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
The massive toroidal transformer in your Lexicon amp is most likely being effected/rattled by DC Offset ... the DC offset is being created by all the switching power supplies in your household appliance's and anything that has a remote control including your cable box/DVR and your flat screen

The DC Offset is created by the switching power supplies which use half wave bridge rectifiers that draw current in uneven pulses ... these uneven pulses will cause big toroidal transformers to rattle, buzz, or hum ... causing the transformer to lose some of it's efficacy and reducing it's headroom and dynamics ... not good in home theater

The DC Offset enters your amp through the power cord so disconnecting ICs and speaker cables will have no effect as the pulsing Offset is entering on the power line ... switching power cords will not help either as they merely act as a conduit to the Tranny

I've also never seen a power conditioner that deals with DC Offset ... although Bryston does incorporates a DC Offset blocking circuit in some of their amps

Channel Island and PS Audio offer units that may be worth looking into
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.
[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]

Here is another Agon thread on the subject of DC offset on the mains.

Found this using Google. Can't say if it any good.

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.


Picture gallery of past builds:

Thanks for the responses all!! On Monday I ordered the PS Audio Hum Buster III. Sorry Gbart!!! It's scheduled to arrive today, so we'll see how that goes. My personal preference is to obviously deal with this at the electrical level. I have stopped using the microwave lights (though that can't be helped if you want to cook on the stove top and need light :-) Responding to Jea, we do have low voltage lighting (the house was built in the 50's) along with "traditional" switches. All the dimmers are Leviton in the kitchen and elsewhere. The only exception is I had three dimmers replaced with Leutron this past week too (don't remember the name for their slider 3-way). I also noticed that I have an older TrippLight surge protector and it too buzzes when plugged in. It's pretty loud from the TrippLight.

I have a completely different electrician coming the week after next to the house. I'm hoping he can find *something* because this is obviously a problem I'm having everywhere in the house and I'd like to get it addressed and find the source. When I spoke to him, he too was baffled as to how to track this down.

Oh! I also had the microwave electrical outlet checked. It came out fine and even with the microwave itself completely unplugged it was STILL buzzing!

Jea, that other quote from Nelson was a good one. I had come across it and printed it out (along with other forum threads) and gave them to the electricians. They are all really baffled. This is not something that they deal with and one guy who has had 15 years experience shrugged and said this is the first time I've come across this.

I'm going to print out that note about testing for DC across the mains too. I hadn't come across that one in my research! Thanks.

I am **so appreciative** for everyone's responses and help here. This is the first time I've come across something like this and as only we audiophiles can truly understand, not being able to use my system properly is just driving me bonkers. I can't wait to finally get a solution here and enjoy my system once again :-)
Jea, specifically to the type of lights on the dimmers, they are regular incandescent lights. They vary in wattage but are mostly the 65watt recessed lights.
Well I unpacked the PS Audio Humbuster III animi absolutely stunned. Literally stunned. No noise at all from the Lexicon amplifier. I even put on the microwave and no buzzing at all. Dead silence. I then took the hum buster out and bang the buzz came back. Put the hum buster back in and the buzz is gone. I cannot believe the audible difference too. Played some concierto de aranjuez, more detail and openness and smoothness and finesse. Followed that with some female rock vocals. Pat Benatar and Sarah McLaughlan and plain old HDTV. I haven't tested dynamics or an A/B with the same piece of music yet. I am sitting here stunned with how the DC current was affecting my system. I'll still see what I can do at the source level but for now I'm a believer in the hum buster and removing DC current from the power lines.