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Help with odd problem: SMSL AO200 emits hissing sound only when connected to a tweeter

Toku

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I don't remember any other Merus amp measured by Amir except the Loxjie A30 which has those 4 SMD chokes on the back of the board, and of course its measurements were better than A100.
Edited: I clearly forgot about the dual Merus Topping PA3s which measured very well. I would bet it also has these 4 chokes somewhere. I have not seen the back of the board pictures.
The Loxjie A30 does not have such an SMD inductor (choke) installed. The amplifier part has the same design as the SMSL SA300, and there is no output filter inductor. The same is true for PA3s.
The following MA12070 chip amplifier products sold on Aliexpress, It has a built-in output inductor.

 

dr_mick51

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The Loxjie A30 does not have such an SMD inductor (choke) installed. The amplifier part has the same design as the SMSL SA300, and there is no output filter inductor. The same is true for PA3s.
The following MA12070 chip amplifier products sold on Aliexpress, It has a built-in output inductor.

Dude, are you sure?.Do you have proof that the Loxjie A30 does not have output chokes/inductors?

As you know the SMD inductors are very small. The Loxjie A30 does have 4 little inductors on the back of the board, 2 on each side of the Merus MA12070 chip. Those little black dots you see on the pictures.

The SMSL indeed does not have those little chokes as you said. I've seen pictures.

On the Topping PA3s I'm not sure. I have not yet seen a picture of the back of the board or any high resolution pictures at all. But based on the design of the Merus chip and the performance this amplifier showed on the test I could bet it has those chokes. Other way we would have seen the same high frequency distortions as on the SMSL A100.

Why SMSL did not include the chokes? There are many theories. For me it's all about cheaping out and trying to cut corners as much as possible. The other theory is they know the amplifiers sound good regardless of the chokes.
I want you to understand that when you connect your amplifiers they have an internal inductance from the woofers and tweeters coils and from the inductors on the crossover. This equivalent inductance acts as a filter for the amplifier. So in real like usage of this amp you should not have this problem. But I'm aware that under some special conditions like bi-amp woofer and tweeter separately it is likely you would get noise because the tweeters alone might not have enough internal inductance. For all the other people including me, there won't be a problem.

If you have pictures of the PA3s I welcome you to share them with the community. I'd love to see them. I like that amplifier.
 

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Toku

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Dude, are you sure?.Do you have proof that the Loxjie A30 does not have output chokes/inductors?

As you know the SMD inductors are very small. The Loxjie A30 does have 4 little inductors on the back of the board, 2 on each side of the Merus MA12070 chip. Those little black dots you see on the pictures.

The SMSL indeed does not have those little chokes as you said. I've seen pictures.
That part of the photo is the soldering point of the output filter capacitor. The SMD ferrite inductor is not mounted there.
 

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dr_mick51

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That part of the photo is the soldering point of the output filter capacitor. The SMD ferrite inductor is not mounted there.
You are right. I don't know what I saw. There are not ferrite chokes in there.
Sorry.
 
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RandomEar

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[...]
At that point, I had the idea that the tweeters on my speakers could lack the capacitance to act as sufficient filters. And as a shot in the dark, I just got myself a couple of 22 µH, 3 A ferrite core chokes for 5 $. Put them in series with the tweeters, connected the amp and - silence. It works! A couple of measurements using my phone and the app "Spectroid":
[...]
"But what about changes in the frequency response or distortion?", you might ask. Well... I'm not 100% sure. My ears say that this sounds absolutely fine and there is no difference to the setup without chokes. Except for the lack of the crackle & hiss, of course. I also measured some test tones (1, 3, 5, 7, 11, 13, 15, 17 and 19 kHz) in front of the speaker with the same mobile app as shown above with and without chokes and they appear to be differing in level. Some tones above 10 kHz changed between 1 to 4 dB, but not in a uniform direction. Some are louder, some are quieter. And they also change inbetween measurements, which makes me suspect that the FFT resolution or the plot resolution of the app just aren't high enough to resolve those peaks properly.
[...]
Coming back to my comment from may about installing chokes on my tweeters to get rid of the amp hiss: I may or may not have acquired a UMIK-1 to tinker with EQs and subwoofer integration and remembered that I could now check if the chokes had any impact on the sound.

BS243 + AO200 choke comparison.jpg

They don't. Thanks for coming to my TED talk ;)
 

Tamerlan

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Coming back to my comment from may about installing chokes on my tweeters to get rid of the amp hiss: I may or may not have acquired a UMIK-1 to tinker with EQs and subwoofer integration and remembered that I could now check if the chokes had any impact on the sound.

View attachment 227305
They don't. Thanks for coming to my TED talk ;)
Hello! I'm new to this forum. I have the same (hiss sound from tweeters) problem, but on smsl AO200 mk2. I want to try your method. I bought the same chokes, but for now I connected them outside the speakers to the cable and terminals. There is no result.
Or is that not how it works? And do I need to solder them directly to the tweeters? It’s just that mine are Acoustic Energy AE109 and only a master can disassemble them.
 
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dr_mick51

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Hello! I'm new to this forum. I have the same (hiss sound from tweeters) problem, but on smsl AO200 mk2. I want to try your method. I bought the same chokes, but for now I connected them outside the speakers to the cable and terminals. There is no result.
Or is that not how it works? And do I need to solder them directly to the tweeters? It’s just that mine are Acoustic Energy AE109 and only a master can disassemble them.
Hello, and welcome. Would you explain a little bit more? Those speakers have separate terminals for Woofer and Tweeter linked by a jumper. Can you try feeding woofers and tweeters separately? just to confirm and isolate the issue. Then try adding one choke (2 per speaker) to each terminal/cable in series, and try again.
Do you have another pair of speakers, or another amplifier? I'm just trying to troubleshoot.
acoustic_energy_ae109_compact__1660381222_a1db5eb7_progressive.jpg
 
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RandomEar

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Hello! I'm new to this forum. I have the same (hiss sound from tweeters) problem, but on smsl AO200 mk2. I want to try your method. I bought the same chokes, but for now I connected them outside the speakers to the cable and terminals. There is no result.
Or is that not how it works? And do I need to solder them directly to the tweeters? It’s just that mine are Acoustic Energy AE109 and only a master can disassemble them.
Hi and welcome! I'm not 100% sure I understood how you connected the chokes right now, but as it didn't help (yet), I assume it's different from my setup. In my case, I did the following:
  • [Amp (+) terminal] -> Cable -> [Woofer (+) terminal] -> Choke -> [Tweeter (+) terminal]
  • [Amp (-) terminal] -> Cable -> [Woofer (-) terminal] -> Short cable -> [Tweeter (-) terminal]
So my setup has the choke connected in series and it only affects the tweeter circuit. I don't think that it is cricitcal that only the tweeter is "choked", but it is 100% critical that the choke is in series with the tweeter. As far as I remember, connecting the choke in parallel did not keep the amp from oscillating/hissing in my setup.
 

Tamerlan

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Thank you!
I have a new version of these speakers and there are only two terminals.
20231012_160253.jpg


And this was my attempt) And naturally the other ends of the wire into the amplifier with the appropriate polarity.
20231012_161034.jpg



This Sunday I will have the opportunity to try this circuit on speakers with separate tweeter connections. Before I got the chokes, I tried the amp on them and the hiss was the same as on my speakers. Before this, I had a first generation smsl AO200 and did not have such a problem.
 
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RandomEar

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Interesting. One choke in either the positive or the negative side should be enough to suppress the problem. But are you sure that it is the same hiss that affected my AO200? Because you say that your first gen AO200 did not even show the problem with these speakers. What I'm talking about here is not some low level slight tweeter hiss - you can see the odd spectrum of the noise in this post: It's a combination of tones around 4 - 10 kHz and is emitted directly from the amp, as well as from the tweeters.
 

dr_mick51

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I think one choke on each positive and negative terminals it's required. These are BTL not SE amplifiers anymore.
1697125943860.png

So, in theory the "negative terminal" is not ground. It's an inverted output signal. It's better to "filter" each output equally. I'm no expert, I might be wrong.
The other thing to consider is that chokes have a saturation current. They will get hot and/or start to distort. So try not to exceed that current, or get another chokes which support more current.
 

Tamerlan

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In my case, the squeak comes only from the high-frequency speaker. The amplifier is absolutely silent.
It's a couple of meters from the speaker:
Screenshot_20231012_185000_Spectroid.jpg

And this is right next to the tweeter:
Screenshot_20231012_185205_Spectroid.jpg

This connection didn't help either:
20231012_183854.jpg

I'll probably wait until Sunday to try it on a speaker with a separate connection.
In any case, thank you very much! I will also report the results.
(I apologize for the large photos, I haven’t figured out how to make attachments yet.)
 
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Tamerlan

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Hello!
Today I tried both connection schemes, unfortunately the result is the same, hiss remains.
In fact, you can no longer hear him a meter or one and a half away. So I'll leave it as it is. But at the same time I listened to how AB amplifiers played, much more natural than this one, even vintage ones. In general, the experience is such that the next amplifier will definitely not be Chinese,
and probably two or three times more expensive, and so on.)
Thanks to the forum, RandomEar and dr_mick51!
20231015_113939.jpg20231015_113930.jpg20231015_120540.jpg20231015_120632.jpg20231015_120632.jpg
 

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RandomEar

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Too bad. It may be a different design problem, but the facts that the choke does not help at all and that it affects multiple speaker configurations suggest that your unit may simply be defective.

Also, there should be no audible difference between a competent class AB amp and a competent class D design in controled testing, as long as both provide enough power for your speaker setup.
 

Tamerlan

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I agree, I also think that this is a clear malfunction on the amplifier side.
Regarding the second... maybe, just noticed two things:
AB amplifiers were fun to listen to, but mine were a little harsh, although this can be attributed to accuracy. But the voices and instruments actually seemed more natural to me. Although this can probably be attributed to the specifics of the human ear. However, I saw two camps.
And the next one will probably be either an more expensive amplifier D or from the same price category AB.
 
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RandomEar

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I agree, I also think that this is a clear malfunction on the amplifier side.
Regarding the second... maybe, just noticed two things:
AB amplifiers were fun to listen to, but mine were a little harsh, although this can be attributed to accuracy. But the voices and instruments actually seemed more natural to me. Although this can probably be attributed to the specifics of the human ear. However, I saw two camps.
And the next one will probably be either an more expensive amplifier D or from the same price category AB.
I respect that this is your impression and I also occasionally had the impression of a different sound when switching amps. But you should consider that human echoic memory is only a couple of seconds and that tiny changes in volume (as small as 0.1 dB, if broad frequency ranges are affected) can have a significant effect on the perceived sound. This is also - but not only - linked to the Fletcher-Munson curve: Playing a song a little louder will increase the perceived "impact" quite a bit, mainly due to more perceived bass and upper treble.

This is all a bit off-topic for a discussion about AO200's, but what I want to convey is: Objectively comparing audio products such as amps or speakers is surprisingly difficult. Sighted comparisons are flawed by design, but even blind ones are still tricky.

Fun anecdote: I once invited a couple of friends over to listen to my new amp. We all had a blast, but one of my friends was convinced that there was a lack of bass (there was). So I went into the menu and set the tone controls to "Bass +2" and my friends were immediately convinced that it sounded better. I was a bit sceptical, since the difference seemed really very minor to me, but OK. A couple of days later, after reading the manual and checking different settings on the amp, I realized that the tone controls were ineffective because the amp was in "Direct Mode" and had been since I got it. I could have turned the bass to 11 and it still wouldn't have changed a thing. But we heard, what we wanted to hear ;)
 

Tamerlan

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RandomEar,​

In continuation of our dialogue and to confirm your point of view, I would like to leave here a link to a YouTube video in which tests are carried out comparing expensive audiophile amplifiers with very inexpensive ones, which show a vanishingly elusive difference in their sound.
The video is in Russian, but I think everything is clear there, and you can also turn on subtitles with translation.
And so that this post is not completely off-topic, I want to say,
I continue to enjoy listening to music through the SMSL AO200 mk2, mainly with their SDB setting, at a low volume, as I am used to, and I am in correspondence with the manufacturer about the possible replacement of the amplifier with a working correctly one.
 
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