Dual Merus MA12070 Amplifier Sabaj A20 fully balanced : pictures inside )

[gasolin75]

Samne chip same sound just a little less power so go for 4 ohm speakers or high sensitive speakers (single chip amp doesn't have much power like the Loxjie A30) https://www.audiosciencereview.com/forum/index.php?threads/loxjie-a30-amplifier-review.17547/

That said the Loxjie A30 can be upgraded in power supply to a linear power supply, the a10 and a20 has a build in power supply and it's possible to upgrade but not so easy and the one in the A20, atleast for me, works great

Genereal question if Sabaj would make an upgraded version of the A20 a with a linear power supply, would it make a diffrence or is it no more difference than using the xlr in instead of rca ?

 

[DACslut]

Samne chip same sound just a little less power so go for 4 ohm spakers or high sensitive speakers (single chip amp doesn't have much power like the Loxjie A30) https://www.audiosciencereview.com/forum/index.php?threads/loxjie-a30-amplifier-review.17547/

That said the Loxjie A30 can be upgraded in power supply to a linear power supply, the a1 and a20 has a build in power supply and it's possible to upgrade but not so easy and the one in the A20 atleast for me workls great

Genereal question if Sabaj would make an upgraded version of the A20 a with a linear power supply, would it make a diffrence or is it no more difference than using the xlr in instead of rca ?

From Google:
What are the advantages of switching power supplies over linear power supplies?

SMPS incorporate higher efficiency, reduced weight, smaller size, increased durability, and they allow a more extensive input voltage range. However, the linear power supply is typically more cost-effective, less capable, larger in size, weighs more, and less efficient.

 

[Moosi]

Genereal question if Sabaj would make an upgraded version of the A20 a with a linear power supply, would it make a diffrence or is it no more difference than using the xlr in instead of rca ?

There is no point in using a linear PSU with a chip such as the MA12070 which is designed to operate efficienctly with switching power supplies. The whole purpose of those chips is to deliver great quality sound at very low power consumption. A linear PSU amp design is pretty much an opposing concept.

Linear PSUs are vastly less efficient. We're talking about double to triple watts both in standby and playing loudly. With the right electronics tho they can sound really good. Assumably even better than all the D-Class chips. However, if you want to have a comparable distortion level to those better D-Class chips, they need to be really expensive, up to thousands of dollars. I'll stick with my Sabaj A20a. Basically as long as it holds. And if it dies one day, there will probably be a new D-Class chip even better than the MA12070. I believe most A/B and A-Class designs will vanish sooner or later. There is little point anymore in spending that energy to gain a subtle increase in warmth and silkyness, for I believe the difference is not that big anymore for the low- to mid tier devices.

 

[milan616]

Looks like I have a project this weekend! Hopefully the A20a isn't too much of a pain to disassemble. Thanks for sending it over @peterwen . Anyone have any picture requests from inside?

​

 

[DACslut]

Looks like I have a project this weekend! Hopefully the A20a isn't too much of a pain to disassemble. Thanks for sending it over @peterwen . Anyone have any picture requests from inside?

View attachment 149910​

Have a look at the 1st post in this thread for your answer. Good luck and I mean that sincerely.
"I tried to open the case to take pictures of the module, the PCB etc .. but unfortunately it is complicated to dismantle ... "

 

[milan616]

Good luck and I mean that sincerely.

Haha yes I do remember @daniboun 's post that got us all started down this road! I'm mostly hoping it's just a matter of being complicated but not necessarily difficult. There isn't much of a reason to disassemble one if someone doesn't have something to fix. I've never run into the PSU clicking other than trying to force it, but Sabaj was kind enough to send it anyway so I might as well install it. Worst case I realize the tools I have won't do the job and move along.

 

[gasolin75]

I have no click sound, no noise what so ever, my upgraded version is to me perfect and im surprised theres so much power with my Mission LX 3 MKII -20db is loud -15db is very loud (and on the good song a punchy bass, no distortion).

I wonder how much more power then 40watt pr channel there is in 4 om compared to a Loxjie A30

 

[Moosi]

Looks like I have a project this weekend!

Please report on how much of a pain in the ass it was to install the new PSU and if you had to open up both sides of the amp. I'm planning on doing the same. I'd even buy myself a better PSU if there is a better PSU to buy. Would there be a Meanwell or other quality brand PSU suitable to replace the Mornsun or is the Mornsun already the best suited? That is the question.

 

[milan616]

Please report on how much of a pain in the ass it was to install the new PSU and if you had to open up both sides of the amp. I'm planning on doing the same. I'd even buy myself a better PSU if there is a better PSU to buy. Would there be a Meanwell or other quality brand PSU suitable to replace the Mornsun or is the Mornsun already the best suited? That is the question.

It was as I hoped, just a little difficult but not at all complicated! I started with just the 6 chassis screws rather than every single one like in the first post in the thread. The boards slid right out. I went slowly so I could make sure nothing was ripping out and saw the two slip fit ribbon cables that connect the front panel (display, volume knob) to the logic board. Gently pull them out with your fingers or thin pliers. At first I thought I fucked up not remembering the orientation but the back side is blue so that was fine. Once they're out you can slide out the entirety of the guts. The PSU is on a daughter board. Disconnect the AC block connector from the front, the positive/negative spades on the back, and then the 4 screws that hold the PSU to the daughter board. Swap in the new PSU and redo everything you undid. The PCBs have rails in the case to slot into and since it was just me I put the case down and dropped the amp in. See the problem with this? Gravity took the ribbons all the way back in! Did it again with threading the ribbons and dropping the case down on to the amp. Get it about half way then reconnect the ribbons. I'm a big guy with big hands so while I could do the narrower ribbon with my fingers I ended up using thin pliers for the wider one due to the location and surrounding components. Powered it on with just AC to make sure I wasn't going to blow up my speakers, everything looked good. Hooked everything else back up, tried @Toku 's test track, no more clicking! The power on click is still there but that has never bothered me.

​

I'd say all in all it took me 20 minutes, but I was being very slow and deliberate. The ribbons were the only part that made it even a little difficult. If they had been at the back of the logic board instead of the middle I'd call it a super easy project.

 

[dunkink]

It was as I hoped, just a little difficult but not at all complicated! I started with just the 6 chassis screws rather than every single one like in the first post in the thread. The boards slid right out. I went slowly so I could make sure nothing was ripping out and saw the two slip fit ribbon cables that connect the front panel (display, volume knob) to the logic board. Gently pull them out with your fingers or thin pliers. At first I thought I fucked up not remembering the orientation but the back side is blue so that was fine. Once they're out you can slide out the entirety of the guts. The PSU is on a daughter board. Disconnect the AC block connector from the front, the positive/negative spades on the back, and then the 4 screws that hold the PSU to the daughter board. Swap in the new PSU and redo everything you undid. The PCBs have rails in the case to slot into and since it was just me I put the case down and dropped the amp in. See the problem with this? Gravity took the ribbons all the way back in! Did it again with threading the ribbons and dropping the case down on to the amp. Get it about half way then reconnect the ribbons. I'm a big guy with big hands so while I could do the narrower ribbon with my fingers I ended up using thin pliers for the wider one due to the location and surrounding components. Powered it on with just AC to make sure I wasn't going to blow up my speakers, everything looked good. Hooked everything else back up, tried @Toku 's test track, no more clicking! The power on click is still there but that has never bothered me.

View attachment 150107 View attachment 150108 View attachment 150109
​

I'd say all in all it took me 20 minutes, but I was being very slow and deliberate. The ribbons were the only part that made it even a little difficult. If they had been at the back of the logic board instead of the middle I'd call it a super easy project.

I hope that was an enjoyable experience for you. I am sorry that you have to go through the replacement by yourself on the new unit.

 

[ModDIY]

Hi,


the Sabaj a20 has not been available for Canada, Amazon and aliExpress.


I can order the Sabaj a10, has someone listen to it and test it?

Thanks

 

[Moosi]

So I suppose they swapped the yellow relay with a new dark grey one (on bottom @comparison pic, right near the 3-pin cable plug). I assume one could just get the new relay, unsolder/rip the old one out and replace it with the new dark grey one. I wonder if you could just rip it out totally. I wonder if that would even improve the sound to a minor degree.

the Sabaj a20 has not been available for Canada

Just buy from china with delivery insurance (+ maybe minor taxes) then. May take a few weeks, but still better than no A20a. Between the A10/20a it really depends on how loudly you want to listen and how hard your speakers are to drive. If your speakers are >88db sensitivity and you are in a nearfield or closely listen setup, for example in a desktop situation, you could get away with the a10a. Overall on low to mid volumes, the difference is not big. But the a10a "falls apart" detail- and instrument seperation-wise a lot sooner compared to its brother. However, it really depends on the speakers, since there are vast differences in the current the take.

 

[milan616]

I hope that was an enjoyable experience for you. I am sorry that you have to go through the replacement by yourself on the new unit.

Haha it really wasn't bad! My desktop speakers are Philharmonic AA+ monitors which were kit speakers, and harder still was building all new crossovers for my Pioneer FS52s to Philharmonic specs. This was a cakewalk in comparison! It would have been much, much worse sending in my A20a to Sabaj at my own expense and waiting god knows how long for them to send me it back fixed/replaced. The clicking PSU never affected me in day to day life, but I'm glad I'll never have to worry about it for any use of the A20a.

 

[milan616]

So I suppose they swapped the yellow relay with a new dark grey one (on bottom @comparison pic, right near the 3-pin cable plug). I assume one could just get the new relay, unsolder/rip the old one out and replace it with the new dark grey one.

Good eye! I couldn't see what was different when I was swapping them but I hadn't gone back to the pics yet. And you also got the correct order of old left side, new right side.!

Edit: I'm also curious about that 2 pin header at the top edge. Wonder if it's a fan header that could be used for active cooling, not that this design comes anywhere close to needing it and is a sealed case to boot.

 

[Moosi]

Good eye!

I wonder if you could just rip it out totally. I wonder if that would even improve the sound to a minor degree.

What are you doing with the old PSU? Are you up for the task?

 

[milan616]

What are you doing with the old PSU? Are you up for the task?

Haha! Not doing anything with it, and also while I'm sure I'm up to it I just plain don't want to . I'm pretty sure we'd need to send two samples to Amir to see if there was any difference, and I doubt it would be audible anyway! I don't know if @peterwen wants it back, but if not and if someone wanted to play with it I could send it out.

 

[Moosi]

I'm up to it I just plain don't want to

Alright, hold your horses. Did you at least adjust the voltage up to the max. in order to squeez a bit more out of the two chips? In the descripton it says: "adjustable voltage range: 22.8-25.2v" hence there must be a screwing-knob with cross slits on it, which you should turn to the maximal right, because those chips can easily do 26v being cooled (which they are in the A20a / I believe they can even take up to 27,5v before they die) instead of the default 24v those Mornsun PSUs deliver, so in theory (with a different PSU) there should be about 10% more power (optimal: 26,4v) to get out of the A20a without endangering the chips. Maybe it already is set to 25.2v from the manufacturer tho. Did you check?

 

[milan616]

So I decided to look up the specs of the LOF350-20B24 like you did and compared it to my picture, and it doesn't seem like there is a set screw for adjusting voltage. I'm guessing it's a resistor or something at the ADJ point. If it's somewhere else it's not listed on the data sheet I didn't see it in my pictures but I can go physically look again at some point.

There were some other interesting things in the specs. It only runs 200 watts in air cooling mode, 350 with a fan. I'm not sure if this is set by a fan being connected, or some other method. The PSU starts de-rating by 2.5% per degree C above 50C. So running the amp in a warm cabinet with other components could lose you power. And of particular interest to the modders if you got the Mornsun LOF350-20B27 (edit: $76 at Digi-Key) then you could feed the the Merus chips 27V (and if you figure out the adjustment method go down to 26V to play it safe).

 

[Moosi]

and it doesn't seem like there is a set screw for adjusting voltage.

This one should be the screw for adjusting voltage:

Spoiler

If you plan to open up again and change it, please report on the position it was fixed in before you turned it. Looks as if it's even lower than 24v.

And of particular interest to the modders if you got the Mornsun LOF350-20B27

I'd rather get this one: https://connexelectronic.com/product/smps240rs-sr/
or if it fits in the case (which i doubt) this one: https://connexelectronic.com/product/smps300re/

Someone in the comments claims to drive a SMSL AS300 with this one. So it should be perfectly fitted. Just anxious it won't fit in the case. It's 10x10cm, but the case is also 10cm in width. https://www.audiophonics.fr/en/smps...-dalimentation-decoupage-300w-24v-p-6196.html

 

[milan616]

This one should be the screw for adjusting voltage:

I just went and looked at it physically and came to report that I missed it from the side, but you beat me to the forum post! I hadn't planned on opening it again as I'm not anywhere near running out of space on the volume dial. My loud listening even with a -4dB preamp in Equalizer APO (from some other thread on ASR about the Windows audio mixer) I still don't go past -24. I did check the old PSU for you though and I think you're correct. I got about 3/4 turn clockwise and barely 1/8 turn counterclockwise.

So if anyone needs a little more headroom you'll have to basically follow my instructions for taking the A20a apart to get to the set screw.