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Purifi 1ET400A new range of class D amp modules

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As people has mentioned before, the stability in impedance is one of concerns as well. (Martin Logan's 0.6ohm at 20kHz)

My other problem is that most amps and modules are to powerfull. I would ideally would like to see a 50W version.

Input impedance is another tricky aspect in my setup as I don't use a pre amp. Currently I use a pro audio DA converter straight into power amps in a multi channel setup.

All my gear is hidden away, so ideally I would like gear that doesn't run very hot.

50W for surround channels, 300W (8ohm) and 2ohm stability, for my center channel, and 200-300W(8ohm) and stable down to 0.6ohm, for my mains.

Are these things possible with these Hypex or Purifi modules?

I use a Sanders ESL for my mains, which is stable down to 0.3ohm and never seem to run hot, and that is using a very large power supply and a large number of output devices. Would a similar design work out the same with class D modules?

Often what I see is 2ohm becomes rather difficult with class D, introducing distortions, and the same often happens with the increase of frequency, which makes the Martin Logan's a nightmare for class D.

Please correct me if I am wrong, as I wouldn't mind giving class D a fair chance.

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1 hour ago, Primare Knob said:

As people has mentioned before, the stability in impedance is one of concerns as well. (Martin Logan's 0.6ohm at 20kHz)

My other problem is that most amps and modules are to powerfull. I would ideally would like to see a 50W version.

Input impedance is another tricky aspect in my setup as I don't use a pre amp. Currently I use a pro audio DA converter straight into power amps in a multi channel setup.

All my gear is hidden away, so ideally I would like gear that doesn't run very hot.

50W for surround channels, 300W (8ohm) and 2ohm stability, for my center channel, and 200-300W(8ohm) and stable down to 0.6ohm, for my mains.

Are these things possible with these Hypex or Purifi modules?

I use a Sanders ESL for my mains, which is stable down to 0.3ohm and never seem to run hot, and that is using a very large power supply and a large number of output devices. Would a similar design work out the same with class D modules?

Often what I see is 2ohm becomes rather difficult with class D, introducing distortions, and the same often happens with the increase of frequency, which makes the Martin Logan's a nightmare for class D.

Please correct me if I am wrong, as I wouldn't mind giving class D a fair chance.

 

Stability is something an amp designer of any type should be mindful of and designing for.  Capacitive loads often cause gain peaking and insufficient phase margin can cause the amp to oscillate into the "wrong load".  This is all able to be modelled and tested, and is why many A/B amps have inductors in their output.

 

However, when does this stop being an amp design issue and becomes a speaker design issue? 

 

0.6 ohms at any frequency *is*, plain and simple, bad design. 

 

Well I can't speak for all class d designs but Bruno Putzeys designs, Hypex ncore and now Purifi, are quite happy at 2 ohms with extremely low distortion.  They will go down to 1 ohm.  They have current limiting protection.

 

See below examples

 

Hypex NC1200

 

image.png.5258a08de6f72e34b4c8bd54df526693.png

 

 

Purifi 1ET400

 

image.png.a8f3a9ff7b76a75ca7568b5fd8cb848d.png

Edited by March Audio

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24 minutes ago, March Audio said:

 

However, when does this stop being an amp design issue and becomes a speaker design issue? 

 

0.6 ohms at any frequency *is*, plain and simple, bad design.

 

 

There speaks an amp designer!  :lol:

 

Electrostatic spkr mfrs don't deliberately engineer in a 0.6 ohm impedance, Alan - it's an unfortunate byproduct of electrostatic spkr technology.  Every electrostatic speaker shows the same kind of issue.

 

As many people like 'statics (once they've heard them) - and own them - it becomes an amp designer issue IMO to come up with an amp design that can master the 'electrostatic problem'.  Some amp designers have been able to do this - like Maarten's Sanders amp or the Maya (by Hugh Dean) ... other designers have not.  When they:

  • have - the amp runs cool and has no problems driving the speakers.
  • haven't - the amp runs hot and may go into oscillation ... resulting in a quick demise!  :(

 

Andy

 

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5 hours ago, andyr said:

 

There speaks an amp designer!  :lol:

 

Electrostatic spkr mfrs don't deliberately engineer in a 0.6 ohm impedance, Alan - it's an unfortunate byproduct of electrostatic spkr technology.  Every electrostatic speaker shows the same kind of issue.

 

As many people like 'statics (once they've heard them) - and own them - it becomes an amp designer issue IMO to come up with an amp design that can master the 'electrostatic problem'.  Some amp designers have been able to do this - like Maarten's Sanders amp or the Maya (by Hugh Dean) ... other designers have not.  When they:

  • have - the amp runs cool and has no problems driving the speakers.
  • haven't - the amp runs hot and may go into oscillation ... resulting in a quick demise!  :(

 

Andy

 

 

 NO its not.  Ridiculously low impedance in speakers IS bad design.  It is NOT a given of electrostatic design.  It is the result of design choices - BAD ones.

 

0.6 Ohms  is utterly stupid.

 

Why do you think its acceptable to present , what to all intents and purposes, is a short circuit to an amp?

 

Quad certainly dont have an issue keeping it sensible.

 

image.jpeg.d8d83938458a356dbde89f82c35fc572.jpeg  image.png.401ad76ceb74de04cb11e64ae364e2c0.png  image.jpeg.af9c5125dc29b094fa46d9395e47f57a.jpeg

 

 

Edited by March Audio

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1 hour ago, March Audio said:

 

 NO its not.  Ridiculously low impedance in speakers IS bad design.  It is NOT a given of electrostatic design.  It is the result of design choices - BAD ones.

 

0.6 Ohms at 20kHz is utterly stupid.

 

Why do you think its acceptable to present , what to all intents and purposes, is a short circuit to an amp?

 

Quad certainly dont have an issue keeping it sensible.

 

image.jpeg.d8d83938458a356dbde89f82c35fc572.jpeg  image.png.401ad76ceb74de04cb11e64ae364e2c0.png  image.jpeg.af9c5125dc29b094fa46d9395e47f57a.jpeg

 

 

 

Mmmm, I myself don't call them "nice smooth spkr impedances".  (From 3 to over 20 ohms ... then down to 4 ... then up to 16!  But, sure, they don't drop to 2 ohms, according to those graphs. 

 

Perhaps you could find the equivalent for Sanders electrostatics - given he designed his amp to be able to handle 0.3 ohms.

 

And irrespective of the graphs you have produced ... many amps do not drive Quad 'statics well.

 

Andy

 

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45 minutes ago, andyr said:

 

Mmmm, I myself don't call them "nice smooth spkr impedances".  (From 3 to over 20 ohms ... then down to 4 ... then up to 16!  But, sure, they don't drop to 2 ohms, according to those graphs. 

 

Perhaps you could find the equivalent for Sanders electrostatics - given he designed his amp to be able to handle 0.3 ohms.

 

And irrespective of the graphs you have produced ... many amps do not drive Quad 'statics well.

 

Andy

 

 

I didnt call them smooth either, but that wasnt the point in question.  It was whether all electrostatics inherently suffer from dumb ass super low impedances such as the 0.6  ohms quoted for the ML.

 

If the Sanders electrostatic goes down close to 0.3 ohms its a bad design. 

 

The question wasnt about "many amps", it was about the Quads being designed such that they dont have dumb ass super low impedances such as the 0.6  ohms  quoted for the ML.

 

 

Edited by March Audio

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Alan can you provide a side by side comparison of the purifi vs the NC1200. 

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On 08/09/2019 at 2:36 PM, March Audio said:

 

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 2nd 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.

 

 

 

Seriously mate, don't bother.  I've tried explaining this to George numerous times before and he just doesn't get it.  Or doesn't want to.  Or both.  It's a pity, as it really doesn't take that much study of engineering (filter theory) to understand, and I have gone as far as to explain that it is a Bessel filter, which could have at least allowed him to read up a bit.  Maybe it is the conversion from phase to time that confuses here - dunno.  But yes, the phase shift in this case is just a uniform delay across the passband.

 

I saw someone question earlier in the thread how the output could be load invariant.  Quite simply, Bruno's design takes the NFB from after the output filter.

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