Hypex UcD Build Problem with Hum

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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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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.
 
The converter board doesn't have input buffer.
And Hypex doesn't sell the OEM parts to consumers.

I now use the LM4562.

After fixing my RCA to XLR cable, the hum is now gone.
I am now in the process to build the input buffer with a nice PCB.
And finally (and hopefully) assembly the amp.

My target is a 6 channel amp in one chassis.
4x UcD250 with 4x LM4562 input buffer
2x UcD400
1x SMPS1200A400 (suppy all the UcDs)
1x SSR04 Super Regulator (supply the input buffer)

This is actually a big project for me to tackle. So might take some time.
But i keep learning from this forum. :)
 
Hello.
Will be the hypex UcD xxxLP OEM converter board a solution?

The UcDxxxLP converterboard is nothing more than a PCBA that makes the 16P header easily accessible for quick evaluation. It does not contain a buffer, only some LED's.

Since your are an OEM yourselves, I suggest you design your own input board, basically the OEM converter with opamp, possibly trigger input or whatever you want. If you wish, you can post your design here and request a review.
 
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