This is a review and detailed measurements of the PS Audio Stellar M700 Power Amplifier. It is kindly sent in by a member and costs US $2998 for a pair from the company direct.
The M700 is quite heavy for a class-D amplifier. I picked it up by hand and nearly hurt my back trying to hold it that way!
The industry design is well, a bit industrial but follows the rest of PS Audio:
Back panel is simple and as expected exception for inclusion of duplicate binding posts for "bi-wiring:"
In use, the amplifier didn't even get warmer. It did shut down when overloaded with my stress test of 20 kHz tone but otherwise was stable.
Overall, I am happy with the look and functionality of the M700.
Amplifier Audio Measurements
As usual, we feed the amplifier a near perfect 1 kHz analog signal and examine what else comes for the ride in its speaker terminal output:
The gain is a bit higher than nominal 29 dB but there are no standards there. And higher gain is not a bad thing in itself.
SINAD which is the sum of noise and distortion is at 83 dB mainly due to high level of distortion. You can see how the third harmonic to the right of our 1 kHz tone (tall peak) is around -85 dB. Add a bit of noise to it, ignore the sign and you get the SINAD of 83.
This puts the M700 slightly above average of over 100 amplifiers measured so far:
Signal to noise ratio shows that at 5 watts there is a bit more noise than I like:
Ideally I like to see dynamic range of 96 dB so that we can hear the full range of CD's 16 bit signal without amplifier adding too much noise of its own. Fortunately the noise doesn't scale with power so if you turn up the volume, that issue remedies itself (right bar graph).
Frequency response is NOT to my liking:
Class-D amplifiers have strong switching noise which needs to be filtered. This filtering needs to be designed in a way that doesn't interact with the speaker and change the frequency response of the amplifier. Here, despite me using a simple resistive load, we are getting strong peaking around 50 kHz. That by itself is not audible but if you go down to 20 kHz, you see some very minor impact. A real speaker may make that impact larger, causing roll off or peaking of high frequencies. Here is an example of Hypex NC400 amplifier showing how it should be done:
Measuring power vs distortion using our 4 ohm load we get:
Seems like there is too little feedback to control the distortion as it starts to rise at just 20 watts or so. Still, lots of power which is good. And it delivers even more if we allow it to have more distortion than above:
This is one powerful amplifier!
Class-D amplifiers have complex "transfer functions" and the M700 is no exception:
Switching to 8 ohm we still get a lot of power:
But with similar distortion profile as before.
Conclusions
The M700 provides tons and tons of power which I consider to be a top requirement in any power amplifier. So many speakers these days are inefficient (due to smaller enclosures) and hence, power is needed to drive them without distortion. The so called Stellar Gain stage though appears to be adding distortion early to the response though. Fortunately not very audible even at the extreme so subjectively it would be fine.
Overall, I personally would get a Hypex NC400 or NC500 based class D amplifiers. They are technically superior although may not quite as powerful. So while this amplifier is not for me, it may be for you.
-----------
As always, questions, comments, recommendations, etc. are welcome.
We have a fenced-in garden to keep our herd of deer out of it. Well, they finally figured out to jump the tall fence and start to feast on our near ripe fruits and vegetables. We can't hurt or hunt them so I need to hire someone to stand guard 24 hours a day to keep them out. If I don't there won't be anything left for us to eat, and I will die of hunger and you won't see more reviews. So I hope this entices you to donate to fund the garden security using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The M700 is quite heavy for a class-D amplifier. I picked it up by hand and nearly hurt my back trying to hold it that way!
The industry design is well, a bit industrial but follows the rest of PS Audio:
Back panel is simple and as expected exception for inclusion of duplicate binding posts for "bi-wiring:"
In use, the amplifier didn't even get warmer. It did shut down when overloaded with my stress test of 20 kHz tone but otherwise was stable.
Overall, I am happy with the look and functionality of the M700.
Amplifier Audio Measurements
As usual, we feed the amplifier a near perfect 1 kHz analog signal and examine what else comes for the ride in its speaker terminal output:
The gain is a bit higher than nominal 29 dB but there are no standards there. And higher gain is not a bad thing in itself.
SINAD which is the sum of noise and distortion is at 83 dB mainly due to high level of distortion. You can see how the third harmonic to the right of our 1 kHz tone (tall peak) is around -85 dB. Add a bit of noise to it, ignore the sign and you get the SINAD of 83.
This puts the M700 slightly above average of over 100 amplifiers measured so far:
Signal to noise ratio shows that at 5 watts there is a bit more noise than I like:
Ideally I like to see dynamic range of 96 dB so that we can hear the full range of CD's 16 bit signal without amplifier adding too much noise of its own. Fortunately the noise doesn't scale with power so if you turn up the volume, that issue remedies itself (right bar graph).
Frequency response is NOT to my liking:
Class-D amplifiers have strong switching noise which needs to be filtered. This filtering needs to be designed in a way that doesn't interact with the speaker and change the frequency response of the amplifier. Here, despite me using a simple resistive load, we are getting strong peaking around 50 kHz. That by itself is not audible but if you go down to 20 kHz, you see some very minor impact. A real speaker may make that impact larger, causing roll off or peaking of high frequencies. Here is an example of Hypex NC400 amplifier showing how it should be done:
Measuring power vs distortion using our 4 ohm load we get:
Seems like there is too little feedback to control the distortion as it starts to rise at just 20 watts or so. Still, lots of power which is good. And it delivers even more if we allow it to have more distortion than above:
This is one powerful amplifier!
Class-D amplifiers have complex "transfer functions" and the M700 is no exception:
Switching to 8 ohm we still get a lot of power:
But with similar distortion profile as before.
Conclusions
The M700 provides tons and tons of power which I consider to be a top requirement in any power amplifier. So many speakers these days are inefficient (due to smaller enclosures) and hence, power is needed to drive them without distortion. The so called Stellar Gain stage though appears to be adding distortion early to the response though. Fortunately not very audible even at the extreme so subjectively it would be fine.
Overall, I personally would get a Hypex NC400 or NC500 based class D amplifiers. They are technically superior although may not quite as powerful. So while this amplifier is not for me, it may be for you.
-----------
As always, questions, comments, recommendations, etc. are welcome.
We have a fenced-in garden to keep our herd of deer out of it. Well, they finally figured out to jump the tall fence and start to feast on our near ripe fruits and vegetables.
We can't hurt or hunt them so I need to hire someone to stand guard 24 hours a day to keep them out. If I don't there won't be anything left for us to eat, and I will die of hunger and you won't see more reviews. So I hope this entices you to donate to fund the garden security using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Last edited:
