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Pops and HF Noise during Power Off/On - B3 DAC

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Could someone please help - I am having an issue where on power on I get a pop through my speakers (or headphones) and power off a pop followed by a short high-frequency sort of garbled/scratchy noise for a second.

I measured for DC offset at the loudspeaker terminals. With no music playing and with the Placids off, I get a reading of around 23mV. When on, this is around 24mV. When I power off, I get a spike for half a second up to around 150mV, dropping to around -24mV then back to 24mV. These measurements were from the Right Channel, strangely, the Left Channel measured at 5mV more.

I am really at a loss as to what the issue is. At first I thought it was an issue with the power supply and DC offset, but I have been starting to think it is an issue with the grounding scheme of the outputs. When I disconnected the balanced XLR cables from my two NCore amplifiers and listened through headphones I don't get the pops and noise. It is all wired as I have seen in the guidance - Positive, Negative and GND wired from the IVY-III to the outputs, Pin 1 not connected to chassis (connected to signal GND), at the NCore side this is the same but Pin 1 is also connected to the chassis. I understand the AES standard is that signal ground is not connected to pin 1 and pin 1 goes to the chassis ground, so I tried this and it makes no difference. I am starting to wonder what else the issue may be? I had a problem with the AVCC module on the Buffalo III board in that it blew and the replacement was a AVCC-SR. Could this be the issue if the other boards are Tridents and not Trident-SR?

I am running out of ideas on what is the issue, any help would be greatly appreciated.

Further details on build as below:
Buffalo III DAC
SPDIF input board
Raspberry Pi with Kali Reclocker
Amanero USB
Arduino Due with DimDim shield to control the DAC
Placid HD
Placid HD Bipolar
AMB Sigma11 PSB for the Arduino and RPi
Good question, I got exactly the same issue and was/am never able to solve it (I always need to turn off the amps first, otherwise indeed "a short high-frequency sort of garbled/scratchy noise for a second" happens when I power off the DAC first).

This with a similar setup(ncores/b3) and I tried the same things with pin 1.

Any input on this subject is more then welcome!

We must be doing something wrong.
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