[Fjendbo]

Hi,

I own a NuForce MCA-20 multichannel amplifier which produces a rather loud hissing noise. It's easily audible when nothing is playing and is still audible at low volumes and through quite pieces even though I'm about 2,5-3 meters away. The amplifier is currently connected to a MiniDSP OpenDRC-DA8. I have also tried connecting it to an older NAD preamplifier with the same results where the NuForce and NAD were the only devices connected to the power outlet. Both with power cords with and without ground to the NuForce.

The hiss is not present when nothing is connected to any of the inputs.

Do you have anything else I can try or could the amplifier be defective?

Any help is appreciated!

Thank you.

[witchdoctor]

Hi,

I own a NuForce MCA-20 multichannel amplifier which produces a rather loud hissing noise. It's easily audible when nothing is playing and is still audible at low volumes and through quite pieces even though I'm about 2,5-3 meters away. The amplifier is currently connected to a MiniDSP OpenDRC-DA8. I have also tried connecting it to an older NAD preamplifier with the same results where the NuForce and NAD were the only devices connected to the power outlet. Both with power cords with and without ground to the NuForce.

The hiss is not present when nothing is connected to any of the inputs.

Do you have anything else I can try or could the amplifier be defective?

Any help is appreciated!

Thank you.

Some amps have a "Gain" knob that needs to be turned down so you can't hear the hiss.

If that doesn't work I would send it in for service.

[Fjendbo]

Some amps have a "Gain" knob that needs to be turned down so you can't hear the hiss.

If that doesn't work I would send it in for service.

Thank you for answering!

The amplifier only has an on/off button for outside controls. Should I be able to find a "gain" knob if I remove the top cover?

EDIT

Just looked at a picture and I may have found a gain "knob"




Am I safe to try and adjust it?

[tubesaab]

Hello fjendbo

to me it looks like a regulator to powersupply... be careful to adjust  without knowing

Best Bjarne

[witchdoctor]

Gain knobs are generally on the back of the amp and labeled as such. I would not adjust anything inside the amp.

See if you can try a different set of interconncets.

[Fjendbo]

Gain knobs are generally on the back of the amp and labeled as such. I would not adjust anything inside the amp.

See if you can try a different set of interconncets.

Okay.

I have already tried 3 different phono cables.

[Fjendbo]

Hello fjendbo

to me it looks like a regulator to powersupply... be careful to adjust  without knowing

Best Bjarne

Hi Bjarne,

I'm no expert but by regulating the power supply voltage aren't you regulating gain then? Of course, I don't know if it regulates the power supply voltage.

[tubesaab]

Hello Fjenbo

no,, regulate supply is not the same as regulate gain

it will maybe lower the watt output,,,but can also destroy the sound,,

you can make a resistor wiring on output of the amp,,,it will lower the output,,,but i do not know the value of this  (you can try a 10kohm potmeter)

[tubesaab]

correction i mene a potmeter on the input   not on output   

but if the hiss are on all niveau on input then the amplifier will still be hissing   

[Fjendbo]

Yesterday, I tried adding a ferrite core to one of the phono cables going to the tweeter. No effect.
I tried disconnecting the phono cable from the MiniDSP going to the tweeter. No effect.
I tried disconnecting the phono cable from the amplifier going to the tweeter as well. No effect.
I tried disconnecting all phono cables from the amplifier. No effect.

Still hiss from both tweeter and woofer.

Am I looking at a defect?

[avahifi]

It would be a very good idea to connect the outputs of the amp to a good oscilloscope to make sure the hiss you hear is not a byproduct of very high frequency oscillations.

These can overheat and damage speaker voice coils.

Frank

[ricardojoa]

I have the nuforce sta100 and the hiss is hearable at 5 feet.

It hiss even without connecting the rca. So i guess it has to do with piwer regulator.
I also read a few people have the sane issue.

[Fjendbo]

Hi,

Thank you for your answers. And sorry for the late reply.

Even the missus noticed the silence when I switched off the amplifier the other day and if she notices, there's definitely something about it. I will try to do a measurement to show how bad it is.

Okay, I will have someone help me check for very high-frequency oscillations. Thanks for the tip.

So it's maybe a general NuForce issue? It really bugs cause I usually don't listen very loud, so the noise is quite noticeable.

[Fjendbo]

Okay, I don't think a measurement really shows it so there's a link to the audio file of the measurement as well. The measurement is taken 1 cm from the tweeter.


Power ON


Power OFF

Audio file: https://www.dropbox.com/s/x1hh3y2m1is8432/Noise.mp3?dl=0

[Fjendbo]

Quick update. I had a friend do a quick measurement of the amp - he kept it for further testing.

Measurement done with oscilloscope over the speaker terminals of a tweeter. As far as I remember, it showed a max low at -17 mV and max high at 24 mV. 41 mW peak to peak!

I asked him to send a picture of the measurement and will post it here when I have it.

[Norman Tracy]

What is NuForce's customer support take on this audible hiss issue? We can speculate but they are the ones with all the public and proprietary technical data and customers' experiences to authoritatively deal with this issue.

[Fjendbo]

Hi Norman,

I am in contact with NuForce support but it's a slow process.

[Fjendbo]

Picture of the measurement. I'm not very good at reading it, unfortunately. If anyone can shed some light on what's happening, it will be appreciated.

[maxflat]

Hello
I face the same Hiss issue. from the beginning the center channel did made a bit of noise. Sent back to dealer who controlled and said it was norl with this type of amplifier
I got used to this minimal hiss
Over time I had a surround channel starting to hiss much more, to a point we noticed it during films as the surround don´t usually function all the time
Now my center makes a huge hiss ...
Don't know what to do ...