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

gasolin75

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This one should be the screw for adjusting voltage:
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.

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

And it will effect warranty
 

gasolin75

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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

 

gasolin75

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I received the A20a a couple of days ago to replace a DA-9 with some wild DC offsets. I have both right now and have been switching them back and forth. The A20a sounds a bit muddier versus the DA-9 that I've been using over the last two weeks. Maybe it just needs 2 weeks of burn-in, but I didn't notice that with the DA-9 when I first got it.

The DA-9 over optical is completely silent at its highest volume. The A20a definitely has a high pitched whine starting at about -8 and very loud at 0. Power supply noise? Is this normal or a bad unit?

I will keep playing the A20a for a week and see if it opens up, but so far I'm not blown away...

HOLY CRAP, my audio switcher is noisy, volume at 75% on the audio switcher, some noise at -0 db on the amp (no sound of course) volume at max there is noticeable hum. 0.30m wbc gotham from my topping E30 and from the audio switcher to the amp cordial 0.6m cfu cc, even at -0db on the amp, the mute enhances the hum

71xoGHfic0L._AC_SL1500_[1].jpg
 

Moosi

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And it will effect warranty
Well, you could set the screw back to default position before you send it in for repair. ;) They might pull a statistic from the chip interface seeing it was run at higher voltage, but even with the screw maxed out, you'd still be within the recommended voltage range of the chips, which is 4-26V. It would be hard for them to deny your warranty on the basis of having used recommended specs.

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.
Of course, you could just check the old one. No need to open up again for that, stupid of me. Thank you. So that means the PSU is running at ~23,3V (-/+2%).
I don't like about 3 volts missing. That's about 12% less power than recommended by Infineon and about 17% less than it could actually do before chip failure. With the headroom you'd have to consider that there is white noise emerging from the speakers starting about -21db upwards. Having 12% more power will probably shift this up to -17db or something (or might even worsen it). It will also give you a little more stability distortion-wise, raising the level at which the amp will start to distort. I believe depending on the track distortion (>0.1%THD) might start around -28db. The 12% might raise this to about -24db or something. Hence if you have hard to drive speakers, as I do, you might benefit from a little more headroom. If your speakers aren't that low of sensitivity and you do not play loudly either, there is no need to hassle. Even with "only" 23-24v this amp has a lot of (clean) power.
 
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milan616

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Mine are quite low in terms of sensitivity, but they're desktop speakers for me so I don't go up too far. Desk is on one end of my large-ish apartment living room and if I start needing more volume (or deep bass) I've always got my home theater stuff 20 feet behind me! Cranking the set screw clockwise will be more likely if the housing market decides to cool down lol o_O
 

Moosi

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Mine are quite low in terms of sensitivity, but they're desktop speakers for me so I don't go up too far.
Those look (maybe not actually look, but sound) great, especially the frequency response. They appear to be more or less "Dynaudio Evoke 20" for about 15% of their MRSP actually. Great find! They're basically the same sensitivity as my KEF LS50 Meta (~83db).
----
I still don't know if there is a "burn-in" of the SabajA20a, but I found that there seems to be a "turn-in" with the volume knob. Maybe I just got used to it and it's still flimsy somehow, but the actual turns feels more solid now after about 2month of daily use. I kind of like it now.
 

gasolin75

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There is a burn in time according to this thread
 

milan616

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Those look (maybe not actually look, but sound) great, especially the frequency response.

Haha oh yeah are definitely not pretty. I've thought about getting them vinyl wrapped something nicer, however that would mean not having them for a few days! My (reasonably priced) end game speaker is probably Dennis' BMR speaker, and those come in some gorgeous finishes, but the ugly little brother will do for now.
 

gasolin75

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xlr vs rca in ??

Im no using xlr male to rca adapter
 

Toku

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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.
Thank you for the inside photo of A20a.

The A20a has a slightly higher noise than other products when the volume is maximized, and the noise sounds like switching noise rather than general white noise (also called hiss noise). In the case of a class D amplifier, noise does not increase in conjunction with the volume position, but in the case of A20a, noise increases in conjunction with the volume from a position of about -10. This indicates that noise is mixed in the circuit before the volume.
Looking at the photo of the internal structure, the power supply unit is located just above the input circuit and the distance is very close. Probably this is the cause of the input circuit picking up the switching noise of the power supply unit.
 

gasolin75

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I don't notice any noise and i won't for shure try to play music at -10db
 

Toku

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I don't notice any noise and i won't for shure try to play music at -10db
I think that the usage you say is common, but when using the A20a as a power amplifier, raise the volume to -00 and use it.
 

milan616

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I think that the usage you say is common, but when using the A20a as a power amplifier, raise the volume to -00 and use it.

I wonder if someone would want to try changing the set screw on the PSU up and down to measure the noise output. Could be worthwhile for those in power amp use cases.
 

6th0

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To summarize my epic journey...

I now have an AO200 to compare it to. The AO200 also picks up USB noise, so I am using optical. However, unlike the A20a, there is no noise at max volume with or without components plugged into it.

At some point I may try USB again, but with some sort of isolator. However, I'm assured that I really won't hear any difference so it might just be throwing money down the drain.

To me, the biggest mystery is why the 3E amp never picked up any interference over USB but all other amps do.

So my journey is at an end. I put on an ifi iDefender with external power and the buzz is gone! Of course, my already ratty cable management now looks way worse....

Now that I have this configuration dialed in, I need a new excuse for gear. I'm kind of bummed that I didn't have an excuse to go balanced XLR. I was contemplating a D30pro with optical and USB, using it as a pre-amp, RCA to the L30 and TRS/XLR to the AO200 to break the ground loop. But it was $350-$400 versus $90 for an iDefender/iSilencer combo and that money could be better spent elsewhere!
 

ModDIY

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Hi, I just ordered mine.

I hope to have the new one with the SMPS corrected.
 

6th0

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Thank you for the inside photo of A20a.

The A20a has a slightly higher noise than other products when the volume is maximized, and the noise sounds like switching noise rather than general white noise (also called hiss noise). In the case of a class D amplifier, noise does not increase in conjunction with the volume position, but in the case of A20a, noise increases in conjunction with the volume from a position of about -10. This indicates that noise is mixed in the circuit before the volume.
Sabaj for their part reached out to me via Amazon to help out. They were very responsive during the email string, which was impressive. They had me record a video of the cabling and sound coming out of the speakers. After review, they told me that the whine was normal without an audio source and was sound from the speaker. Since there was no sound output there was nothing to consume the current.

The AO200 had no such issue so sadly the A20a is going back.
 

Moosi

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they told me that the whine was normal without an audio source and was sound from the speaker
by "whine" you mean a high frequency pitch/tone emerging from the inside of the case or from the speakers? Is that a constant whine or is it like "singing" in short bursts? The speakers can't whine on themselfes, they're passive. If there is a current making "whining" it is being put into the speakers by the amp. However, if there is no sound playing, there should not be any current sent to -or drawn from the speakers.

I believe the only thing that can possibly whine is the PSU itself, because this "whining" is actually "ringing" from the transformer or some vibrating capacitors on the PCB which have not been "glued" properly to prevent this kind of ringing. It is quite common for those stock supplies to have whining/ringing more or less. Even the medical Meanwell PSUs are kind of known for that, so there is always a certain chance to get a whining PSU, regardless of what device you put it into.

edit:
If I put my ear to my A20a, I can definately hear some electrical noise coming from inside the case. There is no whine whatsoever, but I can tell that there is some flow of current going through it, it's a slightly and subtly crackling/buzzing only that it's probably not current I'm hearing, but EMI. I am pretty sure the noise I can pick from within the case is the very same noise I am finally hearing from the speakers amplified as soon as I turn it louder than -21db. You'd have to consider one thing. The case is very small. The space between the PSU and the electronics on the amp-PCB is not big, that goes for wires too. It is actually a lot less distance from one to another than the AO200 or DA-9 PSU have to the circuits. However, you can mitigate this by having a very good/shielded PSU, this is why they choose a medical PSU in the first place. But nonetheless, It is sandwiched right on top of the circuit. I would'nt go as far as calling it a faulty design, but it is definately far from optimal. Usually you would want the power stage as far away from the analog stage as possible. This is one of the main reasons why those broad, flatlined cases kind of set the standart for amplifiers.

edit edit: There is a solution tho. On most PSU's the whining/ringing stops when you set it to max. adjusted voltage (the screw-knob on it), which would be 25.2V with those Mornsun PSUs. (Which should be okay to do with the A20a as we have elaborated on the pages before.) That goes only for a possible high pitched whining/ringing and does not solve the fundamental slight "power-buzzing" from within the case.
 
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ModDIY

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@peterwen

I ordered an A20a yesterday on hifi-express United Kingdom, is this the new version of the SMPS?
 

6th0

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by "whine" you mean a high frequency pitch/tone emerging from the inside of the case or from the speakers? Is that a constant whine or is it like "singing" in short bursts? The speakers can't whine on themselfes, they're passive. If there is a current making "whining" it is being put into the speakers by the amp. However, if there is no sound playing, there should not be any current sent to -or drawn from the speakers.

It was a whine from the speakers when the amp was plugged in. The same does not happen with my AO200. I'm convinced it is a power supply issue.
 

ModDIY

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@peterwen

I ordered an A20a yesterday on hifi-express United Kingdom, is this the new version of the SMPS?

Hi, the SMSL / Sabaj representative just wrote to me that my amp is shipped from China rather than United Kingdom (I live in Canada), and that this is the new version of SMSP .

I really liked the quick response.

As soon as I receive it, I get back to you with my impressions. The Sabaj A20a will be compared with several amps that I have (class AB and class D)
 
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