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LJM MX50 kit amp
LJM MX50 kit amp
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Old 1st November 2019, 02:09 AM   #351
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by t-minik View Post
Yeah, OK, I didn't realize device means transistor.
Device can refer to any active circuit component, but would not apply to a passive component - as far as I've experienced the term.
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Old 1st November 2019, 09:12 AM   #352
audio_tony is offline audio_tony  United Kingdom
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Quote:
Originally Posted by engRviRolandRia View Post
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
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Old 1st November 2019, 10:14 AM   #353
Rallyfinnen is offline Rallyfinnen  Sweden
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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 .
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Old 3rd December 2019, 02:00 PM   #354
ljm_ljm is offline ljm_ljm  China
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Quote:
Originally Posted by Rallyfinnen View Post
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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Old 3rd December 2019, 02:13 PM   #355
ljm_ljm is offline ljm_ljm  China
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Quote:
Originally Posted by audio_tony View Post
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 ljm_ljm@foxmail.com
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File Type: jpg MX50goods.jpg (106.2 KB, 295 views)
File Type: jpg MX50fakes.jpg (94.3 KB, 294 views)

Last edited by ljm_ljm; 3rd December 2019 at 02:16 PM.
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Old 3rd December 2019, 02:19 PM   #356
chalky is offline chalky
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ljm_ljm why do all of the schematics on ebay show the MX50 SE with an emitter follower enhanced ( i.e. darlington ) VAS when all of the pcbs I've seen only have a simple one transistor VAS?
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Old 15th February 2020, 08:32 AM   #357
Rallyfinnen is offline Rallyfinnen  Sweden
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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.
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Old 15th February 2020, 02:11 PM   #358
Clive Brooker is offline Clive Brooker  United Kingdom
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Default 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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File Type: jpg MX50-SE plus ferrite bead.jpg (176.0 KB, 138 views)
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Old 15th February 2020, 03:02 PM   #359
audio_tony is offline audio_tony  United Kingdom
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Quote:
Originally Posted by Clive Brooker View Post
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.
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Old 15th February 2020, 04:25 PM   #360
Rallyfinnen is offline Rallyfinnen  Sweden
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Quote:
Originally Posted by Clive Brooker View Post
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

Last edited by Rallyfinnen; 15th February 2020 at 04:27 PM.
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