balanced volume control

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So it should be like this?
 

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Gear Specs

Roberto,
I find your solution very interesting and I think it probably cost less than $10 but it does require some work. Could you provide some specs on the 3 gears? Spacing between the 3 gears, # of tooth per gear and may be a drawing showing the dimensions? If I were to go to a R/C hobby shop, what should I ask for? Thanks.
 
The more teeth, the better. Big gear should have diameter similar to the pt width, or bigger. Small gear can be actually any size, but 1/4 of a big one is just about right, the only requirement being compatibility with the other ones.;)

I wonder if the size of a center gear has any inluence on the resistance when rotating the pot?
 
Re: Gear Specs

fcel said:
Roberto,
I find your solution very interesting and I think it probably cost less than $10 but it does require some work. Could you provide some specs on the 3 gears? Spacing between the 3 gears, # of tooth per gear and may be a drawing showing the dimensions? If I were to go to a R/C hobby shop, what should I ask for? Thanks.

The small gear has 18 teeth, outer diameter 10mm and has a central hole of 3mm, sorrounded by a collar (you don't see it in the photo, is in the back) of 6mm that fits nicely (with a help of a cianocrylate drop) in a ball bearing. 6mm hole is a common size for small ball bearings inner holes. You need this one, otherwise the assemble won't turn smoothly.

Peter, The size of this gear in this case has no sensible influence on friction, but of course the smaller it is the more torque it gets and the faster it runs, that's why the ball bearing... it also offers a nice way to hold firmly this gear, difficult to do otherwise.

Moreover, it's size influence the distance between the pots. With the current arrangement, there is just enough space for the Alps Pots and the bearing to come along together nicely. Distance center-to-center of the big gears with the small in between is 39mm. You have to be VERY precise on drilling the holes for the assembly or you'll end up (working best case ) with "unpleasant" feeling turning volume. Best practise is drilling the pots holes just little more (~1mm or less) than is needed, so to adjust distances precisely. Also, the total "resistence" you feel is twice what would be using just one pot, but is not excessive.

The big gear is 60 teeth, outer diameter 31mm, with a central hole of 6mm, just right for the pot axe.

I found them on rs-components.com. The catalogue codes from the RS site (the italian one, but should be the same in other countries) are 232-1185 for the small gear and 745-258 for the big one. Prices are about 2 euros/dollars each.

ciao,
Roberto Amato
 
I did it, it didnt worked good, because I dont have equal o/p voltages -> I use single ended input (that will change soon..), theres some losses on undriven side as Nelson said and the voltage doesnt get cancelled 100%, so I get pretty loud volume when I have pot at 0 resistance.. I didnt applied current sources yet, because I didnt buy tip31c transistors (these were proposed to me) yet, Ill have more questions then and I guess ill have to get quad pot somewhere..
 
Ball Bearing

Roberto,

Thanks for the detail information ... which even includes the part number! I want to check with you to see if this is the right part # for the ball bearing that you use. RS-Components has a part # of 285-0841 which has a 6mm ID and 19mm OD. I'm not sure if 19mm OD is a common size for a drill bit to drill the hole to fit the bearing.

I wonder if RS-Component has any distributors in the United States because USA is not listed in the choice of country to pick on their "start page".
 
Re: Ball Bearing

fcel said:
Roberto,

Thanks for the detail information ... which even includes the part number! I want to check with you to see if this is the right part # for the ball bearing that you use. RS-Components has a part # of 285-0841 which has a 6mm ID and 19mm OD. I'm not sure if 19mm OD is a common size for a drill bit to drill the hole to fit the bearing.

I wonder if RS-Component has any distributors in the United States because USA is not listed in the choice of country to pick on their "start page".

Well, my bearing was one of a few sitting in a box, I didn't get it
from RS so I can't help you there. But I checked in the past and they were ok... RS also has some bearings that have a little collar over one of the two faces. That collar helps a lot to keep the bearing "flat" on mounting. If I would do it again I would use it.

19mm is a common size, but NOT for a drill bit, use a... (don't know the word in english) is a small bit (about 6mm) with a crown of teeth around... (maybe someone will tell me). The small bit in the center works as a pilot for the rest. They came from 10mm upwards, and they do the work nicely.

I noticed that RS do not have a US site, weird. In any case you can of course get it by any other RS site... can't resist a smile here, someone from US getting parts from Europe... world is upside down! ;)

ciao,
Roberto Amato
 
It works!

I tried it, and it seems to work really well! (BZLS & SOZ)

Right now I am using a dual 10K log pot (between 221R and 100K to ground on each output and channel).

Does anybody know the most ideal value of this pot, and should it be a lin or log version?:confused:
 
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