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Distorted output [message #16770] Thu, 08 March 2012 14:37 Go to next message
cassent5150 is currently offline  cassent5150
Messages: 341
Registered: August 2009
Senior Member
I have a K200-2 I'm working on and I'm having a problem with the preamp signals when they are both hooked up. Each channel sounds great when hooked up independently. This came in as an empty chassis with a 303 board and face plate. I robbed the transformer, rectifier, power filter caps and output section from a K-III (PC-5065). I got the 303 up and running and installed a PC-105 in the non effects side and ran each pre amp outputs through a 33 K resistor and hooked them together into the input of the PC-5065. I found that this reduced the signal a bit too much. I went strait in with no resistor and had plenty of volume on the 105 but the 303 is dim and distorted. I tried putting resistance in the 105 output but can't get the distortion out of the 303 unless I totally unhook the 105. The 303 is clean and strong then. Anyone have any ideas?????

Steve C

[Updated on: Thu, 08 March 2012 14:38]

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Re: Distorted output [message #16771 is a reply to message #16770] Thu, 08 March 2012 16:16 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Is there any dc voltage present on either preamp output?
Re: Distorted output [message #16772 is a reply to message #16771] Thu, 08 March 2012 18:10 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
Messages: 341
Registered: August 2009
Senior Member
As a matter of fact I do. With no load or input and all controls full open 303 has .31 + and 105 has 1.2 + at the output.

Steve C
Re: Distorted output [message #16773 is a reply to message #16770] Thu, 08 March 2012 18:22 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Try changing the output coupling caps on the two preamp boards.
Re: Distorted output [message #16777 is a reply to message #16773] Fri, 09 March 2012 00:24 Go to previous messageGo to next message
cassent5150 is currently offline  cassent5150
Messages: 341
Registered: August 2009
Senior Member
I replaced both caps at pre amp output wire and voltage is .05+ and .02+. The caps on both boards were in backwards compared to a good PC-105 I had handy. We have clean signal on both channels. I think we're good now. Thanks for the advice!!! Steve C

Steve C

[Updated on: Fri, 09 March 2012 00:29]

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Re: Distorted output [message #16778 is a reply to message #16770] Fri, 09 March 2012 01:20 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Good to hear that it's working.

Just be sure that when you measure the voltage across the cap that it is higher on the positive marked side.
Re: Distorted output [message #16779 is a reply to message #16770] Fri, 09 March 2012 06:20 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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Its so pleasing when a fix is simple is it not?
Re: Distorted output [message #16780 is a reply to message #16779] Fri, 09 March 2012 10:03 Go to previous message
cassent5150 is currently offline  cassent5150
Messages: 341
Registered: August 2009
Senior Member
Yes the simple fixes are a pleasure. Now, maybe I can figure out that PC-900 with the darn + voltage in the output. I'm cooled off enough to give it a rational look over. Steve C

PS Thanks chicagobill for the tip on the higher voltage at the + side of the outputs coupling cap


Steve C
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