I'd like to get a cermet pot that has an audio log law (Vishay L taper). Because the value is pretty high, these are not common (typically linear taper).
I found a reasonably priced one that has a Vishay 'F' taper. Below I copy a snip out of the datasheet. Vishay's F taper looks like it is the exact inverse of the L or audio log taper - pretty uncommon on audio amplifiers I assume. From this here old thread I understand that the F-tapered pot can be used just like an L tapered pot but you turn counterclockwise for increasing the volume. (So where the proverbial '10' on the volume dial is would be zero and vice versa.) So far so good.
Can I also turn the F-tapered pot into an L-tapered pot by reverse wiring it? By reverse-wiring I mean connecting the incoming signal to the 'c' terminal of the pot (see Vishay datasheet image below) and GND to the 'a' terminal? Which then, assuming the arrow at terminal 'b' for 'cw' (clockwise), causes the F and L labels on the log tapers to be swapped. (And the S and W curves to be inverted.) Is that correct?
The old post cited above appears to have contradictory advice on this point. (This post confidently says 'sorry but no', whereas the following one implies it would be no problem. Who among these posters is confused? Or is it just me who is confused?
Your help is much appreciated.
I found a reasonably priced one that has a Vishay 'F' taper. Below I copy a snip out of the datasheet. Vishay's F taper looks like it is the exact inverse of the L or audio log taper - pretty uncommon on audio amplifiers I assume. From this here old thread I understand that the F-tapered pot can be used just like an L tapered pot but you turn counterclockwise for increasing the volume. (So where the proverbial '10' on the volume dial is would be zero and vice versa.) So far so good.
Can I also turn the F-tapered pot into an L-tapered pot by reverse wiring it? By reverse-wiring I mean connecting the incoming signal to the 'c' terminal of the pot (see Vishay datasheet image below) and GND to the 'a' terminal? Which then, assuming the arrow at terminal 'b' for 'cw' (clockwise), causes the F and L labels on the log tapers to be swapped. (And the S and W curves to be inverted.) Is that correct?
The old post cited above appears to have contradictory advice on this point. (This post confidently says 'sorry but no', whereas the following one implies it would be no problem. Who among these posters is confused? Or is it just me who is confused?
Your help is much appreciated.
Yes reverse wiring and turning it ccw will do it. Either of them alone - no.
Check also "law faking", how to do a log pot (B-law) from linear (A-law).
Check also "law faking", how to do a log pot (B-law) from linear (A-law).
Thanks. But. What did you mean by
And my question about the reverse wiring (i.e., GND at a-terminal, input at c-terminal, and output at b-terminal) is: does it turn the F taper into an L taper, assuming cw operation?
My understanding is that, wiring it as per the datasheet (i.e., input at a-terminal, GND at c-terminal, and output at b-terminal), an F-taper pot will operate like an L-taper pot if rotated ccw. That is how I understood PPR's post in the cited thread: no reverse wiring - just turn knob in the other direction for inverted functionality.
Law faking I have looked into. As PPR says in his post, it's rarely fully satisfactory. And it isn't in my case. Made a calculation for a 100k linear pot that adds either a 10k or an 8.2k resistor between the wiper and ground. Vs/Ve graph looks decent enough but the pot's impedance then becomes variable (with a maximum at 10k and minimum ~7.5k). I need 100k in that position, so that would mean starting with a 1meg potmeter. None too many of those around.
And my question about the reverse wiring (i.e., GND at a-terminal, input at c-terminal, and output at b-terminal) is: does it turn the F taper into an L taper, assuming cw operation?
My understanding is that, wiring it as per the datasheet (i.e., input at a-terminal, GND at c-terminal, and output at b-terminal), an F-taper pot will operate like an L-taper pot if rotated ccw. That is how I understood PPR's post in the cited thread: no reverse wiring - just turn knob in the other direction for inverted functionality.
Law faking I have looked into. As PPR says in his post, it's rarely fully satisfactory. And it isn't in my case. Made a calculation for a 100k linear pot that adds either a 10k or an 8.2k resistor between the wiper and ground. Vs/Ve graph looks decent enough but the pot's impedance then becomes variable (with a maximum at 10k and minimum ~7.5k). I need 100k in that position, so that would mean starting with a 1meg potmeter. None too many of those around.
"And my question about the reverse wiring (i.e., GND at a-terminal, input at c-terminal, and output at b-terminal) is: does it turn the F taper into an L taper, assuming cw operation?"
Reverse wiring assumes ccw operation.
Reverse wiring assumes ccw operation.