Reutilization of the MJ-One Sound System

ErikdeBest · 7th January 2007, 09:39 PM

Today I was looking at the German ebay and found several advertisements for the subwoofer http://cgi.ebay.de/Aktiv-HIFI-MJ-Jac...QQcmdZViewItem of the MJ-One sound system http://www.mj-one.com/. Normally I would not spend much time on such a system, but this one, at least, looks interesting, both technically (the incorporated functions), cost wise (36 euros, inclusive postage) and socially (the complete failure of peerless and tepax in selling this product) – look at this interesting link, telling about the great plans involved with this product, back in 2001 http://www.prnewswire.co.uk/cgi/news/release?id=63948 . My question is if someone here already opened such a cabinet, looked how it works, or have a technical diagram.

From what I understood it looks like a unit with three active crossovers and three small power amplifiers: one LP crossover for the lows and two HP crossovers for right and left satellite. My idea is to use one “MJ-one sound system” unit to power a DIY speaker: modify the crossovers somewhat, add some extra active EQ and level controls, and power a low cost, phoenix-clone speaker. This all to make a cheap, but hopefully still good speaker (not for my own use – I like valves – but as a gift for a less critic person, other would say: for an enemy).

First questions that arise: should I start to run?

Are there really three crossovers and amplifiers there? Can I use the amplifiers meant for NXT speakers for normal dynamic speakers?

Some points:
- The subwoofer unit is said to weight 6.5kgs…that’s next to nothing…and there is also a 'sub' included in this weight.
- It seems to be on sell just in Germany, a rapid glance at ebay.com did not turn out any result, neither did google point to anything else than Deutschland.

Well, I thank you all for the time spent reading this thread. I know it may sound silly after all, but I am curious!

Erik

sreten · 8th January 2007, 06:27 PM

Hi,

I'd expect the the amplifiers to be fine with normal drivers, once you
identify the power amplifier IC, very likely will suit 8 ohm loading.

It has a switched mode supply, so no heavy transformer, and probably
a lightweight neobydium magnet in the subwoofer, hence the weight.

A simple full range open baffle could work well with it.

/sreten.

ErikdeBest · 8th January 2007, 08:02 PM

Hi Sreten

Thanks for the useful information! I do not see this project coming up so soon, but I believe the MJ units will be around for a while, maybe even getting cheaper.

Erik

sreten · 9th January 2007, 09:05 AM

Quote:

Originally posted by ErikdeBest

...... but I believe the MJ units will be around for a while, maybe even getting cheaper .......

Erik

Don't count on this happening ........

/sreten.

ErikdeBest · 9th January 2007, 10:00 AM

Hi Sreten

What exactly do you mean?

What I wanted to say is that they will be available cheap on ebay.de for a while, as there is no one interested in them...or will they throw it into the garbage?

I am running to get my pair

Erik

sreten · 9th January 2007, 10:35 AM

Quote:

Originally posted by ErikdeBest
Hi Sreten

What exactly do you mean?

Erik

Hi,

I meant don't wait around for them to get cheaper, they may dissapear.

So your going to get a pair ? Probably a very good idea as the c/o
frequency is likely quite high a a pair would work much better.

Would also allow the satellites to be bi-amped.

/sreten.

bodo · 9th January 2007, 04:36 PM

Hi Erik,

I bought two of MJ one subwoofers two weeks ago and opened one to have a look inside. I'm also owning a Mission NXT set with the bandpass subwoofer and the models are quite different. But let me start with the biggest drawback of the MJ one subwoofer. The bass sounds distorted with a lot of overtones. It's a little bit like the sound of a small pocket radio playing together with the bass. I discovered this while I was testing the subbass without satellites. I think the problem is caused by the tight internal construction of the amp module. The power transformer is just 1 cm away from the amplifier board. The problem occured on both models that I tested. So it seems to be a design problem. Some of the noised is covered by the downfiring operation of the woofer. When I moved the transformer a little away from the amp board the hiss was lower. But let's switch to the good use. There is no switching power supply inside subwoofer. Instead you will find a beefy transformer (about 3 kg). The bass is powered by a LM3886 chip amp. The two other channels are driven by a smaller stereo chip amp (I have to look up the number).The speaker is a Peerless 6,5 inch paper cone driver with a plastified paper cone. So you get a lot of good parts for the money.
More info to come in my next message.

Best,

Bodo

sreten · 9th January 2007, 04:51 PM

Hi,

The pictures clearly show the mains input is 100 to 250V, 50 Hz to 60Hz.

This means it has a switching supply, so it can't be the same model.

/sreten.

sreten · 9th January 2007, 04:56 PM

Hi,

Sorry I missed the voltage selector switch on the back, so its not a switched supply.

May be possible to add a copper belly band to the transformer ?

Or a shielding plate ?

/sreten.

ShinOBIWAN · 9th January 2007, 05:08 PM

http://www.youtube.com/watch?v=Hh9YXT7fVsQ

7th January 2007, 09:39 PM	#1
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Reutilization of the MJ-One Sound System Today I was looking at the German ebay and found several advertisements for the subwoofer http://cgi.ebay.de/Aktiv-HIFI-MJ-Jac...QQcmdZViewItem of the MJ-One sound system http://www.mj-one.com/. Normally I would not spend much time on such a system, but this one, at least, looks interesting, both technically (the incorporated functions), cost wise (36 euros, inclusive postage) and socially (the complete failure of peerless and tepax in selling this product) – look at this interesting link, telling about the great plans involved with this product, back in 2001 http://www.prnewswire.co.uk/cgi/news/release?id=63948 . My question is if someone here already opened such a cabinet, looked how it works, or have a technical diagram. From what I understood it looks like a unit with three active crossovers and three small power amplifiers: one LP crossover for the lows and two HP crossovers for right and left satellite. My idea is to use one “MJ-one sound system” unit to power a DIY speaker: modify the crossovers somewhat, add some extra active EQ and level controls, and power a low cost, phoenix-clone speaker. This all to make a cheap, but hopefully still good speaker (not for my own use – I like valves – but as a gift for a less critic person, other would say: for an enemy). First questions that arise: should I start to run? Are there really three crossovers and amplifiers there? Can I use the amplifiers meant for NXT speakers for normal dynamic speakers? Some points: - The subwoofer unit is said to weight 6.5kgs…that’s next to nothing…and there is also a 'sub' included in this weight. - It seems to be on sell just in Germany, a rapid glance at ebay.com did not turn out any result, neither did google point to anything else than Deutschland. Well, I thank you all for the time spent reading this thread. I know it may sound silly after all, but I am curious! Erik

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8th January 2007, 06:27 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, I'd expect the the amplifiers to be fine with normal drivers, once you identify the power amplifier IC, very likely will suit 8 ohm loading. It has a switched mode supply, so no heavy transformer, and probably a lightweight neobydium magnet in the subwoofer, hence the weight. A simple full range open baffle could work well with it. /sreten.

8th January 2007, 08:02 PM	#3
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Hi Sreten Thanks for the useful information! I do not see this project coming up so soon, but I believe the MJ units will be around for a while, maybe even getting cheaper. Erik

9th January 2007, 10:00 AM	#5
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Hi Sreten What exactly do you mean? What I wanted to say is that they will be available cheap on ebay.de for a while, as there is no one interested in them...or will they throw it into the garbage? I am running to get my pair Erik

9th January 2007, 04:36 PM	#7
bodo diyAudio Member Join Date: Oct 2004	Hi Erik, I bought two of MJ one subwoofers two weeks ago and opened one to have a look inside. I'm also owning a Mission NXT set with the bandpass subwoofer and the models are quite different. But let me start with the biggest drawback of the MJ one subwoofer. The bass sounds distorted with a lot of overtones. It's a little bit like the sound of a small pocket radio playing together with the bass. I discovered this while I was testing the subbass without satellites. I think the problem is caused by the tight internal construction of the amp module. The power transformer is just 1 cm away from the amplifier board. The problem occured on both models that I tested. So it seems to be a design problem. Some of the noised is covered by the downfiring operation of the woofer. When I moved the transformer a little away from the amp board the hiss was lower. But let's switch to the good use. There is no switching power supply inside subwoofer. Instead you will find a beefy transformer (about 3 kg). The bass is powered by a LM3886 chip amp. The two other channels are driven by a smaller stereo chip amp (I have to look up the number).The speaker is a Peerless 6,5 inch paper cone driver with a plastified paper cone. So you get a lot of good parts for the money. More info to come in my next message. Best, Bodo

9th January 2007, 04:51 PM	#8
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, The pictures clearly show the mains input is 100 to 250V, 50 Hz to 60Hz. This means it has a switching supply, so it can't be the same model. /sreten.

9th January 2007, 04:56 PM	#9
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Sorry I missed the voltage selector switch on the back, so its not a switched supply. May be possible to add a copper belly band to the transformer ? Or a shielding plate ? /sreten.

9th January 2007, 05:08 PM	#10
ShinOBIWAN diyAudio Member Join Date: Feb 2004 Location: UK	http://www.youtube.com/watch?v=Hh9YXT7fVsQ

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