DCAudioDIY.com

A long time ago I noticed that the toroidal power transformers in my amps were humming pretty loudly. At the time was experimenting with balanced power and other AC cleaning stuff, so bought a Fluke 43B power line analyzer.

The distortion measurement capability gave interesting results. Checked a friends house and the distortion was 2% THD. Came back to my place and it was 6% THD. We had a lightning strike in the neighborhood a few years prior and that was the only clue.

Called the local electric company with the data and they sent out a crew to check. Verified my data and then looked at the meter base. They pulled it and the contacts were corroded and black. They cleaned them with a cloth and reinstalled the meter. Measure it again and the distortion was down to 2% THD. Checked the toroids and they were quiet again.

Since DC is created when distortions is present (probably due to contact rectification from the corrosion and carboning), that was the cause of the toroid hum. Down to normal levels for years. Recently the meter was changed to the new digital style, so will have to make measurements again to see if there is any change.

Fun with AC power and a good analyzer.

This is interesting. I have two 200 watt SS amps with toroid xformers and the buzz for about a few seconds on turn on,
then quite down but every once in a while the buzz stays on until I turn them off.
I have read that there are circuits to remove DC from the AC line but never built any.
The builder of the amps says the few seconds of buzz at turn on is normal.

I had weird waveforms on my AC line one time and the power company did not believe anything was wrong until I sent scope traces to one of their engineers. They found out it was a power factor correction device on a local pole and one of the capacitors was bad. The fixed it and all was better.

The buzz at turn-on is probably due to the brief period after turn-on where the transformers are actually in an overload situation while charging up the caps...

Roscoe

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I can explain it to you, but I can’t understand it for you.

400AV tranny into 120,000uf lytics

Yes, a big transformer into big caps buzzes until the caps are charged. If they continue afterwards, then maybe DC on the line. Lots of reasons just like Tom said with his problem.

There are plenty of DC removal circuits out there. Best to get rid of it at the source than try and correct it.

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Walt

Pepco is like a lot of other utilities. Having loads on the grid that shift the power factor away from unity causes them a lot of problems so they install banks of switched capacitors to adjust the power factor. I don't know all the details but if you look at the poles in your area you might find a box connected to the high voltage lines. They must have some circuit to detect power factor and add or remove capacitors. These were probably used to balance inductive loads like motors and transformers that have leakage inductance but I wonder how the plethora of switch mode supplies affects their assumptions.

Or their measurements...

Roscoe

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I can explain it to you, but I can’t understand it for you.

To change the subject slightly. In many parts of the world, installation of solar panels and batteries is increasing rapidly. Most systems are still connected to the grid but some are off-grid.

If you were to install either system, what would you do to maximize the quality of electricity used by your amplifier?

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