Amplifier comparison: March Audio P452 (Purifi 1ET400A) vs Buckeye Hypex NC502MP vs AIYIMA A07 (TPA3255) vs Onkyo TX-NR737 (125W Class AB)

[mrmojo2022]

Dummy load ordered. I need to connect to ADI-2's balanced input, right?
Is this the proper way (in series)?
XLR pin 2 --- 8ohm dummy --- amplifier (+)
XLR pin 3 --- amplifier (-)
Correcting myself - should be in parallel with the dummy I believe, not series.

I give up on messing with the scope - it was very useful to volume-match, but to make sure my amplifier is running fine I need a precise measurement.

Yes.

Xlr pin 2 is pos and pin 3 is neg. In parallel across the dummy load.

If you get a load of mains pick up you can connect the screen to the neg.

 

[restorer-john]

Scopes are not good for looking in detail at signals. Even good ones are typically only 8 bit. I'm afraid that one really isn't up to the job.

A 'scope is the only thing to use for looking at signals such as this. No soundcard/REW is remotely useful to accurately capture a 500kHz carrier riding on a LF sine.

The APs top out around 1.2MHz, whereas a decent scope starts at 20MHz. But the AP is for audio frequencies which it does better than most.

The rise time shots of amps taken with an AP in reviews are really just pretty pictures- they tell you nothing as the limiting factor is the sampling rate of the AP.

 

[mrmojo2022]

A 'scope is the only thing to use for looking at signals such as this. No soundcard/REW is remotely useful to accurately capture a 500kHz carrier riding on a LF sine.

The APs top out around 1.2MHz, whereas a decent scope starts at 20MHz. But the AP is for audio frequencies which it does better than most.

The rise time shots of amps taken with an AP in reviews are really just pretty pictures- they tell you nothing as the limiting factor is the sampling rate of the AP.

My understanding is that @f1shb0n3 was trying to make a subjective comparison between amps for which he needed to accurately match volumes(output voltage). An unfiltered 8bit scope is useless for looking at the output voltage(especially on a class d amp) it's not accurate enough and noisy. an 8bit scope will also be useless for looking at noise levels, frequency response and distortion.

 

[abdo123]

My understanding is that @f1shb0n3 was trying to make a subjective comparison between amps for which he needed to accurately match volumes(output voltage). An unfiltered 8bit scope is useless for looking at the output voltage it's not accurate enough and noisy. an 8bit scope will also be useless for looking at noise levels and distortion.

I'm guessing you're out there carrying an AP Analayzer in your backpack for the most menial of tasks?

 

[mrmojo2022]

I'm guessing you're out there carrying an AP Analayzer in your backpack for the most menial of tasks?

Eh? Actually I'm trying to help @f1shb0n3 get some meaningful information. with his ADI2 he can get some useful information about the different amps technical performance. none of which he will see with a scope.

 

[abdo123]

Eh? Actually I'm trying to help @f1shb0n3 get some meaningful information. with his ADI2 he can get some useful information about the different amps technical performance. none of which he will see with a scope.

I'm sure that will prove invaluable to their controlled subjective comparison .

 

[mrmojo2022]

I'm sure that will prove invaluable to their controlled subjective comparison .

Even with a DVM you need to be careful that the switching signal doesn't affect accuracy. also @f1shb0n3 also said he wanted to look deeper for which his scope would be useless.

Now looking further, the waves of left and right channel look a bit different even - the right channel has a wave going through the wave at 1kHz. Not sure if it's the primitive scope or an indication of something potentially wrong with the one of the channels. Sound like I would benefit from better measuring equipment to figure it out!

I have RME ADI-2 Pro, but don't know how to safely connect amplifier to it nor what software to use for measurement and graphs. I know I need a good dummy resistor and such, will look into all that - pointers would be welcome!
If I can make it work, I can also measure the whole chain - from ADI-2 Pro as source going through MiniDSP SHD and D90 DAC to amplifier output fed back into ADI-2 Pro. Wouldn't this be the holly grail of end-to-end SINAD measurement? With a an extra twist that it would be a loop starting and ending at the same place

 

[restorer-john]

My understanding is that @f1shb0n3 was trying to make a subjective comparison between amps for which he needed to accurately match volumes(output voltage). An unfiltered 8bit scope is useless for looking at the output voltage(especially on a class d amp) it's not accurate enough and noisy. an 8bit scope will also be useless for looking at noise levels and distortion.

You're missing the point and the facts.

His 'scope' is a toy. It's 12 bit, which is absolutely fine, but it's bandwidth is useless for anything over 20kHz. The switching frequency of the amp is over 20 times that.

So it captures absolute garbage from the amplifier unless you hard LPF the inputs which he isn't doing.

There is nothing to see here. The March amp is fine, doing its job and when people finally realise just because you can see a signal on a trace doesn't mean it is audible, we'll all be better off.

 

[mrmojo2022]

You're missing the point and the facts.

His 'scope' is a toy. It's 12 bit, which is absolutely fine, but it's bandwidth is useless for anything over 20kHz. The switching frequency of the amp is over 20 times that.

So it captures absolute garbage from the amplifier unless you hard LPF the inputs which he isn't doing.

There is nothing to see here. The March amp is fine, doing its job and when people finally realise just because you can see a signal on a trace doesn't mean it is audible, we'll all be better off.

Glad you agree with me. even A 12bit scope is also useless for looking in any detail under 20kHz.

Jeez what was that all about?

 

[dlaloum]

A simple voltmeter, with the speakers connected should be ample to measure the V out and level match - preferably with a low frequency sine wave... 100hz was proposed.

The sine wave should be at a sufficient level to be at relatively optimum signal/noise on all the amps - that way the high frequency noise which may be present on the class D's should be a very minor part of the signal, and won't affect the matching.

Although not using a switcher, or level matching - I did a purely subjective long term series of tests comparing a very similar Onkyo Class AB AVR (a somewhat more heavy duty upper end model rated at 140w/ch) - to the class D Crown XLS2500, and the current dumping (feed forward) Quad 606 / 707.... My own tests involved alternating the amp in use for several weeks/months then swapping over.... and swapping back and forth over periods of months.... my preferences remained consistent over that time - but in short auditions I found it extremely difficult to seperate the three alternatives - they all seemed very very similar. Quality ranking, best to worst, driving my Gallo Nucleus Reference 3.2 speakers was Crown, Quad, Onkyo.... I had expected the Quad to do better than the Crown... I was wrong.

I look forward to the report of the listening tests...

And I strongly urge longer term, non switching, listening tests.

Based on my own experiences, decent quality, higher powered amps will sound identical given relatively standard easy to drive speakers.

Differences between amps will be exposed with difficult loads - where at certain frequencies the impedance drops to 2 ohm or below, or where the load is capacitive AND drops to very low impedances.... Some amps, just don't have sufficient power supply to feed what is almost a short circuit - other amps get unstable into such loads, and then generate distortion nasties.

With a nice easy load - most decent modern amps with enough power to get the desired SPL - will sound identical... "wires with gain".

In the 80's when I worked in a "Hi Fi" store - I had more opportunities to compare various amps, with various speakers, switched and unswitched... short and longer term... my conclusions were the same then.

Like I said - I look forward to the listening test results.

 

[abdo123]

Glad you agree with me. A scope is also useless for looking in any detail under 20kHz.

Jeez what was that all about?

Scopes and interfaces have different uses. neither one can do the job of the other.

Even the 70 euros oscilloscope i linked has plenty of sample rate for OP's purpose.

Finding an interface with enough bandwidth to read the switching frequency of a Class D amplifier is mission impossible.

They're just two different devices.

 

[mrmojo2022]

A simple voltmeter, with the speakers connected should be ample to measure the V out and level match - preferably with a low frequency sine wave... 100hz was proposed.

The sine wave should be at a sufficient level to be at relatively optimum signal/noise on all the amps - that way the high frequency noise which may be present on the class D's should be a very minor part of the signal, and won't affect the matching.

Although not using a switcher, or level matching - I did a purely subjective long term series of tests comparing a very similar Onkyo Class AB AVR (a somewhat more heavy duty upper end model rated at 140w/ch) - to the class D Crown XLS2500, and the current dumping (feed forward) Quad 606 / 707.... My own tests involved alternating the amp in use for several weeks/months then swapping over.... and swapping back and forth over periods of months.... my preferences remained consistent over that time - but in short auditions I found it extremely difficult to seperate the three alternatives - they all seemed very very similar. Quality ranking, best to worst, driving my Gallo Nucleus Reference 3.2 speakers was Crown, Quad, Onkyo.... I had expected the Quad to do better than the Crown... I was wrong.

I look forward to the report of the listening tests...

And I strongly urge longer term, non switching, listening tests.

Based on my own experiences, decent quality, higher powered amps will sound identical given relatively standard easy to drive speakers.

Differences between amps will be exposed with difficult loads - where at certain frequencies the impedance drops to 2 ohm or below, or where the load is capacitive AND drops to very low impedances.... Some amps, just don't have sufficient power supply to feed what is almost a short circuit - other amps get unstable into such loads, and then generate distortion nasties.

With a nice easy load - most decent modern amps with enough power to get the desired SPL - will sound identical... "wires with gain".

In the 80's when I worked in a "Hi Fi" store - I had more opportunities to compare various amps, with various speakers, switched and unswitched... short and longer term... my conclusions were the same then.

Like I said - I look forward to the listening test results.

DVM accuracy can be affected by the switching signal, I have seen this happen so care needs to be taken.

I totally agree about the more difficult loads affecting the amps frequency response etc.

 

[mrmojo2022]

Scopes and interfaces have different uses. neither one can do the job of the other.

Even the 70 euros oscilloscope i linked has plenty of sample rate for OP's purpose.

Finding an interface with enough bandwidth to read the switching frequency of a Class D amplifier is mission impossible.

They're just two different devices.

To me the point is that the OP doesn't want to see or measure or have the measurement affected by the switching signal. An unfiltered scope is affrcted and the ops plots show this.

 

[dlaloum]

DVM accuracy can be affected by the switching signal, I have seen this happen so care needs to be taken.

I totally agree about the more difficult loads affecting the amps frequency response etc.

DVM can be affected by the switching signal, I agree - but if you have the base signal at a decent level - say 8V or 9V - around circa 10W into 8 ohm.... you should be 70db or more above the switching noise... worst case... in which case the switching noise impact on the V would be negligible.

Unless the switching noise is affecting the DVM circuits in some way?

 

[mrmojo2022]

DVM can be affected by the switching signal, I agree - but if you have the base signal at a decent level - say 8V or 9V - around circa 10W into 8 ohm.... you should be 70db or more above the switching noise... worst case... in which case the switching noise impact on the V would be negligible.

Unless the switching noise is affecting the DVM circuits in some way?

It can do, depends on the dvm.

9v might be pretty loud to a lot of people. speaker sensitivity obviously impacts this. 86dB/1watt could be 95dB at 10 watts.

 

[f1shb0n3]

I hope my experience is useful to some planning to compare amps - wanted to emphasize how I incorrectly volume-matched the amps by ear before getting the ‘scope and heard “crisper highs and more detail” on Purifi when it was actually louder by 0.5dB.

Continuing to compare - not claiming they sound the same just yet, will take my time with the comparison until satisfied. Blind A/B test will be done too if I believe I can hear differences - ordered 2 more A/B switches and will set them up as a swapper of A/B signal for the test proctor.

ADI-2 Pro measurements of amps is a minor diversion for my own education, but could be useful in the comparison. Don’t have reasons to believe any of the amps has issues, will measure them just in case.

 

[mrmojo2022]

I hope my experience is useful to some planning to compare amps - wanted to emphasize how I incorrectly volume-matched the amps by ear before getting the ‘scope and heard “crisper highs and more detail” on Purifi when it was actually louder by 0.5dB.

Continuing to compare - not claiming they sound the same just yet, will take my time with the comparison until satisfied. Blind A/B test will be done too if I believe I can hear differences - ordered 2 more A/B switches and will set them up as a swapper of A/B signal for the test proctor.

ADI-2 Pro measurements of amps is a minor diversion for my own education, but could be useful in the comparison. Don’t have reasons to believe any of the amps has issues, will measure them just in case.

Amps can also have load dependant frequency response variations which can cause subtle differences.

 

[amper42]

I completed my comparison of the Buckeye NC502MP vs the March Audio P452 yesterday. Here's what I noticed.

1. The March Audio P452 Purifi has ETIBP20C binding posts which I prefer a bit more than the Buckeye NC502MP binding posts. Your preference may differ.
2. The Buckeye XLR connectors are a bit tighter than the P452 XLR connectors. Using 3 Foot – Quad Balanced XLR Cables by WORLDS BEST CABLES works well on the Buckeye. Monolith cables were tighter than I wanted.
3. The P452 Purifi amp was built with a 26.5dB gain while the gain on the Buckeye NC502MP is 25.5dB. To volume match the two I increased the volume on the NC502MP by 1dB.
4. The case on the P452 is a solid aluminum body which weighs in at 8.75 pounds vs the 5.5 pound steel metal case of the Buckeye NC502MP.
5. The NC502MP uses 23W while idle while the P452 uses 16W idle.
6. The P452 doesn't really get warm. It stays amazingly cool. The NC502MP will get warm to the touch with a 2 hour run even at 80dB listening levels (24W).
7. In my A/B listening tests both NC502MP and P452 sound great. However, if I pay close attention while A/B'ing the same songs over and over and switching between these amps (with the ADI-2 DAC) the P452 has slightly better bass control and a little crisper sound with many songs. This judgement will be controversial but it's what my ears heard after hours of switching between these amps. The Purifi design is my preference for a really nice speaker setup. I would never notice the difference in power between these two amps at my listening levels and the Purifi measures a bit cleaner. But, P452 is a $1000 more in price. You better get a little something for that extra cash.

Amazon.com: 3 Foot – Quad Balanced Microphone Cable Custom Made by WORLDS BEST CABLES – Using Canare L-4E6S Wire and Neutrik Gold NC3MXX-B Male & NC3FXX-B Female XLR Plugs : Musical Instruments

Amazon.com: 3 Foot – Quad Balanced Microphone Cable Custom Made by WORLDS BEST CABLES – Using Canare L-4E6S Wire and Neutrik Gold NC3MXX-B Male & NC3FXX-B Female XLR Plugs : Musical Instruments

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Binding Posts - ETI Research

The ETI Research offers a range of Binding Posts suitable for all speaker/amplifier types.

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Buckeye Amps: New US based Hypex multichannel amplifier builder, line-up announcement!

Hypex NC502MP specs: - 450w @ 2ohm (per channel, peak) - 500w @ 4ohm (per channel, peak) - 350w @ 8ohm (per channel, peak) Hypex NC252MP specs: - 180w @ 2ohm (per channel, peak) - 250w @ 4ohm (per channel, peak) - 150w @ 8ohm (per channel, peak) PRICING: XL 8ch Aluminum Case (17"x13"x6")...

www.audiosciencereview.com

P452 Stereo Power Amplifier | March Audio Global

The P452 is March Audios' first Purifi based stereo amplifier. This simply elegant product is milled from solid aluminium with a tough anodized treatment. Exceptional fit, finish and build quality. Featuring the new Purifi 1ET400A technology and Bruno Putzeys development of his nCore designs...

www.marchaudio.com

 

[f1shb0n3]

7. In my A/B listening tests both NC502MP and P452 sound great. However, if I pay close attention while A/B'ing the same songs over and over and switching between these amps (with the ADI-2 DAC)

Curious - how did you use ADI-2 DAC for switching amps?

the P452 has slightly better bass control and a little crisper sound with many songs.

I heard the crisper highs of P452 when I was comparing them, but that’s before I got the ‘scope for precise matching, will try it again and listen for that too. FR measurements show that difference and would be surprised if I don’t hear it at all.
What I’ll try (if I hear it) is to PEQ it away and compare again.

 

[amper42]

Curious - how did you use ADI-2 DAC for switching amps?

I heard the crisper highs of P452 when I was comparing them, but that’s before I got the ‘scope for precise matching, will try it again and listen for that too. FR measurements show that difference and would be surprised if I don’t hear it at all.
What I’ll try (if I hear it) is to PEQ it away and compare again.

I used XLR "Y" connectors to connect both the P452 and the Buckeye NC502MP at the same time to the ADI-2 DAC. This way they both had the same quality cable and were connected simultaneously. I only needed to move the speaker banana plugs and adjust the volume by 1dB to quickly change between amps.

I also used REW to measure both amps. The FR curves were very close to identical. The difference between the amps is not based on a different REW frequency curve but they do sound slightly different with close examination.

https://www.amazon.com/SiYear-Balanced-XLR-Splitter-Cable/dp/B07VM4NV2C