Hiss and crackle from a Hypex NCore based amp

[paulzhere]

Hi

I purchased this Hypex NCore power amp HPA-S500NC 2x500W @4ohm from Audiophonics in 2022.

This amplifier has developed a hiss and crackling noise which I think is not normal. When I bring my ear a few centimeters from the tweeters of my speakers, I can hear this noise. But when I connect my same speakers with the same cables to my Emotiva BASX A300 power amplifier, the noise is much lower. Of course, there's a faint hiss but not as bad as this Audiophonics amp. This surprises me because it is based on a hypex module which should have a noise floor way lower than the Emotiva amp. It should be virtually quiet. I have recorded this noise and I try to attach it here as a zip file. Thanks for any help and support.

Cheers
Paul

 

[Golfx]

Hiss might be a gain mismatch between your AV processor and your amp=higher the gain the louder the hiss. Plus speakers with higher efficiency tend to hiss more when using high gain AVPs.

Does your amp offer adjustable gain settings? I am not familiar with audiophonics‘ reputation. I have had Nord, March and Apollon Hypex/purifi monoblocks and multi8 amps and have had zero, zero, hiss.

 

[PENG]

Hiss might be a gain mismatch between your AV processor and your amp=higher the gain the louder the hiss. Plus speakers with higher efficiency tend to hiss more when using high gain AVPs.

Does your amp offer adjustable gain settings? I am not familiar with audiophonics‘ reputation. I have had Nord, March and Apollon Hypex/purifi monoblocks and multi8 amps and have had zero, zero, hiss.

But he said "This amplifier has developed a hiss and crackling noise which I think is not normal. ". and he bought it in 2022. That seems to imply it didn't have that hiss and crackling in the beginning and we don't know when it "has developed.." So, it may just have developed a defect, could even be some loose connections such as in the grounding scheme, and/or loose connections to the I/Os, best bet is to email Audiophonics. I read some posts by at least one or two of their customers, that they did get reasonably good support, that is iirc..

 

[paulzhere]

Thanks for your valuable inputs @Golfx and @PENG . I have an update. I have found the source of the issue and it is the source (pun not intended). I removed the all the inputs and turned on the amp and it is indeed dead silent (as @Golfx mentioned) even though I have quite sensitive speakers - 92dB. I was thus assured that the issue is not with the amp. The amp is fed from a MiniDSP Flex RCA which I recently acquired and this seems to be the problem. Previously I was using a MiniDSP 2x4 HD which didn't seem to have this issue. I upgraded to the Flex to have a lower noise floor and better sampling rates to play with, but ironically it seems to have backfired. This is counterintuitive because the Flex has been measured at ASR to have a much higher SNR than the original 2x4 HD. So I ask myself if my unit is faulty. I purchased it used from a second-hand website here in France. I need to get hold of the guy and ask him if he has the invoice. What is intriguing is that the crackling is very rhythmic... If you listen to the attached recording, it is like 3 crackles per second which gives us a frequency in the ballpark of 180 hz. I wonder if there is something else nearby which is emitting such a frequency. But then why was the 2x4 HD not effected by this?

I already contacted Audiophonics about the issue and they promptly replied asking me to disconnect all the sources from the amp and then test again (which I did). I will come back with further updates, if any.

Best
Paul

 

[PENG]

Thanks for your valuable inputs @Golfx and @PENG . I have an update. I have found the source of the issue and it is the source (pun not intended). I removed the all the inputs and turned on the amp and it is indeed dead silent (as @Golfx mentioned) even though I have quite sensitive speakers - 92dB. I was thus assured that the issue is not with the amp. The amp is fed from a MiniDSP Flex RCA which I recently acquired and this seems to be the problem. Previously I was using a MiniDSP 2x4 HD which didn't seem to have this issue. I upgraded to the Flex to have a lower noise floor and better sampling rates to play with, but ironically it seems to have backfired. This is counterintuitive because the Flex has been measured at ASR to have a much higher SNR than the original 2x4 HD. So I ask myself if my unit is faulty. I purchased it used from a second-hand website here in France. I need to get hold of the guy and ask him if he has the invoice. What is intriguing is that the crackling is very rhythmic... If you listen to the attached recording, it is like 3 crackles per second which gives us a frequency in the ballpark of 180 hz. I wonder if there is something else nearby which is emitting such a frequency. But then why was the 2x4 HD not effected by this?

I already contacted Audiophonics about the issue and they promptly replied asking me to disconnect all the sources from the amp and then test again (which I did). I will come back with further updates, if any.

Best
Paul

That's the good news, but bad news for the Flex. You should contact minidsp about that as they may have experienced similar kind of issues reported by other users. Just make sure you have the most up to date FW and SW. Did the unit has this issue right from start or it just developed?

As you said, the Flex should be silent, if even the 2X4HD was silent to you. There is just no comparison between the 2, the Flex is a major upgrade!

 

[paulzhere]

That's the good news, but bad news for the Flex. You should contact minidsp about that as they may have experienced similar kind of issues reported by other users. Just make sure you have the most up to date FW and SW. Did the unit has this issue right from start or it just developed?

As you said, the Flex should be silent, if even the 2X4HD was silent to you. There is just no comparison between the 2, the Flex is a major upgrade!

I am not sure if the unit had an issue right from the beginning or it just developed. Frankly, I did not put my ears next to the the tweeters when i got the unit and connected it. My bad, should have done it. Another probably important thing I forgot to mention is that I have also changed the interconnect cables recently. I went from what I thought were crappy cables to some decent Oehlbach 75 Ohm double shielded cables. Ironically, that could be the issue too! This has been reported before, for example, in this post here:

Crackling noise with miniDSP after upgrading analog cables

I use a miniDSP 2x4 since some years back. Wanted to improve my cabling, until now I have had some really inexpensive cables with bad fitting RCA-connectors. Bought some double screened (copper braid and foil) low capacitive coaxial cable, Canford SDV-M. Had some goldplated RCA-connectors from...

www.diyaudio.com

This is completely counterintuitive, but well, can happen. I plan to swap back the cables when I get home this evening and see what results.

Cheers

 

[PENG]

I am not sure if the unit had an issue right from the beginning or it just developed. Frankly, I did not put my ears next to the the tweeters when i got the unit and connected it. My bad, should have done it. Another probably important thing I forgot to mention is that I have also changed the interconnect cables recently. I went from what I thought were crappy cables to some decent Oehlbach 75 Ohm double shielded cables. Ironically, that could be the issue too! This has been reported before, for example, in this post here:

Crackling noise with miniDSP after upgrading analog cables

I use a miniDSP 2x4 since some years back. Wanted to improve my cabling, until now I have had some really inexpensive cables with bad fitting RCA-connectors. Bought some double screened (copper braid and foil) low capacitive coaxial cable, Canford SDV-M. Had some goldplated RCA-connectors from...

www.diyaudio.com

This is completely counterintuitive, but well, can happen. I plan to swap back the cables when I get home this evening and see what results.

Cheers

I have never tried using the so called "digital cable" as analog interconnects and would not have thought it could cause issues with noise for short length (say less than 3 meters) but I guess anything can happen. To avoid any such potentially negative effects it is best to the interconnects designed for analog use. Anyway, it is easy to swap the original RCA analog interconnects you had before to see if it makes a difference, and do keep us posted on the results, good luck!

 

[paulzhere]

Thanks @PENG . So the issue is indeed the MiniDSP. I switched back the interconnects to my older ones, the issue persists. Something I remarked is that the crackling gets worse when I use Bluetooth and connect a Bluetooth device to it. So much so that I can hear the crackling from my MLP which is like 3,5 m away! I am starting to form the impression that the Bluetooth chip is interfering with the audio path somehow. Seems like I was better off with the 2x4 HD, no Bluetooth, no issues.