Popping in speakers when starting Wiim Ultra

[chito.limson]

Here’s my setup:

The Wiim Ultra is connected to the Fosi Audio ZD3 preamp/DAC via USB. Trigger out from Wiim to ZD3.

The ZD3 is connected to two Fosi Audio V3 Mono via XLR.

In the ZD3, volume control is BYPASSED. I control volume using the Wiim Ultra on the app or on its remote control.

When I turn on the Wiim Ultra, everything else turns on too as they should. However, two pops come out of the speakers: one soft and one louder than the first pop. Even if I start the Ultra with the volume set at ZERO, the pops still happen. I removed the trigger cable between the Ultra and the ZD3, and turned on the ZD3 a little later after starting the Ultra, but the pops still happen.

To experiment, I removed the USB connection between the Ultra and the ZD3, and switched to coaxial connection between the two. I put back the trigger cable between the two units and the start up pops disappeared.

Why is this happening?

 

[hgo58]

I tried to modify a USB cable and remove first the +5V wire with no success and then the ground wire and still the same behavior.

That is not what I write about.

The DAC startup sequence on USB may be the cause of the popping. This is not needed for optical or coax inputs.