Newbie question to troubleshoot a 100K Pot

[Tronage]

Ok, before I start, let me just say I'm 100% newbie to building anything. In fact this was pretty much my first attempt at building something simple.

I wanted to make a volume to put inline between my IPod and my headphones (yes I know they sell them, but I wanted to build one that was a box w/ a big knob on it, so I could adjust the volume while wearing snowboard gloves).

So I hit up the local radio shack, and bought a stereo 100K pot (part 271-1732) and 2x 1/8" Stereo phone jacks (part 274-246), some wire, a big knob, and one of their project boxes.

Now I did do my research in how to hook up the pot to make it be a volume (following the info located near the bottom of this page: http://www.bcae1.com/potentio.htm. Basicly I have the common grounds from both jacks going to the first pin on the first plater, and then a wire jumper down to the first pin on the second platter so everything was grounded.

I'm then using the top platter for the left chan, and the bottom platter for the right chan. So the 2nd / 3rd pin on each of the platters are the in and out of respective channel comming from and going to the jacks.

Now to my amazement it actually all works... However not quite as I expected... With the pot turned all the way up, it is at 100% loudness. If I turn the knob about 2-3 degrees, the volume drops to about 50%. If I go about 6 or so degrees further it gets to about 10% volume.

I guess the best way to describe it is of the 300 degrees the knob turns it breaks down like this: 0-290 degrees represents 0-10% volume. Then 291-300 degrees represents 10%-100%...

What I would like would to have the entire range of the pot represent the whole range of 0%-100%. So this is where my problem is...

Now like I said I'm a newbie that knows just the right amount to cause myself problems . I'm very happy with the size, setup, etc. so I don't want to change the pot if I don't have to. But I'm maybe guessing 100K is too much for such low level on headphone wire?

So I guess my question is if this problem I'm having is because something is connected wrong, or is the the pot itself. And if it is the pot being too big, is there any way to fix it (like adding a resistor accross pins 2 and 3, and if so, how much resistance to make it work properly).

Thanks in advance to anyone who can help me out. And remember I'm newbie, so please explain a bit more detailed !

[pinkmouse]

You probably have a linear pot. Check the back, it should say. To convert it, you could put a 5K resistor from the wiper to the ground. Normally, a 100K pot is a little small for this, but as the iPod is designed to drive headphones, you should be ok.

[lineup]

you can try to switch Terminal A and Terminal B connections.
It turns potentiometer 'upside down'.
Output is taken from Wiper.

It might help .... if you are lucky

[sreten]

Hi,

one end of the pot - common earth.
input - the other end of the pot.
output - the pot wiper.

You do need a stereo pot BUT you can't get a stereo pot the value you need.

Ideally you need a log pot ~ 2 x the impedance of your phones ~ 50R.

Your problem is caused by the 100K value you have used.

/sreten.

[pinkmouse]

Ideally, yes, but I have an amp sitting next to me on my desk with a 100K pot, and it works fine with whatever I plug into it. Admittedly I don't have an iPod, but it works fine on the headphone outs of my Walkman, (now my only tape source!) and portable cd player.

[Tronage]

Thanks for the advice so far! Just to make sure there is no confusion I'm using this on my IPods headphone out jack (standard 1/8") into my pot, and then into my headphones.

To address some of the suggestions:

1) Unsure of it being linear or not. Here is a link to the pot I have: Radio Shack link And here is what I believe are the specs for it Radio Shack specs. So two 5k resisters (one per plater) from wiper to ground may fix this issue?

2) I've tried taking the output from wiper (esentially since both "ends" are connected to the 1/8" jacks, all I need to do is plug the source into the other jack... though this didn't help.

3) If you mean reverse the pot so that turning it counter-clockwise would turn the volume louder (the reverse of your natural instinct) I have not tried yet, however I don't want to do that since it would make the project feel too "backwards".

4) So I guess my hunch was right then? The pot is too big for the application?

Which all goes back to the first suggestion of adding the 5k resitor from wiper to ground... Would this be all I need to do to make the volume be the full range of the pot?

[sreten]

Originally posted by pinkmouse
Ideally, yes, but I have an amp sitting next to me on my desk with a 100K pot, and it works fine with whatever I plug into it. Admittedly I don't have an iPod, but it works fine on the headphone outs of my Walkman, (now my only tape source!) and portable cd player.

Hi,

sorry but the above is not relevant.

A 100K pot on an amplifer input is fine.

Between a portable out and headphones its very wrong.

An ~ 50R pot is needed, though might get away with 100R.

/sreten.

[pinkmouse]

Doh. That'l teach me to read the question properly...

[Tronage]

Originally posted by sreten


Hi,

sorry but the above is not relevant.

A 100K pot on an amplifer input is fine.

Between a portable out and headphones its very wrong.

An ~ 50R pot is needed, though might get away with 100R.

/sreten.

I warned ya I'm a newbie!

Could you perhaps point me in the direction of a stereo 50R or 100R pot as you suggested. I've done some searches, and can't seem to find what you suggest.

[sreten]

Originally posted by sreten


You do need a stereo pot BUT you can't get a stereo pot the value you need.

/sreten.

Probably your best bet is to remove the volume
controls from a set of headphones and modify them.

/sreten.