[nafets]

Hello,

I just joined this forum, mainly due to the fact that I found quite useful information about "Nuprime" here, but also due to the fact that people seem to treat each other quite friendly here.

My "Nuprime Story"
Since some years, I am using a "Lyngdorf TDAI 2170". And since some month, I upgraded my speakers to "B&W 804 D3".
In my opinion a good combination, but with activated Roomcorrection (Lyngdorfs "Roomperfect"), the sound sometimes can get a bit harsh and annoying.
So I searched for possibilities to reduce the "harshness" of my system. Of course there are several possibilities to do so, but somehow I personally decided to start with trying power-amplifiers... and ended up with Nuprime, also after reading several post within this forum.

So some weeks ago, I ordered a Nuprime STA-9, and in fact: The STA-9 could reduce the harshness of my system. The only issue with the STA-9 was/is a humming sound of the transformer... which I can influence with changing other parts of my system, so that it is still there, but with acceptable level.
Then - curious about Nuprime - I ordered a ST-10. The ST-10 did not remove harshness from my system, but it brought more (or other) details to the music compared to the TDAI 2170.
So I found qualities in the ST-10 (specially when listening at low volume levels) which I personally like, and all in all, the ST-10 could be my personal favorite of the three.

But: The ST-10 is not only producing humming noise from the transformer, but also a constant humming noise at the speakers.
I tried already all possible things (de-connect all other equipment, use different wall sockets, try other pre-amp, etc.):
I can influence the noise from the transformer, but not the noise audible at the speakers. Even if I connect nothing but the ST-10 to the speakers and switch it on, there is an audible noise at the speakers. Also this test I did using different plugs and wall sockets (with and without filters).
So whatever I do, the ST-10 always produces a humming noise at the speakers, and it seems not to be some "classic" problem like ground-loop or similar.
Usually I would think that the ST-10 is defect, but the dealer told that it was checked before it was send to me.
Apart from this, a guy owning two "Evolution One" also told me about humming noise problems... so I wonder if this is maybe a common/known issue, and that other people maybe just don't care about it.

My questions to the members of this forum:
Is this humming noise produced by the ST-10 at the speakers maybe a "known issue" which just every ST-10 produces (due to its construction) or is this definitely a defect?
Could be related somehow to the ST-10 / B&W combination?
If this is a known issue, is there any way to solve it?
Could it be a problem due to the voltage (230V) in Germany?

I can take a look at this forum maybe 3 or 4 times per week... so there is no hurry .

By the way:
If someone may find it helpful, I could write my listening impressions (Lyngdorf vs. STA-9 vs. ST-10) somewhere... but I am not a "review expert" and my English is not really perfect... so writing something needs some time...

Thanks and regards!

[Samoyed]

Can you give us the first three bars?

Seriously, I wish you luck as all I got for my troubles regarding a pop with my evolution DAC was a finger pointed at me.

[mresseguie]

I have no experience with the STA-9, but I used to own an ST-10. I never heard a hum from mine. I used it in the US and in Taiwan. I owned an IDA-8 for 4+ years (my son now has it), and I have owned an IDA-16 for approximately one year. Both units are dead quiet.

I recently sold a chip amp to someone here on AC. It was nice and quiet in my home, but the fellow who bought it experienced a hum. Could your power lines be providing dirty power to your home?

Have you tried using a power conditioner? If yes, did it help quiet the hum?

Michael

Your English is just fine and readable. A mistake here or there by a non-native English speaker isn't an issue . There are plenty of native English speakers whose grasp of English grammar is pretty horrible. I taught EFL for nearly twenty years, and it's all I can do to keep myself from correcting native English speakers' blunders. 

[JackD]

Like Michael I owned both an IDA-8 and an ST-10 and both were dead silent. 

[rustydoglim]

Open the cover of the ST-10, tighten the hex nut screw at the top of the big round transformer.
It can become loose after shipping around and allow the transformer's natural vibration to become loud. The transformer is very heavy so if it is being thrown around (that always happened during shipping, don't expect the shipping staff to handle the box with care), the screw can become slightly loose.
Transformer vibrates at the AC frequency (in Europe it is 50Hz, US is 60Hz and the lower the freq, the bigger the humming noise) so if you put your ear right on top of it, you will hear it.

[nafets]

Seriously, I wish you luck as all I got for my troubles regarding a pop with my evolution DAC was a finger pointed at me.

A "pop" noise when switching on the Lyngdorf TDAI-2170 together with the Nuprime is a different story
In my setup this seems to be related to the Lyngdorf (which also "plays the role" as DAC/Pre-Amp...)

[nafets]

I have no experience with the STA-9, but I used to own an ST-10. I never heard a hum from mine. I used it in the US and in Taiwan. I owned an IDA-8 for 4+ years (my son now has it), and I have owned an IDA-16 for approximately one year. Both units are dead quiet.

Thanks! That's at least an indicator that the problem might be related to "my" ST-10...

I recently sold a chip amp to someone here on AC. It was nice and quiet in my home, but the fellow who bought it experienced a hum. Could your power lines be providing dirty power to your home?

Have you tried using a power conditioner? If yes, did it help quiet the hum?

I do not now if I maybe have issues with "dirty power". I do not use an active power conditioner, but a passive solution (HMS, a german company... at least theoretically this should filter noise from the power network...). But there is no change if I am using this mains-filter or not. Anyhow, up to now other Amplifier-Speaker combinations did not show any issue.
I will not find any other solution, maybe I will try if I can borrow any other power-conditioner from a local dealer... or send back the ST-10 .

[nafets]

Open the cover of the ST-10, tighten the hex nut screw at the top of the big round transformer.
It can become loose after shipping around and allow the transformer's natural vibration to become loud. The transformer is very heavy so if it is being thrown around (that always happened during shipping, don't expect the shipping staff to handle the box with care), the screw can become slightly loose.
Transformer vibrates at the AC frequency (in Europe it is 50Hz, US is 60Hz and the lower the freq, the bigger the humming noise) so if you put your ear right on top of it, you will hear it.

Thanks for this input, I already did this at my STA-9, so I know what you mean. But I am afraid that this might only influence the noise produced at/by the transformer, but not the noise produced at the speaker (=> speaker-output from ST-10 to speaker). Anyhow, I will try it this afternoon and post the result!
Thank you!

[nafets]

As suggested by rustydoglim, I opened the ST-10 (which was bit more complicated compared to STA-9) and checked the screw of the transformer. The screw was already quite tight, anyhow I could tighten it even a bit more.
But this action did not change or influence the humming noise.

Regarding Humming-Noise audible from speakers:
As next test, I took the ST-10 and the speakers to a different room.
1.
Within a first test, I only connected the ST-10 to the speakers (no other device or pre-amp connected) and switched the ST-10 on, result:
also in this other room, the ST-10 produces a humming noise at the speakers.
2.
Within a second test, I connected a second AMP as Pre-Amp to the ST-10 (Instead of Lyngdorf I used for this test Marantz PM-7001 via its "Pre-Out").
With this step, the noise at the speakers produced by the ST-10 was not eliminated, but reduced. Interesting fact: The noise is reduced independently from the state of the Marantz, means: Even if the Marantz-Amp is switched off, the noise audible at the speakers is reduced. Just the fact that there is a connection between ST-10 and Marantz seem to reduce the noise at the speaker compared to the ST-10 without any connection... and audible only at the right channel, at least I cannot hear it at the left channel/speaker within this test-setup...

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.

[Samoyed]

My point regarding the pop was simply that regardless of the condition, you will not likely be happy with the reply.  Enjoy your hum, as I do my pop....

[Westerwälder]

Have you already tried inverting the ST10?
For me there are no problems with DAC10H, ST10 inverted. Speakers are Rowen S6.
For some weeks now AC4 with even more resolution and details.
I uncoupled the speaker cables from the floor.

[nafets]

Have you already tried inverting the ST10?

I guess you are talking about the ST-10 "phase inverting issue". As far as I understood, this makes sense if e.g. the connected device (e.g. pre-amp) would also be phase-inverting.
Anyhow: To give it a try, I also inverted the speakers connection already (means connect "red" outputs of ST-10 to "black" input of speakers).
Result: The hum is not influenced at all, no change.
But thanks for the input!

[rustydoglim]

How loud is the noise? Do you hear it when playing music at very low volume?  I wonder if you are hearing the switching noise by putting your ear close to the tweeter.

[seikosha]

If possible, try hooking it up at a friends house to see if the problem persists.  That will truly tell you if the problem is bad synergy between your house’s wiring and the amp or if it really is just a bad amp.

[nafets]

How loud is the noise? Do you hear it when playing music at very low volume?  I wonder if you are hearing the switching noise by putting your ear close to the tweeter.

At least I hear it all over the room when no music is playing. In my opinion, this is already a not acceptable fact, audio equipment has to be silent. Other Amps which I used up to now did never produce any noise. The noise I am talking about is in the low frequency range (coming from bass units/drivers)... but I can not tell you if it is the 50Hz from power network or a higher frequency.

After your post I also put my ears closed to the speaker and tweeter: And yes... there is also an audible noise at the tweeter...
Please tell me that if this is not common   (neither my Lyngdorf nor my Marantz are having such issues, I just tried them both... and Lyngdorf is also class D).
Maybe I am a bit sensitive to noise, but in my personal opinion audio/Hifi-equipment should be silent... if not, all other discussions about high-res, jitter, high switching frequencies etc. seem to be needless to me. I want to hear the music, and not the device.

[nafets]

If possible, try hooking it up at a friends house to see if the problem persists.  That will truly tell you if the problem is bad synergy between your house’s wiring and the amp or if it really is just a bad amp.

I just made an agreement with "my" dealer: He will get the device back and test it within his setup. Depending on the result, we will proceed... if the device is definitely defect I can maybe just exchange it by a new ST-10 (or AMG STA), if it is not a defect I most probably get my money back... we will see.
I guess this will take all in all at least one or two weeks, but I will post the result here, because the information if it was finally a defect or not, might be useful for others with similar issues...

[Samoyed]

Why bother?  You aren’t happy so get your money back, now.

[rustydoglim]

It is not normal from what you have described.

[nafets]

It is not normal from what you have described.

Thanks for the answer.
Is there somewhere described why this audible high-frequency noise is normal and what is the difference to other Class-D implementations (like Lyngdorf) which are not producing this noise at all?
In fact, this high-frequency noise was/is not my most critical issue, but anyhow it would be interesting for me to learn more about it.

[rustydoglim]

This is not a design problem, others have mentioned that there they have no problem at all. Otherwise you would have heard people mentioned it here, but how often have we heard about noise issue? Keep in mind that we sold thousands of amps of various models, so even if a few people complains, that's less than 1%.
We are dealing with complex electronics and system, so if the amp has no noise at the dealer's place, then what?
That might be interesting. Perhaps pointing to some problem with your home grounding problem? Then you would have the amp to thank for. Or perhaps the ground contact in the amp is loose?