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Re: Reverb won't turn off [message #20508 is a reply to message #20505] |
Wed, 23 April 2014 02:15 ![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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Are you turning off the reverb with a foot switch or turning down the reverb control?
There are a number of revisions to that board that relate to the amount of reverb and vibrato. Do you know which board version you have?
Go over to the technical section of the site and look up the pc303 boards and see if yours is the same as the latest version of the board. You might need to update a few values to get the fx working right.
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Re: Reverb won't turn off [message #20509 is a reply to message #20505] |
Wed, 23 April 2014 06:32 ![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) |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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I dought that any pc303 circuit problem could make for of enough added Gain to make the reverb that sensitive as the level of hum would be quite high also!
I would peel back the protective cover on the reverb pan and look in it as I would bet that one of then two long springs is busted off the input side of the pan and sitting down in the pan.
This is the only way that every little vibration to the amp can make the reverb rustle around.
[Updated on: Wed, 23 April 2014 06:42] Report message to a moderator
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Re: Reverb won't turn off [message #20511 is a reply to message #20505] |
Wed, 23 April 2014 12:48 ![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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Making a quick comparison of the version 1 and version 6 schematics, there are a number of changes that would reduce the amount of reverb signal getting to the power amp stage.
The output from the reverb tank is amplified by the recovery circuit based around Q318 and Q319. The output is then sent to the reverb control through a 1uF cap and then through R382. R382 was originally 100 ohms but was later changed to 22K ohms, a big difference.
Resistor R395, 6800 ohms, which reduced the amount of clean signal going to the reverb control was removed from the circuit and there were changes to the the values of R385 and R386, which increased the amount of clean signal being sent to the power amp stage when the reverb was turned off.
If you feel confident in your soldering skills, you can revise the circuit to the version 6 circuit and see if that is more to your liking.
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Re: Reverb won't turn off [message #20515 is a reply to message #20505] |
Wed, 23 April 2014 18:03 ![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 might want to check Q321. When the reverb is turned off it is supposed to ground out the delay signal.
As for the vibrato, did you happen to check the value of R350?
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Re: Reverb won't turn off [message #20518 is a reply to message #20505] |
Thu, 24 April 2014 00:41 ![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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The simple test for the pot is to bypass it. Jumper the wiper to the CW lug and see if the intensity increases.
As for a replacement, the only place is from another amp.
Read the voltage at the base of Q320/321. It should be positive when the reverb is on and it should be negative when the reverb is off. Check the resistors R388/389/390 values to be sure that the voltage swing is big enough to turn off the reverb.
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Re: Reverb won't turn off [message #20522 is a reply to message #20505] |
Sat, 26 April 2014 01:02 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) |
bluezebra
Messages: 89 Registered: February 2014 Location: Lafayette, LA
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Thanks Stevem..
I'll keep that in mind. I need to research the pot a little more and had to put the Kustom on the side...I had to jump on a Fender Bandmaster to do a cap job for a kid who needed it quick.
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