Question About DC Offset Control

[Gerard]

Peter,

Sorry it is not entirely clear.

1: When do i need to use this?

2: I have never had any problems with this (I think) or could it be different after the latest upgrade.

 

[PeterSt]

In quite some situations (actually countries - but not in Holland that I have seen thus far) this can go wrong.

In the end it it also a check that you have everything optimal.

But here too things can go wring I'm sure, especially when you have dedicated mains control (systems). Hard to explain.

But don't worry about it when all is right in the first place.
Peter

[arvind]

Hi Peter,

I have noticed a situation when the DAC is on & the DC Offset is set correctly, at this time if one reboots the PC the DC Offset changes, in my case both L&R become 1. Is it normal to reset the DC Offset every time the PC is rebooted?

Arvind

[PeterSt]

Hi there Arvind,

No, this is not normal, and indicates a "problem" somewhere. It has been reported more often (well, by one customer) but I guess it can happen to me just the same (I never saw it though).

In between the lines : please notice that the situation of having a large DC offset should not remain. That is, not when you work without preamp (which I think is not your case at this moment) and/or have full gain applied. It would be similar to having a ~1.5V battery connected to the loudspeaker terminals, the diaphragm beging retracted all the time.
(here I talk about the situation that the PC is shut off, when it also can happen)

What will (sort of) happen is that your PC cuts the ground to the USB terminal and/or implies another ground(loop) direction. This can even be temporary, but when the ground loop goes to somewhere else, it will stay like that (no matter the original connection is restored) because of the current flowing (this is hard to break).
Don't focus too much on "how to improve my USB terminal at the PC side" because that is too complicated. However, do try to understand what is causing the offset so you may be able to find out how to solve it. What I suggested to someone else is connect a wire to the shield of the USB plug at the PC end and connect that wire to the Protective Earth terminal of a wall outlet on the other side of that wire. I am not telling that this will help, but it may. Also, I am fairly sure that you next will see a different behaviour on the offset meters (at switching on the DAC etc.).

More generally, a peak in the USB power - or general current peak of the PC into the mains or mains PE - will incur for a current loop to ... name it;
When you have several devices connected to your audio chain (like via a preamp) anything can happen. But, this just the same can happen at switching on any of these devices.
The whole thing is too complex to explain or counterattack, knowing that all will even influence your PE and create an offset already there - that creating an offset in your mains itself. The latter is hardly related (although you will have poor mains performance regarding "audio"), but the PE influence can be devistating. This is because the one device may be connected to it, and the other may not - now that incurring for current flow between the cabinets, that usually going over your signal carrying interlinks.
You most probably will not be able to measure your PE offset because of a lacking reference, but you will have that to some sort of degree, now *that* being related to what happens when you inject a peak (by means of shutting off/on something). Now, when current flow is implied between the DAC and wherever it goes to (your preamp) and the path via the interlinks is shorther than the path via PE itself, there you have it.

So, understand ?
No, of course not ! But it is about these things.

The fewer devices in the chain, the less chance it is out of control.

Peter

[PeterSt]

Arvind,

By some coincidence ...

I just had it myself. Just before the reboot was complete I got the hunch of watching the offset, and indeed, not good at that time. It went OK as soon as the reboot completed.

Now I wonder ...
What is your buffer setting in the Control Panel ? (in ms)

Peter

[vrao]

Hi,
With the PC on, preamp off, during shut down I have seen 1/1 for a couple of seconds when I turn the DAC off (not the power switch in the back), then the numbers slowly count down. Is this unusual?

[PeterSt]

This is the most normal;
What happens is that you shut down the power to the DAC board, and now the plus/minus base (which is your DC level) are under control of emptying capacitors with too low voltage because of "co current". So, at first things are very wrong (because there's current left) and i the end there is 0.00mV Offset because there's just nothing in there anymore (power completely cut, capacitors empty).

For fun you may try the switch at the back (leave Sw#2 On) and observe again. Now you will see that the 1/-1 will last much longer, as it will take much longer for 0.00 is reached (may take hours, a bit depending on your in-room situation). This is because now the large caps on the PSU are (still) in control, but they too empty right away. The current draw is the same though, and since they are so much larger it just takes longer to empty.

I hope this is something for an answer !
Peter

[Claude]

Hi Peter,
I experienced today something like "fluctuating DC". It is about +/- 2.0 going up and down around the ideal point you told me (very fast). This was after about 3 hours of music playing.
I just experimented. When shutting down the dac and starting again, DC starts of at about -0.1/-0,9 and slowly rises. After about 2 Minutes it rised to -0,5/-1,2, now after about 35 minutes it rised to -1,0/-1,6.
I did not use xxhighend (still do not have a pc) but my mac mini with audirvana.
Claudius

[PeterSt]

Hey Claudius,

About the fluctuation, do you mean when music has stopped ?
If so, did you provide other feet under the NOS1 ? (because you should)

Peter

[Claude]

Yes when music stops. I did not provide different feet. I tried the Ayre Myrtle blocks. But they seem to "damp" the sound.
Best
Claudius

[PeterSt]

Ok, try higher feet and let me know what happens. Also jeep notice on the amount of fluctuation, and whether that changed (if the fluctuation is still there of course).

It may be more convenient to just play one track with the original feet, and see whether it happens already then. It makes your testing faster if so.

Btw, I never saw such a thing or heard from it.

What you also can do is (turn the volume down) and unplug the USB cable on the Mini side. Next plug it in again and see whether the fluctuation disappeared.
Lastly (once you are comfortable in reproducing it) try another USB port; they are not to be trusted anyway.

Let me know, but take your time !
Regards,
Peter

[Claude]

I tried to raise the feet (about 4  cm) this does not change what I experience, except that it sounds very very good right now.
I tried to unplug everything and then start again, (computer, dac).
Everything seems fine, until i Hit the play button, then it fluctuates only "Down" to -4 - -10 (base -1.0,-1,6). As soon as i stop, it stops dead on at the basepoint. I tried different USB ports. With each port the maximum "Peak" differs. But not consistent.
I dont think that this happened "before".
I am Not playing Music right now, cause of the fluctuation.
I will try now with different Computers.
Do you have another Idea?
Claudius

[PeterSt]

Do you have another Idea?

Yeah, that you are observing this during playback, which is not what you said before !

This is completely normal because the music implies DC Offset, especially with the longer bass waves. Also, DC Offset can *really* be in the music (then a stead lift or drop), because it wasn't (digitally) taken out after the recording ...

So ... ?

Peter

[Claude]

Oops
Hm, i guess i experienced a problem which is no problem at all. Sorry.
This means, that the dc offset is allways fluctuating when Music is playing?
Claudius

[PeterSt]

Yes, but completely depending on the music.

[AUDIODIDAKT]

What about DC-offsets in recordings?

They can be removed ofcourse, but this needs high-pass filtering.

And the steap high-pass filtering could lead to problems, did you ever experiment with that, Peter?
Or is there nothing to gain and just makes it worse?
And what about removing everything under 20Hz?


Roy

[PeterSt]

This has nothing to do with high pass filtering or anything. Just lower or rise the "zero level".