KB 300 crossover???

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MrBeverage
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Joined: Mon Sep 10, 2018 11:14 am

KB 300 crossover???

Post by MrBeverage » Mon Sep 10, 2018 11:40 am

When I took apart my KB 300, I was expecting to see a passive crossover board, between the amp and speakers, but I didn't see one. There is only the two (blue and yellow) speaker wires going directly to the Motorola horn driver's + and -, from the amp board (along with the other wires that go down to the 15" Scorpion). Where these manufactured without a crossover? I'm very confused.
The reason I took my KB 300 apart:
My beloved KB 300 has developed the intermittent "low volume" syndrome. I have performed all the tests and cleaning, recommended in the other posts. I ruled out the preamp section by using an external mixer and sending the signal to the power amp in jack (no help).
What I noticed though, was that it works fine with the amplifier removed, and set UPSIDE DOWN. Everything hooked up the same, but not HANGING from the top of the amp case (as when it's installed and all screwed in). So, my next course of action will be to disassemble the amp board, and inspect the solder joints underneath it. I hope I find a cracked joint to repair. I hope it's not a cracked trace in the board, giving way to the weight of being suspended upside down.
Thanks for reading, and thanks for any answers or advice you can provide.

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Enzo
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Re: KB 300 crossover???

Post by Enzo » Mon Sep 10, 2018 2:21 pm

The tweeters in that are just piezos, which do not require a crossover, they simply do not respond to low frequencies by their nature. In some amps PV added some resistors just to reduce their output.

If teh amp is mechanically sensitive, put the thing on the bench, run signal through it. I use a CD player. Start poking things on the power amp with a wood chopstick or other insulated object. Looking for anything that affects the signal output.

You may be right about the upside down-ness. But another possibility is that when hanging, it is also bolted up tight, wwhich can put some flex on the board. SO while probing with your wood stick, get under the board edges and give a little pry upwards to see if flexing matters.

Larger parts are more suspect. Like that ugly brown coil of wire near the speaker wire connections.

MrBeverage
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Joined: Mon Sep 10, 2018 11:14 am

Re: KB 300 crossover???

Post by MrBeverage » Mon Sep 10, 2018 2:35 pm

Thanks much for the reply.
I thought about the flex put on the boards when tightened up also. I'm gonna loosen, and remove the 4 screws on top (letting the amp just rest in place on the front and back edges) and test it that way. That should relieve any tension caused by the screws. The problem shows up immediately, so it won't take much time to verify that much at least. Thanks again.

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