2. amps-preamps
  3. 125404-65769

What is DC offset on the AC power line?

I realize this question may be more appropriate in the miscellaneous section so please accept my apologies in advance. This may be somewhat amp related though, as in "don't use it with an amp".  

Can someone comment as to the pros/cons of a  DC offset suppression device, such as Emotiva CMX-2.

https://emotiva.com/products/accessories/cmx-2

I haven't seen this feature in other power strips and/or surge suppressors.

Thanks.


gdhal
gdhal's avatar
gdhal OP
1,641 posts
 
thanks to all who have responded.

davehrab, so here is a question perhaps you can provide an answer for. Your explanation is very good. Suppose that one does NOT have any electronic device with half wave bridge rectifiers and therefore would not have a DC offset problem. What is the disadvantage (if any) in that case if one were to use a DC offset filter (i.e. use the filter in a scenario where there is no DC offset to correct)?
davehrab's avatar
davehrab
375 posts
 

I've seen schematics on the Bryston web site of their big amps and they definitely implement a DC off set circuit ... it's two  electrolytic caps in series by passed by a diode bridge ... the caps center the wave and the diodes prevent damage from reverse biasing ..

Bryston also uses a ground blocking circuit on the safety/ground wire with a diode bridge that allows a fault to be conducted to the ground rod but blocks any voltage being conducted on the ground wire in the opposite direction towards the amp

 Not sure who else or if any employ these circuits

Stringreen ... I'm going to go out on a limb here but I think your amp's protection is against DC (direct current ) riding on the the line and most likely the analog ICs ... the amp shuts down when it senses the DC current so it is not pass onto the speakers were it can damage the drivers ... DC offs set does not harm the speakers only reduces components efficiency

gdhal     if you could develop a perfect world scenario with no switching power supplies and half wave bridge rectifiers there would be no DC off set to defeat and no use for a blocker

But the blocker can serve another important role if and when not defeating the off set

I think the worst offenders are the commercial and industrial users that use 3 phase power ... they create a lot of harmonics that get back on the line and pollute the grid that you draw your power from

The  power your components draw from the grid  is loaded with these line harmonics that do the same thing in reducing transformer efficiency and you have the same issues ... reduced dynamics and head room

So even if you can evade the DC off set scenario some how ... you still have a big issue with the 3 phase users distorting the line and here is where a blocker like the Humbuster can be beneficial    Enter your text ...

jea48
2,944 posts
 
"Just about every appliance in your home including that flat screen TV ... cable box all your computer devices and some of your audio equipment uses switching power supplies and cause this problems with the harmonics they create."


Add to that the micro processors in appliances.

//

"The  power your components draw from the grid  is loaded with these line harmonics that do the same thing in reducing transformer efficiency and you have the same issues ... reduced dynamics and head room

So even if you can evade the DC off set scenario some how ... you still have a big issue with the 3 phase users distorting the line and here is where a blocker like the Humbuster can be beneficia"


I would think anything ahead the primary winding of the utility transformer feeding the house/s, the secondary winding of the Power Company's transformer would not be affected. An isolation transformer will not pass DC.

Of course if your neighbor next door is fed from the same transformer it is possible something in their house could cause a problem in the other houses fed from the same transformer. It would/could depends on the appliance/equipment. In the majority of household appliances/equipment though I would think it would not be a problem to other houses fed from the same transformer. Now if your next door neighbor has something like an arc welder in his garage that could cause a problem.


exlibris
392 posts
 
This is fascinating stuff.  I came to this thread after reading about the  Burmester 948 Power Conditioner which is specifically designed to eliminate DC offset.   I live in an apartment building in a large city and I find that my system often sounds bad (anemic, glassy, cold, strained, two-dimensional, lack of power, no extension into the room) in the early evening (5pm to 8pm). 

I think davehrab may have hit the nail on the head with this:
" the real issue is the loss of efficiency your equipment experiences... 

The issue is that the loss of efficiency is not very audible like noisy RF can be ... your equipment just doesn't play with the authority or robustness it could or should"  




janewyman
59 posts
 
Hope this has not been mentioned earlier.  I had a hum in a Bryston 4ss2, called Bryston, they would get back, blah, blah, blah.  I went online and found a post where the OP suggested testing how tight the transformer was bolted to the chassis.  Not real tight, just good and snug.  I took the cover off the amp and used a wrech to see how tight the bolt was torqued for a reference.  It was not even finger tight, so I snugged the bolt down and the noise is gone.  Easy fix, no thanks to Bryston.
More to discover