Replacing old pots

DeadSpeaker · 17th March 2008, 08:14 PM

I have a friend with an amp from the 60's. When the volume pot is turned, the volume of the amp seems to jump from very quite to very loud at about the 3 to 4 positions and then get a little loud as it is maxed out. I think that it should behave less jumpy. Here is the schematic. http://www.gibson.com/Files/schematics/G20A,%20G30A.pdf

Can I replace the pots with 1/2 watt ones or do they have to be 1watt?

Mooly · 18th March 2008, 07:50 AM

Hi, You can replace with whatever will phsically fit. Wattage does not come into it here. Use a pot with an audio or logarithmic taper for volume, if replacing bass/treble pots these must be linear.
Regards Karl

djk · 18th March 2008, 09:36 AM

The bass/treble pots are also log taper.

Mooly · 18th March 2008, 11:28 AM

Oop's , Absolutely right djk, it's just a passive Baxandall network.
Regards Karl

DeadSpeaker · 18th March 2008, 10:27 PM

Thanks guys. Would a different resistance on the volume pot make it less jumpy?

Mooly · 19th March 2008, 07:39 AM

Hi, You need a 47 or 50 k pot, value is important in this case as it works with the other components around it to determine the characteristics/response curve of the tone controls. It is a common value. the jumpiness is caused by either wear or dirt on the carbon track.
Karl

17th March 2008, 08:14 PM	#1
DeadSpeaker diyAudio Member Join Date: Jul 2007	Replacing old pots I have a friend with an amp from the 60's. When the volume pot is turned, the volume of the amp seems to jump from very quite to very loud at about the 3 to 4 positions and then get a little loud as it is maxed out. I think that it should behave less jumpy. Here is the schematic. http://www.gibson.com/Files/schematics/G20A,%20G30A.pdf Can I replace the pots with 1/2 watt ones or do they have to be 1watt?

18th March 2008, 09:36 AM	#3
djk diyAudio Member Join Date: Feb 2001 Location: USA	The bass/treble pots are also log taper. __________________ Candidates for the Darwin Award should not read this author.

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18th March 2008, 07:50 AM	#2
Mooly diyAudio Member Join Date: Sep 2007	Hi, You can replace with whatever will phsically fit. Wattage does not come into it here. Use a pot with an audio or logarithmic taper for volume, if replacing bass/treble pots these must be linear. Regards Karl

18th March 2008, 11:28 AM	#4
Mooly diyAudio Member Join Date: Sep 2007	Oop's , Absolutely right djk, it's just a passive Baxandall network. Regards Karl

18th March 2008, 10:27 PM	#5
DeadSpeaker diyAudio Member Join Date: Jul 2007	Thanks guys. Would a different resistance on the volume pot make it less jumpy?

19th March 2008, 07:39 AM	#6
Mooly diyAudio Member Join Date: Sep 2007	Hi, You need a 47 or 50 k pot, value is important in this case as it works with the other components around it to determine the characteristics/response curve of the tone controls. It is a common value. the jumpiness is caused by either wear or dirt on the carbon track. Karl

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