LJM MX50 kit amp

Rallyfinnen

Member
2017-01-22 10:18 am
Yes, heat sink needs to be substantial. The attached test setup is what I'm using (L12-2 in the pic), and it's ok, but installed in a chassis, it would probably run too hot.
 

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MX50 kits, low cost but not for all diyers

Enticed by the $12-price for each kit (2 unassembled amps), I made a series of three orders last week. The first one arrived 4 hours ago. My first impression is negative: all components are made in China, contrary to the seller's description. Also, I can foresee a lot of technical problems, so I cannot build it right away.
Verdict: kit not for all diyers
 
What are technical problems you encounter?
I think too those kits are "bang for your buck", semis are honest quality, it's easy to assemble, to fire up and great sounding.
my kit came with sanken output transistors, I replaced input cap with some Chinese mkp, put a bias trimmer and it sounds excellent.
KEC output transistors are not bad at all, I use them on another ljm product and i'm happy with, for sure you can replace it with better quality from reputable reseller but you can try it as is and see/listen.
 
24USD can buy me this amp (copied verbatim from seller's page):

Professional High - Power Electrical Source
300 Watts Output Power 2 way Channel ( 150 Watts per channel )
Connectivity:
Bluetooth
RCA
USB
SD
4 Microphone Ports
Full Function Protect System
Low Noise And distortion
Karaoke Digital Echo Effec
Power
220V - 240V 50Hz - 60Hz
DC12V10A-15A
Input sensitivity : 150mv
Frequency response : 20Hz to 20Hz (+/- 10dB)
 
Enticed by the $12-price for each kit (2 unassembled amps), I made a series of three orders last week. The first one arrived 4 hours ago. My first impression is negative: all components are made in China, contrary to the seller's description. Also, I can foresee a lot of technical problems, so I cannot build it right away.
Verdict: kit not for all diyers

I've built two of these kits with no issues at all.

For $12 you surely wouldn't expect 'Made in Japan' semiconductors?

I paid ~ $15 for a (stereo) kit.

Improved MX50 SE Power amplifier DIY Kits board Dual 2.0 channel 100W+100W HIFI | eBay
 

ljm_ljm

Member
2006-09-26 6:47 am
A little bit strange that they advertise them as the latest version, even if the pictures are of an older version. New board are double sided and a little bit smaller. Easiest way to spot the new PCB's is that there is no ferrite choke next to the input .

This is the latest version.
 

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ljm_ljm

Member
2006-09-26 6:47 am
I've built two of these kits with no issues at all.

For $12 you surely wouldn't expect 'Made in Japan' semiconductors?

I paid ~ $15 for a (stereo) kit.

Improved MX50 SE Power amplifier DIY Kits board Dual 2.0 channel 100W+100W HIFI | eBay

This picture is older. It's the old picture. Maybe the international freight hasn't been updated in time.
Please pay attention to the real goods. And fake goods. The picture can be referred to.
In case of fake goods, please email me [email protected]
 

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Rallyfinnen

Member
2017-01-22 10:18 am
Just want to update a little bit on my findings on this amp.

First a note on the output transistors: The Sanken transistors delivered with the kit perform really well. I have tried other (genuine) 'top performers' but the Sankens that came with the kit have been equal or better in distortion performance.

I would also recommend a bigger cap for the input, I now have 50uF, but that is really too much, maybe 10u would be reasonable. I replaced the feedback cap at the same time with a 1000uF bipolar, even if that is a bit overkill too, but I had them, so I thought I might just do it since I'm in there..
The impression after this is a little bit more control in the low bass, and it measures better on 20Hz sine bursts too.

In my stereo amp (have a 4ch amp too) using these boards I'm running them at 0,6A Iq @ 25VDC, which means the output stage will be in class A most of the time, since I usually don't listen at high levels.
Power supply is linear, transformer with separate secondaries for each channel, one pair of low ESR 10mF caps for each channel. Using a aluminium bar with a PC processor cooling fan with a Noctua fan and temperature controlled fan speed.
I have had some thoughts about a little bright sounding treble on these boards, but I don't think I can improve it further, so I think I will call it 'finished' like this. Bass has always sounded nice, but a little bit bloated in the lowest range on some speakers, I think the bigger input cap has improved this.
It's all a matter of taste anyway.
 
Hey! LJM! Which one is genuine!

LJM it's no use posting photos of fake and real boards whilst you are simultaneously changing the layout. There is currently a version for sale which has a ferrite bead near the input, is this one genuine? How are folks supposed to buy genuine products when you change the layout without updating the version of the board.

Also you need to sort out the bias adjustment on this board by incorporating a trimmer pot.
 

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LJM it's no use posting photos of fake and real boards whilst you are simultaneously changing the layout. There is currently a version for sale which has a ferrite bead near the input, is this one genuine? How are folks supposed to buy genuine products when you change the layout without updating the version of the board.

Also you need to sort out the bias adjustment on this board by incorporating a trimmer pot.

I believe these to be genuine.

I think it's the red boards that are copies.
 

Rallyfinnen

Member
2017-01-22 10:18 am
LJM it's no use posting photos of fake and real boards whilst you are simultaneously changing the layout. There is currently a version for sale which has a ferrite bead near the input, is this one genuine? How are folks supposed to buy genuine products when you change the layout without updating the version of the board.

Also you need to sort out the bias adjustment on this board by incorporating a trimmer pot.

They look genuine, but I think they are not the latest PCB version, he latest version does not have the ferrite next to the input connector.

I beleive the green boards are the latest. I also recommend to get the Sanken transistors, example:
Assembeld LJM MX50 SE Amplifier board 2SA1295 2SC3264 100W+100W ( 2 channle AMP) | eBay
 
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