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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 ;)
 
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