KB300 mechanical vibration (buzz buzz)

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buduranus2
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KB300 mechanical vibration (buzz buzz)

Post by buduranus2 » Wed Jul 14, 2021 7:04 pm

I just picked up a KB300 and replaced the dead Black Widow with an EV. My intention is to use it for electric bass at moderately low volume. The speaker works fine but there's a lot of mechanical vibration, probably coming from the chassis. I had the whole thing apart a couple of days ago, cleaned the controls and reinstalled the chassis, which is kinda flimsy. I've zip-tied all the cables together because I thought that was the problem. It isn't. Also tightened all the external screws, including the handles. Now I gotta take the whole thing apart again, which is a real PITA. Anybody ever encounter this and if so how did you fix it? Or if you haven't encountered this what's your best guess?

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Enzo
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Re: KB300 mechanical vibration (buzz buzz)

Post by Enzo » Thu Jul 15, 2021 5:51 pm

Have I ever encountered an amp that buzzed? Of course. SO many things can buzz.

Pop the grille off. Does it still buzz? Grilles are often a buzzer. Turn it off and listen close. Ball up your fist and whack the cab on top, on the sides, on the front or rear. Do you hear any kind of rattle or noise when you hit it? Did you cinch up the screws that hold the transformer? The circuit boards?

Have someone else play to make it buzz, likely there is a certain note that does it the most. Roll up a magazine and hold it to your ear, now use that as a stethoscope to listen to every area of the amp, does that help pinpoint the noise source?

Turn the amp on its side and try it, any difference? Upside down? Flat on its back facing up?

While someone else plays, or if you can apply a steady tone to make it buzz, press on the rear wall of the chassis. Press down on the top. Press on th front. ANything affect the buzz?

We need to isolate what is buzzing, then we can correct whatever it turns out to be.

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Enzo
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Re: KB300 mechanical vibration (buzz buzz)

Post by Enzo » Thu Jul 15, 2021 5:52 pm

Also try disconecting the horns, a cracked piezo tweeter can buzz.

buduranus2
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Re: KB300 mechanical vibration (buzz buzz)

Post by buduranus2 » Thu Jul 15, 2021 7:19 pm

Got it solved. Crappy design and materials. It was the PC boards vibrating. Stuffed half-round rubber weatherstripping under all of them plus some extra on top to minimize vibration. PC boards should've been twice as thick and should've had iso-mount standoffs. Live and learn!

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Enzo
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Re: KB300 mechanical vibration (buzz buzz)

Post by Enzo » Fri Jul 16, 2021 8:10 pm

Just my personal opinion, but I hate to hear every trouble blamed on "crappy design". They made tens of thousands of these amps, and they made many more thousands of other amps of the era on the same production equipment and made of the same materials and techniques, and designed by the same tams. And yet we don't have tens of thousands of these amps coming in with this complaint. In fact there really isn't any complaint that seems to taint all of them. The amps of that era were sturdy, well made and reliable. I'd take those old Peaveys on tour in a heartbeat.

The 30-35 year old amp developed a buzz. So have many other amps of all brands and all models. Especially when they get to that age.

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