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Old 2nd July 2011, 12:16 PM   #1
Join Date: Jun 2011
Default Power factor correction for audio?


Please could i confirm that Power Factor Correction is not required for Audio Amplifiers made for Electric guitars?

...i.e. any SMPS built to supply an audio amp in a guitar amplifier enclosure, would not have to pass EMC laws, - if it was of power level above 75W?
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Old 2nd July 2011, 01:22 PM   #2
DF96 is offline DF96  England
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Join Date: May 2007
EMC and power factor correction are not quite the same thing. Any item put on sale commercially in the EU has to have, among other things, reasonable EMC performance - unless you are Chinese in which case you just put a CE sticker on the back.

Power factor correction would only apply to higher power equipment, but I don't know where the threshold is. Someone on here is bound to know.
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Old 2nd July 2011, 10:48 PM   #3
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Location: Carlisle, England
Originally Posted by DF96 View Post

Power factor correction would only apply to higher power equipment, but I don't know where the threshold is. Someone on here is bound to know.
There are no limits for:
- Equipment with input power P ≤ 75 W.
- Professional equipment with input power P > 1 kW. *
- Symmetrical controlled heating elements with input power P ≤ 200 W.
- Independent dimming devices for light bulb
* Note: Professional equipment for use in trades, professions or industries and which is not intended for sale to
the general public. The designation shall be specified by the manufacturer
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
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Old 3rd July 2011, 03:54 PM   #4
Join Date: Jun 2011
At present, power supplies (30W to 500W+) internal to class d guitar amplifiers use 50Hz mains transformers, folowed by a rectifier, then a large capacitor bank.

-therefore, they are obviously not power factor corrected.

Ao i am wondering , if such a power supply was replaced with an SMPS, would that need to be power factor corrected?
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Old 4th July 2011, 08:38 AM   #5
hesener is offline hesener  Germany
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Location: Munich, Germany
Hi, nigelwright7557 is correct, according to EN61000-3-2, class-A equipment (to which this would belong) needs low harmonic current emission (== good power factor) if rated power is > 75W. That includes audio equipment. So yes, a guitar amplifier with a 50Hz mains transformer and bridge rectifier and large caps (perfect recipe for producing a lot of current spikes) would need a filter at the input, or a active power factor correction circuit.

just my two cents
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Old 4th July 2011, 04:01 PM   #6
Join Date: Jun 2011

This is getting very interesting indeed...because i can assure you that currently sold guitar amplifiers that are plugged into the mains, and are above 75W in power, are definetely not power factor corrected.

So howcome the authorities have not clamped down on the world of guitar amplifiers?

Last edited by eem2am; 4th July 2011 at 04:02 PM. Reason: spell
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Old 4th July 2011, 05:17 PM   #7
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Location: Oakmont PA
I though there was an exemption for audio amplifiers, perhaps as consumer electronics, but as the IEC standards are expensive I don't have copies.
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Old 4th July 2011, 06:09 PM   #8
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Frank Berry's Avatar
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Location: Midland, Michigan
Are you asking about Power Factor Correction or EMC?
They are very different.
If your amplifier operates in Class D mode, it will generate lots of RF noise and EMC filtering is necessary.
Power Factor Correction should not be necessary for such a small amplifier.
The phase angles of the current vs. voltage (Power Factor) becomes important only when the input impedance of the power transformer is low and the transformer is drawing a lot of current from the mains. When that happens, Power Factor Correction capacitors or inductors can improve the efficiency of the power transfer into the transformer.
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Old 5th July 2011, 12:49 PM   #9
Join Date: Jun 2011
PFC is by EN61000
EMC is by EN55055

...But they are one and the same.

PFC is concerned about not only about the phase of the fundamental of current and the mains voltage.

-PFC is also concerned about all those same harmonics that EMC is concerned about.

PFC and EMC are one and the same.
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