Hypex Ncore

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igy137

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Joined 2005
igy137 said:
Hi All,

I'm almost done building my nc400 based amp, but struggling to identify the source of some noise at amp output.

The amp is a single-chassis combination of a dsp board running an active crossover, a multichannel dac and 6 channels of smps600+nc400 combo.

It runs and sounds good, but when I'm listening very close, a few cm from the driver a periodic noise can be heard on all channels.

I tried to identify the source of noise, but could not manage to find it out.
I made recordings of the dac output with my sound card, and there it seems to be pretty clear, down to around -118db. Normalizing the recording (~88db), the noise seems to be a white noise with no evident periodic patterns. (Recording was done with an emu 1820m, it should be pretty much free of any sound card artifacts).

However, at the same time I also recorded directly the loudspeaker output. That's around -69db at level, but when normalized to 0db, one can clearly hear a periodic pattern. It's roughly every 50ms.

I attached the two audio files recorded, probably somebody has some hints what this can be.

Thanks in advance,

igy
Click to expand...

Anybody any idea solving this issue?
 
J

Julf

Member
Joined 2011
igy137 said:
The amp is a single-chassis combination of a dsp board running an active crossover, a multichannel dac and 6 channels of smps600+nc400 combo.

It runs and sounds good, but when I'm listening very close, a few cm from the driver a periodic noise can be heard on all channels.
Click to expand...

First thing to do is to figure out if the noise comes from the amps, the DACs or an interaction of the two. What happens if you disconnect the DACs from the amps? Have you tried the DSP board + DACs with another amp? Are the connections between the DACs and the amps balanced or unbalanced? What is the earth/ground scheme?
 
D

diyaudnut

Member
Joined 2015
I am currently putting together an active setup with Najda as a DSP pre-amplifier connected to 4+4 channels of amplification for a 4-way speaker system. The connection is pseudo-balanced as recommend in the documentation and as discussed here.

The amplifiers are built in 2 ch boxes. 2 boxes per side (2xNcore + 2xUcD400).

With these independent chassis am i inviting any serious ground loop issues? Looking at igy137's issue being troubleshooted, I just want to watch out for pitfalls as i do this. Please advice.
 
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igy137

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Joined 2005
Julf said:
First thing to do is to figure out if the noise comes from the amps, the DACs or an interaction of the two. What happens if you disconnect the DACs from the amps? Have you tried the DSP board + DACs with another amp? Are the connections between the DACs and the amps balanced or unbalanced? What is the earth/ground scheme?
Click to expand...

The amps are totally silent when the dac is disconnected.
The dac is twisted pear buffalo iii in channel config, using balanced connections. I tried both direct voltage output mode of the dac direct to amp and the original buffalo iii + ivy output stage to amp. No difference, when the dac and the amp is connected, the periodic noise is there.

However, I see/hear no sign of this periodic noise on the dac output (I attached recordings in the original post #8029). (or it's really well buried in the noise).

So far seems like an interaction between the dac+amp?

Grounding. Amp setup is Nc400 + SMPS600, safety earth connected to chassis at connector only. Smps600 standby not used. No external audio connectors used as dac+amp is in the same chassis (so is dsp=input). Speaker connectors are isolated from chassis. Dac and amp is connected using the nc400 supplied cables directly connected to dac (or output stage) output, balanced.
DAC is using it's own linear PS from TP. Nc400 AmpOn signal is tied to ground of DAC PS. (I tried also connecting AmpOn to dac signal ground with no difference). No other connections exist between dac and amp.

Other components in the system (DSP and control mcu) are galvanically isolated with Si8660 (i2s) and Adum2250 (i2c of dac). The I2S output of DSP is checked to be all zeros (using logic analyzer) when the periodic noise is heard.

Thanks in advance for any hints.

igy
 
J

Julf

Member
Joined 2011
igy137 said:
Grounding. Amp setup is Nc400 + SMPS600, safety earth connected to chassis at connector only. Smps600 standby not used. No external audio connectors used as dac+amp is in the same chassis (so is dsp=input). Speaker connectors are isolated from chassis. Dac and amp is connected using the nc400 supplied cables directly connected to dac (or output stage) output, balanced.
DAC is using it's own linear PS from TP. Nc400 AmpOn signal is tied to ground of DAC PS. (I tried also connecting AmpOn to dac signal ground with no difference). No other connections exist between dac and amp.
Click to expand...

Is the DAC connected to the chassis? Is there a reason you don't connect nAmpon to the nc400/smps600 ground?
 
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igy137

Member
Joined 2005
Julf said:
Is the DAC connected to the chassis? Is there a reason you don't connect nAmpon to the nc400/smps600 ground?
Click to expand...

The dac is not connected, at least not intentionally to the chassis - I'm not sure though if the standoff holes are fully isolated on it or not (or on it's PS). Need to check.

Regarding the nAmpon to ground, I seen many builds connecting to the xlr input ground (or was it chassis?), so just took it there. Should it be better connected on the nc400 or smps600 itself? If yes, what's the proper place to connect it?
 
J

Julf

Member
Joined 2011
igy137 said:
The dac is not connected, at least not intentionally to the chassis - I'm not sure though if the standoff holes are fully isolated on it or not (or on it's PS). Need to check.
Click to expand...

Worth checking - there could be a ground loop that way.

Regarding the nAmpon to ground, I seen many builds connecting to the xlr input ground (or was it chassis?), so just took it there. Should it be better connected on the nc400 or smps600 itself? If yes, what's the proper place to connect it?
Click to expand...

The input connector is handy because it is directly connected to the shield of the input cable that goes straight to the nc400 ground. Not sure it really makes any difference, but going via the DAC ground and from there through whatever ground connection between DAC and nc400 sounds like a convoluted route.
 
B

barrows

Member
Joined 2010
TPA boards/ground

igy137 said:
The dac is not connected, at least not intentionally to the chassis - I'm not sure though if the standoff holes are fully isolated on it or not (or on it's PS). Need to check.

Regarding the nAmpon to ground, I seen many builds connecting to the xlr input ground (or was it chassis?), so just took it there. Should it be better connected on the nc400 or smps600 itself? If yes, what's the proper place to connect it?
Click to expand...

Just so you know: Twisted Pear Audio boards do not connect
ground to the mounting holes, so there will be no ground connection to chassis via their standoffs,
 
I

igy137

Member
Joined 2005
Julf said:
OK, so I assume the only ground connection is through the shielding of the cable between the DAC and the nc400.

Worth trying connecting the DAC ground to chassis earth.
Click to expand...

I tried connecting dac ground to chassis, but no success. I now disassembled everything and going to give it a try with a single channel very basic setup using my sound card as balanced input trying to make sure what's ok and what's not.
 
D

diyaudnut

Member
Joined 2015
ChrisPa said:
Nampon

If it floats the amp is muted
Connect to the amp's 0V, the amp produces an output
Click to expand...

can i connect to chassis?

here is the first of 2 nc400 amps and 2 ucd400 amps under construction.
Havent powered it up.

Please suggest some basic tests to avoid sending it up in smoke as i power them on.
 

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