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KJF Audio MA-01 Review (Multi-channel Amplifier)

amirm

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#1
This is review and detailed measurements of the KJF Audio MA-01 6-channel Amplifier populated with Hypex NC252MP stereo modules. It was kindly sent to me by a member. I configured it using their online tool and it shows a cost of US $1,868.

Not much to see or talk about as far as the case other than dual fans on top:

KJF Audio MA-01 Review MC252MP Hypex.jpg


Thankfully they did not come on during my testing but it is good insurance to have given the total power this unit can generate.

The rear panel shows the usual balanced inputs although in this case it is 1/4 inch/XLR combo jacks:

KJF Audio MA-01 Review balanced multichannel MC252MP Hypex.jpg


For my testing, I focused on channels 1 and 2. Did plan to test the rest of the channels for total power but forgot that I had no way of generating that many balanced outputs so what you are about to see is for stereo only. Seeing how the amp modules are stereo anyway, this should be representative of what you get even if turned on the rest of them at full power.

KJF MA-01 Measurements
As usual we start with our dashboard:

KJF Audio MA-01 Measurements MC252MP Hypex.png


We expect excellent performance from Hypex and we get it there, producing well above average SINAD which represents level of noise and distortion:
Best multichannel amplifier review 2021.png


Signal to noise ratio is very high indicating a very quiet amplifier:

KJF Audio MA-01 SNR Measurements MC252MP Hypex.png


32-tone test signal simulating "music" shows very low distortion as well:
KJF Audio MA-01 Multitone Measurements MC252MP Hypex.png


Frequency response is essentially flat with almost no dependency on whether I used 4 or 8 ohm test load:

KJF Audio MA-01 Frequency Response Measurements MC252MP Hypex.png


This means the frequency response should not change much when you switch one speaker for another (an issue with cheap desktop amplifiers).

Crosstalk is very good:

KJF Audio MA-01 Crosstalk Measurements MC252MP Hypex.png


The meat of an amplifier review is the amount of power versus distortion+noise so let's start with 4 ohm:
KJF Audio MA-01 Power into 4 ohm  Measurements MC252MP Hypex.png


Spec is 250 watts which is what we get if we allow more distortion than I do in the above graph:

KJF Audio MA-01 Max and Peak Power into 4 ohm  Measurements MC252MP Hypex.png


Seems that the power supply is designed to power the amp exactly as specified and no more and hence the lack of increase on bursts (above right).

Switching to 8 ohm we get:
KJF Audio MA-01 Power into 8 ohm  Measurements MC252MP Hypex.png


I like the lower noise with 8 ohm better than 4 ohm.

Finally, there is a bit too much disturbance when we change frequency and sweep for power than I like:

KJF Audio MA-01 Power vs Distortion vs Frequency Measurements MC252MP Hypex.png


But as noted on the graph, there are far worse examples.

Conclusions
The hypex NC252MP stereo amplifier modules do their job to product above average performance while running cool and efficient. While I have not yet looked inside the KJF amp, from the outside it seems like they have not done anything to lower the performance of these nice modules.

I am going to put the KJF MA-01 with Hypex NC252MP on my recommended list.

Edit: see teardown here: https://www.audiosciencereview.com/...ma-01-hypex-nc252mp-amplifier-teardown.22770/

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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levimax

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#2
Looks pretty good but the 20 Hz power sweep with over 0.5% distortion and goes it into protection mode early seems a little weak. I guess you would not want to use this as a sub amp.
 
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amirm

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Thread Starter #5
Can't help but notice that proliferation of Hypex based amps makes audio landscape a bit dull.
Helps me with not having another grief ridden, argumentative review thread! :)
 
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amirm

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Thread Starter #7
Sure, but you could just refer us to the module spec sheet and save your time.
They don't run the same tests I run so we are stuck having to test them ourselves. Otherwise you can't compare them to others.
 

Music1969

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#9
Sure, but you could just refer us to the module spec sheet and save your time.
This is no different referring to an ESS DAC chip or AKM DAC chip and saving time.

We have enough data points for DACs to show that the RCA/XLR analogue outputs need to be measured, if possible.

No different to amps in my opinion.
 

gvl

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#12
This is no different referring to an ESS DAC chip or AKM DAC chip and saving time.

We have enough data points for DACs to show that the RCA/XLR analogue outputs need to be measured, if possible.

No different to amps in my opinion.
There's more places where things go wrong in DACs than a couple of wires IMO.
 

Music1969

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#13
There's more places where things go wrong in DACs than a couple of wires IMO.
By 'couple of wires' are you referring to RCA/XLR analogue outputs?

One could argue this is the only important place to check if a DAC has gone wrong... it's analogue outputs...

We've seen Hypex implementations that measured (by @amirm ) worse than Hypex spec sheet.

If Amir didn't measure these for us, we wouldn't know
 
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#14
I see that they have a rack mount version and offer speakons. Also i like the protection/longevity the fans can add especially since you can use 4 252 making it 8 channels or 502 doubling power. Well thought out amp.

Never understood why most hypex based amps don't use the features of the module. It provides tempature, clip indicator, power problems from my beginner reading of the spec sheet. Yet most manufacturers stick them in a box and never connect to that info or cool the modules.

A couple things i don't like. 1) wish it was here in us to make shipping faster and cheaper 2) wish the fans were front to back allowing stacking

Also nice is that it uses 2 relatively big fans. Smaller fans and single fans are much louder. I doubt you could hear and with ASR testing they didn't come on.

I
 

gvl

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#15
I mean there's usually a wire from the input of the amp to the Hypex module, and a wire from the module to the speaker output. Sometimes there's a buffer. The attempted analogy was with DACs, but there's much more complexity there up and downstream of the DAC chip. I'm not saying it's a useless exercise, but perhaps Hypex based amp reviews should be put into a "Hypex Corner" subsection. Personally if I wanted a Hypex amp I'd just source the modules from eBay and build the amp myself.
 

DerRoland

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#16
Some of many interesting facts from the product page:
Due to keeping the costs affordable, huge heat sinks were out, we decided on 2 large silent pulse width-controlled fans. The internal temperature of the amplifiers is fed back to the microprocessor which in turn can regulate thermal limits. If the amplifiers start operating above their nominal range the microprocessor starts turning the fan slowly enough that they are inaudible, pushing the volume and potentially the temperature even higher, the fans speed up to compensate, even at full RPM they are <20dbA. They are electrically isolated from the rest of the system so as not to interfere with delicate audio signals in the rest of the amp.
DC connected inputs (make sure you have no DC on the inputs)
Some manufacturers provide the ability to change the op-amps in the input stage of the amplifiers to change or ‘improve’ the sound, do you?
These latest N-Core modules have got a buffer already built in, Bruno Putzney (N-Core designer) is one of the most talented audio designers on the planet so I’m pretty sure he’s got this well sorted in these modules. Most of these off-board buffers use op-amps which must exist in a circuit that is designed and optimised for that op-amp. Op-amp ‘rolling’ should be discouraged, as putting a supposedly high performing op-amp into a circuit not designed for it can cause oscillations in the circuit that will cause non-linearity further down the line. I don’t provide this functionality, I want to make amplifiers that are unconditionally stable into all loads.
 
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amirm

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Thread Starter #17
One thing I forgot to mention. The gain is a bit low. Usually I target 29 dB and here it is 25 dB. To get full power, I had to get about 1.6 volts or so. If you pair these up with an AVR, make sure they can produce their optimal output there.
 

carlob

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#20
2 posts up it says no additional buffer is used in this amp, as in many others too.
That makes it unsuitable to use with most commercial AVRs as Amir noted above. As an example let's see what happens with the recommended AVR-X4700H:

Screenshot 2021-04-24 at 10.41.18.png
 
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