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Replacing a 100k pot with a 50k (plus series shunt mod question)

98.113.134.135
Posted on October 27, 2011 at 05:57:18
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002
 The motorized 100k 4 gang(quad) Alps blue velvet pot I'm using has become scratchy in the right channel.

There are only 50k quad replacements available.

Currently I have a 47.5K series resistor and 47.5k shunt resistor on the 100k pot. This combination works perfectly for me.

What value series resistor and shunt resistor should I use with the 50K pot to give me the same range of operation and performance as I now have with the 100k pot.

Thanks for your help.

 

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Have you tried cleaning the old pot?, posted on October 27, 2011 at 06:35:33
Tweekeng
Audiophile

Posts: 2093
Joined: September 9, 2005
 Usually scratchiness is caused by dirty contact area.

A quick squirt of tuner wash (Do they still make tuner wash?) or contact cleaner could fix it.

Beware of contact cleaners that leave behind a lot of lubricant as that can become a dust magnet.

 

RE: Have you tried cleaning the old pot?, posted on October 27, 2011 at 06:51:38
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002
 Alps pots use carbon film. I'm not so sure spraying any contact cleaner in there is a good idea.

 

RE: Replacing a 100k pot with a 50k (plus series shunt mod question), posted on October 27, 2011 at 09:54:18
rick_m
Audiophile

Posts: 6230
Location: Oregon
Joined: August 11, 2005
 Just change your shunt to 91K.

Rick

 

RE: Replacing a 100k pot with a 50k (plus series shunt mod question), posted on October 27, 2011 at 10:03:16
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002
 There are 2 resistors for each phase of the quad pot. A series and a shunt.

Shunt change to 91K- thanks

Change the series to 91K also?

 

RE: Replacing a 100k pot with a 50k (plus series shunt mod question), posted on October 27, 2011 at 11:15:09
rick_m
Audiophile

Posts: 6230
Location: Oregon
Joined: August 11, 2005
 "Change the series to 91K also?"

Nope, just leave it as is. The network will be just as it was except that you get to benefit from a lower output impedance.

Rick

 

RE: There are two resistors connected to ground. , posted on October 28, 2011 at 06:48:04
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002
 Which one (A or B) is considered the shunt resistor?

A) Signal input is wired to resistor lead that is then connected to pot pin #1 ground.

B) Pot pin #1 ground is directly connected to pot pin #3 input with the 2nd resistor.



 

RE: There are two resistors connected to ground. , posted on October 28, 2011 at 08:42:10
rick_m
Audiophile

Posts: 6230
Location: Oregon
Joined: August 11, 2005
 Well, I'm plenty confused!

Here is what I thought you had initially...


Input hot
|
Rseries (47K)
|
|-----------------Pot hot
|
Rshunt (47K) Pot wiper---------------- output hot
|
|-----------------Pot Gnd----------------- output Gnd
|
Input Gnd

If that's the case just change the shunt to 91K. If not, then what is?

Rick

PS hope you can make it out, between the limitations of my iPad, HTML and proportional fonts it's insane to do a sketch!




 

RE: There are two resistors connected to ground. , posted on October 28, 2011 at 09:04:40
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002



Yes, thats the way I have it wired.

 

RE: Have you tried cleaning the old pot?, posted on October 28, 2011 at 19:47:59
basilio89@hotmail.com
Audiophile

Posts: 125
Location: USA-MIDWEST
Joined: November 29, 2005
 Hello: I've had to replace a new Noble pot on a preamplifier once. On the other hand, I've also
had good success cleaning or, a better way to put it, is maintaining the new pot w. periodic cleaning w. Caig products. Take Care, Vasil

 

RE: Have you tried cleaning the old pot?, posted on October 28, 2011 at 20:01:18
basilio89@hotmail.com
Audiophile

Posts: 125
Location: USA-MIDWEST
Joined: November 29, 2005
 Sorry, I ment to say that I replaced a Noble pot w. an Alps pot. But, maintenance is the same. Vasil
BTW, have you considered cryoing the pot. I did and in helped. Night and day difference? No, but a definite improvement -as it is w. most cryoing in my experience.

 

RE: Have you tried cleaning the old pot?, posted on October 29, 2011 at 12:32:21
reb
Audiophile

Posts: 1867
Location: NY
Joined: January 28, 2002
 Due to the way it is assembled, its not possible to disassemble a motorized alps pot for cleaning.

 

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