Thursday, August 26, 2010

Upgrading the B&K ST-140 amplifier

This was an easy upgrade - on both boards, replace the 100uF/100V and 47uF power supply electrolytics. The 47uF electrolytic input capacitor was replaced by a 10uF film unit. You can use anything from 10uF to 47uF here. Due to the size of the film capacitors, I bypassed the circuit board capacitors with wire and installed the new units inline on the leads from the RCA jacks.

The end result was an amplifier that sounded much more detailed and immediate. Gone was the treble roll off and plummy bass. The big 47uf electrolytic input definitely added some major coloration to the sound as now it sound much more neutral. Though not in league with my big Threshold S/500, the B&K is now one heck of an amp for the money.



andy tj said...

I did compare your schematic with original PCB from the product

Your schematic seems missing C3

can you help me ?

DividebyTube said...

there are three different version of this amplifier out there and there could also be production differences over the life of these too. Sadly I no longer own a B&K ST-140, so I can't exactly check.

DividebyTube said...

just replace any of the old PCB electrolytics and you should be good to go. Just make sure the polarity is correct.