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KEF Subwoofer

INTRODUCTION

I open this project because for the second time a my friend brought me a KEF subwoofer to repair.
Established in 1961, KEF is a renowned British manufacturer of audio products.
All the KEF Subwoofer models PSW2000 (Aug 2002), PSW2010 (Jun 2003) and PSW2500 (Jun 2003) have the same problems and only the PSW3000 have a different design.
Both problems are in the power supply section of the subwoofer, the first concerns the absence of switching off the amplifier when it is in stand-by and the second one is an excessive heating of some resistances.

 

FIRST PROBLEM

This problem cannt be solved because also adding a second transformer for the driver stage and other services many parts of the amplifier are always switched on during standby so the solution is remember to turn off the switch after use if you do not want to risk your house can go fire.
Here an interesting article in which this change is suggested KEF PSW2000/2010.

 

SECOND PROBLEM

The main transformer with about 35V-0-35V AC is used to create the 50V-0-50V DC to power the final section of the amplifier and for the driver stage and other service a lower voltage is obtained by linear regulators like 7815  and 7915.
These linear regulators cannot accept an input voltage greater than 35V so the KER designer have created a resistive divider to reduce 50V.
A resistive divider create much heat and the 2W resistors used cannot support this for long time H24.

The KEF service replace the 2k2 with 1K8 to reduce the input voltage for the voltage regulators and this avoids the breaking of these.
Both the resistors create much heat that goes to destroy the capacitor from 47-100uF close to the big 8200uF 50V to replase is the standby led blick and you ear infinite click on woofer.

The solution is repacle the 4 resistors in the divider with 4 x 5W and fix all on little heatsink.

WOOFER REPLACE

In same case it is necessary replace the woofer probably because the original (the 10" have the cod. 8900-6140-0) cannot support all the power of the amplifier 27Vrms on 4ohm with 0.5% THD so 182W.

I have searched on the market a valid substitute because the original is no longer available as service part after the acquisition of the brand by the Chinese.

 

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