Audible Buzz from Lexicon: dimmers & microwave?

Thanks for this Dave. Really great info. I'm wondering if anyone else has a way to deal with this at the panel and isolate my A/V gear?? Jea, this is a good link but I'm not an electrician and not sure what this means in practical terms. I've had electricians come in with no real luck here. Polarity and phase are fine, voltage registers fine, the outlet is a Shunyata and is fine, the circuit is a dedicated 20 amp and it's fine. The neutral is fine. They also moved the circuit from the sub panel to the main panel. No luck. One thing that gets the buzzing on the lexicon amp's transformer is the microwave oven's stove lights (it's over the stove and has a hood light). If it's on "low" the buzzing from the Lexicon is VERY loud (again only from the chassis). The kitchen dimmers also appear to (sometimes) impact the loudness of the transformer buzz. I ordered the PS Audio Hum Buster III from Music Direct in Chicago (Mark there was FANTASTIC). WE'll see how that goes. Now, is there ANY WAY AT ALL to check for DC offset? The electricians plugged in their meter and DC registered as "0" but they were perplexed at the notion that DC could be on the AC lines. I printed out forum threads, etc. but they really didn't know how to do anything different. Thanks all.

One more question here.... is there anything specific in terms of tests or meters, etc. that I can tell the electrician. It's obvious that the electricians are not used to seeing a high end home theater/music setup and are really baffled by this. Much appreciated!

Now, is there ANY WAY AT ALL to check for DC offset? The electricians plugged in their meter and DC registered as "0" but they were perplexed at the notion that DC could be on the AC lines.
10-05-10: Internetmin

Not that simple.... you cannot measure DC on the AC lines just by putting a DC volt meter across the mains.

You need to make a DC blocker or buy one. It will need to be installed at the Lexicon.
>>>>>>>>>>>>>>>>>>>>>>>>>>

If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.

The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.

You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +.
Nelson Pass

If you can not build the DC blocker yourself then you will need to find an electronic tech to build it for you.

http://sound.westhost.com/articles/xfmr-dc.htm
[quote]It is the mean value that appears as "DC" on the mains. It can also be measured, but to do so requires that one works on live components. This is not recommended as it is inherently dangerous. However, if you must (and PLEASE take extreme care), you need a 100k resistor and a 10uF non-polarised capacitor, wired in series. Connect this circuit across the mains (power off!), and connect a DC voltmeter across the capacitor. This attenuates the AC enough to prevent the front-end of the meter from being overloaded, and the DC voltage is easy to measure.[/quote]
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Internetmin,

Here is another Agon thread on the subject of DC offset on the mains.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1209767274&openflup&6&4

Found this using Google. Can't say if it any good.
http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=62&Itemid=27

Also should add when the toroidal transformer is buzzing loud from the offending devices causing the the DC offset the transformer will run hotter than normal.

Suggest not using the low light setting on the microwave hood.

What kind of dimmer on kitchen lights? Under (upper cabinet) low voltage lighting?

Internetmin, I have a DC blocker I built for a guy who backed out of the deal, all packed and ready to go. I've built a few as a favor to several Audiogon members. Send me a PM if interested.

"Testimonial": http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1247693407&openflup&23&4#23

Picture gallery of past builds: http://img.villagephotos.com/p/2003-5/191557/2020464

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