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

NellTones · Aug 3, 2023

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 · Aug 4, 2023

W

Nigel Goodwin said:
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 · Aug 4, 2023

NellTones said:
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 · Aug 5, 2023

NellTones said:
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.

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

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