely clouds the picture. In the case of the 1ET400 module it’s just under 1 degree at 20kHz

 

 

[March Audio]

1 hour ago, georgehifi said:

 

You said you have zero phase shift, now Burno says there's 20 degrees phase shift at 20khz. If it uses 500khz switching frequency there's either a lot more phase shift or there's  a lot of switching noise on the speaker outputs, you can't have it both ways.

That's why Technics with GaN Tech raised the switching frequency to 1.5mhz!!!! so the output filter can do its job properly without any phase shift into the audio band.

 

Post your own 10khz squarewave, without the A.P. test filter, you do have a scope and sig gen  don't you?

 

 

George please read again

 

in the case of the 1ET400 module it’s just under 1 degree at 20kHz.

 

and understand the following:

 

Bruno:  The 1ET400 module has the frequency and phase response of a 2^nd order Butterworth filter cornering at 60kHz. If you look at the phase shift of that, it’s very nearly “linear phase” in the audio band.

 

To take some rough numbers, it if you have a circuit that has a 0.2 degree phase shift at 200Hz, 2 degrees at 2kHz and 20 degrees at 20kHz, that’s the same as saying it has “0.001 degree per Hertz” phase shift. That’s another way of saying that the whole signal is simply delayed by 2.8 microseconds. If you plot phase shift on a linear frequency scale that’s immediately obvious because you get a straight line. Of course a simple delay doesn’t change the sound. It’s literally the same as starting your music a few microseconds later.

 

So a linear phase change is a fixed (and in this case very small) delay across the audible frequency range. A delay is of no audible consequence.  The older design of the Hypex ncores seem to follow this.  I have certainly measured 19 deg at 20 KHz although admittedly the above logic never occurred to me so havent measured at the frequency points Bruno mentions.

 

The newer Purify design has just taken that delay away

 

Then, as I keep mentioning, ask yourself how much your speakers are changing phase.

Edited September 8, 2019 by March Audio

[March Audio]

George

 

I have already shown what an NCORE amp does with a square wave.

 

Please explain in technical detail what precisely you think you understand/conclude from the plot if I produce one.

 

You are demonstrably wrong about requiring 1.5MHz switching frequency.

Edited September 8, 2019 by March Audio