Question about pots

[MikeH]

I recently built a box that called for a 1KA volume pot, which I didn't have, so I used a 10KA instead.  When the volume is turned up, you get the entire volume range in the first 5% or so.  Yeah, no good.  My instincts tell me that the value needs to be increased (100K or 250K), but the schematic called for a 1K.  Or could it be a problem not related to the pot?  It seems to me using a 10K instead of a 1K shouldn't make that big of a difference.

[captntasty]

Which effect are we discussing?  Can you post the schematic?  This would be helpful to determine what might/could/should be done to improve performance....  The difference in values CAN have a dramatic effect or not, often it is dependent on the circuit taken as a whole.
Peace

p.s. I almost forgot!  Welcome to the forum!

[MikeH]

It's basically a Parallel Universe, but I made some changes; I added some Ge diodes to try and smooth out the clipping, tweaked the cap values to adjust bass, etc., and left off the "gate" switch and the resistor in conjunction with it.  Here's the vero layout I started with:


Oh, and looking at the diagram again, I noticed it calls for a 5K volume pot, not a 1K.  So really, I'd think a 10K pot would make almost no difference at all.

[Nasse]

Did you use linear or logarithmig pots...

[GibsonGM]

10K shouldn't make much difference, I'd think...unless the designer just threw it in and it wasn't ideal.  Some of my pedals use off-spec volume or drive pots...I just live with the 5%.  Perhaps you didn't use an audio taper (10KA)?  Not using one will create a very noticeable compressed range since the resistance is over a logarithmic scale, not linear.  Visit the GEOFX site in the links and read "The Secret Life of Pots" for more info 

[MikeH]

I definately used an audio taper pot... maybe it's NFG (Not Functioning Good), although I've never heard of that happening.  I guess I'll just stop being lazy and break out my iron and my box o' pots and start swapping them out.

[Roobin]

Ive had dodgy pots. I had a plastic shaft, cut it (quite stupidly) and then it didn't work unless you pushed it down. At least I now know how a pot works.  But the strange thing is I cut the shaft of another one, and it worked perfectly fine.

[Paul Marossy]

Could be a mis-marked linear pot. I've heard of that happening before. It sounds like a linear pot in the way that you describe how it works.

[GibsonGM]

Could test it out with a DMM, and assure yourself you've got the wires to it oriented correctly, maybe?  That damn wiper connection will screw you every time, LOLOL.     

If all else fails, while it's still in there, measure the resistance at the top & bottom of that 5% you've described...you'll get something like 1 ohm to 2K or something, maybe.  This should help you figure out which new pot to put in there (provided the old one functions ok). 
Good luck! At least you know the ckt works, the rest is just details 

[MikeH]

I pulled out the old pot and replaced with another 10K log and it behaved the same way.  So I threw a 100K log in there to see what I got, and it actually works better than the 10K.  There's still a sharp spike in the first %5, but it doesn't go up all the way.  Then there's a nice smooth increase until about 75-80% of the way up, and then it goes through the roof immediately.  Still not great, but at least more functional now.  I'm stumped, it's totally weird.

[captntasty]

So, it sounds like you are truly "perceiving" the logarithmic behavior of the pot rather than how the ear "normally" percieves volume increase (or something like that) - that we normally perceive volume increases in a logarithmic fashion but as the brain processes the logarithmic info it produces the perception of a smooth linear increase.  Does that make any sense?  I couldn't figure out a coherent string of words 

So, I wonder if a linear taper would be worth a try? 

[Paul Marossy]

Hmm... maybe this is the odd case where a linear pot would work better. 

[MikeH]

Hmmmm... I know they're rare, but perhaps a "Straight line" audio taper is the key.  Like in this picture:

http://www.geofex.com/Article_Folders/potsecrets/pottaper.gif