Does Power Factor Correction for Amplifers makes any sense?

[Hari Iyer]

I have been contemplating on this subject for quite some time and am unable to decide this as there are varying opinion on this topic which makes even more tougher to conclude. Some high power pro amps using SMPS ckt already have some PFC circuits inbuilt into their amplifiers. Also its mandatory to have PFC for high power devices. But home audio amplifiers which consumes lesser than 100Watts do not fall in the ambit and there are seldom any penalty for lower PF.

An ideal PF for a resistive load is 1.0 and for inductive and capacitive load if is less than one. Most audio amplifiers provide a non-linear load to the AC grid. I measured the PF in my amplifier load and it varies from 0.6 to 0.65 depending upon the time of measurement. I measured using the 3 voltmeter method as per this link http://www.giangrandi.ch/electronics/cosphi/cosphi.shtml

I was able to calculate a PFC capacitor directly connected across the AC line to be around 6.2uF. Adding this capacitor brings the PF back to around 0.95. This will bring the current and voltage back in sync. The capacitor can also help in reducing odd harmonics in the AC line and do some kind of line current clean-up too. The capacitor will be connected in the same AC powerline and will be switched on / off along with the amplifier.

I am not looking at power savings or energy bill reduction, but wanted to check if bringing the current and voltage to some sync, will this reduce some heat in my transformer and will my PSU run a little cooler as i am actually reducing the I2R losses in the transformer lamination. Also odd harmonics above the fundamental (50Hz) will be filtered by the inductive transformer and the capacitor by forming a Low Pass filter..

Please suggest your opinions as this could also be a wasted exercise by me - but nothing to loose in checking out. I may plan to check the PF again after adding the capacitor to see if did any magic.

 

[Nikhil]

IMO in an audio amplifier sound quality is paramount.
The way I would look at it is - does adding the PFC affect the sound?

Regards.


.

 

[Hari Iyer]

Dont know if it improves SQ, but doing a PFC the current spikes (odd harmonics) can be reduced. This can also help in an otherwise noisy AC power chords as now the current and voltage are almost in phase. The amplifier transformer have to work less to transfer the same current and core losses are minimum. But cant say if these will relate to improved dynamics unless someone with golden ears can confirm.

Links to discussion in other forums http://www.diyaudio.com/forums/pass...tion-pass-firstwatt-stock-diy-power-amps.html

 

[arj]

Hari, I have found Power supply to make a big difference in Digital equipment. The way i understood it is that most power supply rectification output is not really a constant DC but still a fluctuating AC and the more the spikes/harmonic content the lower the quality of the DC output. cleaning up the input supply apparently improves this. Some Equipment are insensitive since the power rectification they provide is of very high quality.

I presume this holds true for Amplifiers int eh same way as long as the dynamic power especially for Class AB amps do not get choked i guess if the power rating of the device doing the PFC may need to be 3-5 times the RMS rating ?

Again the above is a simplistic view the way I have understood this hence may not be technically correct

 

[Hari Iyer]

I finally added an 8uF EPOCS MPP capacitor in parallel to the Line and Neutral yesterday evening after changing the AC power cable. There is a certain improvement in the dynamics, but i am not able to pinpoint if its due to cable change or addition of PFC capacitor. I have run the amp only for 30 minutes and am not able to confirm about the heat too as the PSU was not that hot in 30 min. May be this weekend i would be able to add some updates.

 

[prem]

There is passive PFC and active PFC. I am not sure but what you are trying is passive PFC. Active PFC done correctly works well

 

[Hari Iyer]

Active PFC are found on expensive SMPS based PSU where in higher power Pro amp its mandatory to have PFC. For amps having power consumption lesser than 75 watts its not mandtory to have PFC. Hence most home amplifiers may not have PFC. I am not sure if adding a simple capacitor across the AC lines will help to compensate the inductive reactance created by the transformer. The capacitor can add a capactive reactance and balance out the inductive reactance created by the transformer. So ideally the AC mains will find a resistive load and reduce heat in the transformer core as it does not need to compensate for I2R losses. Will check if the heat generated is less by this weekend.

 

[jls001]

Do read Rod Elliot's page on power factor correction.

 

[Hari Iyer]

Do read Rod Elliot's page on power factor correction.

yes, many times