Pot as a Variable Resistor

[Bombacaototal]

Hi all, Just wanted to double check something.

I attach a sketch of a 1MB Pot set as a varaible resistor, and having it reverse wired in a way that as you turn it clockwise (to the right) you are decreasing the resistance. So all the way to the left you have max resistance of 1Meg and all the way to the right you have minimum resistance of 0Meg

1st question, does it make any difference having the input (ie from the circuit) on the lug 3 or on wiper (lug 2)? And havig the output of the pot (ie back to the circuit) on the wiper or lug 1?

And lastly, should I connect the unsused lug 1 to the wiper?

Many thanks

[sluckey]

Assuming your pic is showing the pot as viewed from the rear, the jumper needs to go between lugs 2 and 3. Makes no difference which lug you call input or output, well, as long as you don't try to use the jumpered lugs as input and output.

You could test this yourself in much less time than it took to create that pic and make this post.

[Bombacaototal]

Assuming your pic is showing the pot as viewed from the rear, the jumper needs to go between lugs 2 and 3. Makes no difference which lug you call input or output, well, as long as you don't try to use the jumpered lugs as input and output.

You could test this yourself in much less time than it took to create that pic and make this post.

Thanks a lot Sluckey, yes the drawing is meant to be the view from the rear of the pot. Your input surely helps.

One thing that I am wondering about is why usually presence pots (or Vox cut control) do not have the jumper.

[sluckey]

One thing that I am wondering about is why usually presence pots (or Vox cut control) do not have the jumper.

Lazy design. Faster assembly. Bottom line $$$. The circuit will function without the jumper. But if the pot wiper fails to make contact with the resistive track, you will have an open circuit if the jumper is not used. With the jumper, the resistance would simply be the same as if you turned the pot to one end. It's generally more desirable to use the jumper, at least in industrial/military design.

I like using the jumper for another reason too. With the jumper in place, I use lugs 1 and 3 to connect to the circuit. Now if the pot operates backwards all I have to do is move the jumper to make it work correctly.

[Bombacaototal]

Many thanks again! Makes sense, and I will make sure to use the jumper on mine

[sluckey]

It's easy to get the jumper wrong. Usually, the longer I ponder it, the more likely I am to get it wrong!

[pompeiisneaks]

It's easy to get the jumper wrong. Usually, the longer I ponder it, the more likely I am to get it wrong!

Then why is it, with a USB port that you have a 50% chance of plugging it in wrong, and it takes me 5 tries?

~Phil

[sluckey]

You need a little hair around the hole! Another trick that I use is... You know that little USB symbol on the connector? If the connector body is dark colored, I paint that symbol white so it can be seen easily. If the connector body is light colored, I paint the symbol black so it can be seen easily. That little trick has drastically reduced the number of times I miss the hole.

[Reeltarded]

It's easy to get the jumper wrong. Usually, the longer I ponder it, the more likely I am to get it wrong!

-cough-

I've never had this problem, once..

[pompeiisneaks]

You need a little hair around the hole! Another trick that I use is... You know that little USB symbol on the connector? If the connector body is dark colored, I paint that symbol white so it can be seen easily. If the connector body is light colored, I paint the symbol black so it can be seen easily. That little trick has drastically reduced the number of times I miss the hole.

[tubeswell]

Whether the wiper is shorted to the input lug or the other one makes no difference for a linear tracking pot, but it does affect an audio taper. Also the choice of lug you short the wiper to matters in some tonestacks.

[Bombacaototal]

I while back I came across an amp's feature, I cannot remember exactly where I saw this but it crossed my mind recently. The design had a pot right before the Global Negative Feedback resistor (on the PI connecting side). The cable connected the pot on the far right lug (looking from the rear). The other 2 lugs were not connected to anything.

Has anyone came across a similar desing? I was wondering what would be the purpose of doing this, as the pot is not grounded or the output conected anywhere?

[R.G.]

A pot with only one lug connected is doing nothing to the circuit. Electricity must flow in complete loops; Monodes (one terminal devices) are limited to being antennas or capacitive pickups.

I'd say that this was probably either a mistake, a hurried and incomplete repair, or a sneaky attempt to confuse copiers.

Of course, I frequently recommend in my day job that we produce pedals with a knob not connected to anything that is labeled only "More".

[Bombacaototal]

A pot with only one lug connected is doing nothing to the circuit. Electricity must flow in complete loops; Monodes (one terminal devices) are limited to being antennas or capacitive pickups.

I'd say that this was probably either a mistake, a hurried and incomplete repair, or a sneaky attempt to confuse copiers.

Of course, I frequently recommend in my day job that we produce pedals with a knob not connected to anything that is labeled only "More".

Thaks RG, makes sense. I was scratching my head as I did not understand the purpose, but it is clear now. Probable a mistake.