[Samoyed]

Predictable.

[nafets]

Hello rustydoglim,

maybe you understood my last question/statement wrong, I guess it is getting a bit confusing now:
my main/initial issue was the low frequency noise produced by the ST-10 at the speakers output which was/is easily audible all over my room. If this noise is finally a defect of the ST-10 or if it is/was related to something else, we will see. As mentioned, I have send the ST-10 back to the dealer, he will do some additional testing, and hopefully send me the results. So let's first wait for the result before making further speculations, up to now many things are possible.
By the way: The STA-9 does not show this noise/effect.

Another issue was/is: you gave me the hint regarding the high-frequency noise, which is in fact very, very low and is audible only when I am very close to the speaker (about 20 cm), exactly as you wrote. If you wouldn't have told me, I most probably would never had heard this.
If I understood your statement correctly, this audible higher-frequency noise is "normal".
But other Class D amplifiers (e.g. my Lyngdorf) seem to not show any similar (audible higher-frequency) noise at all. Or am I wrong?
So I am just interested, why this audible high-frequency noise is "normal" (or is it just normal for Nuprime Amps?).
Means: I am just interested to know and learn a little bit about the technical details behind it (hoping that there is some "ready" information available). That's all.

I just want to find out the root cause for mainly two issues, my intention was not to "blame" Nuprime (the sound of the STA-9 and ST-10 e.g. I still like... only the noise from the ST-10 not so much... but that's why I am working on it and posting questions here ). If others do not have any issues or questions: fine!
But of course I understand that this kind of topic can make someone from Nuprime feel uncomfortable... but please do not feel attacked, I did not want to blame anyone.

[nafets]

Predictable.

Well... maybe... at least I understand now what you mean...
But as most answers have been quite constructive up to now, it was all in all helpful and anyhow worth a try .

[seagreen]

Hello rustydoglim,

maybe you understood my last question/statement wrong, I guess it is getting a bit confusing now:
my main/initial issue was the low frequency noise produced by the ST-10 at the speakers output which was/is easily audible all over my room. If this noise is finally a defect of the ST-10 or if it is/was related to something else, we will see. As mentioned, I have send the ST-10 back to the dealer, he will do some additional testing, and hopefully send me the results. So let's first wait for the result before making further speculations, up to now many things are possible.
By the way: The STA-9 does not show this noise/effect.

Another issue was/is: you gave me the hint regarding the high-frequency noise, which is in fact very, very low and is audible only when I am very close to the speaker (about 20 cm), exactly as you wrote. If you wouldn't have told me, I most probably would never had heard this.
If I understood your statement correctly, this audible higher-frequency noise is "normal".
But other Class D amplifiers (e.g. my Lyngdorf) seem to not show any similar (audible higher-frequency) noise at all. Or am I wrong?
So I am just interested, why this audible high-frequency noise is "normal" (or is it just normal for Nuprime Amps?).
Means: I am just interested to know and learn a little bit about the technical details behind it (hoping that there is some "ready" information available). That's all.

I just want to find out the root cause for mainly two issues, my intention was not to "blame" Nuprime (the sound of the STA-9 and ST-10 e.g. I still like... only the noise from the ST-10 not so much... but that's why I am working on it and posting questions here ). If others do not have any issues or questions: fine!
But of course I understand that this kind of topic can make someone from Nuprime feel uncomfortable... but please do not feel attacked, I did not want to blame anyone.

I have an ST-10 that I bought used and came with high frequency noise (mosquito level, prob >10kHz). It was loud enough to hear from my chair when the room was quiet. At that frequency, different ears may or may not hear or be bothered by it, but it's not normal. I sent mine in for authorized service and a bad amplifier module had to be replaced. The guy who did the service said that earlier versions of that module were problematic. Perhaps you have one of those. In any case, high frequency noise is not normal so either send in for service or return if possible. Once mine was fixed it was dead silent.

As for lower frequency noise/hum, that's usually a ground look issue vs a product issue, so try the usual diagnostics for that (ie, still there when you unplug from the source, or float the ground?)

[nafets]

As for lower frequency noise/hum, that's usually a ground look issue vs a product issue, so try the usual diagnostics for that (i.e, still there when you unplug from the source, or float the ground?)

Thanks for the helpful input! I would be happy if the device could be fixed!
Regarding lower-freq noise at speakers I tried already everything that I could try within my rooms and limited equipment (I posted results here). Right now the ST-10 went back to the dealer, and he will check it also. I guess it will take at least one or two weeks until I get an answer.
All in all, most probably this issue will be either a defect or something that makes the ST-10 feel uncomfortable in my rooms .

[rustydoglim]

Predictable.

Samoyed, you are not welcome here. I believe this is against the policy of audiocircle.  You should not insult the circle owner when all I have posted is to point out that the noise is not due to design problem. 

[John Casler]

Regarding Humming-Noise audible from transformer:
The noise of the transformer seems to be slightly lower in the other room... but this is most probably a different story (transformer noise of ST-10 and STA-9 I can anyhow influence depending on other devices/connections within the system).

But as some people already reported that their ST-10 is absolutely silent in their system, maybe I just have to accept the fact that my ST-10 is defect or that within my rooms and/or system a ST-10 will just not work like I wish it to do... this would also be a conclusion.

Hi Nafets,

What I'm going to suggest might sound a little strange, but some electrical wiring in some houses have an inhearant powerline problems.

This may only affect certain gear. 

If you haven't already tried this and you have the cables, try this:

1) Run  L&R Stereo XLR cables to your ST-10 from your Preamp
2) Run a single RCA cable from any open "INPUT" on the Preamp to one of the RCA inputs of the ST-10.

I am not sure why this sometimes helps, but it is likely something to do with grounding the two units more effectively.

Make sure the RCA connection you use is an INPUT, not an OUTPUT.

Hope this helps.

[Samoyed]

A statement of objective fact is not otherwise an insult, nor intended to be an insult.

[rustydoglim]

Fair enough, perhaps I mistaken about the context of your reply. Cheers.

[nafets]

Finally I received a feedback from the dealer, therefore I would like to summarize this thread and give "my final conclusion":

I had all in all three different Noise-Issues with "Nuprime STA-9" and "Nuprime ST-10":

1. Humming noise from transformer (reproducible with STA-9 and ST-10)
As already mentioned, this was not a critical problem. In my case this was mainly influenced by the switching power-supply of another device.
This noise was quite low: audible up to a distance of about 1m from the amplifier.
So In my opinion this was not a critical issue, it was easy to solve (e.g. chose a different power socket).

2. Higher Frequency noise at tweeter (reproducible with STA-9 and ST-10)
There is an audible noise in the higher frequency range which can be heard at the tweeter. The volume of this noise is very low, according to a "Sound Analyzing" App mainly within a frequency-range from about 6-12 kHz, with a maximum level in the range of about 8-10kHz, and this maximum level about 35 - 40 dB(A), measured at a distance of about 1-2 cm from the tweeter.
That means: It has more or less the volume level of a whisper, if you put your ears close to the speaker...
Concerning to an answer here, this noise is normal. I also asked in other forums etc. where I got quite good Feedback (also from other STA-9 and ST-10 users), reporting that this noise is in fact "common" for both STA-9 and ST-10.
I also got the feedback, that there are several other amps out there which produce a similar noise (so this is not a "Nuprime-only" issue), but on the other hand there are also several amps from other manufacturers out there, which do not produce this noise at all (which does not automatically mean that these devices are better, if you take all your needs into concern).
I asked "Nuprime" here for a technical explanation of this noise but this question was not answered, so I cannot give an exact technical explanation about the root cause.
Please note: As mentioned, this noise is very low and should be usually not be audible at the listening position... so everybody has to judge for themselves if this kind of noise is acceptable or not.
In my personal opinion it is acceptable in the price range of the STA-9, but not in the price range of ST-10. But that is just my personal opinion.

3. Lower Frequency noise produced at the "speaker output", audible all over the room (reproducible with ST-10 only)
As already described within this thread, this noise was an issue of the ST-10 only. I never had any similar issue with any other device, also the STA-9 does not show this problem at all.
The noise was audible all over the room, but I did not measure the frequency range and volume level in this case.
I did all tests which I could do within my rooms, it could be maybe slightly influenced, but not solved.
This issue was the most critical for me (not acceptable) and the reason that I finally send the ST-10 back to the dealer.
I expected that the dealer would check the ST-10 briefly, but unfortunately he answered after more than one week just with some "political rhetoric" like:
"... if the noise is not clearly audible and annoying when listening to music, then the noise is no problem...".
Strange: He denied even to execute the most simple test (connect just the ST-10 to power and speakers (no pre-amp at all to eliminate any influence or possible loop)).
A bit suspicious within this context: I was not the first one who send this ST-10 back.
Means: he already got this device at least two times send back, but is not willing to check it briefly... this seems really strange to me, but I cannot change it.
My conclusion regarding this issue:
There have been some people here assuming that this noise must be related to powerline issues within my rooms, but due to the mentioned facts I do not think so. I also do not think that this a general issue (because this special low-frequency noise would then be an issue also for others).
I assume that this one ST-10 simply had an internal defect, but of course I cannot give a final proof of this assumption now.

Anyhow, the end of my "Nuprime Story": I will keep my STA-9, returned the ST-10, and will search now for absolutely quite amplifiers

[nafets]

And thank you all for the answers!

[Samoyed]

Try Nord in the UK.

[nafets]

Try Nord in the UK.

That's indeed already a favorite on my list... but this will be a different story and not part of the Nuprime-channel here. 

[Samoyed]

If you want my help, Colin is a friend.

[rustydoglim]

If you listen close to the tweeter (within a feet), all variants of Class-D amps have the so called switching noise. That is normal and does not affect the listening experience. The noise level is dependent on the speaker's efficiency and tweeter. 

All transformers also naturally produce noise since they operate at AC frequency - ie if you put your ear very close to the power supply. The noise level depends on how tightly the wire is winded and sealed.

In some amps, we added even order harmonics that resulted in additional "noise" that make the music sounded natural.

Ultimately you should find an amp that pleases you at your listening position. But if it bothers you or the noise is real, then go with something else. I can't stand listening to vinyl record because all I can hear is the very loud noise.

[nafets]

If you listen close to the tweeter (within a feet), all variants of Class-D amps have the so called switching noise. That is normal and does not affect the listening experience. The noise level is dependent on the speaker's efficiency and tweeter. 

Sorry, but I think this statement is not correct. Lyngdorf TADI 2170 does not have any noise, TDAI3400 does not show any noise either (both have been running at exactly the same speakers like the Nuprimes).
Dynaudio Focus XD (well... this is an active speaker, but including several class D amps) does also not show any noise at all (also not closed to the tweeter).
And I am quite sure that there are even more (class D) examples out there which do not have any audible noise at the tweeter, but the mentioned three above I can definitely confirm by myself, all of them I used and tested for weeks, months or even years...

[rustydoglim]

You are taking my one statement out of context, please refer to the entire paragraph.
As I mentioned, all Class-D has switching noise. This is a FACT. But, the level of noise is depending on several factors.
The fact that one amp doesn't have noise in your system doesn't mean that the amp has no noise.
STA-9 is supposed to have more noise (because even-order harmonics is added for the warmth) than ST-10.  Unless we have a chance to test that particular ST-10, we just don't know why it is causing problem in your system.

The noise comes from modulation: https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3977.html
If we make it too clean by suppressing all the noise, the amp can sound less musical. What we have learned in the lab is that as the switching frequency goes beyond 1GHz, the noise becomes irrelevant.   

[nafets]

Yes... all Class-D amps have switching noise, but this is not the point, the point is that I still wonder why the switching noise should be related to the AUDIBLE noise.
I never talked about "switching noise", I talked about AUDIBLE noise, and I am still wondering about your statement, that the AUDIBLE noise should be the "so called switching noise":

If you listen close to the tweeter (within a feet), all variants of Class-D amps have the so called switching noise.

Switching noise:
The "switching noise" introduced at the output of a Class-D amp has the same frequency as the switcher (and some harmonics of that frequency, means even higher frequencies).
Means: "switching noise" within Class-D amplifiers is NOT within an audible frequency range, because it is several hundreds of kHz.

Audible noise:
As mentioned several times, I was talking about the AUDIBLE noise at the tweeter (range from about 8kHz to 12kHz).
So, within your argumentation is either a fundamental explanation/argument missing (explaining why a noise of several hundreds kHz should result in ranges from about 8kHz to 12kHz at the tweeter), or your statement (that this AUDIBLE noise at the tweeter is the "so called switching noise") is not correct.
That's why I think, that this AUDIBLE noise is not related to the switching noise, but of course I am willing to read good argumentation.

And: If I quote an important statement from you with fundamental importance, than this is not "taking something out of context".

[Samoyed]

I have a Nord One Up, revision D-it is dead silent.  I know Colin if you want help.

[rustydoglim]

Switching noise resulted in audible noise. I think this argument is getting way off from the original intent of assisting a customer in identifying the problem. We are really talking about two different issues here:
1. I agree with you that the ST-10 that you have tried could have problem but until we can confirm it, we just don't know.
2. I stated separately that all switching amps have noise, and there are various factors that determine if an amp has audible noise.

ST-10 has been widely reviewed in the US and Europe, and won Power Amp of the year award from TAS. And I don't dispute about your report or your ST-10 noise. Our discussion is not going anywhere because your have already sent back the ST-10, and we haven't been able to test it.