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Unpowering Input Channel [message #10543]

Wed, 25 February 2009 10:58

77Pbass
Messages: 18
Registered: February 2009

Junior Member

I have a K200B-1 that I recently purchased and want to use on a gig this weekend. The Bright channel adds considerable noise when the amp is idle.

In another post, someone came up with the idea of un-soldering the power to the PC board as a way of eliminating the noise. Is this valid?

From what I can see, the power is supplied by the red wire in this photo:

http://lh3.ggpht.com/_ewHoYRtd1Ec/SZ9GU-kUvAI/AAAAAAAAABw/HGieyCynF8I/s144/IMG_1425.JPG

I plan on doing some repair work in the future to replace the resistors and caps if necessary but I want to get through this gig with diminished noise.

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Re: Unpowering Input Channel [message #10544 is a reply to message #10543]

Wed, 25 February 2009 11:17

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Here is a link to the picture if you want to get a better look:

http://picasaweb.google.com/77Pbass/KustomK200B102#530503727 0827940978

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Re: Unpowering Input Channel [message #10545 is a reply to message #10544]

Wed, 25 February 2009 11:29

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

If you're sure that the pre-amp is causing your noise, you can remove the power from the board. That will stop it from adding any noise to your sound.

There are two power supply lines going to the board, one positive (red) and one negative (green). If you go this route unhook them both.

You could also just unhook the pre-amp output line that goes to the power amp board. Look for the blue wire that goes to the power amp board.

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Re: Unpowering Input Channel [message #10546 is a reply to message #10545]

Wed, 25 February 2009 11:53

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Great, thanks Bill...I'll probably unhook the output to the power amp as you suggest.

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Re: Unpowering Input Channel [message #10548 is a reply to message #10543]

Wed, 25 February 2009 12:12

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

If I can add my 2 cents here I would unpower it by removing the red wire, as unhooking the blue would may invite noise pick up as you would have a open input and even though both preamp inputs to that transistor have 33k resistor they feed into you still can use the methode of shorting that unused blue wire to kill noise input.

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Re: Unpowering Input Channel [message #10549 is a reply to message #10548]

Wed, 25 February 2009 12:25

77Pbass
Messages: 18
Registered: February 2009

Junior Member

So if I understand you correctly, if I was to unhook the blue lead to the poweramp, I ahould run it to ground to prevent noise entering from an open circuit.

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Re: Unpowering Input Channel [message #10550 is a reply to message #10549]

Wed, 25 February 2009 12:34

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I would unhook the wire at the power amp side and just tape it off.

As Steve pointed out, if you unhook it from the pre-amp side it will become an antenna of sorts while it is still hooked up to the power amp input.

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Re: Unpowering Input Channel [message #10552 is a reply to message #10543]

Wed, 25 February 2009 12:50

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

On amps that are that dusty and with possible corrosion like yours I would slide the 4 slip on output transistor connectors up and down 3 to 4 times to clean off any possible garbage so they can pull the full current they need.

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Re: Unpowering Input Channel [message #10554 is a reply to message #10552]

Wed, 25 February 2009 13:45

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Already did. The pictures were taken immediately upon opening the amp the first time. I got contact cleaner from Rickety Shack and sprayed the pots and connectors.

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Re: Unpowering Input Channel [message #10555 is a reply to message #10543]

Wed, 25 February 2009 20:21

77Pbass
Messages: 18
Registered: February 2009

Junior Member

Ok...unhooked the red and green wires...had to solder two reds and two greens together as they were jumped to the other PC board.

Noise is now only white noise. Before it was white noise and other annoying noise.

After this gig I will begin the tweaking to reduce overall noise level.

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