Thanks for posting the schematic! I saw the ad and wondered if it was worth buying. Looking at the schematic there appears to be some drawing and/or design mistakes, but maybe they know something I don't. The collector and base of Q2 seem to be swapped, and Q2 and Q4 are drawn 90 degrees although that's just confusing and doesn't matter. C4 is dangerous, C5 needs ~1K in series, R22,R27 should be in the emitter of Q13, Q17 unless D2,D3 connected to them instead of directly to the output, etc etc. Which brings us to the biggest reason to use PNP outputs, ie cross coupling is not as easy if possible with quasi-complimentary (all NPN) output transistors. The best option for using all NPNs is to use a real small base resistor (R20, R25 < 33), and a big PNP driver. You need a heavy drive turning power transistors OFF or they shoot through when driven fast. I should share some of my spice creations but I want to build them first so I have time to reconcile theory with reality, cause some times theory overlooks something important.
I'll test improved constantly. So you can use 0 r15 will be better.
Directly using my match is the best.
Hello ljm
Very nice update!
Which is the best seller for the new version? I only found the old version on aliexpress and ebay.
Also, how do they compare to the L7 in terms of sound quality? I have a couple of +-48VDC power supplies I want to use.
Greetings
You have to redesign the circuit it is not designed for your voltage.
Though if you got experience is not a complex thing to do.
it takes time though. Amplifier design is not a hour task.
I can answer a few. points.
You need higher Vce bjt for front. emitter resistors recalculate.
Heatsink for 2sa649 669 needs to be bigger. Bigger output bjt maybe Mg9411-R mg 6331r nice bjts from semelab.
Cdom check if stable for the freq. 20-20000hz
More thing but bye maybe ljm will answer.
Thanks for the reply. 
Both the L7 and MX50 X2 are rated for more than +-48VDC (I will be using regulated switch mode power supplies). . I was just curious which one the designer would prefer.
After a little bit of searching I managed to find a seller for the new MX50 X2 on aliexpress for a good price.
I think I'm going with this kit, since the L7 is rumored to spontaneously let the magic smoke out and take the speakers with it.
I don't need very much power since the modules will be used for a 8-channel surround/Atmos amp.
Greetings
Both the L7 and MX50 X2 are rated for more than +-48VDC (I will be using regulated switch mode power supplies). . I was just curious which one the designer would prefer.
After a little bit of searching I managed to find a seller for the new MX50 X2 on aliexpress for a good price.
I think I'm going with this kit, since the L7 is rumored to spontaneously let the magic smoke out and take the speakers with it.
I don't need very much power since the modules will be used for a 8-channel surround/Atmos amp.
Greetings
Hello
Does anyone tried both mx50SE and Mx50x2 and can explain what he think of both.
I just pulled an Mx50x2 pair on a fried Marantz Pm50 and added some psu capacitors, it sounds really good and is extremely quiet, I just had to put an opa2134 non inverting buffer between 50k volume pot and input to match Zin correctly (perhaps I'll try some 3db later).
Nice airy and detailed sound, black background.
I need to listen to it a bit more but I can say you can't go wrong with it.
As I have two spare 28-0-28 100w toroid transformer, I'm thinking to build a monoblock pair for myself.
100w transfo is probably a bit low...
Does anyone tried both mx50SE and Mx50x2 and can explain what he think of both.
I just pulled an Mx50x2 pair on a fried Marantz Pm50 and added some psu capacitors, it sounds really good and is extremely quiet, I just had to put an opa2134 non inverting buffer between 50k volume pot and input to match Zin correctly (perhaps I'll try some 3db later).
Nice airy and detailed sound, black background.
I need to listen to it a bit more but I can say you can't go wrong with it.
As I have two spare 28-0-28 100w toroid transformer, I'm thinking to build a monoblock pair for myself.
100w transfo is probably a bit low...
The mx50x2 is now all green. It's all up to date.
Maybe some agents didn't update the photos.
But it was a new version a long time ago. green.
In contrast, L7. MX50X2。 They have different styles
If your voltage is below + - 50V. I think the mx50x2 will be better.
The L7 can use a higher voltage.
I generally use + -50v DC mx50x2
So there's no problem with this voltage.
But I never used SMPS. There may be many problems with SMPS.
I'm not sure.
no problem.
The voltage of mx50se should not exceed + - 45V
AC 24-0-24 200va transformer is recommended.
There is no problem with the 100VA transformer.
We don't care much about transformers. And voltage.
I often use ac15-0-15 50VA transformer. Connect the mx50se.
The sound box uses small whirlwind Photo 8 speaker.
No problems, very good.
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This is making amplifiers. Problems we often encounter.
Generally, there are two kinds of noise.
1, caused by signal input. You can try to short-circuit input + - or turn off the potentiometer signal. If there is still noise. The noise is caused by the power supply.
2. Noise caused by power supply. The common situation is switching power supply. Or transformer interference.
Hi LJM,
Thank you for your support. This is not a hum caused by the input signal but rather by the power supply, which by the way, very good quality.
I solved the hum problem. I build an "Earth loop breaker" based on the circuit discussed by Rod Elliott. So I have a functional channel, I still have to mount the 2nd channel.
It is a prototype assembled quickly to validate the quality of the amp. If I am satisfied, I will order a new case.
I'm going to compare it to my L12-2, which is really excellent.
Thanks LJM
Denis
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Hi,
my MX50X2 prototype is mounted and plugged in. There's no hum, pretty quiet. I plugged in an external hp shield for my main speakers.
The sound is quite clean, it's too early to give more comments. I let the break-in advance a bit and I will compare it with the L12.2. As a source I have an AK4497 DAC and 2 ES9038 DACs.
Edit : The transformer gives 37vdc with 250VA. My main speakers are 4 ohms, with good efficiency.
my MX50X2 prototype is mounted and plugged in. There's no hum, pretty quiet. I plugged in an external hp shield for my main speakers.
The sound is quite clean, it's too early to give more comments. I let the break-in advance a bit and I will compare it with the L12.2. As a source I have an AK4497 DAC and 2 ES9038 DACs.
Edit : The transformer gives 37vdc with 250VA. My main speakers are 4 ohms, with good efficiency.
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Hi,
here's a little feedback on the tone of the MX50X2. I really like the sound of this amplifier. At first I was a little skeptical.
I found my L12-2 superior especially in the mid-high and high resolution.
On the MX50X2, I changed the input signal condo with the addition of an Ero MKT bypass, and some Wima bypass condos on the power board condos.
Then I received a new DAC based on double ES9038 and racing OP. In short, the result is above my expectations, the soundstage and the volume and positioning of the instruments is higher with the MX50X2 than the L12-2.
Make no mistake, the well-powered L12-2 is still a great amplifier, but the MX50X2 has a lot more depth in the soundstage. Also with the small modifications on the PCBs and my new DAC, the MX50X2 comes close to the resolution of the L12-2 in the highs, at least that's amply satisfactory.
But I would have liked the L12-2 to remain the best, because of the case and its power supply.
So I am thinking of removing the L12-2 from the case and putting the MX50X2. The voltage will go from 37vdc per rail (250va) to 47vdc and 500va.
here's a little feedback on the tone of the MX50X2. I really like the sound of this amplifier. At first I was a little skeptical.
I found my L12-2 superior especially in the mid-high and high resolution.
On the MX50X2, I changed the input signal condo with the addition of an Ero MKT bypass, and some Wima bypass condos on the power board condos.
Then I received a new DAC based on double ES9038 and racing OP. In short, the result is above my expectations, the soundstage and the volume and positioning of the instruments is higher with the MX50X2 than the L12-2.
Make no mistake, the well-powered L12-2 is still a great amplifier, but the MX50X2 has a lot more depth in the soundstage. Also with the small modifications on the PCBs and my new DAC, the MX50X2 comes close to the resolution of the L12-2 in the highs, at least that's amply satisfactory.
But I would have liked the L12-2 to remain the best, because of the case and its power supply.
So I am thinking of removing the L12-2 from the case and putting the MX50X2. The voltage will go from 37vdc per rail (250va) to 47vdc and 500va.
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