This is a great (a few month ago, 220nf max for a 1206 case /50v).
Several new higher cap small C0G's ; thanks Murata...
Since I swapped the Mornsun with a Meanwell RPS-400-24 I am having about double the energy consumption in standby. I always wondered if this PSU does not have any low-energy state switching, but it turns out to be a factor of it being adjusted to max. voltage and running >350ma due to the E30 DAC being plugged to the 5Vout.
Aside from double the standby power there is no "click" when turning on the A20a with the Meanwell. There is a "click" when turning on the A20a with the Mornsun. Therefore I figure the Mornsun is running in switching/burst mode basically all the time up to high currents.
- "I’ll add a few comments on my investigation into the Mean Wells’ performance for those who stumble across this thread but have a different end-use in mind. As Tom indicated, the ‘fix’ for the Mod686 design is to use the output trim pots on the power supplies to increase their Vout to the max, which is right at 40V. While this works for the Mod686, it is a serendipity that may not occur for other applications of this particular supply. Here is a brief summary of what’s going on:[*]- Many switch-mode supplies, when outputting small amounts of power relative to their max rating, work in a ‘burst’ mode, essentially turning themselves on and off to inject small bursts of power into their outputs to keep the output voltage within tolerance. This switching on/off of the supply’s switcher occurs at frequencies in the audio band (varying with load conditions) and somehow gets into the audio amplifier’s output, revealing itself as audible noise. Still to be determined in this particular application is how this happens, but it does not appear to be a simple case of power supply noise getting through the amplifier’s power supply rejection (PSRR).
- - What makes this ‘fix’ work is that, oddly, this Mean Well supply exits it’s low-power burst mode of operation when the output voltage is cranked up to 40V _AND_ the load is drawing more than approximately 350mA.
[*]- Second, the quiescent (no-signal) current consumption of the Mod686 is just a bit more than this minimum current. Thus this fix works just fine for this target amplifier.
[*]- It’s not clear why the Mean Well behaves in this manner. You can adjust the output voltage to a lower value, draw quite a bit more output current/power, but the supply will operate in the noisier burst mode.
- The bottom line is that if you’re using this model of Mean Well power supply in a slightly different application that has less quiescent current consumption, you likely will need to add a bit of resistive loading to the supply’s output to keep the minimum current consumption at least approximately 350 mA.
[*]Different switch-mode supplies likely will work differently – there are a number of different common circuit topologies - and perhaps even different Mean Well models will behave differently. You can’t assume that this fix will work for a different supply without extensive characterization." - Link to thread
Aside from double the standby power there is no "click" when turning on the A20a with the Meanwell. There is a "click" when turning on the A20a with the Mornsun. Therefore I figure the Mornsun is running in switching/burst mode basically all the time up to high currents.
The issues with the relay clicking rapidly has been solved by Sabaj. But with the new Mornsun PSUs there is still a single click at turning it on. This click is switching on the burst mode (low energy mode), which stays active until you hear another click. If the new Mornsun PSUs are drawing less than ~7W from the wall in standby (old one was ~3W), we can be sure they have this mode. Unfortunately I only have the old Mornsun PSU to compare (which has the rapid-clicking issue)
With you @daniboun, I believe you have the old Mornsun PSU (with the rapid clicking issue) because you bought the A20a before me and I had it. The reason you might not be hearing it is a)your speakers are very high sensitivity, or b)you never play bass heavy tracks louder than -28db, or c) there is physical distance between you and the amp >0,5m. It's a mechanical clicking from within the case. Like a switch being triggered. You only hear it with really heavy and deep bass and if you are not close to the amp the overall volume is probably overlaying the clicking to an extent where it's no longer audible. If I remember the pictures of your room&setup correctly, this might be the case for you. However, I strongly assume both the old and updated Mornsun PSUs are running in burst mode. This might induce noise into the audio spectrum due to the users post quoted above.
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Interesting - I never noticed any clicking sound but perhaps it was just not loud enough to catch my attention. By now I have installed the Meanwell PSU set at 25V (just in case....) - sound is mighty fine (very clear and authoritative). I am using the amp on my horn speakers now (more than 110db sensitivity) and it remains very quiet indeed - yes, from about -10dB there is a small amount of faint "noise" if I am directly in front of the speakers - but from the listening position it remains inaudible and I couldn't possibly play music at his volume anyway. The caps I had ordered somehow seem to have got lost in the mail - hence this mod is going to follow later - and yes, I still love this amp and do not feel any need to replace it with something else (which I take as a good sign indeed).
Just to be clear, you have installed a Meanwell RPS-400-24 into the A20a, running at 25V?
If this is the case, you should check how much it actually draws from the wall plug in on/standby. If it pulls less than 6-7W the Meanwell is running in burst mode too. If the user quoted above is correct, the Meanwells only exit this mode (drawing about double standby watts) when being adjusted to max. voltage which is 26.13V according to the report.
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Yes, I am now using the Menawell RPS-400-24 running it at 25V and it sounds very good indeed. Perhaps it is running in burst mode - so how would I check how much it actually draws? Plus if the 25V are correct for the input caps I am slightly reluctant to go up to the voltage figure you have mentioned.....
Just received my A20a & unfortunately it looks like it's going straight back 
There is a constant high-pitch whine around 6.68KHz. It is already loud enough at -60dB that I can clearly hear it from my normal listening position. It makes no difference whether I use XLR (impedance balanced source), RCA, or even disconnect both inputs entirely. The whine gets noticeably worse when I activate EQ, which I need to use for my speakers.
I have tried different power cables, different power sockets, moving the amp & cables completely away from any other electronics, nothing makes any difference.
This is the second amp I have bought this week that is immediately being returned, I am starting to think that I am cursed ;_;
There is a constant high-pitch whine around 6.68KHz. It is already loud enough at -60dB that I can clearly hear it from my normal listening position. It makes no difference whether I use XLR (impedance balanced source), RCA, or even disconnect both inputs entirely. The whine gets noticeably worse when I activate EQ, which I need to use for my speakers.
I have tried different power cables, different power sockets, moving the amp & cables completely away from any other electronics, nothing makes any difference.
This is the second amp I have bought this week that is immediately being returned, I am starting to think that I am cursed ;_;
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Yes, you might be for 6.68KHz might actually be 6.66Khz due to little measurement abbreviations and you know what those numbers stand for do you?
No, seriously. I suppose it is a defective PSU or the speaker cables have not been soldered correctly inside the amp. There is one thing you could do. That is opening it up and setting the V-adst. knob to max voltage and see if that changes the tone. But I'd probably return it too in your case and get a new one. If the new one (third amp) has the same noise you can at least be sure you have a problem with some device of yours radiating lots(!) of noise. Trying different ferrits might help. I'd start with N30 ferrite in your case for they go low down to 10khz or something, but there might be others going even lower.
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You can measure what the amp pulls from the wall with a device like this: Digital LCD Energy Meter Wattmeter Uberwachung Gerat Leistung Strom Kwh Power Mess Analyzer|Energy Meters| - AliExpress. They come for all different country plug versions and are really cheap, about 10-15bucks. Where I live, basically every hardware store has them lying around. I'd strongly advice to own such a device anyway to see what your typical power hungry devices pull (off your energy bill).
@25V caps
I'm not sure if this is a problem for those numbers on caps are not max. ratings. What destroys the caps eventually is heat+THD(Ripple). There is supposedly less THD coming from the Meanwell mains and unless you play it really loud for hours there is not much heat to be expected inside the case. Anything below 40°celsius ambient is not decreasing the lifetime of a cap at all. Overvoltage to 26V might be a ~4% decrease of lifetime. Besides, those big caps should be fairly easy to solder, even for someone with little experience. I'm actually thinking myself to replace those sooner or later, but I am waiting for the user Overeems report on his advances in changing the caps. For an amp with this little voltage, you might notice about every single volt, besides the problems that might or might not appear with burst mode.
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I'm sure there is a shop that will sell me cables blessed by priests to combat this
But yes, my assumption is a power supply issue. None of my other amps (LM3886, TPA3116) have the same problem when connected to the same source, speakers, power, etc.
I am communicating with Sabaj now for a replacement. I hope it is just the power supply, because this amp sounds really nice... until the music stops & the devil's whine can be heard!
Thanks for the feedback - so I might open up the amp again - hopefully without disconneting those bl...y cables ribbon cables again....
.Thanks for the feedback - so I might open up the amp again - hopefully without disconneting those bl...y cables ribbon cables again....
I would get such a wall socket wattage meter first, but If you open it up, the trick is to never let them ribbons slip out of the front panel sockets. Pull the back panel with the boards out just to where the two aluminum heatsinks are about to slip out and then use a tweezer (Anti statische Prazision Pinzette Set Pinzas Pincet Edelstahl ESD Pinzette Elektronik Reparatur Werkzeuge|Industrial Tweezers| - AliExpress) to pull the ribbon cables from the boards first before you pull the entire back out. Plugging them back in on the board is far less of a hassle than getting them back into the front panel sockets. The tweezer helps a lot. And I would wait for a minimum of 2 hours with the amp off and unplugged for the caps to decharge, before I open it.
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I have just put the last puzzle piece to this amp. My journey has come to an end now. It's as close to perfection as it gets.
An N30 Ferrite ring from Epcos/TDK (B64290L40X830) has been installed to the AC cable from outside. Huge improvement! Not only to white noise, but from to my subjective ears even to the blackness of the sound. From this last expriment I am certain that there is HF noise leaking from the AC mains to the speakers-out-panel. You might not notice it right away. Putting the lighting match box inlay to the spkout-panel has improved it a bit, but the ferrite ring is far better at it. Thanks to daniboun for recommending ferrite. However, I did not want to put any inside the case to the speaker cables, for some people claim it to "choke the sound". Putting it to the AC cable is a "safer" solution.
Noise reduction roadmap (all RCA, all ear to speaker):
default amp: from -26db
I highly recommend to get such a ferrite ring, for they cost only a few bucks and are probably having the most effect on cleaning the amp up. It's crazy detailed now. I could hear a hamster coughing on most tracks.
An N30 Ferrite ring from Epcos/TDK (B64290L40X830) has been installed to the AC cable from outside. Huge improvement! Not only to white noise, but from to my subjective ears even to the blackness of the sound. From this last expriment I am certain that there is HF noise leaking from the AC mains to the speakers-out-panel. You might not notice it right away. Putting the lighting match box inlay to the spkout-panel has improved it a bit, but the ferrite ring is far better at it. Thanks to daniboun for recommending ferrite. However, I did not want to put any inside the case to the speaker cables, for some people claim it to "choke the sound". Putting it to the AC cable is a "safer" solution.
Noise reduction roadmap (all RCA, all ear to speaker):
default amp: from -26db
- insulating SPcables(inside) +lighting match box cover to SPout-panel : from -21db
- replacing Mornsun with Meanwell RPS-400-24 PSU: from -17db
- galvanic mains isolation for DAC: from -12db
- N30 ferrite ring to AC power cable: from -02db
I highly recommend to get such a ferrite ring, for they cost only a few bucks and are probably having the most effect on cleaning the amp up. It's crazy detailed now. I could hear a hamster coughing on most tracks.
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I am using Ferrites in many of my projects.
This is well explained in the"CookBooK" from NewClassD. Ferrite help a lot to reduce RFI / EMI.
Will share some pictures of my tips )
In my SABAJ A20A, I put Ferrites in the Signal speaker path and also internally between the DC connector PSU > Module. The amplifier is almost dead silence even @ max volume.
I also made a AC bloc plug with this Audio Grade filter :
Another great AC filter is the Fo-Felix AC :
GB: Round #7; Fo-Felix AC Filter
This is well explained in the"CookBooK" from NewClassD. Ferrite help a lot to reduce RFI / EMI.
Will share some pictures of my tips )
In my SABAJ A20A, I put Ferrites in the Signal speaker path and also internally between the DC connector PSU > Module. The amplifier is almost dead silence even @ max volume.
I also made a AC bloc plug with this Audio Grade filter :
Another great AC filter is the Fo-Felix AC :
GB: Round #7; Fo-Felix AC Filter
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Ok if I can check the photo of a previous post, the entire cable goes through the ferrite. I don't think I have a ferrite of this size. I'll have to order one for myself.
I am currently using the XLR input directly from the DAC. There is no whistling even with the ear close to the tweeter.
But I will test some modifications and improvements but I will not change the Morson SMPS, the sound is excellent.
I am currently using the XLR input directly from the DAC. There is no whistling even with the ear close to the tweeter.
But I will test some modifications and improvements but I will not change the Morson SMPS, the sound is excellent.