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-   -   What does my potentiometer do? (https://www.diyaudio.com/forums/analog-line-level/352132-potentiometer.html)

TomC1970 3rd April 2020 04:38 AM

What does my potentiometer do?
 
First off...yes...I'm a *******. "I know just enough to be dangerous" would be an overstatement. If I put a pot at the output of my opamp circuit...do I have a gain control? Or a volume control? Or a variable output impedance control? Thank you all for your patience. ---Tom

jaddie 3rd April 2020 09:28 AM

You have all of them, though a volume control is a specific function with a purpose and the others are generic

What are you trying to achieve?.

JonSnell Electronic 3rd April 2020 09:36 AM

You will have a volume control if the wiper is the output.
It will not adjust the gain but may have an effect on the impedance feeding the next stage.

jaddie 3rd April 2020 09:54 AM

Quote:

Originally Posted by JonSnell Electronic (https://www.diyaudio.com/forums/analog-line-level/352132-potentiometer-post6145845.html#post6145845)
You will have a volume control if the wiper is the output.
It will not adjust the gain but may have an effect on the impedance feeding the next stage.

Connected that way it will adjust the total system gain by applying varying degrees of attenuation.

The output impedance will vary with wiper position.

Mark Tillotson 3rd April 2020 01:26 PM

If the pot's a 1M ohm one, its also a notable Johnson noise generator. If its 2k its nice and quiet and within the capabilities of most opamps to drive without extra distortion.


If the next stage is bipolar you need a coupling capacitor in series with the wiper output to prevent loud crackles.

TomC1970 3rd April 2020 02:15 PM

Thank you all. The concept in mind is a preamp with 2 outputs....with a switch to choose the output. Output one is a single opamp unity gain "buffer" circuit.....output 2 sends the signal through a second opamp to serve as a "driver" for going to tubes and transformers. The pot in mind would be at the output of the second stage. ---Tom

jaddie 4th April 2020 03:59 AM

Quote:

Originally Posted by TomC1970 (https://www.diyaudio.com/forums/analog-line-level/352132-potentiometer-post6146127.html#post6146127)
Thank you all. The concept in mind is a preamp with 2 outputs....with a switch to choose the output. Output one is a single opamp unity gain "buffer" circuit.....output 2 sends the signal through a second opamp to serve as a "driver" for going to tubes and transformers. The pot in mind would be at the output of the second stage. ---Tom

Put the buffer(s) after the pot.

There's no need for a special driver for going to tubes and transformers if the output buffer is correctly designed. This is a world of low source Z drivers and high to very-high Z inputs, so it doesn't take much.

You might want to make sure your opamp buffer is unity-gain stable. Some aren't, some need compensation. Or run a bit of gain. And a small build-out resistor on the output...stuff like that.

TomC1970 4th April 2020 05:53 AM

Thanks for the advice and info guys!


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