# Control volume with a pot [closed]

I'm trying to build a small synth with two pots to control tone and volume, i got the tone one working but I'm not sure how to control the volume since I'm planing to send it to an amp and just setting the second pot in series with the output didn't work. I saw this picture and it seems like this is what i want but flipped so that it starts silent and becomes louder.

i tried to follow this schematic but i got no sound

So how am i supposed to do this?

Edit: As it turns out, I'm stupid. it was not a second pot but it was instead a force sensitive resistor and that got me confused. So i suppose the real question is how do i get the force sensitive resistor to control the volume

• "second pot in series": what do you mean? a simple voltage divider should work. – Marcus Müller Nov 13 '16 at 23:37

## 3 Answers

Does your circuit pass sound with the 1uF capacitor removed? If not, then you have some fundamental problem with your "output buffer" circuit.

Using a shunt transistor (your BC549) to control audio signals is an old trick from decades ago in cheap tape recorders, etc. It is not a proper level control in the modern sense. There are plenty of voltage-controlled amplifier circuits and digital pots that would be a proper way to do this here in the 21st century.

• "not a proper level control in the modern sense" is putting it very nicely, isn't it? It's both extremely nonlinear with control voltage, and extremely nonlinear in signal transfer function – i.e. you'll get all the funky distortions that other people pay money for in guitar effects :D – Marcus Müller Nov 13 '16 at 23:52

A very simple voltage divider would do:

simulate this circuit – Schematic created using CircuitLab

You mention that "a potentiometer in series did not work", but you probably just connected the poti wrong – one end to signal, the opposite one to signal ground, and the middle one as adjustable voltage divider output. The Opamp-buffer is just so that your circuit stays as perfectly a voltage source as possible.

• As it turns out, I'm stupid. it was not a second pot but it was instead a force sensitive resistor and that got me confused. So i suppose the real question is how do i get the force sensitive resistor to control the volume – Malgranda Nov 14 '16 at 0:11
• yep, that's pretty far off from your first question. So: Accept one of the answers given, ask a new question. Or, really, just by a potentiometer, if that is what you want. – Marcus Müller Nov 14 '16 at 0:26
• that doesn't even have anything to do with the graphic you used. ahem. Please don't do that again. – Marcus Müller Nov 14 '16 at 0:29
• Yeah I'm not that good at this, sorry. but thanks for trying to help me. – Malgranda Nov 14 '16 at 0:37

how do i get the force sensitive resistor to control the volume

You read the force sensitive resistor value with your microcontroller, and then set a new value to send to the digital pot (or controllable-gain amplifier) or whatever. Or you multiply the audio data value if you are processing audio in the digital domain. Since we don't know what the rest of your project looks like, we can't really give you any kind of useful answer.