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looking for a potentiometer

post #1 of 18
1/9/12 at 6:45pm
Thread Starter 

I'm looking for a 50-100k stereo pot

dimensions need to be 1/2 in x 1/2 in (width and height), could be smaller, or slightly larger. depth (along the knob) is not important

pinouts won't matter, I'll wire it

 

low volume tracking is the reason I'll be changing the existing one, so I need something that's not too cheap

 

a stepped attenuator would be nice, even one with 3 steps altogether, but I have not seen one yet

 

thanks

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post #2 of 18
1/9/12 at 7:12pm

ALPS and TKD pots are usually 1"x1" or more. http://www.partsconnexion.com/controls_pot_alps.html

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post #3 of 18
1/9/12 at 7:19pm

Yea 1/2 by 1/2 is really small... you may have to do something custom for yourself.

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post #4 of 18
1/9/12 at 7:48pm

Seems like the ALPS RK097 would fit the bill quite nicely.  It's more or less the standard for DIY portable amps around here.

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post #5 of 18
1/10/12 at 10:30am

TKD 2CP-601 (2CP-601S stepped) 16 x 16mm, 16.5 mm(L).

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post #6 of 18
1/10/12 at 11:01am

I have always liked TKDs, though I've never used the 601. I believe the 601S is still a conductive plastic pot with detents, not a real stepped attenuator. Alps pots are available this way as well, or at least they used to be.

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post #7 of 18
1/11/12 at 6:11am
Thread Starter 

Thank you, all.

 

It seems like I've got my work cut out for myself. I've either got to open up the faceplate of the amp so the pot will stick out, and/or move the capacitors around. Or I've got a put a hole on the top of the amp enclosure.

 

I HATE mechanical work on enclosures and pcbs.

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post #8 of 18
1/11/12 at 3:46pm
Quote:
Originally Posted by recephasan View Post

Thank you, all.

 

It seems like I've got my work cut out for myself. I've either got to open up the faceplate of the amp so the pot will stick out, and/or move the capacitors around. Or I've got a put a hole on the top of the amp enclosure.

 

I HATE mechanical work on enclosures and pcbs.

Why?  Two of us spec'd ALPS and TKD pots that met your requirements.

 

If you really have to have a stepped attentuator, that's different - but you didn't indicate that was a particular requirement, just that it "would be nice."

 

 


Edited by tomb - 1/11/12 at 3:47pm
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post #9 of 18
1/12/12 at 6:24am
Thread Starter 
Quote:
Originally Posted by tomb View Post

Why?  Two of us spec'd ALPS and TKD pots that met your requirements.

 

If you really have to have a stepped attentuator, that's different - but you didn't indicate that was a particular requirement, just that it "would be nice."

 

 


you're right!

but what I did not write was that

-the amp originally had an alps pot, a small one

-it was laughably mismatched at low volumes

-I hacked away at the amp, changed the opamps, took out the pot, replaced it with a voltage divider for fixed volume

-since then I've acquired a new dac and it has high output.

 

Seeing as the small alps pot was not good for my purposes, I'm thinking (and I don't know for a fact) that the TKD would not be much better. It seems that in order to be able to drive the amp at low, and variable volumes, I've either got to put in a pot of far better quality, or put a stepped att. once and for all

 

is it not the case that the larger the pot, the better the low volume tracking, since it's all about resistor material deposited over a surface with a viper running over it?

 

what I was really hoping for was a tiny stepped attenuator, and I'd be willing to live with 3-5 steps, too. :-)

 


Edited by recephasan - 1/12/12 at 6:25am
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post #10 of 18
1/12/12 at 7:23am

These pots, particularly the small ones like the Alps RK097, have quite a bit of sample to sample variance in them. Since they are cheap, you could buy several and hopefully find one that has better low range tracking than the one you currently have. If you have a good DMM, you could test them outside of the amp, and put in the best matched one.

 

I've never seen a small stepped attenuator; it would have to be built with surface mount resistors, and even the mechanism (the switch) could be problematic. My preamp has a 64 step relay based attenuator in it (Pass Aleph P) and I sometimes find myself wanting a step in between those. That is one reason why I have always preferred pots over stepped attenuators.

 

One other thing you could look at is reducing the gain of the amp so that the normal listening range is in the middle of the pot travel, rather than at one end (particularly the low end).

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post #11 of 18
1/12/12 at 9:29am

Have you considered software volume control using a burr brown pga or cirrus cs type chip?

 

Another option, if you have room in the case but just not where the pot goes, is AMB's delta1 + lcduino system. This is a 256 step relay attenuator controlled by an arduino board. You can interface a cheap mono pot to it for the actual control of the volume, it can also be remote controlled via rf. You do need a fair amount of space for it though. You can check out the details at AMB's site.


Edited by bcg27 - 1/12/12 at 9:34am
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post #12 of 18
1/12/12 at 10:04am
Quote:
Originally Posted by Pars View Post

<snip> 

One other thing you could look at is reducing the gain of the amp so that the normal listening range is in the middle of the pot travel, rather than at one end (particularly the low end).


Could you also go to a lower ohm pot?  From 50K to 20K for example?
 

 

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post #13 of 18
1/12/12 at 10:06am

I'm controlling volume on my pc.

I want to get rid of my potentiometer.

Want to have fixed resistors setting  volume to half on the amplifier.

      ----------------------------------------------

      IN                  OUT         GROUND

      ----------------------------------------------

       47000 ohm-------------3300 ohm

      ----------------------------------------------

Do you think is the right values?

 

pot.PNG

 

 

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post #14 of 18
1/12/12 at 11:04am
Quote:
Originally Posted by Tribbs View Post


Could you also go to a lower ohm pot?  From 50K to 20K for example?
 

 



 That wouldn't really change anything

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post #15 of 18
1/12/12 at 11:07am
Quote:
Originally Posted by 2dyclectic View Post

I'm controlling volume on my pc.

I want to get rid of my potentiometer.

Want to have fixed resistors setting  volume to half on the amplifier.

      ----------------------------------------------

      IN                  OUT         GROUND

      ----------------------------------------------

       47000 ohm-------------3300 ohm

      ----------------------------------------------

Do you think is the right values?

 

pot.PNG

 

 



 I believe half volume should be around -10 dB so assuming your spreadsheet is correct (too lazy to check it) then you would want the step 19 spot.

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