Faking a reverse taper?

[nee]

Greetings!

I have a 100K pot  as a tone control, connected between a .047uf capacitor and ground just before the 100K output pot. I've tried both log and linear taper but all the treble-cut action seems to happen at one end of the pot (though the linear is perhaps slightly better). Do I need a reverse taper pot to smooth the response out? Or is there some other way? I thought maybe a smaller value pot might help, but of course that just cuts down the overall level.

Thanks!

IanG

[zyxwyvu]

Greetings!

I have a 100K pot  as a tone control, connected between a .047uf capacitor and ground just before the 100K output pot. I've tried both log and linear taper but all the treble-cut action seems to happen at one end of the pot (though the linear is perhaps slightly better). Do I need a reverse taper pot to smooth the response out? Or is there some other way? I thought maybe a smaller value pot might help, but of course that just cuts down the overall level.

Thanks!

IanG

http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

[nee]

Thanks for the link to the post. I did do a search before I posted but for some reason that post wasn't in the results.


IanG

[DougH]

I'm surprised this wasn't linked in that thread:

http://www.geofex.com/article_folders/potsecrets/potscret.htm

[MikeH]

It could also have something to do with the size of you cap too.

[jacobyjd]

This may not work in some cases, but when I run into this issue with tone pots, I tend to prefer wiring a standard log pot backward.

The trick is to label it creatively...

[DougH]

Yes, I did that with a gain control once.

[MikeH]

This may not work in some cases, but when I run into this issue with tone pots, I tend to prefer wiring a standard log pot backward.

The trick is to label it creatively...

enot?

Yes, I did that with a gain control once.

niag?

[jacobyjd]

This may not work in some cases, but when I run into this issue with tone pots, I tend to prefer wiring a standard log pot backward.

The trick is to label it creatively...

enot?

Yes, I did that with a gain control once.

Ummm...I was thinking something more like 'Treble Cut' and 'Gain Cut'

...but I like your idea better 
niag?

[nee]

Yeah, I tried wiring it backwards too (so it functioned like a Vox "Cut" control) but the effect was the same: lots of tops until you get near the end of the pot travel, then the cut kicks in.

This, I would have thought, would indicate that either the cap or pot value is wrong, but changing the cap value up or down makes the "tone fully off" position too bright or too dull. Changing the pot value (down) reduces the overall gain (for want of a better word) of the box. Changing it up just exacerbates the problem.

[MikeH]

What is the circuit?

[nee]

This is the output section. Q3 is a J201.

If the pot range is between 0 and 10, when the pot is at 0, the amount of cut I'm getting with the .047u is what I want. When I start turning up the pot, by the time it's at about 2, just about all the treble has come back, and moving from 2 through to 10 has very little further effect.

I've tried using a 500K linear pot and changing the taper in accordance with details in RG's "Secret Life of Pots", and using calculations from here:

http://www.diystompboxes.com/analogalchemy/emh/emh.html

but the result always seems to be the same: all the action down one end.

For example, with a 500K lin pot, connecting a 10K resistor between lugs 1 and 2, and a 150K resistor between 2 and 3 produces (approximately) a 100K pot with a 90% taper. This still produced the "bunched-up" effect, so I thought I had just wired the resistors to the wrong lugs. Swapping them around decreased the overall level coming out of the stompbox, but did nothing to the taper. It all seems very odd. Is it something to do with that old mystery we call impedance?

(I've tried different pots too, in case of faults.)