K200B-2 Hissing [message #25659] |
Sun, 23 October 2016 11:32 ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
slk854
Messages: 192 Registered: January 2015
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Senior Member |
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I have one of my 200's that has a hiss when you power up the amp. All knobs can be turned down to nothing but still the hiss. When you start playing the sound does drown out the hiss, but it is still there. I can flip the power switch left or right and no difference. It is not unbearable but it is annoying to hear. Any suggestions to try???
Steve
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Re: K200B-2 Hissing [message #25662 is a reply to message #25661] |
Mon, 24 October 2016 14:29 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
slk854
Messages: 192 Registered: January 2015
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Senior Member |
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Ok I plugged into the rca jack on the back of the hissing amp, and the other end went into the input of another amp. I did not get any hiss at all through the second amp that I plugged into. Now keep in mind that the hissing occurs with the volume all the way off. Turning the volume up on the hissing amp DOES NOT increase the volume of the hiss/white noise in the slightest.
Steve
[Updated on: Mon, 24 October 2016 14:33] Report message to a moderator
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Re: K200B-2 Hissing [message #25663 is a reply to message #25659] |
Mon, 24 October 2016 16:44 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
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Senior Member |
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You have just proven that the hiss is being generated in the power amp. Which would make sense as the controls don't change the hiss level.
In my experience, hiss can be caused by multiple things. The two most common causes are transistors and carbon composition resistors. Finding the problem will not be easy. Sometimes heating or cooling parts will cause the problem to get better or worse.
Sometimes the only way to fix it is to rebuild the entire circuit.
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Re: K200B-2 Hissing [message #27102 is a reply to message #27101] |
Tue, 13 November 2018 06:07 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) |
stevem
Messages: 4758 Registered: June 2004 Location: NY
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Senior Member |
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like Bill posted on this question back in 2016 it could be many things , and even some in concert with each other.
I would start off by replacing Q701 and Q702, or at least take voltage measurements and compare them to the PC703 schematic to see how Q700 thru Q703 are biased.
If you do such then note the test settings on the lower right of the schematic.
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