[Wayner]

Robin,

My several systems are dead quiet as well. However, my studio room has many things going on in it and from time to time I have had issues. I think most people have to some degree. A friend of mine bought a new laptop that he was running thru his system, only to have hum he couldn't get rid of. Turns out, the hum was caused by his laptops' screen. He brought that one back and got a different brand and the trouble went away. I doubt many people are having problems with amps, preamps and CD players. I think many are having problems with turntables and computer peripheral devices. Hopefully a cure for someones ailments will come out of this.

Wayner

[satfrat]

From all the complaints I've heard in threads, I think you make a valid attempt to identify and come up with solutions. I guess I'm just fortunate to have a HTPC computer sitting on top of m 6 shelf rack, have everything plugged into my BPT and not have so much as a hiccup. Then again I don't own phono which I think has the most issues with hum. For the life of me tho, I can't imagine why a laptop screen would create a hum but it's definitely a good thing to know in todays world of increasing laptop use. Maybe you'll be able to actually identify the reason for screen interference? That would be a good thing. Good luck Wayner.

Cheers,
Robin

[Wayner]

One explination is a poorly shielded video/and or audio card. A possible work around would be a USB to Coax breakout board, then to a DAC.

Yes tables can be bothersome at times. However, I just finish a listening session with my Empire 598 that may have been some of the finest vinyl I have ever heard.

Wayner

[es347]

Hum

Sometimes its just because the unit does not know the words. 

Frank

Seriously, it is often caused because wires are not zero resistance, chassis can pick up electomagnetic radiated noise, and of course that hellifweknow issue too.

Ground loops occur when there is more than one ground path with a real resistance between them causing current to flow where it is not supposed to flow - such as with three wire AC grounded audio components mixed with two wire ones.  There are now two ground paths, one between the equipment through the audio cable grounds, the other between chassis grounds through the power cords.  Finding and fixing all these issues in new design is a real headache, even when you think you are obeying all the "rules" of good design.

If only wires all were zero resistance our work would be easier.

Regards again,

Frank Van Alstine

If we could only get a handle on that absolute zero thing 

[turkey]

Anyone know of a good source of 1 to 1 isolation transformers suitable for a big power amp (15 amp at 120V AC) at a reasonable price?

I would like to have something to recommend to clients who may have that DC on the AC line issue.

Powervar and OneAC both make these. You can often get them on that auction site for a good price.

Or you can try this:

http://sound.westhost.com/articles/xfmr-dc.htm

[avahifi]

http://sound.westhost.com/articles/xfmr-dc.htm

Thanks much for the information to this link.

It is one of the most informative and interesting I have read in a long time. Low level DC setting on your AC power lines?  I did not know it happens, and happens so easily, and how it does damage.  Great article.

I wonder if an isolation transformer would be subject to the same problems it is trying to eliminate to power toroid transformers downstream?

Read this one, and your comments about it are welcomed here.

Regards,

Frank Van Alstine

[jtwrace]

http://sound.westhost.com/articles/xfmr-dc.htm

Thanks much for the information to this link.

It is one of the most informative and interesting I have read in a long time. Low level DC setting on your AC power lines?  I did not know it happens, and happens so easily, and how it does damage.  Great article.

I wonder if an isolation transformer would be subject to the same problems it is trying to eliminate to power toroid transformers downstream?

Read this one, and your comments about it are welcomed here.

Regards,

Frank Van Alstine

Hi Frank,

Take a look here http://www.ciaudio.com/ and look at his XDC2.  Maybe that can give you some ideas....

[BradJudy]

Frank - the approach shown in the article has been discussed in The Lab section here a few times.  Paul's original thread includes a link to a discussion on the topic at DIYAudio - http://www.audiocircle.com/index.php?topic=12706.0

A follow-up thread includes a couple variations of the design - http://www.audiocircle.com/index.php?topic=50908.msg457186#msg457186

[turkey]

Hi Frank,

Take a look here http://www.ciaudio.com/ and look at his XDC2.  Maybe that can give you some ideas....

Not really. It doesn't say how it works, and doesn't show any specs to indicate that it does anything at all.

[turkey]

I wonder if an isolation transformer would be subject to the same problems it is trying to eliminate to power toroid transformers downstream?

Yes, that would be the logical conclusion if the isolation transformer is toroidal and has a low primary resistance.