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

[capslock]

So Amir, how did you use unbalanced or balanced in on your AP to measure this amp?

 

[amirm]

So Amir, how did you use unbalanced or balanced in on your AP to measure this amp?

??? I used balanced XLR cables as input to it. If you mean output, they use a 4-wire "Kelvin" measurement scheme that route one pair to my dummy load and another to me AP AES filter and then to the balanced input of the AP. It is no different than any other amp with balanced input.

 

[A.West]

I bought one of these a year ago configured 5 channel with two 502mp and on 500mp. It sounds good! I'm sure it must run cooler and use less power than a comparably powerful A/B amp design would, and I like its auto-sleep feature. (I had previously left a Harmon Kardon Citation 24 amp switched on nonstop for 10 years to power my fronts.) I use average efficiency 4ohm PSB Stratus Silveri and PSB surround speakers and this amp has no problem taking them to very loud output level, despite being fed by a Marantz SR6014.

 

[KJF audio]

I'd like to answer a few of the above points but cannot work out for the life of me how to quote specific posts, can someone give me a heads up?

Stefan

 

[Semla]

I'd like to answer a few of the above points but cannot work out for the life of me how to quote specific posts, can someone give me a heads up?

Stefan

You can press the reply button on multiple posts and group them in a single reply, every post will be quoted in the reply field in the correct order.

 

[KJF audio]

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.

This is a very interesting finding for me. The modules are quite low gain but are rated at 26dB, I have typically found some at a shade over and some at a shade under. 25dB is the minimum rating, so at least it wasn't under that. It is worth noting though that I spoke to Hypex about this very thing and they said the individual modules are in fact much tighter toleranced than this which given this is a multi channel amp is important! The gain is related to the input AC voltage, less voltage less gain.

To give a complete picture the different modules all have the same gain and so to drive them to full output require the below voltages to drive them to full.

NC122MP - 1.17 V rms
NC252MP - 1.66 V rms
NC502MP - 2.35 V rms

 

[KJF audio]

You can press the reply button on multiple posts and group them in a single reply, every post will be quoted in the reply field in the correct order.

Thanks, got it

 

[KJF audio]

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

Thanks for these comments.

It was really important to be able to use all the facilities for me. A no brainer really. I never actually mentioned that after power up sequence I keep the modules muted for an extra couple of seconds so there is no start up thump either

I am afraid I am not moving to the USA sorry and there was just no room for fans front to back, especially as I wanted bigger ones that would be quiet in the event they have to come on. I'd not stack them on top of each other ideally, I do have customers who do though, with the feet there would be about 8mm separating them. They have never got in touch about overheating, or the fans coming on. I would leave 0.5 RU between them in a rack. I have only really heard of the fans coming on for my gig/studio customers

 

[Bsinger]

Honestly, this seems like the perfect high performance home theater amp. More amp options are available for 2, 5 maybe 7 channels set ups but when you have atmos and multi sub class d is the only option IMO (assuming you don't have a separate equipment room or special ventilation and power). After that, you want to be able to cool equipment. If you want to run 11÷ channels near reference you need power, resonable size and cooling. This eliminates most amps and even most Hypex based fanless amps.

This amp meets those requirements and at a reasonable price per channel.

Then add great sound, triggers, rackmount options, clip indicators, inline rush, muting, power fault indicators, power and channel flexibility, speakons even color choice.

There are cheaper modules-in-a-box amps and more expensive modules-in-a-box amps. Then there are custom packages like the NAD at 2x the price.

 

[KJF audio]

There are some more thing I want to answer, I promise to come back and do so, time is never on my side though. I am the UK Hypex distributor and the UK Mark audio distributor and between then both and the amp building I am a bit stacked. I will ge round to it. Any specific requests, I can be emailed or facebooked messaged, I'll answer those quicker normally.

 

[Matias]

I am afraid I am not moving to the USA sorry

Isn't it possible to sell them fulfilled by Amazon US? Build a few units and ship to Amazon US, and have them store and ship to the customers? Sure it must be more expensive on the product price, but shipping would be a lot cheaper (and faster) than international + customs, so in the end probably better for the customer. Of course this requires building and sending out a few units of each model in advance (working capital), so maybe just the top selling models? Food for thought.

Same for @Apollon Audio, @boXem | audio, @Buckeye Amps (Amazon EU).

 

[KJF audio]

We thought about a USA partner either building or shipping but there are dozens of different configs so couldn't really find a way of doing it. That said most of the amps we sell are the the USA so it isn't prohibitive and only really ads a week or so to delivery.

 

[Matias]

I suppose there must be an ABC curve with a few models/configs having the lion share of the sales, so only these models would apply. But anyway, just an idea.

 

[Spacekop]

I ordered one a year or so ago and when I got it I was pretty disappointed. There was significant crosstalk between channels. I don't remember the precise configuration except that it was 500W for the first two channels and then less for the other two or three. They helpfully mark the configuration on the rear panel, but I put it in storage when I moved so I can't just look over at it.

I tested it by hooking up my hifiman he6-se with the included inverter box and then sending the output from my RME-ADI2 to various input channels on the MA-01. The most damning thing was that I could very clearly hear the signal when I plugged it into channels I wasn't monitoring the output of. So, for instance, channels 1+2 were loaded with the headphones and channel 3 or 4 would be unloaded but receive an input signal (not both at once). I always started with the DAC at -inf gain of course because I'm paranoid. But after turning it up to a reasonable level, I could hear the signal very clearly, albeit faintly on the channels that had no input. I don't know if loading the other outputs would have made a difference, I didn't check. I was so disheartened by that and the noise issues* that I turned it off and vowed to do a teardown and look for grounding issues with the chassis or something else simple one day. Never got around to it.

*Something about the location of that house was pretty bad for sensitive audio equipment (power, or the fact that we lived very close to an FM radio transmitter) which resulted in very audible noise from speakers at 3 meters or so away. I was plagued with ground loops and AM radio pickup issues in nearly everything I set up in that house. This amp was no different and did what most other power amps seemed to do in producing what sounded like one of those cell phone signals, only all the time and at a higher frequency. New place seems "magically" immune to any such issues, even for the tube headphone amp I have which was by far and unsurprisingly the most temperamental device.

 

[Deleted member 31750]

any reason for not including square waves?

 

[sarumbear]

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.

But as the power amp modules the same, aren't you just testing the input buffer modules differences?