DC Blocker for H390 - experience

WARNING: In this post I talk about the DC Block which is rated at 150 Watts combined power or 300 Watts MONO. There is a real possibility to overload this device and in the worst case cause damage/fire when used with high powered amps like H390 which has 250 Watts per channel @ 8Ohms. I recommend you go for a bigger unit like the DC Block 6 if your amp exceeds 150 Watts per channel. Pay attention that the output is even higher at 4 Ohms (2x 490 Watts)!

Hi guys,

Today I’ve received the Audiolab DC Block DC Block – audiolab

I bought it because I wanted to take care of the transformer hum that my 390 has. I bought it only for this reason alone because from all the information I gathered I thought that ‘power conditioning’ is marketing bs and can’t possibly make any audible difference.

You know what? I’m no longer so sure about this assumption…

When I first got a Hegel H120 I fell in love with its sound. It created emotions. Since it was underpowered for my speakers I then sold it and went with the H390.

What can I say. The emotions weren’t there anymore even though it sounds amazing!

This changed today after I introduced the DC block.

The first thing I noticed immediately was that after pressing the power button on the Hegel there was only the clack but absolutely no transformer hum whatsoever which was very audible beforehand. Completely gone. The H390 is totally silent now.

The second thing I’ve noticed is that I feel now more connected to the music - as if the emotional connection got ignited again.

I observed that music hits deeper than before without me wanting it to or expecting the DC block to have any impact on sound.
There weren’t any other changes to my setup.

My observations came without paying attention or expecting that ‘that box made an audible difference’, it just became obvious that something has changed.

If you want to try something (especially with a H390) I can recommend to check out that little box and give it a try.

I can’t rule out that the transformer hum was responsible for me not being able to connect to the music but I’m glad that that changed either way.

(I’m not affiliated with Audiolab😃)

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The Hegel has two toroids on board. Toroids are easily saturated by DC offset, which leads to very undesirable behaviours:


Scroll down a little from the top to reach the article.


I had an audible hum from my H390 (from the H390 itself, not through the speakers), which I could correlate with the use of dimmer switches elsewhere in the house. Pretty typical DC offset. A HumDinger (HumDinger DC Line Blocker – Audio by Van Alstine) completely solved the problem. I perceived no effect on the output of the H390 itself, although I never bothered with any sort of AB or ABX comparison.

@Graeme_Finlayson, thank you for the paper!

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I had similar experiences with my H360 (and use a Puritan Audio PSM136) - given how susceptible the Hegels are to DC offset, particularly as the transformers are not encased, it’s a bit of a shame it’s not addressed in the amp itself (like, for example, the much cheaper Kinki Studio Ex-M1).

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Whether encased or not, DC offset still causes core saturation. All that encasing the transformer does is limit the magnetic spray’s effect on other components. You still need to address the core saturation by removing the DC.


Something to bear in mind with DC blockers is that you need to choose one with a sufficiently high VA rating to ensure it has low enough impedance to allow your amps to reach full power. The higher the VA rating, the greater the total capacitance needed in the filter.


Not a Hegel user but still affected by occasional DC on the incoming power. My power amp was making a lot of noise when the missus is running the hair dryer and neighbours doing their thing.

I bought a PCB from Sjöström Audio and tried it out. This solved my issues also, with my now completely silent (mechanically) Karan KA S270.
So, i actually rebuilt the DC-filter point to point, and built it into my Nordost QB8 power distributor.

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Another one that a friend used was also helpful for toroidal based amplifier setups

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completely solves this problem H390

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That DC blocker looks really small considering what you would normally put into a conventional DC blocker.

I’m not sure you understood my comment - a DC blocker utilises capacitors to block DC, but pass AC. On a mains application, that means presenting a sufficiently low impedance at 50/60 Hz to be able to deliver the level of current required for an amplifier.

Typically thousands of microFarads, which you can’t squeeze into a small space. So I wonder what compromises were made in iFi’s DC blocker to enable its diminutive dimensions?

I didn’t open it. I just took it for a test and listened - as a result, I’ve been using it for a year now. This does not affect the listening experience

But the capacitors will be low voltage types so can be physically small for large values of capacitance. The schematics I have seen show the capacitors shorted with diodes to keep voltage across them below 3V. What actual value a humongous thick mains cable has in this connection scenario is anyones guess though.

In my DC blocker they are 400V items, for longevity and the ability to handle spikes.
But there are likely more than one way to skin a cat…

Indeed, a potentially explosive way!

you do know the audiolab DC blocker isn’t rated for anywhere near the power of a 390?

|Peak Load :|600VA|
|Audio Power Amplifier Compatibility|<2x150W or <1x 300W|

You risk damaging it, and / or your amplifier if you keep using that model.

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DC Block 6 – audiolab

Their new DC block 6 seems to handle more throughput

on UK mains, up to about 1800w per socket!

Why is that? H390 power output is 250 Watts and the DC Block is rated for 300 Watts.

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250 watts per channel… thats 500w… and thats only a 8 ohm… into a dynamic load, the amp could be pulling 800+ watts into 4 ohms.

Plus the DAC and pre sections of the amp consume power on their own. The single outlet audiolab DC blocker is not suitable for your amplifier.


Omg thank you for making me aware of this! Honestly I didn’t think about it the correct way then which kind of sucks😂
I’m running 8 ohm speakers and am not going anywhere near max load thankfully.

Anyone wants to buy a DC Block in Europe?:sweat_smile:

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