Noise and other peculiarities of NuForce amplifiers

rustydoglim · « **on:** 6 Sep 2005, 06:59 am »

Why does NuForce have audible hissing noise when the amplifier is idling (no input signal)?

NuForce amplifier has SNR (Signal To Noise Ratio) of 120db (at 100W) so it is exceptionally quiet when playing music. NuForce's feedback and control system runs at 1MHz and actively performs noise cancellation in real time (comparing noise with music signal) at every switching cycle. But when there is no input signal, it merely amplifies noise in the system and occassionally you can hear swash/hissing noise if you are very close to the speaker. When the source device (Preamp or CD player) is turned off, it acts as a noise receiver/transmitter and could generate even more noise for NuForce amplifier during idling time.

Why some NuForce amplifiers have more noise than others? Why are there variations from unit to unit?

Switching amplifier uses hundreds of components in its circuit and their values have variations so it is expected that some units have slightly more idling noise than others.

Why is there a small DC offset between the two +/- speaker terminals?

The op amp has variations and will result in 0.05 to 0.13 volts on the speaker terminals. 0.13V is equivalent to 2mW at 8 ohm load. This is hardly a concern for your speakers.

Why some units have turn on/off noise?
The low level turn on/off noise (pop) even though sounded unpleasant, there is no voltage spike that can harm your speaker. Contact NuForce if you still have concern.

Charles Calkins · « **Reply #1 on:** 6 Sep 2005, 01:31 pm »

Lason:
If the preamp is in mute mode do you still hear the hiss?

Cheers
Charlie

rustydoglim · « **Reply #2 on:** 6 Sep 2005, 08:41 pm »

I will like to add that the hiss is very low level and most people never notice it. We only have one or two inquires once in a while about the issue. There are people who like to put their ear right next to the speaker

The noise would be louder if the preamp is turned off as the components in the preamp become source of noise if they are powered off.

John Casler · « **Reply #3 on:** 6 Sep 2005, 08:49 pm »

I can adjust the volume of my preamp to 100% full volume (Bryston BP26DA) and I can hear absolutley nothing from any of the drivers.

kenk · « **Reply #4 on:** 6 Sep 2005, 09:17 pm »

Quote from: nuforce-jason

Why does NuForce have audible hissing noise when the amplifier is idling (no input signal)?

I had a PS audio HCA-2 digital amp that drove me crazy with hissing sound too. I believe interconnect cable (shielding) has an impact on the hissing.

rustydoglim · « **Reply #5 on:** 6 Sep 2005, 11:52 pm »

Hey, like John said, the hissing noise that I am talking about is very minor and it varies from unit to unit. It can be heard about 1 ft away on very high efficient speakers. I am just trying to explain that NuForce is not absolutely quiet at idling but has awesome 120db SNR.

NewBuyer · « **Reply #6 on:** 14 Sep 2005, 08:09 pm »

I was just about to purchase two of the new Reference 9 units until I read this thread.

The issues with hiss, and with turn-on thump, are two of my biggest pet peeves in audio. I think it was very up-front of Nuforce to put this information in public for potential buyers.

Thank you for warning me about these issues regarding the Nuforce amps, as I would have been very disappointed to receive them and then to find that they do those things!

Regards-

hometheaterdoc · « **Reply #7 on:** 14 Sep 2005, 09:12 pm »

Quote from: NewBuyer

I was just about to purchase two of the new Reference 9 units until I read this thread.

The issues with hiss, and with turn-on thump, are two of my biggest pet peeves in audio. I think it was very up-front of Nuforce to put this information in public for potential buyers.

Thank you for warning me about these issues regarding the Nuforce amps, as I would have been very disappointed to receive them and then to find that they do those things!

Regards-

There is no "thump" like you are thinking or have experienced with other amplifiers. It's more of a squelch than a thump.... Thumps absolutely drive me nuts. There is nothing that aggravates me more. While the turn on noise was a little unsettling at first, I have no problem with it at all. But then again, because the amps are so efficient power wise, I just leave them powered on all the time. My electric bill is virtually unchanged (actually its a lot cheaper than when I was running big tube amps)

The "hiss" is something I haven't really experienced. All of the demo amps I have on hand are dead quiet. Even on 92+dB efficient speakers, you have to be within an inch of the tweeter to hear it. In fact, compared to all the other amplifiers I have ever owned, they are eerily quiet... I applaud Nuforce for being up front with folks about the possibility of this hiss....

It's certainly your perogative to bypass Nuforce amps based on something posted here. I would have at least tried out the amps to see whether it would be an issue for you. Nuforce has a very liberal return policy and most dealers have good trial options. To skip over an amp without ever hearing it is not something I usually do

gostan · « **Reply #8 on:** 15 Sep 2005, 01:19 am »

I was lucky enough to demo three Ref 9's for four days last week and I did not notice any hiss or hum coming from my speakers. The zipzip type sound from my speakers when turning the amps off was a little bit disconcerting, but I dealt with this by simply keeping the amps on for the duration. And the music sounded like I had purchased new speakers. Simply fabulous. Demo them, you will love them.

tdangelo · « **Reply #9 on:** 15 Sep 2005, 03:01 am »

I have the Ref 8B's that I'm using with some relatively efficient VMPS RM40's and hear virtually nothing unless I put my ear directly on the midrange ribbon and then I have to strain to hear it - same as my previous amps. The amps tend to be slighly more hissy until they settle down for a few minutes. Turn on/off is a very quiet blip

Tony D.

DeanSheen · « **Reply #10 on:** 15 Sep 2005, 05:57 am »

I have a pair of 8's on demo now.

No noise whatsoever.

Ric Schultz · « **Reply #11 on:** 19 Oct 2005, 08:33 am »

I have been troubled by the amount of hiss from the original Nuforce amps. I had one amp here that you could hear the hiss 15 feet away!!!! So, Nuforce sent me another board for that amp and the hiss went down to the same level of the other amp (you could here the hiss from about 2-3 feet away)...no big deal but my speakers are 88db effecient so if you had a 96db efficient speaker it could be quite noticeable.....

Well...I was finishing a mod on a pair of Nuforce amps today to send to Brazil and when I fired them up they both had noise....one as loud as the 15 feet away jobbie and the other one had slight hiss but slight popcorn noise....I almost went ballistic!!!! as these amps were already late getting out. Then I remembered that the latest Nuforce amps had an extra cap on the input that bypasses/filters the positive input/feedback (I believe) of the input opamp. So, I put a .33 uf cap on that spot and WHOA BABY! no noise of any kind....nada from either amp. I put the caps on my own pair and it reduced their hiss to nada and I now could hear deeper into the ambience in live recordings.

So, if you have any hiss coming from a Nuforce amp....you must have one of the ones that were made before the 8.01 rev. Because that is when they did this cap mod. I sold one pair of level one modified amps a couple of months ago to someone and he loved the sound but had hiss from across the room (naturally, he returned them). The same amps today with the cap mod would be dead quiet.

If you have bothersome hiss using any older Nuforce amp then I would contact Nuforce to have the mod done. I had talked to a person a few weeks ago that had some hiss on his very sensitive speakers and he sent the amps to Nuforce and when he got them back they were quiet....only now, do I realize what he had done and how effective it is. I believe all Ref 9s have this mod and all Ref 8s made since July something have it as well. Thanks, Nuforce, for continuing to make your products better and more reliable!

madders · « **Reply #12 on:** 19 Oct 2005, 10:56 pm »

I'm guessing these amps wouldn't be a good choice for Zu Druids then? (101db efficiency)

miklorsmith · « **Reply #13 on:** 19 Oct 2005, 11:05 pm »

Srajan said in his review of the Ref. 9's that neither mono made a shred of a peep on his Definitions, which actually are more sensitive than the Druids (lower impedance).

mmakshak · « **Reply #14 on:** 22 Oct 2005, 05:45 pm »

I've had my Nuforce 8b's on for more than a week. Nuforce may kill me for saying this, and it can be dangerous around lightening, but, boy, they sound much better leaving them on most of the time( This idea is nothing new.).

rustydoglim · « **Reply #15 on:** 23 Oct 2005, 01:16 am »

The IEC socket has a fuse and if anythig get hit first, it is the SMPS. But I am sure you should be wise to have a surge protector

rustydoglim · « **Reply #16 on:** 30 Oct 2005, 08:52 pm »

We want to get the word out about certain things with NuForce amp that people should be watching out for:
1. Don't turn on the amp when the speaker is not connected to it.
2. Turn off the amp if you decide to turn off your preamp.
To get the high performance we need, the amp switches at 500Khz and the system runs at 1Mhz. When there is no load or if the preamp is off (which act as a noise receiver), the amp could overheat. This doesn't happen all the time. We added overheat protection circuit to shut the amp down and restart it when it cools down. Well, if accident do happen, you're covered by our 3 year warranty.

If your newly arrived NuForce amps create loud humming and hissing noise when first introduced into your system, there is a very high probability that it is due to ground loop noise between the amp and your preamp.
Check if the noise goes away or significantly reduce:
1. Turn off the amp, remove interconnect and turn on again
2. Turn off one amp
3. Turn off or change source device

Don't spend more than 15 minutes on the problem, contact NuForce support. We're not that busy with support issues so we can response quickly (and we're very experience in dealing with it). Take a photo of the internal of the preamp and email to us too. Focus on the ground wiring (these are wires connecting the circuit board or connectors to the chassis). In a few cases that we encountered, it is a matter of adjusting the ground wiring.

kharma · « **Reply #17 on:** 10 Nov 2005, 03:37 pm »

When I turn off the Nuforce Ref 8B, is that normal I heard a little noise from the speaker?

KJ · « **Reply #18 on:** 10 Nov 2005, 04:36 pm »

Hi kharma. Yes, the noise you hear is normal as the power drains out of the units.

-KJ

mmakshak · « **Reply #19 on:** 10 Nov 2005, 04:52 pm »

I don't know what this means, but recently our power went off. Now, normally, I leave preamp and amps on. When the power came back on, I didn't even hear that little squeegy(I don't know how to spell this.) noise that normally occurs when powering up the Nuforces. BTW, I understand why I was asked to turn off my preamp, with my amps on, and listen for the noise(as per what Jason said not to do-overheating, I believe).