2nd order filter and pot resolution

[Gold]

How about  using a switch to split the range of the pot  in two or more pieces.? Then you can have as fine a resolution as you want with the ranges. Like old test equipment.

 

[john12ax7]

As I wrote earlier, standard 10% Log pots are optimized for a 1:100 ratio.

This is true,  but when you slug the pot you essentially change the taper to a higher value. If there is still a big gap after this there is probably  something going on with the pot itself.

 

[abbey road d enfer]

This is true,  but when you slug the pot you essentially change the taper to a higher value.

That is true for a potentiometer (3-wire connection), but in rheostat mode (2-wire), law-steering resistors have a very limited effect.

 

[john12ax7]

That is true for a potentiometer (3-wire connection), but in rheostat mode (2-wire), law-steering resistors have a very limited effect.

I would disagree.  Take a 100k pot with 10% taper. Put 100k in parallel and you end up with a 50k pot at 18% taper.  Put 50k in parallel and you end up with a 33k pot at 25% taper.

 

[abbey road d enfer]

I would disagree.  Take a 100k pot with 10% taper. Put 100k in parallel and you end up with a 50k pot at 18% taper.  Put 50k in parallel and you end up with a 33k pot at 25% taper.

Not with a Log or RevLog pot. 33k over 10k (for a 10% Log pot) does not do much.

 

[warpie]

So what is considered good? 20% taper or even higher?

Also, is there any elegant solution for using a linear pot on this specific topology?

 

[abbey road d enfer]

So what is considered good? 20% taper or even higher?

It depends on the range you want to achieve. 20% is good for 1:25, 30% for 1:10

Also, is there any elegant solution for using a linear pot on this specific topology?

Not really, unless you accept a limited range like 1:4 or 1:5

 

[warpie]

Sorry abbey but I'm not sure I fully understand what these range ratios are. 

 

[abbey road d enfer]

Sorry abbey but I'm not sure I fully understand what these range ratios are.

That's the ratio between the lowest frequency and the highest.

 

[warpie]

So for a 20Hz-250Hz that will be 1:12.5? Do I get this right?

 

[abbey road d enfer]

So for a 20Hz-250Hz that will be 1:12.5? Do I get this right?

Yes.

 

[warpie]

Thank you. So in my case I guess a 25%-30% pot would be the most suitable.

 

[abbey road d enfer]

Thank you. So in my case I guess a 25%-30% pot would be the most suitable.

That's correct.

 

[john12ax7]

Not with a Log or RevLog pot. 33k over 10k (for a 10% Log pot) does not do much.

It works quite well with log and revlog,  or maybe we are discussing different things? Certainly at the midpoint of a log pot the parallel resistor will have less effect,  but that's  exactly the point,  since it's effect changes over the whole rotation subsequently changing the taper.

Suppose you need a 50k log rheostat @ 20% taper.  To mimic this you can take a 100k log @ 10% taper and put a 100k resistor in parallel.  You effectively end up with a 50k @ 18%.

 

[abbey road d enfer]

It works quite well with log and revlog,  or maybe we are discussing different things? Certainly at the midpoint of a log pot the parallel resistor will have less effect,  but that's  exactly the point,  since it's effect changes over the whole rotation subsequently changing the taper.

Suppose you need a 50k log rheostat @ 20% taper.  To mimic this you can take a 100k log @ 10% taper and put a 100k resistor in parallel.  You effectively end up with a 50k @ 18%.

Agreed!