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Old 8th September 2014, 05:11 PM   #1
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Question Repair a PolkAudio psw111

Hi all
A friend brought me an amp'd subwoofer psw111 (120V) to repair and use in France (230V).

I checked some power supply input components and replaced the dead ones I found. Unfortunately the fuse still flashes when I power up (with his 230/120v transfo )... So I decided to remove all this main supply to make room, but I can't guess what the value was. Please any advise?
What I can say is the following:
8 inches speaker 4ohm
The unit is rated 150Wrms in specs
Main fuse was 1.6AT
Main caps for the audio power stage are one 470F/63V for each half-wave.
Power audio transistors are 1 IRF640 for one half-wave (not really sure for the second half-wave as I didn't removed the fixation part, maybe a 9640 if exists).
The preamp was suppied from a single separated coil from the mains transformer to make +/- 15V (mono alternance 2 diodes rectifier + 7815 7915 TO220).

I already tested the preamp which is ok with a 20vac xfrm, but now I reach my skills limits so I can't figure the rating of a suited main xfrmr.
The original power suppy was a cheappo pwm and the main secondary power coil was with a central connection for the ground, and rectified with 4 bigger diodes MUR420).

Thank you for tips

[EDIT]: my error: maybe the amp is not a class D. I can't see the specific snubbers and LC output filter on the PCB . Please admin, move the post to the good forum section.
Thank you.

Last edited by HumNSmoke; 10th September 2014 at 06:25 PM.
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Old 22nd September 2014, 12:46 PM   #2
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News:
I reached to test the power amp with two 500VA 220/2*50Vac transformers I connected in series to get a 2*25Vac power supply which gave me 2*~36Vdc.
It works, although with some noticable hum, maybe from the huge toroids near around.

Please do you think I could buy 2 PWM 48Vdc or how could I calculate maximum voltage & minimum amperes. This subwoofer was specified 150W rms and the LS is 4 ohms.

Thanks
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Old 22nd September 2014, 01:22 PM   #3
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Join Date: Oct 2012
I just had a look here : The Signal Transfer Company: Power Output

from this:
Assuming I'd like to use DC supplies:
P=U^2/R, U=(PR)^(1/2)=(4*150)^(1/2)=24V
I=U/R=24/4=6A
P=24*6=~150W

So I'd need 2 24Vdc 150W supplies?

Thanks
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