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Audible Buzz from Lexicon: dimmers & microwave?

Greetings all, I've scoured through the forums here and other sites to try and find an answer to a perplexing buzz that's been coming from the chassis of my Lexicon LX-7. The buzzing does not come through my speakers--ever. The buzzing comes from the Lexicon.

I have done the following:
1) I have brought my Lexicon in to be serviced. It passed with flying colors and *no buzzing*
2) I have switched power cords three times (Shunyata, Transparent, stock)
3) I have disconnected all balanced cables and speaker interconnects from the Lexicon. It sill buzzes regardless of whether or not something is connected.
4) I have plugged my Lexicon into my Panamax power conditioner
internetmin

Showing 3 responses by jea48

jea48
4,311 posts
 
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html
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jea48
4,311 posts
 
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.
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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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jea48
4,311 posts
 
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?
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