What is DC offset on the AC power line?
gdhal, Lots of stuff inside there. I do not have any experience with the Emotiva device. Are you experiencing a loud mechanical buzzing/humming sound coming from a torrid transformer in a piece of your audio equipment? There is a member here on Agon that used to build DC blockers. I might be able to find his username if you need a blocker. Edit: Gbart is the Agon member's username. If interested you might try sending him a PM over the Agon message system. |
wolf_garcia, thanks for that post. Obviously use of that kind of filter can "work" (have the intended effect of reducing hum). Actually, they describe rather well what I was looking to understand. http://www.psaudio.com/wp-content/uploads/2011/11/HumbusterIII_-Manual.pdf jea48, no, I am not currently experiencing a loud mechanical buzz or otherwise think I would need such a device. However, in the past using a Carver MXR130 on the same outlet I have my current M6Si the Carver transformer did have a hum. Besides the PS Audio Humbuster III posted by wolf I wasn’t sure if this was something perhaps widely used in a audiophile grade system. But it’s because I do not have a problem that I’m looking to solve by virtue of a DC Filter that I’m asking what the drawback of using one is. Perhaps my electric system emits a "noise" of some kind amplified by the audio system and I merely cannot hear it. I doubt it, nevertheless, a possibility. Its also seems conceivable that a filter of some kind could eliminate or reduce something "unwanted" whether or not a person can detect it from an audible perspective. So again, this begs the question that why wouldn’t a DC Filter be used more widely in an audiophile grade system? |
My SS amp stopped humming (note this is a physical transformer hum not audible in the speakers) on its own even before the Humbuster was added…DC gremlins taking a break? Some amp designer do put DC filtering of some sort in their stuff as my addled brain seems to remember reading about that in reviews…but hey…they certainly all should do some damn thing. I use a couple of "after market" power supplies for my DAC and phono pre that claim to have that feature. |
NP nails it. It’s a little unusual to have DC on the AC line but it does happen, and as he points out, it happens from a device that draws current only when the voltage is going one direction, but not the other. Dimmers, but also some digital power supplies may cause this. Any oscilloscope will show this problem, Usually you won’t just see a shift int he AC signal, but you’ll also see some nasty noise along with it. The traditional fix is an isolation transformer, which are usually not toroids and present an AC at the output with little or no DC. DC may occur in cheap isolation transformers as a result of uneven winding if they are center tapped at the secondaries. One approach that is sometimes cheapest is to put the offending device itself on an isolation transformer. Other fixes are to move to another circuit, or especially to a circuit that’s on a different phase than the one causing the problem. More expensive solutions MIGHT be to improve the wiring to the service transformer, allowing the device (dimmer) that is causing the problem to draw more current without a voltage sag. If the house is old, uses fuses, etc. it's not a surprising thing to have, there may be other reasons to seek a wiring upgrade from a qualified professional. Best, Erik |
DC off set is a much bigger problem than most audiophile's realize ... the humming transformers are merely the symptom ... the real deliberating disease is the loss of transformer efficiency DC off set is caused by the half wave bridge rectifiers used in all switching power supplies that draw current in uneven pulses .. this drives the sine wave off it's proper zero degree crossing point when the phase turns from positive to negative in the cycle The humming in the transformers is caused by the transformer drawing an extra cycle and the plates snapping back ... but the real issue is the loss of efficiency your equipment experiences 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 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 I have a Emotiva CMX2... which also has some common mode filtering ... on my wife's plasma I never A/B-ed it just bought it and installed it when I bought her a new 60 plasma .. along with the Oyaide R1 outlet and matching carbon fiber plate .... happy wife happy life I also use two PS Audio Humbuster III which I wouldn't be without in my 2 channel set up ... they had a profound impact Just today someone on Audio Circle put a used Emotiva CMX2 up for sale for $70 I would have posted the link or sent it to the OP but the last time I tried to be helpful I was blocked Enter your text ... |
