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NAD M28 Seven Channel Power Amplifier Review

Apollon Audio

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Does that mean you're also having to drive half the channels out of phase to combat pumping? How does that hold up if the channels aren't loaded symmetrically?
The smps 3k power supply does not feature the 2-quadrant operation like other Hypex power supplies do. A workaround for this is reversing phase for half of the channels like suggested by Hypex. Of course the phase is reversed back at the output.
 
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bobof

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The smps 3k power supply does not feature the 2-quadrant operation like other Hypex power supplies do. A workaround for this is reversing phase for half of the channels like suggested by Hypex. Of course the phase is reversed back at the output.
Yes, I'm aware of the workaround, how it works, and reason for it. I'm asking if you know how well it works in practice as you're integrating a system like this.

The pumping is a function of the signal being driven, and the inversion of groups of channels is an attempt to balance this out. Of course, you can only achieve a perfect balancing when the inverted and non-inverted channels are outputting the exact same signal. When they're not, there will still be pumping to a greater or lesser degree.

In a multichannel application it likely places some importance on which channels are used in signal pairs - you'd probably want to make sure your front left and right were inverted relative to each other to have the best chance of a good balancing. Having both front and left on the same phase setup with your heights on other would be a much worse way to have things hooked up.

Do you make it clear which channels are wired up which way, and advise on the best way to load speakers onto the channels used? How and at what level of imbalance does the strategy fail and result in protection kicking in?
 

Apollon Audio

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Yes, I'm aware of the workaround, how it works, and reason for it. I'm asking if you know how well it works in practice as you're integrating a system like this.

The pumping is a function of the signal being driven, and the inversion of groups of channels is an attempt to balance this out. Of course, you can only achieve a perfect balancing when the inverted and non-inverted channels are outputting the exact same signal. When they're not, there will still be pumping to a greater or lesser degree.

In a multichannel application it likely places some importance on which channels are used in signal pairs - you'd probably want to make sure your front left and right were inverted relative to each other to have the best chance of a good balancing. Having both front and left on the same phase setup with your heights on other would be a much worse way to have things hooked up.

Do you make it clear which channels are wired up which way, and advise on the best way to load speakers onto the channels used? How and at what level of imbalance does the strategy fail and result in protection kicking in?
Yes it is clearly written in the manual supplied with this amplifier how the channels work and how they should be connected. This system performs and measures perfect. It actually performs the same as our Purifi mini stereo amplifier.

For instance in a 7.1 surround system the speakers should be connected to the amp like this:

Channel 1&2: Front L&R
Channel 3&4: Surround L&R
Channel 5&6: Rear L&R
Channel 7: Center speaker

The center speaker should be always connected to the last channel of the amp.

For instance if you are powering a 4-way speaker system the speakers should be connected to the amp like this:

Channel 1&2: L&R Bass drivers
Channel 3&4: L&R Low drivers
Channel 5&6: L&R Mid drivers
Channel 7&8: L&R Tweeters

For this reason each pair of channels have their own dedicated gain switch on the back and xlr-rca selector switch.

One of the amazing features of this amplifier system is the amplifier is upgradable. For instance if you buy a 7 or 8 channel version and decide to extend your surround system with more speakers, the amp can be upgraded to more channels all up to 12 channels in one enclosure. Because of this feature this amplifier system will have a very good resale value as well.
 
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bobof

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Yes it is clearly written in the manual supplied with this amplifier how the channels work and how they should be connected. This system performs and measures perfect. It actually performs the same as our Purifi mini stereo amplifier.

For instance in a 7.1 surround system the speakers should be connected to the amp like this:

Channel 1&2: Front L&R
Channel 3&4: Surround L&R
Channel 5&6: Rear L&R
Channel 7: Center speaker

The center speaker should be always connected to the last channel of the amp.

For instance if you are powering a 4-way speaker system the speakers should be connected to the amp like this:

Channel 1&2: L&R Bass drivers
Channel 3&4: L&R Low drivers
Channel 5&6: L&R Mid drivers
Channel 7&8: L&R Tweeters

For this reason each pair of channels have their own dedicated gain switch on the back and xlr-rca selector switch.
Thanks, so have you measured them under uneven loading of LR channels? Measuring with both L&R driven simultaneously with the same signal would of course measure fine as they would be perfectly out of phase and cancel each other out at the PSU. If you really wanted to go for maximum cruel when measuring such an amp, you'd feed one channel with in phase and one channel out of phase out of a test rig, which would effectively "undo" the phase reversal in the unit.

I'm intrigued by this as Purifi in their own manual for the modules state it's not enough to just put one bank out of phase, yet it sounds like that is all you are doing, and it also seems like that is all that NAD are doing with the M28 (though their PSU is an unknown wildcard in this, exactly how it behaves isn't completely known). There obviously must be >some< kind of external signal you could feed the unit that would be an issue, otherwise there would be no point in reversing the phase on one set and asking folk to pair like channels together...!
 

Apollon Audio

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Thanks, so have you measured them under uneven loading of LR channels? Measuring with both L&R driven simultaneously with the same signal would of course measure fine as they would be perfectly out of phase and cancel each other out at the PSU. If you really wanted to go for maximum cruel when measuring such an amp, you'd feed one channel with in phase and one channel out of phase out of a test rig, which would effectively "undo" the phase reversal in the unit.

I'm intrigued by this as Purifi in their own manual for the modules state it's not enough to just put one bank out of phase, yet it sounds like that is all you are doing, and it also seems like that is all that NAD are doing with the M28 (though their PSU is an unknown wildcard in this, exactly how it behaves isn't completely known). There obviously must be >some< kind of external signal you could feed the unit that would be an issue, otherwise there would be no point in reversing the phase on one set and asking folk to pair like channels together...!
We ran all sorts of tests and with uneven loading as well. If you are using the amp as I described above and like it is described in the manual it behaves and performs perfect. The only issue I see is if you would run a subwoofer on one channel and another subwoofer on third channel for instance. But that is against what’s written in the manual and recommended by us.

I have never heard or seen anyone complain about the performance of NAD M27 or M28 for instance and they are using one 1200 watt smps power supply for powering 7 channels.

I did not say that reversing the phase was all that we did. We also added capacitance to the rails. As far as I know NAD also has additional capacitance added on the rails.
 

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Well as promised I would disclose my experience with the M28 compared to the M27.
The m28 is a lot better than the m27. I was really impressed with the sound compared to the m27. Unlike mentioned before i noticed more power, which showed in a lot more dynamics and control of the Dyn's I drive the NAD with. Vocals are more clear and it sounds more musical.
The advice would be to listen instead of drawing conclusions based on this test. What is even more shocking is that I see in this tread other vendors try to sell their purify product for 3k in this same tread. Which is weird, since this is about the m28 and not about other vendors trying to sell their equipment, Or am I wrong ? My advice would be next to test data. also include the data of user experience and other vendors not trying to sell their product in the same tread, to avoid the idea of bias.
I would not go back to the m27, despite I was very content with the m27. I had the m27 for the last 5 years. so I know how it sounds and therefore can compare both machines and give a fair opinion. The m28 is a step forward compared to the m27.
 

Vincentponcet

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Well as promised I would disclose my experience with the M28 compared to the M27.
The m28 is a lot better than the m27. I was really impressed with the sound compared to the m27. Unlike mentioned before i noticed more power, which showed in a lot more dynamics and control of the Dyn's I drive the NAD with. Vocals are more clear and it sounds more musical.
The advice would be to listen instead of drawing conclusions based on this test. What is even more shocking is that I see in this tread other vendors try to sell their purify product for 3k in this same tread. Which is weird, since this is about the m28 and not about other vendors trying to sell their equipment, Or am I wrong ? My advice would be next to test data. also include the data of user experience.
I would not go back to the m27, despite I was very content with the m27. The m28 is a step forward compared to the m27.
That's a very interesting point of view.
I'm very curious to understand what is missing in the measurements to explain this gap between measurements and perception.
 

SIY

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I'm very curious to understand what is missing in the measurements to explain this gap between measurements and perception.
Peeking. Audio measurements can't account for non-auditory phenomena.
 

SIY

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And that is why you allways should listen, instead of making a decission based on testresults.

Depends. If you care only about the sound, measurements are sufficient for electronics. Peeking is useful to make decisions based on looks, feel, reputation, and the like. And of course, if the measurements are sufficient, then (if you're approaching things rationally) the feature set becomes the deciding factor.
 
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Depends. If you care only about the sound, measurements are sufficient for electronics. Peeking is useful to make decisions based on looks, feel, reputation, and the like. And of course, if the measurements are sufficient, then (if you're approaching things rationally) the feature set becomes the deciding factor.
Well that is not true, the measurements never showed that this is a way better sounding amplifier. A different method of testing would therefore be required. I was really surprised about the difference in sound. Again test results are fine, but it is allways better to listen and experience the amplifier before making a decission to purchase the m28. I was very skeptical due to the test results and the bigger the surprise was, that this was way better sounding than the m27. Oke enough said, hope you all enjoy this beautifull hobby,because this is what counts. Stay safe
 
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Yes it is clearly written in the manual supplied with this amplifier how the channels work and how they should be connected. This system performs and measures perfect. It actually performs the same as our Purifi mini stereo amplifier.

For instance in a 7.1 surround system the speakers should be connected to the amp like this:

Channel 1&2: Front L&R
Channel 3&4: Surround L&R
Channel 5&6: Rear L&R
Channel 7: Center speaker

The center speaker should be always connected to the last channel of the amp.

For instance if you are powering a 4-way speaker system the speakers should be connected to the amp like this:

Channel 1&2: L&R Bass drivers
Channel 3&4: L&R Low drivers
Channel 5&6: L&R Mid drivers
Channel 7&8: L&R Tweeters

For this reason each pair of channels have their own dedicated gain switch on the back and xlr-rca selector switch.

One of the amazing features of this amplifier system is the amplifier is upgradable. For instance if you buy a 7 or 8 channel version and decide to extend your surround system with more speakers, the amp can be upgraded to more channels all up to 12 channels in one enclosure. Because of this feature this amplifier system will have a very good resale value as well.
Why are using this tread to sell your product ? why not pay for advertisement like any other decent company. It is far from ethical to hijack this tread to sell your product. If you do not have the marketingbudget I wonder how your service levels are and your aftersales.
 

mSpot

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Why are using this tread to sell your product ? why not pay for advertisement like any other decent company. It is far from ethical to hijack this tread to sell your product. If you do not have the marketingbudget I wonder how your service levels are and your aftersales.
This thread has veered off course and the Apollon discussion should be taken to a different thread. However, if you follow the discussion back, Apollon has merely been responding to members questions about Apollon products. Also, I don't know what you mean by advertising because there isn't any on this forum.
 
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It is frustrating to follow a thread and see loosely related things discussed. I get that. At the same time Apollon's responses to questions asked seemed more informative than marketing. I learned. If manufacturers follow, listen, provide insight and answers, i think it is mostly additive. Who draws the line? Amir
 
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What is the status ? I didn't see news on your website or here.
I ordered a unit with 7 channels in November for HT use.
We agreed delivery for some time in February. Haven't heard anything back yet....
I'm curious to know if there are other people on the forum who also ordered a multichannel amp from Apollon Audio.
 
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I would be very interested to see a retest with a more recent example, it's possible the problem has been fixed.

I tested the M28 with the M17V2 processor and my B&W CM10S2s and found the 2k region over emphasised. Hi hats were too in your face and the treble has a chirpyness too it, like the sound was smeared (sorry about the terms, best I can think of).

Was one of the first off the production line.
 

Dj7675

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I would be very interested to see a retest with a more recent example, it's possible the problem has been fixed.

I tested the M28 with the M17V2 processor and my B&W CM10S2s and found the 2k region over emphasised. Hi hats were too in your face and the treble has a chirpyness too it, like the sound was smeared (sorry about the terms, best I can think of).

Was one of the first off the production line.
Did that show itself in a frequency response measurement Between this Amp and your previous amp with your speakers?
 
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Did that show itself in a frequency response measurement Between this Amp and your previous amp with your speakers?
Don't have any measuring equipment, it's just how it sounded.
I've heard something similar many years ago with some Kef references speakers (can't remember the amp). Seems to be an issue with high end kit over emphasising the treble, just sounds wearing after a while.
 
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