Having -50dB in the middle of the pot is not usable. Plus, i use this in different contexts so it's an interesting general question for me. nothing to do with obstinacy, that's was the original question and it's still the question.

If it walks like a duck, and quacks like a duck, it just might be a DUCK!

 

That's a new requirement I wasn't aware of (would have been nice to know at the beginning).
So I'll let others guide you on your quixotic quest.

that is a direct quote from earlier, I can hardly be held responsible for what you do and don't pay attention to. As for Quixotic - I have taken some trouble to explain the question and what I am trying to do, I find it churlish of you to talk to me in this way. If you struggled to keep your attention on this thread I wonder however you made it through Don Quixote, or maybe you just weren't paying attention to half of it. Ill concede it's an unorthodox problem, but that's the question and if you aren't able to give an answer, I would rather not have to put up with being condescended to

First decide on your minimum and maximum points, and set R1 accordingly. The pot will always be at 0V and 5V at the ends of its range. Then decide on what attenuation you need at the centre, and calculate the value of resistor to put between wiper and one end of the pot.

I understand what you mean, but there is no value of R1 which makes this a satisfying solution to me - I want to have the most control over the relatively audible range and cut off quickly after that. It may seem unimportant to you but it makes a big difference. It's useful in lots of circuits but think for example of a crossfader - it's important for two channels of audio to fade into each other so you get detailed gradations in the mixture of two sounds, if you cut one or the other off too quickly it just won't have the intended effect.

 

hat is a direct quote from earlier, I can hardly be held responsible for what you do and don't pay attention to.

It should have been said up front, not buried somewhere in your long, confusing posts.
But I'm not responsible for your crappy attitude either.

 

I understand what you mean, but there is no value of R1 which makes this a satisfying solution to me - I want to have the most control over the relatively audible range and cut off quickly after that. It may seem unimportant to you but it makes a big difference. It's useful in lots of circuits but think for example of a crossfader - it's important for two channels of audio to fade into each other so you get detailed gradations in the mixture of two sounds, if you cut one or the other off too quickly it just won't have the intended effect.

In that case, it seems like an impossible task, so I concede defeat.

 

In that case, it seems like an impossible task, so I concede defeat.

I still believe it's possible, but thanks anyway!

I'm not responsible for your crappy attitude either.

if you can't handle someone talking back to you, its best not to start in the first place

 

if you can't handle someone talking back to you, its best not to start in the first place

Good advice.
I just didn't know beforehand that you had such a crappy attitude to those trying to help you.
You might mention that at the start of your next thread.
(I'll be sure to ignore it).

 

Good advice.
I just didn't know beforehand that you had such a crappy attitude to those trying to help you.
You might mention that at the start of your next thread.
(I'll be sure to ignore it).

cmon this is the most stimulating thing that's happened to you in probably 20 years. you think i believe you won't be back for another round?

 

cmon this is the most stimulating thing that's happened to you in probably 20 years. you think i believe you won't be back for another round?

I'd call it more a PIA then stimulating.
But I'll still be around, since I enjoy helping people who appreciate the help.
Just won't be you.

 

Happy trolling. Glad I didn’t bite

 

"" .......... It's useful in lots of circuits but think for example of a crossfader ........... ""
.
Are You actually looking for a solution to a custom Crossfader-Pot ?
.
.
.

 

+1 to the list

 

Are You actually looking for a solution to a custom Crossfader-Pot ?

Not specifically but you could use it for that. I was trying to use to illustrate why it's not desirable to increase dB / rotation

 

"" .............. use to illustrate why it's not desirable to increase dB / rotation ""
This statement makes no sense ???

If You would explain in detail, the end result that You are trying to achieve,
and in what kind of environment You are working in,
and what type of equipment You are using,
we could very likely come up with several viable solutions to your problem.

The actual problem with this discussion,
is that You think that You know what the solution to the problem is.

According to the Title of this Thread, "" creating 'realistic' log pot taper ""
it would appear that You are asking the wrong question.
There is no such thing as a "realistic" Log-Pot-Taper,
because there are no "Volume-Control-Knobs" in Nature,
there is only each individual persons, personal perceptions, and personal preferences.

There can also be environmental problems, or problems with other pieces of equipment,
that are creating an undesirable effect.
For instance, Frequency-Response changes with Sound-Pressure-Level,
or possibly room-resonances which come and go at different Sound-Pressure-Levels,
Speaker distortion levels can also play a part,
the Frequency-Response of your Ears with varying SPLs is a big one, etc., etc..
.
.
.

 

The actual problem with this discussion,
is that You think that You know what the solution to the problem is.

I appreciate your effort to try and explain why you think this has gone off the rails. I accept that the wording of the first post, or the title may have been confusing. But after simulating the problem, showing a schematic, re-explaining the problem a few times over, there isn't much left to say about it.

From my point of view the problem with this thread is that people are telling me that they know what my requirements are better than I know my requirements are.

"" .............. use to illustrate why it's not desirable to increase dB / rotation ""
This statement makes no sense ???

We are talking about the schematic and simulation I posted earlier in the thread. The solution being suggested is that I increase the resistor and make the control voltage on the VCA reduce more steeply as I turn the pot to minimum, dB is a measure of amplitude, pots rotate. I don't see why dB / rotation is so confusing. If you want to clarify it's written in more detail in earlier posts

I said in post #6 and I still have to tell people it's not a satisfactory solution, I have no idea why they don't listen to me. I have been designing with these VCAs for years, in the past I would do these things but I think it can be better. Hence the question.

 

What is the reason for needing a mathematically "perfect" Taper ?
Maybe I missed it.
.
.
.

 

I’ve been reading all this again, and it has just dawned on me what your requirements might be.
The VCA is linear in dB, so logarithmic overall, but it is really properly logarithmic, unlike a logarithmic potentiometer, which can’t be properly logarithmic because it goes to zero at the end, and a really logarithmic response never goes to zero.
Is that what you are trying to say?

 

I’ve been reading all this again, and it has just dawned on me what your requirements might be.
The VCA is linear in dB, so logarithmic overall, but it is really properly logarithmic, unlike a logarithmic potentiometer, which can’t be properly logarithmic because it goes to zero at the end, and a really logarithmic response never goes to zero.
Is that what you are trying to say?

Yes, if the VCA is logarithmic, a linear pot will produce a logarithmic response. What the TS seems to be saying is that the lowest setting is not low enough. Well, the only way to change that is to change the range of the VCA so that at zero on the pot it has the desired output. Changing the pot cannot make it go lower than zero!

 

I’ve been reading all this again, and it has just dawned on me what your requirements might be.
The VCA is linear in dB, so logarithmic overall, but it is really properly logarithmic, unlike a logarithmic potentiometer, which can’t be properly logarithmic because it goes to zero at the end, and a really logarithmic response never goes to zero.
Is that what you are trying to say?

yes. that's exactly what I mean

Well, the only way to change that is to change the range of the VCA so that at zero on the pot it has the desired output. Changing the pot cannot make it go lower than zero!

I don't know what you mean by "lower than 0", I never requested such a thing.

I solved this problem myself. I used a diode to put a non linearity in the gain response. see attached plots.