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Old 24th October 2014, 04:09 PM   #1
daly2k is offline daly2k  United States
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Default power factor correction in class a amps

Next to trying to figure out dark matter and dark energy's affect on the universe the next pressing question for me is -- will power factor correction work on Class A amps to make them more efficient (green) and suck less power from the AC wall sockets? I read an interesting article in audio express about an amp manufacturer actually using it in his amp (switching power supply) and it got me thinking.

We all know that are speakers are reactive loads on the amps output and it would seem that this science would work on a linear amp. Has anyone ever tried these circuits on a Pass project? I know that most of us are happy to reduce ripple with voltage regulators so this would be more a project to gain efficiency and reduce heat. Any ideas anyone?
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Old 24th October 2014, 06:16 PM   #2
Zen Mod is offline Zen Mod  Serbia
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naah ........ that matter is just too dark

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Old 25th October 2014, 11:53 AM   #3
AndrewT is offline AndrewT  Scotland
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The amplifier uses power.
The connection between the mains and the amplifier will not be 100% efficient.
Different topologies will have different losses/efficiencies.

Capacitor input filters, whether into an SMPS or a transformer fed rectifier/capacitor are both terrible for creating distortion of the mains waveform.
Some SMPS have circuitry for reducing this distortion effect.
Many SMPS, especially the lower power types, have no distortion reducing circuitry.
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Old 25th October 2014, 12:24 PM   #4
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Originally Posted by daly2k View Post
gain efficiency and reduce heat.
Bothered to estimate what the gain will be ? In power, not lb.

(A crane and my 7.5' x 7.5' hot tub arrive tomorrow, 1000+ lbs. Just found out it requires more than 2 circuit breaker/groups, 16A/230Vac, to cook a white man)
It doesn't count how one deals with winning, but how to handle a loss (© DjT)
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Old 25th October 2014, 02:03 PM   #5
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Another green option to try is be able to reduce plate voltage and cathode current when you do not need full power. I typically reduce both by 20% when I do not need it. Power required can be cut in half.
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Old 25th October 2014, 05:37 PM   #6
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Power factor is more a matter of losses in the AC line and transformer
windings, and correction will improve that, but I don't expect that it will
much affect the audio performance.

Many SMPS manufacturers are also including power factor correction in their
products as it is becoming a requirement in various countries and classes of

As an indicator of how much energy we are talking about, power factor on
things like Pass Labs and First Watt amplifiers is about 80%.

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Old 25th October 2014, 05:54 PM   #7
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Originally Posted by daly2k View Post
We all know that are speakers are reactive loads on the amps output
Do you mean something like speaker impedance equalizing?
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Old 25th October 2014, 08:36 PM   #8
daly2k is offline daly2k  United States
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No equalizing-just an idea based on an Audio Express article. During my professional years I was responsible for designing and building Pharm and chem plants. Of course all the mains transformers had three phase PF correction but this was the first time I had seen it used on an Audio amp. I understood that it would not make an audio improvement but would lessen the electric consumption. Not a problem for me just an idea. dave
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Old 25th October 2014, 09:46 PM   #9
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PFC networks can be used to attenuate some noise. The Uberbuss uses one. The details are not available, and I don't know how much attenuation.

Are you just looking to improve noise in the class A? I need to get to work on my dual rail PSU board...

What's the amperage used by all these Pass DIY projects? (The range, v is like 12-40 right?)
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Old 25th October 2014, 10:04 PM   #10
jcx is offline jcx  United States
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rectifier-capacitor input supplies draw current in large pulses for few milliseconds at the peaks of the line V waveform - the pulse current peaks are very much larger than the average or rms current

PFC circuits use switched inductors up front to give near continuous, proportional to line V current - like a pure resistive load

if the high frequency switching transients are well controlled with careful EMI design then the PFC smoothed line current draw means the PFC equipped devices "play nice" with every thing else plugged in nearby

since most EMI measures work reciprocally good PFC supplies will also have better immunity to external EMI sources
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