-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Dual Merus MA12070 Amplifier Sabaj A20 fully balanced : pictures inside )
- Thread starter daniboun
- Start date
Thank you Toku. I believe the main source of noise is bleeding in from the AC cables tho, for the alterations I made pointed to that.
My very first step with this amp was wrapping the speaker-cables and the DC-24V-cables into a layer of copper foil each wrapped around multiple times and then coated with shrink rubber sleeve. Because of copper being conductive, I was really careful here to not expose any of it to any live/hot wires closer in proximity than ~1cm to avoid arcing. In addition I took the inlay of a lighting match box and because it fits perfectly, I put it as a cover to the SP-out-panel to shield this panel (where the sp-outs are soldered into openly) at least a little from the noise of the ACins of the PSU being very close.
Result: small improvement (noise starting from old: 57% / new: 70%)
After that swapped the Mornsun with the Meanwell RPS-400-24@26V. Even smaller improvement to the noise (it did improve the sound to my subjective* ears, giving it cleaner dynamics and more punch&spark). Only the last step with the ferrite ring to the AC cable before it gets into the amp really made it close to being free from any white noise (97%). Therefore I conclude there is a problem with that SPK-panel being unshielded and too close. There is one thing you must consider though. I live in Europe. We have 230V AC coming from the wall, not just 120V. I believe more voltage also creates more noise. Maybe it's both the op-amps and volume controller being too close to the SPK-cables and the SPK-panel being too close to the AC wires with 230V-countries having a more severe problem with the AC ins.
Lastly, there might be a problem with the Mornsun PSUs running in low energy mode (burst mode) consuming only about 3W in on/standby. Those big multiple hundred watts PSUs maintain a stable voltage at such low levels only by giving out short bursts of voltage of which might induce problematic noise into the audio band which can even somehow bypass the Merus chips PSRR reduction. There is a post about this issue from another user in DIY audio forum:
However, I am thrilled that this little amp can be modded to be nearly free of any noise and it sounds tremendously good after those modfications. I'm overblown with subtle detail on my tracks. If I watch sports on youtube, every time they blend in the little info bars they make this "swooosh" sound which feels like a slap in the face from a ghost every time with this amp. Dynamics are as clean and powerful as I could imagine. It's more clean, controlled and detailed than my soundmagic E80 ear phones on the FiiO X3 DAC with the Wolfson WM1870 chip of which I used to play when I really wanted to listen into certain tracks. Both not high end, but quite decent.
*there is a brain connected at the output. Results of sound being better or worse may be depended on expectation, even though I tend to keep them as low as possible. White noise from speakers is measured by ears directly to speakers in a quite room (closed windows) with RCA input from the DAC running from galvanically isolated mains on a 12-5V converter module.
My very first step with this amp was wrapping the speaker-cables and the DC-24V-cables into a layer of copper foil each wrapped around multiple times and then coated with shrink rubber sleeve. Because of copper being conductive, I was really careful here to not expose any of it to any live/hot wires closer in proximity than ~1cm to avoid arcing. In addition I took the inlay of a lighting match box and because it fits perfectly, I put it as a cover to the SP-out-panel to shield this panel (where the sp-outs are soldered into openly) at least a little from the noise of the ACins of the PSU being very close.
Result: small improvement (noise starting from old: 57% / new: 70%)
After that swapped the Mornsun with the Meanwell RPS-400-24@26V. Even smaller improvement to the noise (it did improve the sound to my subjective* ears, giving it cleaner dynamics and more punch&spark). Only the last step with the ferrite ring to the AC cable before it gets into the amp really made it close to being free from any white noise (97%). Therefore I conclude there is a problem with that SPK-panel being unshielded and too close. There is one thing you must consider though. I live in Europe. We have 230V AC coming from the wall, not just 120V. I believe more voltage also creates more noise. Maybe it's both the op-amps and volume controller being too close to the SPK-cables and the SPK-panel being too close to the AC wires with 230V-countries having a more severe problem with the AC ins.
Lastly, there might be a problem with the Mornsun PSUs running in low energy mode (burst mode) consuming only about 3W in on/standby. Those big multiple hundred watts PSUs maintain a stable voltage at such low levels only by giving out short bursts of voltage of which might induce problematic noise into the audio band which can even somehow bypass the Merus chips PSRR reduction. There is a post about this issue from another user in DIY audio forum:
- "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 source
However, I am thrilled that this little amp can be modded to be nearly free of any noise and it sounds tremendously good after those modfications. I'm overblown with subtle detail on my tracks. If I watch sports on youtube, every time they blend in the little info bars they make this "swooosh" sound which feels like a slap in the face from a ghost every time with this amp. Dynamics are as clean and powerful as I could imagine. It's more clean, controlled and detailed than my soundmagic E80 ear phones on the FiiO X3 DAC with the Wolfson WM1870 chip of which I used to play when I really wanted to listen into certain tracks. Both not high end, but quite decent.
*there is a brain connected at the output. Results of sound being better or worse may be depended on expectation, even though I tend to keep them as low as possible. White noise from speakers is measured by ears directly to speakers in a quite room (closed windows) with RCA input from the DAC running from galvanically isolated mains on a 12-5V converter module.
Last edited:
Yes, Sabaj changed the operating mode of the power supply immediately after receiving a report from me. And they sent me an improved new A20a to check the operation.
There are many different sizes of ferrite cores. Please prepare some and actually clamp them to choose the most suitable size.
The greater the number of ferrite cores, the greater the effect. The speaker wiring is clamped together for four, but it may be clamped separately for the left and right channels. The clamp position is most effective near the connector on the front panel side.
@Moosi
Thank you very much for your detailed noise suppression report.
This kind of noise countermeasures is made while making predictions based on some experience, but the actual effect cannot be understood until it is tried. The experimental element is strong.
I don't think there's a big difference between me and your thoughts on the point of noise mixing, but you can't tell if the noise is from the power line or the amplifier output until you actually try it.
I would like to explore the cause again from various directions from the detailed report from you.
Thank you very much for your detailed noise suppression report.
This kind of noise countermeasures is made while making predictions based on some experience, but the actual effect cannot be understood until it is tried. The experimental element is strong.
I don't think there's a big difference between me and your thoughts on the point of noise mixing, but you can't tell if the noise is from the power line or the amplifier output until you actually try it.
I would like to explore the cause again from various directions from the detailed report from you.
jokan
Addicted to Fun and Learning
Instead of copper foil, please use something similar to Oyaide Electric *MWA-010T*.
There are online retailers that ship the tape internationally. They also have the same material in sheet form in varying thicknesses.
It is also extremely effective and helps to bring out a cleaner and possibly "purer" sound from your loudspeakers when applied in strips by the inputs of your speakers binding posts.
The tape is also coated with a dielectric so is non-conductive. Just before posting this, I did use a multimeter to check for continuity. I've used it in various amplifiers including several tube amplifiers to great effect. I will stress one thing which is that it can absorb sometimes too much extraneous noise and make things sound a bit flat. Of course this is a subjective impression. The material itself is a patented "Sendust"
en.wikipedia.org
The tape, and sheet is both non-conductive due to its coating which is possibly clear rubber?
Copper doesn't absorb EMI/RFI, it reflects it or scatters it. This material absorbs. The amount of magnetic flux around so many electronic components such as amplifier internals, power supplies, speaker binding posts and crossover parts is shockingly huge, most of them negative. I've been using it as a simple fix part for many years with great success.
Do a google search for the part, and find an online retailer, there are a few. If you're in Japan it is readily available. The stuff works. The wiki page will tell you what it's made of and why it works. There are other companies that are very small scale that sell similar sendust materials but I've not found one that sells it as a 0.1mm thick, 10mm wide tape.
@Toku, perhaps you have used this tape or material yourself?
There are online retailers that ship the tape internationally. They also have the same material in sheet form in varying thicknesses.
It is also extremely effective and helps to bring out a cleaner and possibly "purer" sound from your loudspeakers when applied in strips by the inputs of your speakers binding posts.
The tape is also coated with a dielectric so is non-conductive. Just before posting this, I did use a multimeter to check for continuity. I've used it in various amplifiers including several tube amplifiers to great effect. I will stress one thing which is that it can absorb sometimes too much extraneous noise and make things sound a bit flat. Of course this is a subjective impression. The material itself is a patented "Sendust"
Sendust - Wikipedia
The tape, and sheet is both non-conductive due to its coating which is possibly clear rubber?
Copper doesn't absorb EMI/RFI, it reflects it or scatters it. This material absorbs. The amount of magnetic flux around so many electronic components such as amplifier internals, power supplies, speaker binding posts and crossover parts is shockingly huge, most of them negative. I've been using it as a simple fix part for many years with great success.
Do a google search for the part, and find an online retailer, there are a few. If you're in Japan it is readily available. The stuff works. The wiki page will tell you what it's made of and why it works. There are other companies that are very small scale that sell similar sendust materials but I've not found one that sells it as a 0.1mm thick, 10mm wide tape.
@Toku, perhaps you have used this tape or material yourself?
I have never used this Oyaide product for audio equipment. I have used a product similar to the EMI failure of industrial instruments in a factory before.Instead of copper foil, please use something similar to Oyaide Electric *MWA-010T*.
There are online retailers that ship the tape internationally. They also have the same material in sheet form in varying thicknesses.
It is also extremely effective and helps to bring out a cleaner and possibly "purer" sound from your loudspeakers when applied in strips by the inputs of your speakers binding posts.
The tape is also coated with a dielectric so is non-conductive. Just before posting this, I did use a multimeter to check for continuity. I've used it in various amplifiers including several tube amplifiers to great effect. I will stress one thing which is that it can absorb sometimes too much extraneous noise and make things sound a bit flat. Of course this is a subjective impression. The material itself is a patented "Sendust"
Sendust - Wikipedia
The tape, and sheet is both non-conductive due to its coating which is possibly clear rubber?
Copper doesn't absorb EMI/RFI, it reflects it or scatters it. This material absorbs. The amount of magnetic flux around so many electronic components such as amplifier internals, power supplies, speaker binding posts and crossover parts is shockingly huge, most of them negative. I've been using it as a simple fix part for many years with great success.
Do a google search for the part, and find an online retailer, there are a few. If you're in Japan it is readily available. The stuff works. The wiki page will tell you what it's made of and why it works. There are other companies that are very small scale that sell similar sendust materials but I've not found one that sells it as a 0.1mm thick, 10mm wide tape.
@Toku, perhaps you have used this tape or material yourself?
The effect is on a case-by-case basis and there is no choice but to try it.
jokan
Addicted to Fun and Learning
The tape @Toku is extremely effective, sometimes too effective. And you are completely correct, it is a trial and error type of tape, fortunately it is easy to remove and removes with no sticky glue residue. It works extremely well around binding posts. I thought it was a snake oil article in the Japanese "Stereo" magazine but it was not the case. I had already used it in the past for a few tube amplifiers but never thought to try it by the speaker terminals. I was shocked that a very short strip above and below the speaker terminals on the speakers themselves made a huge impact that I could immediately hear. "Better"? I'm not sure that it's better, but I do prefer with tape than without the tape. I only used a 65mm length above and below the speaker terminals, so 65mm x 4. I used it on my DA-9 when I had one as the display driver itself was audible. The noisy display wouldn't change by increased brightness, or if it was on any source, or with the amp turned all the way down. I applied a short strip around the driver and the noise was immediately gone. Probably a 8-10khz whine. Of course turning the volume up would make the noise disappear into the background, but it was still there. The tape, a short length of tape made the whine, high-pitched noise go away. The AO200 of course doesn't have that problem at all from day one. The PSU location is different. They had placed the PSU and the LCD driver within a few millimeters of the back wall of the amplifier. A poor internal layout.
EMI/RFI noise is an increasing problem with all of the switching power supplies we use in our everyday lives that all switch with varying frequencies and different levels of shielding. I can count at least 10 in my room and unfortunately I need every single one of them. LCD screen, Computer, hard drives etc. They all use one. I think one day they might get smart and make a standard for switching frequency and EMI/RFI emissions that is regulated with a global standard. Switching Power supplies are convenient but full of compromise. High powered graphics cards are especially bad about emissions.
EMI/RFI noise is an increasing problem with all of the switching power supplies we use in our everyday lives that all switch with varying frequencies and different levels of shielding. I can count at least 10 in my room and unfortunately I need every single one of them. LCD screen, Computer, hard drives etc. They all use one. I think one day they might get smart and make a standard for switching frequency and EMI/RFI emissions that is regulated with a global standard. Switching Power supplies are convenient but full of compromise. High powered graphics cards are especially bad about emissions.
Thank you for the advanced foil you were pointing too. I don't believe I'll find the motivation to open it up again for it's close enough to perfect to my ears now with the copper foil. But isn't the PC case made of aluminum and does "cage in" EMI from graphics cards to some extent for it reflects off the surface bouncing around inside the case instead of passing through?
No, I'm afraid that is a different thing. They've just changed the operation mode of the swichting relay from being load dependend to being time dependend. There is still a single click when you turn on the A20a with the updated Mornsun, isn't there? That single click means it's switching to burst mode which will stay active until you hear another click (with the new ones, probably never). With the Meanwell there is no click at all. The only way to find out which mode the new Mornsuns is running at would be to measure how much they actually pull in watts from the wall (with a device like that: Link ).
If new A20a pulls notably less than ~6W in on/standby, we can be sure it's running in burst mode. Do you have the ability to measure wattage from the wall plug on your updated A20a?
Besides: Internal switching frequency of the Meanwell RPS series is @90-100khz. There are some PSUs reaching down to much lower khz areas. Unfortunately we do not have that data from the factsheets from Mornsun.
Last edited:
Then it must get quite warm?
jokan
Addicted to Fun and Learning
@dr0ss as a very generalised rule, EMI/RFI will find any possible weakness to get out and escape. I don't believe there is a single ultra powerful graphics card that is completely shielded, as you mentioned heat would be the primary factor. If there's a fan, that's a huge hole for directed exhaust of EMI/RFI. I believe and I may very well be incorrect, but copper is either the best in thermal conductivity or is very nearly the best. But when we're talking about trying to eliminate noise, it's not necessarily the best in and of itself. The tape material is convenient because Sendust is just that, a powder. It can be made into a paint, or made into a sticker. It's been around since I believe the 30's? and it is from Sendai Japan, hence Sendust. The issue with graphics cards in PC's is that they don't fall under the same regulatory emissions as audio equipment. And of course switching PSU's can switch at 50khz like on the Mornson, or 500khz on some ultra high end *expensive* hi-fi gear. The best is to get away from switching PSU's altogether but it costs a lot more and is definitely much larger and much heavier. In audio gear, all companies do a cost/performance analysis. The Audio Engineer will always want the best and most expensive parts. The EE will look for efficiency in both thermal and electrical efficiency, the person who controls the finances will have the ultimate say. It's always a matter of budget. Open up mostly all of the $500/pr ~ $1500/pr speakers and you will very likely find electrolytic capacitor for the woofers crossover section. Why use electrolytic capacitors for woofers? 2 reasons, both are probably equally important. First is cost, the other is internal air volume or cabinet volume. Film capacitors that are over 10uf and rated for 400v and higher get bulky and large. So it's always going to be a balancing act. Also they want the lower priced speakers to sound great for a year or so and then be replaced. Planned obsolescence is very commonplace with audio equipment.
jokan
Addicted to Fun and Learning
Sendust - Wikipedia
It doesn't get particularly warm. We are talking about wavelengths here!
follow the link that explains magnetic permeability:
Permeability (electromagnetism) - Wikipedia
These somewhat occult things in the audio world are where tiny gains are found and add up to a well executed, good sounding device regardless of how they measure using SINAD which doesn't tell us how something sounds to our ears.
SINAD - Wikipedia
As ASR loves to use measurements *I'm not against measurements, I don't consider it to be the only valid measurement*. Ultimately our ears will tell us when something sounds right and wrong. If we need our ears to tell us something sound terrible the device in question must be incredibly poorly designed or executed.
Human ears are actually very fine measurement devices with most people, except the very old. The Problem ist the brain. If we could somehow decouple them from it and connect the ears to an audio precision, there would be a lot of notes to take from that. I've already seen people starting with ferrite beads clipped to their ear laps and big ferrite rings pinched right through the ears. While these people are on the frontier of audio science, I wonder if they might be lowpass filtering some of the brains switching frequency for we might not know all of them yet.
Eggs Ackley
Active Member
- Joined
- Sep 20, 2021
- Messages
- 152
- Likes
- 267
I just got some messages about A20a and A10a that I purchased from Amazon seller HiFi Booster Store. Message said to connect a "power adapter" between the unit and power cable. The message was not very clear. I assume they are sending some sort of ferrite device. I'm waiting for their response.
HorizonsEdge
Active Member
- Joined
- Dec 20, 2019
- Messages
- 224
- Likes
- 319
Looks like they just sent everyone this cryptic notice. I await their explanation.
HorizonsEdge
Active Member
- Joined
- Dec 20, 2019
- Messages
- 224
- Likes
- 319
This was the response to my inquiry as to why they contacted me with their nebulous message. Can anyone decrypt?
Eggs Ackley
Active Member
- Joined
- Sep 20, 2021
- Messages
- 152
- Likes
- 267
Me: There is no "power adapter" just a power cable. I'm not sure what your message means. Thank you.
Response: Gald to see you. It has the same meaning, the power cord is connected to the product first, and then to the socket.
Well I think better tip would be to switch the unit off before doing anything with the power cord.
Response: Gald to see you. It has the same meaning, the power cord is connected to the product first, and then to the socket.
Well I think better tip would be to switch the unit off before doing anything with the power cord.
Last edited:
I am confused by the fact that I often receive such incomprehensible replies from China to my inquiries.
Is such a response a Chinese cultural thing?
jokan
Addicted to Fun and Learning
I think that the use of google translate doesn't help with automated emails when dealing with Chinese companies in general. I think a lot must be lost in translation. They would do better to NOT send emails that amount to nonsense than to send emails that native english speakers/readers can't understand. If you're going to say something it had better make sense and not create unnecessary confusion.
Similar threads
