Little ifi DC+ Blocker

S

Soundbaron

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Aug 19, 2025
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I'm embarrassed to say I've never heard of, or a least never paid attention to anything called a DC blocker. I have an amp with a fairly large toroidal transformer that I noticed buzzing one day. This can't be good I thought, so I started to look for the cause and quickly noted that thankfully it wasn't coming through the speakers, but from the amp itself. It was the transformer making the noise mechanically which would be noticeable sometimes and not at all other times. Not wanting to pack up the amp because it's heavy, or ship it away because it's expensive, I decided to do a little AI research on how to cure the problem. I really didn't have high hopes of finding a solution, but much to my surprise I found one......or AI did, credit where credit is due.

Anyway, apparently larger transformers are prone to mechanical buzzing due to small amounts of DC in the AC current. I've never heard of such a thing before, and assumed maybe it was part of the why people buy power conditioners. What I found is a little device called a DC blocker which plugs into the power receptacle in the back of your amp and then which you plug your power cord into. It actually works beautifully, and I can hear virtually nothing in the way of buzzing now. The device I bought was around $149.00 and very compact. There was only one company I could find that makes them called ifi "silent power" and the product name is DC Blocker + intended for larger amps, and they have a second for smaller amps for about $100.00, but which is the same physical size and look which is kind of nice.

Yeah, as I mentioned, it actually works, which in my life's experience things rarely do. So long story shorter if you have the same issue, here's the likely cure, at least if it's caused by DC voltage in your AC.
 
Does it buzz 24 by 7 all year or just at certain times?
In a residential neighborhood, there is not much that can cause a continuous DC offset.

Also check the AC line voltage. Some toroidal transformers are sensitive to high line voltage.
(most DC blockers reduce the line voltage a bit)
 
Speedskater said:
Does it buzz 24 by 7 all year or just at certain times?
In a residential neighborhood, there is not much that can cause a continuous DC offset.

Also check the AC line voltage. Some toroidal transformers are sensitive to high line voltage.
(most DC blockers reduce the line voltage a bit)
Click to expand...
No, it had varied in both intensity and times, but as I mentioned the DC blocker worked. According to AI dc in the ac can be caused by numerous things like a poorly functioning appliance somewhere else in the house, or dimmers on light bulbs, and several other things I can't remember off the top of my head.
 
Well this little DC blocker plus has worked so well that I've bought a second one. I got the smaller brother ( DC blocker) for my preamp, because although the original buzzing was mechanical and not coming through the speakers, I could swear I heard an improvement in overall sound quality. I won't claim that though, because I realize these things can be highly psychological. So on the off chance that it's not my imagination getting the better of me I'm using the second one as mentioned on the preamp with the theory that for it's modest price it can't hurt. All this to say I recommend these little devices. Oh yeah, and one last thing. I've noticed there's a company selling a power cord for nearly $3000.00 which has a dc blocker in it. As if to say, there's dc in your current whether you know it or not. I won't pass judgement on the wisdom of spending that kind of money on a power cord, but I will say the ifi dc blockers are a lot less expensive.
 
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