Hum problem with Mini-I Pro 3

[John_2356]

Hi, I have just got my Matrix Mini-i Pro 3. When playing music, it sounds fantastic. There's one problem, however: whenever the unit is powered, including in standby mode, it emits a slight hum. What I mean by this is that there's a hum or buzz sound coming from the unit itself, not through the headphones, which have a totally silent background. It means the unit cannot be left with power in standby mode (its distracting when working) and the sound can also be heard during quiet passages of music. Is this a fault in the unit?  I'd be grateful for your help. 

[Wei Cao]

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)?

[John_2356]

Hi Wei Cao,

Yes - I'm happy to do that. I've ordered a voltage tester from Amazon and will do and video the test later today.

Thanks very much for your help.

John

[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

[John_2370]

Hi Wei Cao,

Please can you confirm you're able to access the recordings, videos and photos through the Dropbox link.

I look forward to hearing from you soon.

Thank you.

John

[Wei Cao]

Hi John.
Yes I downloaded the recordings.
A linear power supply composed by transformers has a specific input range, in theory, all toroidal transformers will have varying of humming noises during working, different transformer individules have different resonance points. But most of the time, it's not loud, with the input voltage increases, the noises also increases.
Your power voltage is obviously higher than the limit of the transformer input voltage range. (The limit of the transformer is 240V which is mentioned on our website and user manuals.) The transformer can work under this voltage, but may have a higher noise.
Hope you understand.

[John_2370]

Thank you, Wei Cao. I'm going to try plugging it in at work and testing the voltage there today to see if that makes any difference.

John

[John_2370]

Hi John.
Yes I downloaded the recordings.
A linear power supply composed by transformers has a specific input range, in theory, all toroidal transformers will have varying of humming noises during working, different transformer individules have different resonance points. But most of the time, it's not loud, with the input voltage increases, the noises also increases.
Your power voltage is obviously higher than the limit of the transformer input voltage range. (The limit of the transformer is 240V which is mentioned on our website and user manuals.) The transformer can work under this voltage, but may have a higher noise.
Hope you understand.

 Hi again, Wei Cao. I have tried the Mini i Pro 3 at work and the constant hum problem just is the same there. The other thing I have tried is using a step down convertor to reduce the socket voltage to 110 v, carefully resetting the voltage on the unit to the lower setting and then plugging it in. Again, there is the same hum problem. That strongly suggests it's not a voltage level issue but a problem with the transformer on this particular unit, because the lighter 110 load should eliminate any issues of my power supply. Is there anything else you suggest I try before returning the unit to the seller? Thak you again, John 

Here are the details of the step down convertor I used: 

https://www.amazon.co.uk/gp/product/B081...UTF8&psc=1 Yinleader 500VA 220V - 110V Step Up & Step Down Voltage Transformer Converter UK to US 110V & 220V outlets

[John_2370]

Hi Wei Cao, I'm keen to get this sorted soon, so would really appreciate any ideas you have for devices that would address the voltage issue you have identified.

John

[Wei Cao]

Hi John,
Sorry for the delay.
As a electronic component, we will check whether the transformer has a correct voltage and output power. The noise from itself is not the object of consideration for this component. The transformer of mini-i Pro 3 comes from Noratel, a well-known supplier in the industry. The transformer applied to this product has also passed the inspection of Noratel.