Strange sound from speakers with Ncore amp + Apollo Twin X

[ppataki]

Dear All,
I have an NC250 based amplifier (Audiophonics PA-S250NC) and I am really happy with it!
I have connected various DACs to it: Focusrite Clarett, Motu M2, SMSL M300, Audient ID44 - it worked fine with all of these

Yesterday I connected an Apollo Twin X to it - then I got a surprise: there is a strange crackling/clicking sound coming from the speakers; it is not ground loop, it is not the "sound" of my PC; it sounds more like a "clock generator" noise or a switching power supply noise (it is a periodic noise that gets faster when I start playing silence in Jriver)
The Twin X is brand new; also I have tried an Apollo X4 and that did the same...really strange

Does anybody have any idea what could be the root cause and how I could fix it?
The only thing I am planning to try is to connect them in an unbalanced fashion but first I need to get some adaptors for that
Many thanks in advance

 

[ppataki]

I made a video about the noise:
https://drive.google.com/file/d/1Sz52Po35YxCEUIM2R14u5IEvWz92_Msy/view?usp=sharing

 

[Doodski]

Can you install a oscilloscope software and send post a file/pic/video of the noise?

 

[ppataki]

Can you please recommend such a software?
Thank you

 

[Doodski]

Are you on Windows or Linux?

 

[ppataki]

Windows

 

[Doodski]

Okies. Let me look about and maybe even test drive some stuff before recommending something.

Do you have a microphone?

 

[Doodski]

Hmmz. The last time I did this finding a good oscilloscope for Windows audio was pretty straightforward. I've downloaded maybe 20 softwarez to my "disposable PC" and all are wonky, buggy, deleted, inoperative or blocked by my security suite because they are a apparent security threat. SorrY.

 

[Doodski]

I suggest start by dividing and conquering. Figure out if the sound is coming from the PC by using headphones from the PC and then use a separate audio source connected to the amplifier to determine if the sound is coming from the amp or from the source. You may need to use a separate amplifier instead of your Audiophonics PA-S250NC.

 

[March Audio]

Can you

Dear All,
I have an NC250 based amplifier (Audiophonics PA-S250NC) and I am really happy with it!
I have connected various DACs to it: Focusrite Clarett, Motu M2, SMSL M300, Audient ID44 - it worked fine with all of these

Yesterday I connected an Apollo Twin X to it - then I got a surprise: there is a strange crackling/clicking sound coming from the speakers; it is not ground loop, it is not the "sound" of my PC; it sounds more like a "clock generator" noise or a switching power supply noise (it is a periodic noise that gets faster when I start playing silence in Jriver)
The Twin X is brand new; also I have tried an Apollo X4 and that did the same...really strange

Does anybody have any idea what could be the root cause and how I could fix it?
The only thing I am planning to try is to connect them in an unbalanced fashion but first I need to get some adaptors for that
Many thanks in advance

Can you record and post the sound, just on a phone will do. I have a strong suspicion of what it is.

 

[dezza]

Can I suggest try other USB cable.

I spent close to a week trying to figure out a random crackle sound, while using a usb dac, and it turned out to be the usb cable, which had been in use for years without a problem.

 

[ppataki]

Can you

Can you record and post the sound, just on a phone will do. I have a strong suspicion of what it is.

The recording is in this thread; the second post
Thank you

 

[ppataki]

Can I suggest try other USB cable.

I spent close to a week trying to figure out a random crackle sound, while using a usb dac, and it turned out to be the usb cable, which had been in use for years without a problem.

This is a Thunderbolt interface

 

[ppataki]

I suggest start by dividing and conquering. Figure out if the sound is coming from the PC by using headphones from the PC and then use a separate audio source connected to the amplifier to determine if the sound is coming from the amp or from the source. You may need to use a separate amplifier instead of your Audiophonics PA-S250NC.

With other amps there is no noise; however the same amp has no noise with other DACs either
So only the combination of any Apollo X interfaces + the NC250 results in noise
Really strange
I have ordered some adaptor plugs so next week I will try unbalanced connection - I have a gutfeel that the balanced connection of the Apollo and that of the amp are somehow not 'compatible'

 

[March Audio]

With other amps there is no noise; however the same amp has no noise with other DACs either
So only the combination of any Apollo X interfaces + the NC250 results in noise
Really strange
I have ordered some adaptor plugs so next week I will try unbalanced connection - I have a gutfeel that the balanced connection of the Apollo and that of the amp are somehow not 'compatible'

It is (quite) possibly high frequency noise from the dac intermodulating with the switching frequency of the amp.

If the case there are 2 issues here. The dac output has excessive HF noise (in the region of 400kHz). The other dacs have sufficiently filtered this out.
The amp does not have RF filtering on the audio input.

To prove you would need to measure the output of the dac in the 400kHz region and or put a filter in line with the audio input (not something you can buy off the shelf)

 

[sfabio]

It is (quite) possibly high frequency noise from the dac intermodulating with the switching frequency of the amp.

If the case there are 2 issues here. The dac output has excessive HF noise (in the region of 400kHz). The other dacs have sufficiently filtered this out.
The amp does not have RF filtering on the audio input.

To prove you would need to measure the output of the dac in the 400kHz region and or put a filter in line with the audio input (not something you can buy off the shelf)

Many thanks for the hints Alan, I've solved my issues with Motu ultralite mk4 with an input RF filter
My solution
Thanks again for your help!

 

[March Audio]

Many thanks for the hints Alan, I've solved my issues with Motu ultralite mk4 with an input RF filter
My solution
Thanks again for your help!

Excellent

All amps should have input RF filters, not just class d. AFAIK we are the only manufacturer of this type of amp (Hypex OEM) implementing them.

 

[sfabio]

Excellent

All amps should have input RF filters, not just class d. AFAIK we are the only manufacturer of this, type of amp (Hypex OEM) implementing them.

Hats off to You

 

[pos]

The dac should not emit such noise in the first place.
Out of curiosity do you know if neurochrome implements such a filter in its buffer?

 

[March Audio]

The dac should not emit such noise in the first place.
Out of curiosity do you know if neurochrome implements such a filter in its buffer?

Whilst yes you are correct that it shouldnt, out of band junk causing a problem is always a possibility (even if unlikely) whether from a dac or external sources. Its just good practice to input filter.

The input filter in our amps is separate to and before the buffer, at entry on the xlr socket. The buffer should also have appropriate bandwidth limiting. I dont know what the neurochrome does in this respect.