[borndevil]

... this would be a feedback as I was lucky enough to have one of this perl in test before buying..
but this evening something very frustating happens, so my little review has to wait.

I connected pre-out of my IA-7 to my Audio Analogue Donizetti monoblock and turned off booster switch.
Every device was disconnected from AC main. So I plugged main again and Donizetti, as usual, turned on.
So I went to turn on NF and I heard something of the kind very difficult to forget, a very high "Thump" or "bump" with a initial fast high noise followed by two enormous low peak. Never heard this from my Klipsch RF-5s, I tought my woofers went out from my bedroom to the kitchen. I discover that it seems to be all ok at a first look, and sound well, I really hope I'll not have some bad new for the future of my speakers that were still in warm-up time.

Yes, I should turn on first pre and after monos but I never find this happens with every pre I tried. I'm very disappointed.
Another issue concerning sweeping noise. This came from my speakers even from 2 meter away, is less noticeable with some music but if too low I can recognize shhhh and sweep noise very well. It seems to be... as a far away radio-station, a very high frequency that sweep from tweeter-hornes plus a continue-component from middles and bass... all these even with no souce connected or in mute position. As soon as relay swap high-pitch noise starts.

Beyond this, I really would to solve this noise issue and hoping that my speakers are overall ok as I have heard a champion.
Waiting for some feedback, thank you very much,

Marco, Italy

[rustydoglim]

I don't understand why you would buy IA-7 and then use it as a preamp.
P-8 would be a much better solution.

My best guess is that this is due to ground loop noise somewhere.
Do you have any problem if you only use IA-7 by itself (ie with the booster switch on to turn on the amp) and power the speaker directly?

[borndevil]

Thank you for your interest.
I used IA-7 as preamp for three reasons: First, I would to try how good was preamp section. Second I would to compare differences of this new technology respect to traditional one, both tries with two power amps I know very well. At last, IA-7 is a preamplifier too, isn't? 
If NF wouldn't I use IA-7 as preamp I'd not never found a pre-amp out and a switch for power section 

However, I were not clear. After I had a try as pre-amp, I disconnected and used IA-7 as integrated. Noise is present in this last case. Used as preamp is absolutly silent.

[rustydoglim]

That make more sense to me.  I urge that any customer who post online please be very clear when you describe the problem or else it confuses other people and they might not be following closely with the thread.

With the amp section powered off, IA-7 acting as preamp with other amp is quiet.
With IA-7 alone driving your speaker, there is noise in your system.  There must be some ground loop noise with the amp and source device.
I assume that you now have CD->IA-7->speakers. Correct? Are you using any unshielded interconnect or speaker cables ? What kind of CD player do you have?
Remove the CD player and try another source, such as a portable MP3/Ipod, do you still hear the noise? Any you using any kind of output from PC that is also very noisy?
Please provide complete and clear description of your setup. Or contact support@nuforcec.com.  We will not be monitor this forum closely between August 11 and August 21 as we'll be travelling.

[borndevil]

With the amp section powered off, IA-7 acting as preamp with other amp is quiet.
With IA-7 alone driving your speaker, there is noise in your system.

Correct! Sorry for bad explaination.

I assume that you now have CD->IA-7->speakers. Correct?

Correct

Are you using any unshielded interconnect or speaker cables ? What kind of CD player do you have?

Signal cables are AM-Audio or Audiogram, shieldied, of course. Supra PLY3.4 unshielded for power cords.

Remove the CD player and try another source, such as a portable MP3/Ipod, do you still hear the noise? Any you using any kind of output from PC that is also very noisy?

Just done! So strange, I used DVD player and the very first time no sweeps but a little shhhh very low. I was excided, so I connect CD Player and tried again. No sweeps. Turned off and on IA-7 -> sweeps, many tries and still there. I have a Rotel RCD-02.
Speaker are Klipsch RF-5

[rustydoglim]

So now we confirm that there is ground loop noise between Rotel RCD-02 and the IA-7. You tried it with a difference source (such as your DVD player) and it is quiet (meaning no hissing from 2 feet away from the speaker)
Correct?

Check if RCD-02 has ground. Try the following:
1) Connect RCD-02 to a different power circuit as the amp. Or at least connect RCD-02 to a good power conditioner or surge protector with RFI/EMI filter. We sell the modified Monster power center unit for such purpose.
2) Try a shield power cord with ground.
Having good ground throughout the system is important for Nuforce (or other switching type devices).

[borndevil]

You tried it with a difference source (such as your DVD player) and it is quiet ...
Correct?

Not exactly. The very first time I plugged DVD instead CD Player (turning off all devices, of course) was the first time I heard IA-7 silent. A very low shhh from speakers but absolutely in range with other amplifiers. So I connected also my CDP and it was silent too.

But as soon as I turned off IA-7 and in a while turned on again sweeps start again.
I tried to replay all sequences I had just done but it never gone. I'm sure at least that time it was as it meant to be.

[rustydoglim]

Ground loop noise is hard to trace. I am sure your DVDP can also play CD.
So connect the DVDP (or try an MP3 or Ipod) WITHOUT connecting the other source device!  Do you have noise?
If not, then remove the DVDP (don't connect more than one source for testing purpose) and connect another source. Do this for each source.

One of the source could be interferred by the noise from the amp can sometimes can't lock the signal. You should also tried the other suggestions that I mentioned.

[Dig]

Rotel equipment usually doesn’t have ground on the power cord.
Check also the connections and contacts on interconnects, if they don't make a very nice contact on (-), you can get noise. Yesterday after changing cables, I heard noise (like tube microphony) in one speaker and it was a cable connection.

[borndevil]

Connecting DVD Player with different cable doesn't change noise. Here what I notice today.

First time I turn IA-7 on from back switch, and after with remote, I hear "swisss, sweeps" from speakers, with any source (even ipod) and cable.
I increase volume when CD's playing and when enough a channel switches on, increase again ad after 3 or 4 steps of volume other channel switches on too.

From this time "swisss and sweeps noises" are gone BUT with low volume (and mute) I hear a little "shhhh" (white noise) perfectly tolerable AND an high pitch constant frequency very noticeable from two meters. This last is the one I wouldn't hear as I can hear with low music volumes too, and doesn't depend on source is plugged in. It comes from amplifier!

If my ear is nearly amplifier I can hear the same frequency from the unit 

[rustydoglim]

Do you have ground in your house AC? Does it matter if you flip the two pin AC plug to the wall (i.e pull it out, rotate 180 degrees and plug it in again). In Europe it is hard to tell which one is ground or there is even a ground.
Did you hear the IA-7 playing in the dealer's showroom?
What is the serial number of the IA-7?

[borndevil]

Do you have ground in your house AC?

Yes!

Does it matter if you flip the two pin AC plug to the wall?

Switching phase and neutral have no benefit

Did you hear the IA-7 playing in the dealer's showroom?

No. He came in my city and I asked him to have one.

What is the serial number of the IA-7?

sent via PM

Thank you for support, I really would discover reason of noise as I want to keep this exceptional ampli.

[borndevil]

Ok, I've done so many tests, with grounds, cables and many other things.
I'm sure my IA-7 is noisy so I returned it to my dealer that is going to have test with it.

I tried with ungrounded power source, heavy grounded powersource (in my factory ground is at state of art), shielded and short speaker cables, different speakers, different sources, and it's noisy.

There's an high frequency noise came from the power unit of IA-7 that can be heard very well from speakers. In all these tries it didn't change neither a little bit.

I hope you could fix it as i can buy it again. This is amp I need and has an awesome sound.
Can't wait to have it fixed...

[rustydoglim]

I will wait for your dealer (Dimitri?) to confirm the noise problem.
We seems to have more problem with IA-7 coming from countries with 220-230V AC and the problem is also country dependent. We sold 32 IA-7 to France and haven't heard any complain. But we ran into higher failure rate in China and now we advice customers in area where the power supply is less reliable to use good surge protector with IA-7.   In our lab test, a continuous 265V (above our published rating) power supply voltage will kill IA-7.

[pjbarata]

I will wait for your dealer (Dimitri?) to confirm the noise problem.
We seems to have more problem with IA-7 coming from countries with 220-230V AC and the problem is also country dependent. We sold 32 IA-7 to France and haven't heard any complain. But we ran into higher failure rate in China and now we advice customers in area where the power supply is less reliable to use good surge protector with IA-7.   In our lab test, a continuous 265V (above our published rating) power supply voltage will kill IA-7.

I’ve just got an IA-7E for testing from a local store in Portugal. My setup is based on a Rotel RCD-1070 player with QED Qunex 3 interconnects, plugged to a power conditioner with RFI/EMI filter from Olson and a Supra Lorad power cord. IA-7 is connected directly to mains (220V/50Hz) with original power cord. Speakers are Monitor Audio Silver 8i with QED XT-350 speaker cable.

Fist impressions are quite good, this little integrated seem to have good dynamics and transparency, is quite fast, sound stage is wide and overall sound is quite warm and not fatiguing.

However I can hear a permanent hiss that came from my speakers even from 2 meter away. This is less noticeable while playing music, but during music silences the hiss is quite audible, especially now that I found is presence. It doesn’t increase much while increasing the sound volume, neither disappears with source disconnected (pause or switched off).  This noise is however tolerable, but in my opinion, not acceptable as I’ve different gear from Rotel and Classé Audio, and none of this gear was such an effect.

As I’ve the habit to listen to music late in the evening, Jazz most of the time, this hissing can became quite annoying and tiring.

Will NuForce address fix this problem?

[rustydoglim]

This question was repeated at http://www.audiocircle.com/index.php?topic=33927.10
See my reply there.

[edmond]

Connecting DVD Player with different cable doesn't change noise. Here what I notice today.

First time I turn IA-7 on from back switch, and after with remote, I hear "swisss, sweeps" from speakers, with any source (even ipod) and cable.
I increase volume when CD's playing and when enough a channel switches on, increase again ad after 3 or 4 steps of volume other channel switches on too.
From this time "swisss and sweeps noises" are gone BUT with low volume (and mute) I hear a little "shhhh" (white noise) perfectly tolerable AND an high pitch constant frequency very noticeable from two meters. This last is the one I wouldn't hear as I can hear with low music volumes too, and doesn't depend on source is plugged in. It comes from amplifier!

If my ear is nearly amplifier I can hear the same frequency from the unit 

Hi Jason,

I've just bought an IA-7E and tested it for a few days.   I use Philips DVP9000s SACD/DVD Player as sound source and Isotek Solus as power filter/surge protector.   IA-7E sounds great but it has the same problems as described by borndevil, particularly that only the left channel has sound when switching on the IA-7E at low volume level.   The right channel only gives hissing noise, no music.   If I raise the volume to medium level, everything will be back to normal (both channels sing).

By the way, I have tried other switching power amplifiers, say Philips DFR9000s (Hypex UcD inside) and Aivin DT300 (a china-made digital amplifier which employs Tripath TK2150+TC2000).   Both have no problem and give dead quiet music background.   So I don't think it is the 220V power supply in my living area causing the problems with switching power amplifiers.

Now I have the query:  Is there any manufacturing defect or damage inside the IA-7E? 



Regards,

edmond, from Hong Kong

[rustydoglim]

If I understand you correctly, this problem only happened at startup time (when first power up). See the note posted on our support trouble shooting section:
http://nuforce.com/cgi-bin/helpdesk/pdesk.cgi?do=tr_shooter&tshooter_id=3&branch=12


Repeated here:
The principle of Nuforce amplifier is based on self-oscillation with the speaker as part of the loop. The self-oscillation requires input signal around 20mV (+/- 2mV) to start. Due to the analog based design, speaker’s impedance and natural variations in components’ values, the self-oscillation might start with different input signal strength and delay. After the oscillator has started (within the initial 3 seconds), it will continue to oscillate even when input signal is not present. This design characteristic resulted in different startup input signal strength or delay time observed from amplifier to amplifier (it could be different between two channels within an integrated amplifier).

[edmond]

Dear Jason,

Thanks for your quick reply.

Yes, you guess right.    The problem only happens at start-up time, but I don't agree to the explanation.

Basically, the L/R channels should be balanced and symmetrical.    When both L/R channels are fed equal signals at the same time, they should either sing or mute together.    But now, input signal can activate the L channel only and a stronger signal is further required for activating the rest.    That means the two channels are asymmetrical and different in sensitivity.    Does it make sense?!   


Regards,

edmond

[rustydoglim]

That means the two channels are asymmetrical and different in sensitivity.

Not true, unless there is a defect.  Since the amp design is analog and the way the self oscillation get started, we can't precisely control the "start up".  Self oscillation is a natural circuit behavior and we don't use any external PWM (Pulse Wide Modulation) generator in our design. We are able to push the SO switching frequency to 500KHz (higher than any switching amp on the market).

After the power up with music, turn down the music volume to level 1 LED and as low as possible, if the input sensitivity of the two channels are different (between leve 1 and 2 is huge), you will hear it.  The two channels in IA-7 use identical amp module from production and each module has been tested indepentently.  You can also switch the L/R input to the IA-7 and do the listening test. Obvioulsy I am asking you to do a subjective test with music. If you have access to a sine wave generator to provide a pure input signal, then it will be easier to listen or measure the output of the amp.

Jason