Constant 1kHz whine on audio with Daisy Pod

I’ve just hooked up my Daisy pod for the first time, and running through the example projects through the web programmer, I’m finding I have a really loud 1kHz tone on the audio (about 40dB above the noise floor). Looking at the waveform in a scope in my DAW, I can see it looks a 15% duty cycle square wave so I’m guessing it’s related to a poor power supply (from USB) ?

Is there anything I can do about this ? It’s pretty unusable as it is right now. Is there a way of powering the daisy pod from an external PSU? I don’t see any suitable terminals.

Try running Daisy from a rechargeable USB battery pack, such as is used for charging mobile phone.

Good idea. However, when I power the pod from a USB power pack which is fully charged, I get massively loud mains hum which gets louder when I touch the case of the USB battery pack. I do not get the same louder buzz when I touch the metal chassis of the jack plug, so can only assume it’s something about the earth connection on the pod ?

Looking at the schematics I can see the AGND and DGND are joined via the pod, so not sure where to go next.

Turned out it was a dry solder joint on gnd pin of the line out jacks. They were all a bit dry actually, but now I’ve touched them up, it’s all running much better with a hugely improved noise floor!

Thanks

Actually, there is still a 1kHz tone when powered from a passive USB hub but it’s much lower in level and goes away completely when running from the battery pack or powered socket.