Potentiometer VS variable resistor for level adjusting

[Bricolo]

I ever wondered why we use a pot, connected to in, ground, and the wiper to the output, for volume control

why not only a variable resistor, and no ground connection? (a pot with only 2 used pins)

[dhaen]

Hi Bricolo,

One reason is that we can reduce the level to zero.
If we use series, this cannot be done.
If we use shunt, it is possible, but we need a series resistor which looses signal.
So, we use a compound seires/shunt circuit: A potentiometer

Cheers,

[UrSv]

Originally posted by Bricolo
I ever wondered why we use a pot, connected to in, ground, and the wiper to the output, for volume control

why not only a variable resistor, and no ground connection? (a pot with only 2 used pins)

Maybe because in most cases that would not work as volume control? The input current is so low that adjustment would not made by that arrangement as that would essentially be a current input control. The "normal" set-up works as a voltage divider giving true adjustment of input level.

[Bricolo]

ok

and how to determine the pot's value?


I used a 100k logarithmic pot on my headphone amp, and I had to turn it 3/4 turn before having an attenuation

a strange thing is that this pot, when turned reverse clockwise (the way to turn volume down) first change it's value very slowly, and near the end, the value changes a lot when moving it a little

isn't it supposed to be the contrary? a good precision on low volume, and change rapidly the value on high volume?

[EC8010]

Originally posted by Bricolo
I used a 100k logarithmic pot on my headphone amp, and I had to turn it 3/4 turn before achieving attenuation. A strange thing is that this pot, when turned reverse clockwise (the way to turn volume down) first changed its attenuation very slowly, and near the end, the attenuation changed a lot when moving it a little.

Isn't it supposed to be the contrary? Good precision at low volumes, and rapid changes at high volume?

I hope you don't mind me fine-tuning your English. I'm filled with admiration for people who conduct technical conversations in a foreign language.

Yes, this does sound wrong. I wonder if the pot is actually inverse logarithmic? I'm assuming that you are loading this pot with a valve stage. If you load a 100k pot with a (typically 10k) transistor amplifier, you can expect odd results.

[Doug]

I thought that there was two kinds of "tapers" when dealing with potentiometers (1) linear taper and (2) log taper. The linear taper pot increases and decreases in a linear fashion when you turn it up and down. I think the log taper pot does not increase and decrease the resistance in a linear fashion ie: towards the end of the volume control travel, there is a big jump in resistance, which would explain the behavour of Briloco's potentiometer. Anyone know about this?

I don't mind Bricolo's broken English. I talk to so many people on the internet, that I have learned to read between the lines LOL!! I have always spoken English, but I'm sure that when a person from another country reads my postings and e-mails, it seems a little funny to them also.

I take the English language for granted, but I am told that English is the hardest language to master????

Doug