Good morning!
I'm in brain-cooking mode, trying to figure out how I could display the difference between 2 potentiometers (like, volume left to volume right).
It would be for a balance- or volume-indicator of two independent knobs (with a "master" volume-pot being present), so it would be interesting to see the difference of those two...
Like:
L is -6, R is -6 = 0
L is 0, R is -6 = -6
L is -6, R is 0 = +6
I was able to come up with a mechanical possibility (think gears + springs), but it would be interesting to see if others have come up with other methods? How would this be done the electronic way?
Have a nice day
david
I'm in brain-cooking mode, trying to figure out how I could display the difference between 2 potentiometers (like, volume left to volume right).
It would be for a balance- or volume-indicator of two independent knobs (with a "master" volume-pot being present), so it would be interesting to see the difference of those two...
Like:
L is -6, R is -6 = 0
L is 0, R is -6 = -6
L is -6, R is 0 = +6
I was able to come up with a mechanical possibility (think gears + springs), but it would be interesting to see if others have come up with other methods? How would this be done the electronic way?
Have a nice day
david
If the controls are carrying stereo audio then it is not easy.
You could feed a low level inaudible HF signal to both channels and pick and filter that off and derive absolute values from the amplitude of those.
You could feed a low level inaudible HF signal to both channels and pick and filter that off and derive absolute values from the amplitude of those.
I have done this by adding a small DC voltage to the top of the pot. Then read the DC from the taper and display that on a meter.
If you add 1V, then at say 1/3rd down it would show 0.67 or so.
You can even get fancy with a log converter showing values in -xdB format.
Don't forget to include DC blocking coupling capacitors after the pot, and possibly before if they are not yet present.
Jan
If you add 1V, then at say 1/3rd down it would show 0.67 or so.
You can even get fancy with a log converter showing values in -xdB format.
Don't forget to include DC blocking coupling capacitors after the pot, and possibly before if they are not yet present.
Jan
Thanks, mooly and jan!
Do I understand it correctly: I would have to feed the pot with some additional DC (or HF) which means there would be a generator of sorts, and so I‘d have to either mess with the signal, or add an additional gang per channel, correct? (It seems so logical since a music-signal is not linear…)
Jan, since you already made somesuch, I take it that it’s so to say an invasive-but-non-disturbing method (without a losing quality)?
Do I understand it correctly: I would have to feed the pot with some additional DC (or HF) which means there would be a generator of sorts, and so I‘d have to either mess with the signal, or add an additional gang per channel, correct? (It seems so logical since a music-signal is not linear…)
Jan, since you already made somesuch, I take it that it’s so to say an invasive-but-non-disturbing method (without a losing quality)?
Yes, either an HF generator or a DC voltage source. I think for Jan's method for example a 10k pot could be fed from a series 100k? and say 1 volt DC applied to the 100k. So the wiper would give a 0 to 91 millivolt DC voltage as it was rotated. The audio would be AC coupled at each point, into and out of the pot.
The HF method is similar in superimposing it onto the audio at the top of the pot.
An additional gang would be much better because it simplifies things asnd there is no possibility of unwanted effects.
The HF method is similar in superimposing it onto the audio at the top of the pot.
An additional gang would be much better because it simplifies things asnd there is no possibility of unwanted effects.
The pots won't be perfectly matched L to R. So I don't know you could do this. Another approach would be an A/B switch, in position A the normal input is present, but in position B an oscillator sends a mono signal through both pots and the normal input jacks disconnect. This B mode is "calibration mode" now you just compare the output of each pot, because you know the input is identical coming into each side and you can adjust balance to compensate the pots to match. I'm not too keen on passing DC or a high freq all the time, a calibration mode switch you'd only use from time to time.
Not sure if I'm way off here from what you want to accomplish.
Not sure if I'm way off here from what you want to accomplish.
Use a program like ARTA in the FR2 (differential) mode. Just feed the same excitation signal to both pots and you can look at wiper difference to a very high degree of accuracy.
This is a very easy way to see how dual pots track, set one relative to the other in a precise way, etc, etc.
Dave.
This is a very easy way to see how dual pots track, set one relative to the other in a precise way, etc, etc.
Dave.