Is DC on the AC line bad for sound quality?

I’ve been told by a couple of audio dealers and end users that they’ve found that DC on the AC line, which is common, undermines sound quality, whether in tone — costing warmth — or causing hum. Is that true? NW Energy came today and measured a varying 2 to 7 volts DC (+/-) at a number of wall outlets, and even out of one of my P15’s outlets. My own measurements with a $25 multimeter were 0.6 to 1.24 volts (+/-), with a couple of jumps to 1.47. I would think that if filtering DC is needed for audio equipment, something like the P15 (and P20) and most of the better conditioners would include a snubber, but I don’t know, and it may be more involved than that.

That sounds very high to me! I’ve never measured more than, at most, a few hundred millivolts - and I thought that was high!

My own $25 multimeter’s measurement was 0.6 to 1.47 volts, but presumably the tech’s meter is better.

I have both a Fluke 87 V and a Tektronix 2465B. :grin:

I should add that the electrical engineer I messaged on WBF said that DC on AC is hard to measure,

Yes, that is the case.

DC on your AC mains will cause your component transformers to audibly hum if they’re not encapsulated. You can buy or build a DC blocker for short money and this works well.

Have a link? On Amazon, the iFi and Audiolab versions ($125-150) get mixed reviews.

I do have a lower amplitude hum that seems to come from the Lampi Golden Gate dac and goes up with the volume. My having the DC tested actually came up at the suggestion of the Puron power filter importer, who said getting rid of his 3v DC warmed his system. The thing was, though, that the Nordost QK1 that I had been using had a bit of warmth. Plus, what is striking looking around at a number of higher level power conditioners, I couldn’t find mention of DC except at Wyred, which the Puron guy mentioned and has a DC snubber. Some years back on these forums, Paul said DC wasn’t a problem at low levels with the BHK.

Most of those “everyday” DC blockers are limited to 1 or 2 volts DC, are current limited.

When I refer to hum I mean mechanical noise at 60/120Hz from the transformer itself. This would be present without music or any other components powered on.

It would be important to understand if the noise you experience is from your speakers or the equipment itself. 60/120Hz AC hum from your speakers is more likely a grounding issue (ground loops are very common and can be tricky to eliminate and manage.)

I made my own DC blocker with a bridge rectifier and some electrolytic capacitors. The commercial ones are probably similar. Also note the device was placed inside my amplifiers.

Example for $40: DC-Block Kit

NOTE: After I upgraded my amplifiers to ones with fully potted/encapsulated toroid transformers there’s no need for DC blockers anymore.

DC offset on the AC mains definitely causes transformer buzz (that’s lamination noise). I’ve never encountered any impact on tonality (costing warmth). Frank Van Alstine over at has been offering his HumDinger DC line blocker for years. $140. If it’s a problem, head on over to his product page and read up on the HumDinger. Frank is clear about what it does and doesn’t do in his usual BS free way.


Based on the recommendation of Mark Schifter (Vera-Fi Audio), the guy who among other things created Core Audio Technologies conditioners before selling the brand to Walt at Underwood HiFi, the best first step is to try the Wyred, Pro Power Stream power conditioner – Wyred 4 Sound. Btw, Mark related that he and one of Paul’s sons created the progenitor of the power plants.

Since receiving the Wyred conditioner— before the P15 — the hum is no longer audible at my normal range of volumes. Well, most of the time. Every so often it returns for awhile. Not obvious why re lights or appliances. Was it like that before? I don’t think so, but will have to investigate. In the meantime, with the preamp’s volume knob way up, there a light hash with a bass hum.

From a sonic standpoint, the Wyred is using the supplied base power cord until the VooDoo 15–>20A adapter arrives, and it is in the early stages of burn in, but with it the volume is higher, soundstage wider and more precise, the bass stronger and tighter, the tone appealing and the precision and delineation of notes much improved, e.g., piano, trumpet. 50 hours in, it’s turning the P15 into a monster.

Are you using it in series, between the wall and the P15?


Like you, I recently bought a conditioner (see other thread) in order to fight buzz coming from my P15 (used only for ampli M1200s).
I purchased the Puritan SPM156 and it arrived yesterday.
At the moment I’m trying it without the P15 because the latter has a faulty oscillator board to be replaced. But next week I’ll try to put it between the wall and regen, too.

What happens if you use only the conditioner without the P15?

What do you think the source of your noise is? The P15 or one of the individual components in your system. Seems to me that you’ve thought the Lampi was the source in the past.

The Wyred has only four outlets. I switched the TV over and maybe something else eventually to free up a couple on the P15.

I did think it was the dac, but lately it’s been dead silent. The use of the Wyred hypothesizes some or most of the noise is DC. Wyred’s EJ suggested that the remaining hash could just be residual system noise being amplified. He said to go through the wiring and making sure lower voltage signal wires are not near AC or other noisy suspects. That would not be wholly possible in my set up.

I was hearing the buzz only from the P15 and P20, other components are dead silent.
Do you hear buzz noise also from the P15? Is your a 230V model?

120 volts. Now, no hum from any component, only through speakers (as described above using 5he Wyred). Never P15. Previously, the Lampi dac put out a light one, but lately dead silent. Was also that way on an A-V shop’s test bench.

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