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Class D Switching Power Amplifiers and Power D/A conversion

Hypex UcD Build Problem with Hum
Hypex UcD Build Problem with Hum
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Old 10th February 2017, 11:55 AM   #1
doritos123 is offline doritos123  Netherlands
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Default Hypex UcD Build Problem with Hum

Hello everyone,

I am hoping to get some help here with my little DIY amp project here.
It is based on Hypex UcD250LP OEM.

The OEM module doesn't have an input buffer, and has quite low 1k8 ohm input impedance. So i also need an input buffer board.
I decided to try and build an input buffer based on Hypex recommendation.
The input buffer board is now done and built with stripboard pcb.

For now, i have 2x Input buffer and 2x UcD250LP.
They are all powered by Hypex SMPS1200.
The input buffer board is powered by the Vaux of the SMPS.

Yesterday i finished wiring everything together, and there is HUM from both channel. And the input to the input buffer is not yet connected. I tried to disconnect the power to the input buffer board, and the HUM is gone.

In the attachment is the diagram how everything is wired.

Do i make mistake with the wiring? Or any other mistakes?
Thanks!
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File Type: jpg SMPS_UcD_buffer.JPG (115.1 KB, 279 views)
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Old 11th February 2017, 06:27 AM   #2
ds23man is online now ds23man  Netherlands
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The aux voltages ain't regulated.
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Old 11th February 2017, 12:51 PM   #3
ungie is offline ungie  Canada
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Remove the GND connection from your input buffer to the UcD board. You only need the GND from the SMPS. The way you have it wired creates a ground loop.
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Old 11th February 2017, 01:24 PM   #4
ds23man is online now ds23man  Netherlands
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Because it is a balanced connection, no groundloop. You will need some regulators for the power supply of the input buffer. All Hypex OEM converters have them on board.
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Old 11th February 2017, 10:42 PM   #5
sumotan is offline sumotan  Indonesia
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Hi Ds23man,
Is the aux supply a clean & quiet supply . Do you think
there's an advantage to power the regulators on
the UCD with this supply instead ?

Thks
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Old 12th February 2017, 06:18 AM   #6
ds23man is online now ds23man  Netherlands
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The aux outputs on all Hypex SMPS are unregulated. You will need to add power regulators.
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Old 12th February 2017, 06:40 AM   #7
sumotan is offline sumotan  Indonesia
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Yes ds24man this Im aware. What Im asking is , is it worth the effort
to bypass the supply of the regulators on the UCD & power the regulators
with Aux supply of the smps

Thks
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Old 12th February 2017, 07:14 AM   #8
ds23man is online now ds23man  Netherlands
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Quote:
Originally Posted by sumotan View Post
Yes ds24man this Im aware. What Im asking is , is it worth the effort
to bypass the supply of the regulators on the UCD & power the regulators
with Aux supply of the smps

Thks
No.
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Old 12th February 2017, 07:24 AM   #9
doritos123 is offline doritos123  Netherlands
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Hi ds23man,

According to the spec sheet, SMPS1200A400 has the jumper to select regulated or unregulated Vaux.
I have the jumper in the regulated position.

I also tried to power the input buffer board with battery source, same problem.

Now the HUM is gone after i moved everything into a chassis. It is quiet now with the input disconnected.
I guess without chassis, the circuit is just acting like an antenna.

But now, there is still HUM when the input is connected to the source.
I suspect this is caused by the cable.
My source has RCA out, and my amp has XLR in. And i use converter cable from RCA to XLR. The converter cable has 2 leads, with pin 1 and pin 3 soldered together at the XLR end.
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Old 12th February 2017, 07:50 AM   #10
ds23man is online now ds23man  Netherlands
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Ground loop. Source and amp both connected to the mains ground?
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