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Class D Switching Power Amplifiers and Power D/A conversion

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Old 26th January 2017, 08:44 AM   #11
diyaudnut is offline diyaudnut  United States
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I did some debugging with an oscilloscope (Gnd probe to chassis and signal probe to +ve speaker out)
I mostly only seem to locate what appears to be switching frequency of the module around 400KHz. The test tone freq i am playing does appear as an envelope. I couldnt figure out a way to trigger to stably display just the test tone freq at the amp output. However, the waves dont appear to be clipping.
Not sure what any stability related oscillations would look like.

Also observed the DAC output (one signal out of the balanced pair) on the osclloscope and it appears fine.

But looking at the signal levels on the oscilloscope i have a theory. Please advice if this is a possibility.
I seem to be playing very close to the base noise level of the DAC during nominal listening. This is because the speaker is 94dB sensitive and are driven by high power UCD400.
At these low levels the noise output of the DAC seems to modulate with the music playing.
At higher output levels, things get too loud for comfort but the distortion isnt noticeable.

Is this just an issue with my gain stages?
If i can reduce the gain of the amp modules, or add a clean balanced passive attenuation to the XLR cable from DAC to amp, maybe i can play the DAC at a level where it performs the best.

I am new to this oscilloscope, so still figuring things out. Over the weekend if i can get back on this i will try and post some pics.

Please comment.

thanks

Last edited by diyaudnut; 26th January 2017 at 08:47 AM.
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Old 26th January 2017, 09:06 AM   #12
Julf is offline Julf  Europe
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Quote:
Originally Posted by diyaudnut View Post
I mostly only seem to locate what appears to be switching frequency of the module around 400KHz. The test tone freq i am playing does appear as an envelope. I couldnt figure out a way to trigger to stably display just the test tone freq at the amp output. However, the waves dont appear to be clipping.
Good!

Quote:
Is this just an issue with my gain stages?
If i can reduce the gain of the amp modules, or add a clean balanced passive attenuation to the XLR cable from DAC to amp, maybe i can play the DAC at a level where it performs the best.
Worth testing - just make a passive attenuator out of a couple of resistors. If it turns out to solve the problem, you can then change the feedback resistor of the ncore.
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Old 26th January 2017, 09:43 AM   #13
ds23man is offline ds23man  Netherlands
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Or change the gain of the dac outputstage.
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Old 27th January 2017, 08:17 AM   #14
berga12 is offline berga12
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Hi guys
I'm facing some problems, i'm not able to put in Ready state my NC500OEM

it seems I'm not able to show "HW mode" or the right NAmpON to the module...

Any suggestion? I also tried without Flat cable and just turning the switch, but No Ready Led turn on.
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Old 27th January 2017, 03:27 PM   #15
diyaudnut is offline diyaudnut  United States
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Quote:
Originally Posted by Julf View Post
Good!

Worth testing - just make a passive attenuator out of a couple of resistors. If it turns out to solve the problem, you can then change the feedback resistor of the ncore.
Quote:
Originally Posted by ds23man View Post
Or change the gain of the dac outputstage.
Thanks Guys.

Changing the DAC output stage gain is harder as i dont have the schematic or much help.
I will try a passive attenuator on the XLR interconnect from DAC to the amp.
If things improve i will remove the gain adjustment resistor in ncore and ucd400
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Old 28th January 2017, 08:39 PM   #16
Antana is offline Antana  Europe
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Quote:
Originally Posted by berga12 View Post
Hi guys
I'm facing some problems, i'm not able to put in Ready state my NC500OEM

it seems I'm not able to show "HW mode" or the right NAmpON to the module...

Any suggestion? I also tried without Flat cable and just turning the switch, but No Ready Led turn on.
Did it work before or is this a new build?
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Old 29th January 2017, 06:47 AM   #17
Julf is offline Julf  Europe
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Quote:
Originally Posted by berga12 View Post
I'm facing some problems, i'm not able to put in Ready state my NC500OEM
Maybe talk to your supplier? The nc500OEM is (as the name implies) an OEM product, not sold directly to customers.
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Old 29th January 2017, 06:58 AM   #18
ds23man is offline ds23man  Netherlands
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Quote:
Originally Posted by Julf View Post
Maybe talk to your supplier? The nc500OEM is (as the name implies) an OEM product, not sold directly to customers.
+1
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Old 29th January 2017, 09:30 AM   #19
TNT is online now TNT  Sweden
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Originally Posted by ds23man View Post
+1
Your naming of this thread just set it up for the good ol discussion that was closed. Thats why I suggested "Hypex NC400 build thread".

//
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More distortion to the people!
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Old 29th January 2017, 09:34 AM   #20
ds23man is offline ds23man  Netherlands
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Well, there will be Ncore based plate amps for the diy market. Fits nicely in this thread.
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