This is a review and detailed measurements of the five channel Classe Sigma AMP5. It was kindly sent to me by a member and originally cost US $5,000. I see one on ebay for $1,900 right now.
This is one heavy amplifier for a class D architecture:
At first I thought it had a linear power supply and its transformer was the reason behind the weight. Alas, looking into other reviews and pictures inside, it uses a switching power supply. So all the weight is from the enclosure and likely the very thick front plate.
At first I was hoping that the glossy front where the logo is, is an LCD display with VU meters and such. But there is not. It is just for looks. I must say as high-end products go, it is not that attractive to me relative to the high cost of the enclosure. It has sharp corners which is not nice.
The back shows quality selection of parts:
I like the staggered speaker binding posts which makes it easier to plug things in. XLR connections is what I like to see in an amp in this price range and we have them. This amp was mated to their processor of the time which I suspect is discontinued longer than this amp.
Amplifier Measurements
I tested two channels (Ch1 and Ch2) using XLR input. Here is our dashboard:
Rather high second and third harmonics dominate causing the overall ranking to be middle of the road:
Nice to see precise channel matching though.
Frequency response showed unexpected results:
Researching I found out there is an analog to digital converter which explains the sharp cut off. I thought that meant DSP functions but there is none. Instead, the digital signal is used as part of a protection circuit. I can see that as a parallel path but not as the main path compromising the response this way. This amp came out in 2015 so it is not like we didn't have higher sample rates available then to at least go up to 48 kHz and get us flat audible response.
Signal to noise ratio is middle of the road as well:
Crosstalk is "OK" but should be better:
Power vs distortion shows odd response at 4 ohm which gets worse at 8 ohm (see later):
Very strange noise response at the start and the multiple sources of distortion take over, each causing their own non-linearities.
On the positive front, we have healthy amount of power. Not much more is available though in burst mode (typical of class D amps with their regulated power supplies):
Here is power into 8 ohm:
That step function is quite bizarre.
Worst measurements came when bandwidth was increased to 45 kHz and frequency sweeps were used:
No way this amplifier is so well behaved. Instead I think there is high amplitude noise that is masking any distortion present (until clipping). We can see that if we perform a wideband frequency analysis:
We see sharp increase in noise right above audible band. This is either caused by noise shaping in the ADC, the Amp or both and explains the previous graph.
There is naturally switching spikes (near 400 kHz) but I am disappointed that its level is just 8 dB or so below our fundamental. I like to see 20 dB or more attenuation.
Conclusions
This is a custom Class D design and switching power supply from Classe. It clearly shows deficiencies of the design and creating a market for Hypex to come and show how class D is done. Digitizing the input is not a good idea if there is no user benefit to it and there is none here.
We could get depressed about the above or look at copious amount of power this amplifier produces while remaining cool (a bit above room temp in testing). Since lack of power is the #1 reason amps sound bad, I am going to put enough emphasis on this as to not give it a failing grade.
Overall, I am neutral on the Classe Amp5. At current sale prices, you have about $400 per channel for 400+ watts of power. It may be hard to match this with Hypex amp so you decide if it is worth it or not.
------------
As always, questions, comments, recommendations, etc. are welcome.
Have not been to the garden for a week as I have been busy with our septic tank issues. Nor can we preserve anything because we can't use any water in the house. So here is a picture at the start of our harvest season:
This is the first year we had good success growing corn. Had so much that we couldn't eat it all and some became starchy.
You see our most prized and delicious pears in there too. They turn that pink/red color and are the most delicate, juicy and sweet pears you have had. Alas, the tree produces at least a couple of hundred and they go from being barely ripe to overripe and useless in a week or two. We ate and canned a bunch. So will be enjoying them in winter.
About to spend a ton more money on the forum so donations are appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
This is one heavy amplifier for a class D architecture:
At first I thought it had a linear power supply and its transformer was the reason behind the weight. Alas, looking into other reviews and pictures inside, it uses a switching power supply. So all the weight is from the enclosure and likely the very thick front plate.
At first I was hoping that the glossy front where the logo is, is an LCD display with VU meters and such. But there is not. It is just for looks. I must say as high-end products go, it is not that attractive to me relative to the high cost of the enclosure. It has sharp corners which is not nice.
The back shows quality selection of parts:
I like the staggered speaker binding posts which makes it easier to plug things in. XLR connections is what I like to see in an amp in this price range and we have them. This amp was mated to their processor of the time which I suspect is discontinued longer than this amp.
Amplifier Measurements
I tested two channels (Ch1 and Ch2) using XLR input. Here is our dashboard:
Rather high second and third harmonics dominate causing the overall ranking to be middle of the road:
Nice to see precise channel matching though.
Frequency response showed unexpected results:
Researching I found out there is an analog to digital converter which explains the sharp cut off. I thought that meant DSP functions but there is none. Instead, the digital signal is used as part of a protection circuit. I can see that as a parallel path but not as the main path compromising the response this way. This amp came out in 2015 so it is not like we didn't have higher sample rates available then to at least go up to 48 kHz and get us flat audible response.
Signal to noise ratio is middle of the road as well:
Crosstalk is "OK" but should be better:
Power vs distortion shows odd response at 4 ohm which gets worse at 8 ohm (see later):
Very strange noise response at the start and the multiple sources of distortion take over, each causing their own non-linearities.
On the positive front, we have healthy amount of power. Not much more is available though in burst mode (typical of class D amps with their regulated power supplies):
Here is power into 8 ohm:
That step function is quite bizarre.
Worst measurements came when bandwidth was increased to 45 kHz and frequency sweeps were used:
No way this amplifier is so well behaved. Instead I think there is high amplitude noise that is masking any distortion present (until clipping). We can see that if we perform a wideband frequency analysis:
We see sharp increase in noise right above audible band. This is either caused by noise shaping in the ADC, the Amp or both and explains the previous graph.
There is naturally switching spikes (near 400 kHz) but I am disappointed that its level is just 8 dB or so below our fundamental. I like to see 20 dB or more attenuation.
Conclusions
This is a custom Class D design and switching power supply from Classe. It clearly shows deficiencies of the design and creating a market for Hypex to come and show how class D is done. Digitizing the input is not a good idea if there is no user benefit to it and there is none here.
We could get depressed about the above or look at copious amount of power this amplifier produces while remaining cool (a bit above room temp in testing). Since lack of power is the #1 reason amps sound bad, I am going to put enough emphasis on this as to not give it a failing grade.
Overall, I am neutral on the Classe Amp5. At current sale prices, you have about $400 per channel for 400+ watts of power. It may be hard to match this with Hypex amp so you decide if it is worth it or not.
------------
As always, questions, comments, recommendations, etc. are welcome.
Have not been to the garden for a week as I have been busy with our septic tank issues. Nor can we preserve anything because we can't use any water in the house. So here is a picture at the start of our harvest season:
This is the first year we had good success growing corn. Had so much that we couldn't eat it all and some became starchy.
You see our most prized and delicious pears in there too. They turn that pink/red color and are the most delicate, juicy and sweet pears you have had. Alas, the tree produces at least a couple of hundred and they go from being barely ripe to overripe and useless in a week or two. We ate and canned a bunch. So will be enjoying them in winter.
About to spend a ton more money on the forum so donations are appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
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