iFi audio DC Blocker+ eliminates transformer rumble noise

[yamamoto2002]

This winter, I purchased a humidifier. It causes mechanical rumble from my isolation transformer , Genelec 8030A, and 7350A active speakers.

 

With iFi audio DC Blocker+, this noise is reduced by 20dB.

 

I'm not salesperson of iFi

 

Humidifier. I guess this device uses triac.

 

Genelec 8030A active speaker. A toroidal transformer is used to its power circuit, that emits acoustic noise when humidifier is working.

 

My isolation transformer, it eliminates ground loop buzz noise.

But, when humidifier is working, this transformer rumbles and makes very annoying noise.

 

iFi audio DC Blocker+ and power tap

 

Experiment

 

Noise from the isolation transformer is recorded with AKG C414 microphone, placed about 50cm distance with microphone stand.

 

The isolation transformer is powered from

• Wall receptacle, or
• Power tap with iFi DC Blocker+

 

Humidifier is

• Switched on, or
• Switched off

 

Record and compare acoustic noise from the isolation transformer.

 

Results

 

• Transformer powered from the wall receptacle, Humidifier ON : -16.34 dBFS
• Transformer powered from iFi DC Blocker+, Humidifier ON : -37.21 dBFS
• Transformer powered from the wall receptacle, Humidifier OFF : -39.71 dBFS
• Everything switched off : -33.83 dBFS

 

There is a significant improvement of noise level about 20dB with iFi DC Blocker+.

It is not anechoic chamber test, run-to-run variations on the noise levels is something like 6dB or so.

 

 

Isolation transformer connected to wall receptacle, Humidifier working. Transformer rumbling noise is heard.

Transformer_50cm_and_Humidifier.flac

Isolation transformer connected to iFi DC Blocker+, Humidifier working. Transformer rumbling stopped.

Transformer_50cm_with_IfiDCBlockerPlus_and_Humidifier.flac

 

Isolation transformer connected to wall receptacle, Humidifier switched off. Transformer rumbling stopped.

Transformer_50cm_d.flac

 

Everything is switched off.

Everything_Disconnected.flac

 

[bogi]

Did you try to use the DC blocker only with your Humidifier? Since it caused the change, perhaps it could help to isolate it from the rest. I expect your Humidifier to be connected to different wall socket than your audio equipment.

There may be also higher frequency noise generated by the Humidifier which cannot be caught by DC blocker. Product to address this is iFi AC Purifier.

 

I don't know what was the price of your Humidifier and if you still can return it and try something else.

[yamamoto2002]

2 hours ago, bogi said:

Did you try to use the DC blocker only with your Humidifier? Since it caused the change, perhaps it could help to isolate it from the rest.

 

When DC blocker only connects to Humidifier, it is somewhat effective, buzz noise from the transformer that connected to wall receptacle becomes very small, but slight buzzing remains and the noise level fluctuates. Maybe other home appliances in my house or neighbor's cause the transformer buzz.

 

From the observation, in my case, the transformer buzz problem is solved when all the audio equipment connected to one DC blocker+, DC blocker+ is rated 10A, so it is OK for my setup, but it is YMMV

 

The humidifier is not high-end product it is pretty powerful and I like it.

 

[yamamoto2002]

I measured Humidifier current draw with Picoscope 4444 and CATIII probe and found it is half wave rectifier when it is operated in low power mode!
It definitely causes DC offset to rumble audio transformers