P15 and DC blocking

Can anyone provide specific info regarding the reported DC blocking capability of the P15? For instance, “the DC blocker in the P15 shall be capable of blocking up to XX mV DC from the incoming AC line and shall generate no more than YY mV DC at any Power Plant output”


My Hegel H20 power amplifiers hummed before introducing the P15. Not playing any music, I heard the humming/singing strong at 2.5 m distance. With the P15, I have to put my ear in touch to hear anything. The P15 itself doesn’t hum either - a P20 I first had on loan did.

Should block about 2 volts which is a HUGE amount and not normal and will output no more than about 50mv.

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If that’s the expectation, Paul, then mine may not be doing its job. I have (according to my Fluke DMM) about 900mV DC offset at the wall and about 850mV DC offset in Sinewave mode coming out the P15. I intend to check this on a scope.

Well, if you’re measuring it correctly you’ll measure no more than 50mv overall. Unfortunately, it is a very difficult measurement to properly make and most people don’t have that ability.

Even on a Fluke it’s typically wrong. What needs to happen is the meter has to be on the same scale as the full output of the AC peak voltage (which is about 180 volts on a 120 volt unit). Problem is, when most meters are at their 200 volt scale
their low level accuracy is pretty bad for low level signals.

There’s a whole complicated engineering procedure we perform to test all these (and that procedure takes place on every Power Plant we ship).

Trust us. With 900mv in you’re Power Plant isn’t giving you more than 50mv output.


Thanks a Paul. Would this be better done on a scope?

Well, you have the same sort of problem on a scope but perhaps easier to see the slight shift. Remember, you’re trying to see 50mv through 180v.

There’s a whole complicated procedure we go through to accurately measure this. If it’s interesting I can at some point get the whole process memorialized and publish it.


I’d actually love to see that someday, Paul.

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Strange that it’s so different, I mean my P15 hums a lot, depending on how I use the MW Strength and Phase Tuning settings.

Mmm, I haven’t varied the MW or done phase tuning more than once. I may test that a bit. I also have a ISOTEK EVO3 SYNCRO UNI that blocks DC. I shall put it in before the P15 and see if the P15’s sine wave graphic becomes symmetric, which it isn’t now.

If it isn’t symmetric you perhaps use MultiWave instead of Sine.
Try to use Sine instead to see if doesn’t become as you want.

What I meant was (just for fun) test how good the Isotek Syncro is to remove DC (make the sine curve symmetrical into the P15). Out of the P15 everything is marvellous as it is now.

Just curious if you ever tested it. I have an Isotek EVO3 Syncro as well and was curious about trying just what you say. Haven’t done it yet. I will say, my P12 DC blocking works crazy good.

Ok, so curiosity got the best of me and I tried running the Isotek EVO3 Syncro ahead of the P12. It notably improved the sound and I’m not sure why other than having a better sine wave coming into the P12. My LM805ia amp has never been quieter and the sonics are more vivid - with better impact and extension on both ends of the range. Glad I tried it!