Basic voltage divider question

[mckenzie]

Hi, sorry for the very basic question. I am modifying a synthesizer & need to control the pulse width of a square wave oscillator manually with control voltage via a pot. In my attached scribble can I use say 10k for the resistors & then a 10k pot to achieve variable +/- 5v at the pot wiper, would this work ? I assume I can get +/- 5v from the basic voltage dividers but then not sure about the pot value & whether this needs to be 10k again ? The +/- 10v shares the same ground as the pulse width control circuit. Thanks for any help

 

[bertus]

Hello,

The output range will be smaller as the +/- 5 volts range as the potmeter will be a load for the voltage dividers.
I would use a circuit like this:

The opamp will make a buffer to the synth.
The opamp can be powered from the +/- 10 Volts.

Bertus

 

[mckenzie]

Hello,

The output range will be smaller as the +/- 5 volts range as the potmeter will be a load for the voltage dividers.
I would use a circuit like this:
View attachment 53817
The opamp will make a buffer to the synth.
The opamp can be powered from the +/- 10 Volts.

Bertus

Thanks a lot for your reply, yes I see using an opamp would make the most sense. However if wanted to keep things as simple as possible (passive) could I get away with what I suggested perhaps? I am happy to just maybe get a range of say around +/- 3v, it wouldn't give me a full PW swing but close. Is my diagram & suggested values correct for doing this or is getting anywhere close to +/- 3v unachievable doing it this way because of the pot load? Im just not sure how to calculate it. Thanks

 

[Alec_t]

This would give you a +5V to -5V swing, provided the load on the pot wiper is small (say 100k or so) :-

 

[mckenzie]

Thanks for the help I appreciate it, I understand it now. Very simple but obviously my brain wasn't working at all yesterday.