Faking log pots (API) - Webpage

Hello,

I was looking around for a 22K reverse log potentiometer for the API clone and came across a site that tells you how to fake log pots, and reverse log pots, with standard linear pots.

The problem was to find the switch and resistors for the switch on Fabios API, so I thought it might be eaiser/cheaper with a pot.

I now wonder if anybody has tried the examples mentioned on the webpage? Would it work? I am not good at these things, but it sure looks interesting!

http://www.booyaka.com/~al/audio/parts/secret_life_of_pots.mht

thanks if anybody is willing to take the time!

Robert

You could try Omeg in East Grinstead - I got a 5meg pot sample from them a couple of years ago.
Stephen

that article is in easier to read form on RG's site, geofex.com

dave

You guys might think that I am crazy, but what if the solution to our reverse log potentiometer problems was a little different.
There are many very good log (audio) taper pots to be had for decent cost. What if I made a small gearbox that reverses the rotation on the shaft of the pot? It would not work for repairs on existing products where there is no room to add the gearbox, but it would work great for DIY and new products.
Anyone knows places on the web where one can purchase small metal or plastic gears?

Tamas

I did some testing and I have dropped it...
Looks like none of that gives the right curve really, there was a post on the old BB all about this. Lost or backed up? :grin:

You don´t need to use the expensive Grayhill, you can grab a $3 bucks Lorlin and wire it to the board, or get some CTS switches, they are not sealed but inspire confidence. Cheap and good enough to the job. Or use a log pot and label it ATTENUATION :razz: I do it all the time...

Ha, gears sound like fun Tamas!

cheers!
Fabio

I never saw the big deal with having the pot go "backwards". Anyone used to working on neve gear is already used to that...

dave

I thought a reverse log wasn't just a backward log, but rather an inverse taper. That is, where a log pot is (-) in relation to linear, a reverse log pot will be (+) the same amount in relation to linear. So a linear is actually closer to the actual taper of a reverse log, than a regular audio log pot is.

I have found a dual 22k rev log pot now... maybe I can just remove the second one...

Do you think a cheaper pot (the one I found was a simple Omeg pot) would add much noise to the circuit, or should I be ok?

Thanks for all your comments, now I at least know what not to do...

Robert

> fake log pots

You can make a poor fake of a log pot.

You can't fake a log rheostat (which is what most mike preamp gain-knobs really use).

> What if I made a small gearbox

That works. (Assuming there really are that many GOOD log pots in the low values a mike preamp usually uses.) Or a dummy knob and a rubber-band wrapped figure-8 around two knobs.

But as soundguy says: I never saw the big deal with having the pot go "backwards".

After all, which way is "right"? Volume knobs all go one way, and it seems gain knobs should go the same way (clockwise for louder). But look in the kitchen. All (US) stove knobs turn counter-clockwise for bigger flame. Same as calculator keypads go one way, telephone keypads go another way: you don't even notice.

One reason stoves "work the other way" is they put the numbers on the knob, not the panel. So HI is clockwise from LOW, going around the knob. Even though you have to turn the knob counterclockwise to get to HI, your brain sees it "clockwise".

On a live performance PA mixer, I might obsess about getting it to go "the right way", so "up" is the same on Gain as it is on Bass, Treb, and Fader. But on a studio recording rig, where you don't adjust Gain very often and not in panic, it isn't a great big deal.

Thanks PRR. Again. Errr... something. Always the side of reason. :thumb:

I think the SCA stuff has reverse gain controls? I'm so drunk. Sorry.

[quote author="tk@halmi"]You guys might think that I am crazy, but what if the solution to our reverse log potentiometer problems was a little different.
There are many very good log (audio) taper pots to be had for decent cost. What if I made a small gearbox that reverses the rotation on the shaft of the pot? It would not work for repairs on existing products where there is no room to add the gearbox, but it would work great for DIY and new products.
Anyone knows places on the web where one can purchase small metal or plastic gears?

Tamas[/quote]


Joergen Bergfors has done this. Take a look at
http://www.idg.se/personal/bergfors/bergfotron/vcf.htm

JH.

Thanks for the link.

Tamas