Sub Issue : Sub Low End Drops off and stays at a consistent low volume

[NellTones]

Been having a weird issue with my KRK 10 S subwoofer. Hopefully someone might be able to give some insight on what’s going on.

So when I got my sub it worked great, low end sounded amazing but the issue I’m having is the low end drops off and stays at a consistently low volume even when I turn the volume knob up high. If I turn my foot switch off and then on again the low end hits properly for a second then drops off again to the consistent low volume. If I turn the volume knob down and up again, again hits properly for a second then drops off again to the low consistent volume. No matter how high I turn my volume knob up the sub stays at its low consistent volume.

Thinking it could possibly be a component issue in the circuitry that may have gone bad?

Thanks again! Can’t find anything on the internet about this issue and I’m just baffled so Anything helps!

 

[NellTones]

W

I'm afraid not, we really need a schematic to see what's going on.

However, there is a schematic for a KRK RP10S, though there's no resistor of that designation. BUT, there are a couple of 270 ohm resistors, R338 and R339, which feed +vcc and -vcc to a pair of comparators (U3-A/B) which feed a muting circuit using FET Q6. Presumably this is to do with anti-thump?, as the amplifier turns ON and turns OFF.

So that resistor having burnt-up (I presume you've tried measuring it with your meter?, and it's O/C?) would mean the -vcc feed to the comparator is missing, so presumably causing it to stay muted?.

There's nothing in that circuit though that could cause R339 (the -vcc feed in the RP10S) to burn up, as it just feeds to a 47K resistor, so would need a short to ground from the output of the burnt-up resistor to damage it.

But that's just guessing, based on the RP10S schematic.

Well I was sent a schematic for my 10S sub by someone at the company but I’m a little weary about posting it on a public forum as it is a proprietary copyright and I’m pretty positive the guy I talked to wasn’t even supposed to send me the schematics :/
Trying to steer clear of any legal issues I may encounter by posting it

 

[Lightium]

W

Well I was sent a schematic for my 10S sub by someone at the company but I’m a little weary about posting it on a public forum as it is a proprietary copyright and I’m pretty positive the guy I talked to wasn’t even supposed to send me the schematics :/
Trying to steer clear of any legal issues I may encounter by posting it

It's discontinued, there are no issues.

 

[Nigel Goodwin]

W

Well I was sent a schematic for my 10S sub by someone at the company but I’m a little weary about posting it on a public forum as it is a proprietary copyright and I’m pretty positive the guy I talked to wasn’t even supposed to send me the schematics :/
Trying to steer clear of any legal issues I may encounter by posting it

If you post it, we can help you, if you don't, we can't - it's quite simple.

It's an old model there should be no issues, and upcoming legislation (assuming it's not out yet?) will require manufacturers to make service information and spares freely available.