DC offset, anyone know how to address this issue

[pcosta]

I have what is commonly termed DC offset and it causes the transformer on my amp to physically hum. It doesn't hum through the speakers, very quiet otherwise.
I was told an isolation tranformer would eliminate the problem. I borrowed an Equitech 2Q and it did nothing to quiet the transformer.
I did borrow a product from Gilbert at Blue Circle Audio and it did eliminate the hum, but I felt it was a sonic compromise. That product confirmed to me that the problem is not in the amp either. I have heard the transformer work quietly. So lets eliminate the problem being the amps transformer.

Any thoughs, ideas?

 

[joeinid]

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or

Vesuvius dc

™

Direct Current on an AC line will make toroidal transformers hum. Sometimes they rattle and hum. Oh well. There are several circuits out there that claim to eliminate the DC from AC lines. DC becomes a problem when it exceeds 1 volt.

We have developed a Vesuvius power cord that includes a heat-sinked with DC blocking circuitry to help eliminate this troublesome artifact of poor power generation. What is even more interesting is that in listening tests, we found that the inclusion of this circuit actually increased dynamic “slam” and detail in the music. I believe it’s a result of the theory of unintended consequences, or the travels of the Three Princes of Serendip. This is not what we were looking for, but we’ll take it. Reducing DC and increasing dynamics.

The Vesuvius dc

has a long and a short portion connecting to the heat-sinked box. One has the AC plug and one has the IEC connector. The short portion is 2 feet and is available with either the AC plug or the IEC connector. The long portion is 5 feet. Both portions connect to the box with Neutrik Powercon® 20-amp rated connectors.

Our thought is that most folks will want to have the box on the floor beneath the AC receptacle. Some may prefer the opposite. Your choice.

The Vesuvius dc

is available with either a 15-amp or 20-amp IEC connector.

 

[microstrip]

Most DC suppressors are just made using one of more capacitors with some diodes in parallel to protect them. Some people refer that they compromise sound quality, although some brands include them as standard in their high quality power amplifiers.

A PSAudio power regenerator or similar will solve your problem, but it is not cheap. Burmeister manufactures a power conditioner optimized to suppress DC from mains, the 948, but I think it is even more expensive.

 

[joeinid]

Most DC suppressors are just made using one of more capacitors with some diodes in parallel to protect them. Some people refer that they compromise sound quality, although some brands include them as standard in their high quality power amplifiers.

A PSAudio power regenerator or similar will solve your problem, but it is not cheap. Burmeister manufactures a power conditioner optimized to suppress DC from mains, the 948, but I think it is even more expensive.

I've tried both the PS Audio Power Plant Premier and a PurePower 2000 and neither removed dc. I thought they would do the trick but not for me. My Burmester 948 does indeed work very well but it is expensive.

 

[Occam]

If your amplifier's power transformer continued to hum when powered through an Equitech balancing isolation transformer, the problem is not dc offset on your mains. An isolating transformer is galvanicly isolated and cannot pass dc, so if that amp's transformer is still humming, I don't see how the problem could be dc offset. ( if it were dc offset, one might hear the Equitech's transformerhumming, but not the amp's.)

You don't mention which of Gilbert's gee-gaws did eliminate the hum. If it was one of his across the line, parallel cap power conditioners, it might be indicative of a really bad power factor on your ac mains. Also, you might also try tightening/loosening the central fixing bolt of the amps transformer, if it a toroidal transformer to see if that helps.

FWIW,

Paul

 

[pcosta]

Joe

I was directed to the PS Audio as a solution and I am willing to investigate the P5 or P10. But there is talk of reliability issues.

The cord from Silver Circle is a filter probably similar to the Blue CIrcle item I tried. http://www.bluecircle.com/page129.html
Like I said effective at removing the hum but a sonic compromise. I will investigate the SIlver Circle cord and try and borrow a PS AUdio unit.

There is a company called Vibex that manufactures a DC blocker, anyone heard or seen one in action?
It seem odd how many manufactures recommend an isolation transformer to rid DC and the one I tried didn't work. Perhaps another company?

 

[joeinid]

pcosta,

Let us know how things work out. I also have PS Audio Humbuster III's which I felt worked very well. I have since installed new dedicated outlets to my panel and a fresh ground and my problem largely went away but I still have the 948 in use.

 

[pcosta]

If your amplifier's power transformer continued to hum when powered through an Equitech balancing isolation transformer, the problem is not dc offset on your mains. An isolating transformer is galvanicly isolated and cannot pass dc, so if that amp's transformer is still humming, I don't see how the problem could be dc offset. ( if it were dc offset, one might hear the Equitech's transformerhumming, but not the amp's.)

You don't mention which of Gilbert's gee-gaws did eliminate the hum. If it was one of his across the line, parallel cap power conditioners, it might be indicative of a really bad power factor on your ac mains. Also, you might also try tightening/loosening the central fixing bolt of the amps transformer, if it a toroidal transformer to see if that helps.

FWIW,

Paul

HI Paul

Thanks for your reply. I have checked all the bolts on the amp and everything is tight and they are decoupled from the chassis with rubber things.

I was ready to purchase a big Topaz 5kva transformer from someone who had them for sale and asked his opinion on DC through a transformer and he felt it wouldn't help, this is his reply to me

Having the TOPAZ Isolator transformers, in my opinion, won't help reduce/eliminate that.

The kind of 'noise' that these isolation Xformers remove is 'electrical voltage noise' riding on the AC lines coming into your house.
This noise, which translated into THD of the 60 Hz AC line frequency comes from power lines and inside your house from other sources. (fridge, computers, TV's, floursecent lights, etc.)

From the two phase AC supply coming into your house, generally the noise is the same on both "Lines".
(Black wire phase and Red wire phase) By using the 240 VAC connection, the common noise will cancel.

I use the Isolation Transformers primary connected to the 240 VAC. The output is run as two phases on 120 VAC. I guess you can call this wired primary in balanced mode.

I found the TOPAZ not to be as quiet as the MGE units. Yes...There is a slight hum on the TOPAZ Isolation transformers. The best location for these is near your breaker panel, away from the listening area.

The MGE unit (I have one for sale....See other ad) is very quiet and I have it located in a closet in the listening room.

Something interesting I found is when the power amps are NOT switched, on the THD from the MGE is 1.2% THD.
With the amps on, the induced noise goes up to 2.0-2.3 THD. This means the amps' power transformers are feeding noise (modulated AC) back into the MGE output voltage. Very interesting in fact!


Any comment?

 

[Occam]

Hi pcosta,

Dunno.... Real transformers, with separate primaries and secondaries, are AC coupled and can't pass DC. If the secondary actually has a dc offset, the only source I can think of is via dc on the safety ground which is bonded to the center tap of the secondary of the balancing transformer. But this wouldn't be the source of dc offset without the Equitech. My WAG, if (and only if) you've dc offset with both straight from the wall outlet and through the Equitech, would be that you've a dc offset on both your safety ground and neutral (grounded conductor) indicating a mis-wired receptacle or similar problem than bonds safety ground and neutral somewhere other than a breaker box, as well as a source for that dc offset. But this doesn't seem probable, so I've no real clue as to the source of that hum.

As to the mains increased distortion when the amp is powered, a capacitor input linear power supply typically has a wretched power factor/THD.
FWIW

 

[pcosta]

With a little advice from the manufacture of the amp I was able to lower the sound of the hum significantly. The cover that is fitted over the transformer is essentially amplifiying the hum.
The odd part of this whole experience that still bothers me a bit is how the product from Blue Circle Audio was able eliminate the noise when most of the noise is amplified by the case work.

 

[Nyal Mellor]

If your amplifier's power transformer continued to hum when powered through an Equitech balancing isolation transformer, the problem is not dc offset on your mains. An isolating transformer is galvanicly isolated and cannot pass dc, so if that amp's transformer is still humming, I don't see how the problem could be dc offset. ( if it were dc offset, one might hear the Equitech's transformerhumming, but not the amp's.)

You don't mention which of Gilbert's gee-gaws did eliminate the hum. If it was one of his across the line, parallel cap power conditioners, it might be indicative of a really bad power factor on your ac mains. Also, you might also try tightening/loosening the central fixing bolt of the amps transformer, if it a toroidal transformer to see if that helps.

FWIW,

Paul

+1 DC can't couple through an isolation transformer. See the third paragraph here here for a table of which power conditioning technologies address which power issues.

 

[Empirical]

Have you thought about power factor correction? This might be the cause. The current and voltage are so out of phase that the transformer behaves very inefficiently. I believe you can get devices to correct for this. It may be the other things that are plugged into the same circuit as well.

Steve N.

 

[tunes]

any success with eliminating the hum?
chris