Here's one other thing you can try while waiting to get some good cleaner and lube for your switches and pots. The hum just recently became noticeable correct? Can you try plugging it into a different outlet? What about trying it at a friend's place that's not in your building? Though the hum could be the beginning of capacitor issues, I'm trying to rule out the "dirty power" issue. So, getting it on a different home circuit might help, even though you've tried turning off other lights etc. Did you replace any major appliances? Did the building manager make other changes to heating/cooling/electrical systems?
If these ideas don't yield any improvement, the issue most likely does lie in your amp. MTF will be able to guide you through some of the voltage troubleshooting to narrow things down, but a rebuild of the power supply and/or protection boards may be in store. To me it seems that the preamp section is doing what it's supposed to, amplifying a low-level signal to send to the power amp boards. In this case it's an unwanted signal (AC or DC somewhere it's not supposed to be) that's now being amplified to audible, annoying levels.
If the rebuild is in order, and you've had no experience soldering and replacing electronic components, hopefully there's a decent repair tech in your area. With a near TOTL amp, you don't really want to go mucking about in it for your first repair attempt. There's a KA-7100 1st recap thread currently in the Kenwood section that will show what can happen if you've never soldered electronic components before.
Not trying to be harsh or scare you off of it, but before you dig into THIS amp, get your feet wet in a "disposable" BPC receiver or amp first, or just something else electronic. Since you didn't know what the Pre-out/Main-in jumpers were until I posted a pic, my confidence level isn't real high that you've had a lot of electronics experience and that you won't do more harm than good trying to chase down a VERY faint hum.
If these ideas don't yield any improvement, the issue most likely does lie in your amp. MTF will be able to guide you through some of the voltage troubleshooting to narrow things down, but a rebuild of the power supply and/or protection boards may be in store. To me it seems that the preamp section is doing what it's supposed to, amplifying a low-level signal to send to the power amp boards. In this case it's an unwanted signal (AC or DC somewhere it's not supposed to be) that's now being amplified to audible, annoying levels.
If the rebuild is in order, and you've had no experience soldering and replacing electronic components, hopefully there's a decent repair tech in your area. With a near TOTL amp, you don't really want to go mucking about in it for your first repair attempt. There's a KA-7100 1st recap thread currently in the Kenwood section that will show what can happen if you've never soldered electronic components before.
Not trying to be harsh or scare you off of it, but before you dig into THIS amp, get your feet wet in a "disposable" BPC receiver or amp first, or just something else electronic. Since you didn't know what the Pre-out/Main-in jumpers were until I posted a pic, my confidence level isn't real high that you've had a lot of electronics experience and that you won't do more harm than good trying to chase down a VERY faint hum.
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