Hum problem with Mini-I Pro 3

[John_2370]

Hi John,
Are you able to measure the voltage of your power supply? Can you record a video and share it to me via private message (by link to cloud drive)?

 Hi again, Wei Cao. 

Here's a link to a Dropbox folder with links to recordings of the sound and the videos that you suggested I should make. Hopefully the labelling of the recordings and pictures is clear but do please say if it not:
 

https://www.dropbox.com/sh/e5k7lzo3ti2uzez/AAAUqI0aGuSs_1v0DkXNheHla?dl=0

Here’s what I used to measure the power:



https://www.amazon.co.uk/gp/product/B0BG...UTF8&psc=1



The best audio recording to listen to understand the problem is the 7.22 AM one when I start with the unit switched off at the mains power supply, switch it on (so the unit is on standby) and then off again. The strong hum is clearly audible as soon as it’s switched on at the mains and disappears once it’s switched off there. It makes no difference if the unit is on standby, switched on without playing music, or playing music. As long as it has power, the hum manifests itself.  

One other thing. I thought there possibly could be a problem with the power supply in my home being corrupted with a DC current - sometimes this can cause transformers in amps to hum. 



But I got hold of a £100 Audiolab DC blocker:

https://www.audiolab.co.uk/dc-block/

and even when powered through this device which eliminates DC interference, the unit emits the same hum. 

I’m sorry that the problem is persisting. Apart from this, the unit is fantastic. I think there must be an issue just with this particular transformer inside it because this is not mentioned in any reviews and I have asked others who have this unit and they have experienced no such hum at all.



Thank you for your help.


John