Hi everyone.

This question might seem silly, but I don´t see any difference between A and B system.



Thank you

Kind regards

 

You only posted "b". What is "A"?

 

The image does not show all the image for connection A.

Connection A has the unused pin of the rheostat connected to the slider so that if the slider becomes disconnected by some dust in the track then the rheostat will be the resistance of the track instead of a complete disconnect.

 

They are both connected as rheostats. The common reason for tying the wiper to one end of the resistance is that when the device is rotated there may be momentary openings in the connection, and so the jump in resistance is huge. Connect the wiper to an end and that resistance jump is much smaller.

 

A might be considered preferred but I almost always use B.

 

Here is one example, possibly it is similar.
This application uses a three terminal potentiometer. The wiper is connected to the first terminal as a variable resistor.
As the wiper turns clock wise the resistance decreases. As the ratio between R1 and R2 changes the voltage across R2 the voltage
is adjusted. By choosing the appropriate resistance values the arrangement fits the application.
In this case the voltage is 0.156 V when the 2.5V source remains steady. (using voltage reference and divider becomes a finite control)

5000*60%=3000Ω
if you want modify this check out the voltage divider calculator page.
https://www.allaboutcircuits.com/tools/voltage-divider-calculator/

 

Ahh ok ok, thank you for your answers

 

The way I would define it is that A forms a variable resistor while B forms a voltage divider.

With A, you can vary the resistance from zero ohms to max ohms. With B you can pick and choose a point within the range that can set a reference voltage for something like a comparator or amplifier. But for sure there are many more uses and reasons for using one over the other.

 

Here, I'm using a 22KΩ pot as an adjustable negative feedback gain control.

 

Tony, your opamp has a gain control from 1 to typically 200,000 times.
Its 0.1uF input resistor feeding the low value 10k resistor cuts 800Hz a little, cuts 160Hz at -3dB and cuts lower frequencies at -6dB per octave.

 

the original post asked about connecting the wiper to one end of the pot.
Look here:

 

the original post asked about connecting the wiper to one end of the pot.
Look here:

AG is correct, and I answered that post explaining the industry standard reason for the "B" connection scheme. ButI am used to having my advice ignored and then guilty of saying "I told you so."

 

Tony, your opamp has a gain control from 1 to typically 200,000 times.
Its 0.1uF input resistor feeding the low value 10k resistor cuts 800Hz a little, cuts 160Hz at -3dB and cuts lower frequencies at -6dB per octave.

The world of audio amplification is well on my low end of understanding. That said - the reason for the post is to show the TS what I consider the correct way to wire up a pot. Even though both ways (A & B) are done. In fact, my variable regulator has the "A" configuration.

Perhaps some day I will learn more about audio stuff, attenuation and such. For now I can only work from what I see on the internet and HOPE it's right.

 

Thank you