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Transformer buzz or hum

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raindance

Re: Transformer buzz or hum
« Reply #20 on: 2 Dec 2010, 11:43 am »
OK, someone asked me why I don't buy the DC on the AC thing. Here you go:

Most devices residing in a home pull power through a transformer for isolation (safety) purposes. A transformer cannot pass DC. Not ever. Your mains power is provided to the house by a transformer. This transformer cannot pass DC. Ever. What can cause "problems" however is that some devices in your home introduce harmonic distortion onto the mains, providing your equipment with a less than perfect 60Hz sine wave. Some equipment may have faulty transformers and this can set off the buzzing that seems to annoy so many people.

By the way, while DC cannot reside on AC, the opposite does occur and is called ripple.
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BaMorin

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Re: Transformer buzz or hum
« Reply #21 on: 2 Dec 2010, 04:34 pm »
Quote from: raindance on  2 Dec 2010, 11:43 am
OK, someone asked me why I don't buy the DC on the AC thing. Here you go:

Most devices residing in a home pull power through a transformer for isolation (safety) purposes. A transformer cannot pass DC. Not ever. Your mains power is provided to the house by a transformer. This transformer cannot pass DC. Ever. What can cause "problems" however is that some devices in your home introduce harmonic distortion onto the mains, providing your equipment with a less than perfect 60Hz sine wave. Some equipment may have faulty transformers and this can set off the buzzing that seems to annoy so many people.

By the way, while DC cannot reside on AC, the opposite does occur and is called ripple.

Umm, while the theory is correct, there's always the " i before e" rule.  My car battery is 12vDC. the primary winding of my ignition coil sees that DC. My spark plugs might see 50Kv at times. Granted, the coil is not working on DC(transforming) it is transforming pulse DC.
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raindance

Re: Transformer buzz or hum
« Reply #22 on: 2 Dec 2010, 04:37 pm »
Pulses are AC.
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Speedskater

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Re: Transformer buzz or hum
« Reply #23 on: 2 Dec 2010, 05:07 pm »
Direct Current - abbreviated "DC". An essentially constant-value current that flows in only one direction.
In the past, automotive ignition distributors would mechanically switch the DC source to  generate AC pulses.
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Wayner

Re: Transformer buzz or hum
« Reply #24 on: 2 Dec 2010, 05:21 pm »
I suggest you all have a read:

http://sound.westhost.com/articles/xfmr-dc.htm#dc1

Wayner
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