NC502MP - Hiss in one channel

[sergedc]

Hi,
I acquired a DIY made NC502MP Hypex 2 channel power amp, second hand.

After connecting everything, without music:
- When I put my hear on the right channel tweeter, its dead silent
- When I put my hear on the left channel tweeter, I can hear a very very slight hiss. At 5cm (2 inch), I definitely cannot hear it. It's that small.

I have done all the necessary test to ensure that its not coming from the dac, cables, speaker. It's the amp.

Does it mean there is something wrong with the amp? Or it is possible that 1 channels are not as silent as the other one. In the review, there was a difference in THD+N between the 2 sides. Is it possible that I am hearing this difference?

From the review of another NC502MP (https://www.audiosciencereview.com/...keye-nc502mp-review-6-channel-amplifer.27607/):

 

[staticV3]

In the review, there was a difference in THD+N between the 2 sides. Is it possible that I am hearing this difference?

It's possible, yes.

 

[valerianf]

@sergedc Your real life issue proves that a hiss test metric needs to be added to the measurement of Class D amps.
What is the sensitivity of your speakers?

 

[sergedc]

@sergedc Your real life issue proves that a hiss test metric needs to be added to the measurement of Class D amps.
What is the sensitivity of your speakers?

Speakers are Totem Mani 2. Not that sensitive.
Sensitivity: 85dB/W/m (2.83V). Nominal impedance: 4 ohms.

 

[jimk1963]

Speakers are Totem Mani 2. Not that sensitive.
Sensitivity: 85dB/W/m (2.83V). Nominal impedance: 4 ohms.

Did you ever figure out the issue? Looking at NC502MP amps as well.

 

[Deleted member 48726]

Since it is DIY I would look inside to see if anything's amiss.

Someone here made a point in resale value and reliability with DIY assembled class D amps. Seems like true prophety.

 

[Sokel]

Someone here made a point in resale value and reliability with DIY assembled class D amps. Seems like true prophety.

The "someone" only follows common sense that says after sales support is more important than the actual sale

Edit:How can NC502MP be diy?
That module is only for OEM customers.
Someone is not playing by the rules as it seems...

 

[pma]

The "someone" only follows common sense that says after sales support is more important than the actual sale

Edit:How can NC502MP be diy?
That module is only for OEM customers.
Someone is not playing by the rules as it seems...

I have seen several advertisements here when the end user, not OEM contractor, was selling the Ncore module alone.

 

[pma]

I have done all the necessary test to ensure that its not coming from the dac, cables, speaker. It's the amp.

Have you tested the amp with input connector shorted? Almost any beginner who complains for buzz/hiss does not do it properly. The test with open input connector (connected to nothing) would be invalid.

 

[jimk1963]

Have you tested the amp with input connector shorted? Almost any beginner who complains for buzz/hiss does not do it properly. The test with open input connector (connected to nothing) would be invalid.

Interesting comment - why is that?

 

[pma]

Because it catches all interference EMI fields from the surrounds into the input impedance of the amp. The higher the input impedance, the worse. And because the physical placement of two channels is different, so is the induced voltage. The plot posted in #1 is of no relevance to this.

 

[jimk1963]

Because it catches all interference EMI fields from the surrounds into the input impedance of the amp. The higher the input impedance, the worse. And because the physical placement of two channels is different, so is the induced voltage. The plot posted in #1 is of no relevance to this.

Ah I see, thanks. I guess amp inputs are several 10’s of kOhms while pre-amp outputs are maybe 5-500 ohms… So in normal operation, the amp input is fed from a low impedance. And besides that, the super high input impedance of the amp is just a pick-up magnet for any kind of nearby noise. Thanks, that’s a great debugging tip.

 

[Chaos01]

Hi, i got similar Problems. posted also here:

Audible noise/hiss from Hypex NC502MP based amp (KJF MA-01), is it to be expected?

Hi. I've recently received a KJF MA-01 amplifier configured with 3x Hypex NC502MP modules. When testing it with my speakers (Ascendo Immersive Audio CCRM12-P), which are specified as fairly sensitive at 99 dB/W, I can hear a hiss from the speaker. My room is a dedicated mancave/tiny home...

www.audiosciencereview.com

Do you have cables or rca/xlr inputs near to the power capacitors or the green coil?

Maybe it will help, i will let you know if i got a update.