Hi, I'm a new member and have a question or two about pots.

[anselmo107]

 Hi everyone, I've been looking through this forum for a while now for reference etc and it is full of very helpful information, thank you. I have decided to join the forum and hope to gain more knowledge by reading the posts and asking the odd cheeky question . If you haven't already guessed I am a complete newbie! I've done a few mods including the DOD 308 pedal to "Grey" spec and I have wired up a (ready made) pcb of a DOD 250. I have now moved on to something a bit more tricky. I am attempting to build a Riot clone on veroboard. I have done all the cuts, jumpers, resistors, capacitors and Ic's, but I was wondering if anyone would be able to help me with a Potentiometer problem. I have looked through the forum at very similar questions but didn't quite understand some of it. I need a 10k Reverse Log pot for the tone control, which I could not find anywhere! I did read that you can take a 20k linear pot and wire it in parallel(?) with a 20k resistor to achieve a near enough 10k Reverse Log pot. The bit I am unsure of (due to my lack of knowledge!) is how do you wire the resistor to the pot. For example do you do it from Lug 1 to Lug 3 or Lug 1 to lug 2 etc. Or is it connected completely differently? Sorry asking a similar question to other posts but I couldn't quite understand enough how to do it.

Any help would be greatly appreciated  .

Thanks in advance.

David.

[blooze_man]

Smallbear has reverse log pots.

http://www.smallbearelec.com/Detail.bok?no=116

[KazooMan]

You should be able to find a 10K reverse taper many places.  Your phrase "odd cheeky question" leads me to believe that you are probably not in the states, but here is an example of what Smallbear has to offer.

http://www.smallbearelec.com/Detail.bok?no=116

     Note added:  Bloozeman beat me to the post with this one!

As far as "rolling your own"  you should go to RG's website:

http://www.geofex.com/index.htm

From the left hand menu select "fx skills / how to's"  This will lead you to a page with a LOT of good reading for a newbie.  Select "The Secret Life of Pots" and you can learn all about converting a linear taper pot into a reverse taper and you can even select the taper you want!

[anselmo107]

Hi, thanks for your replies. Yes you're right, I am in the UK. I had already looked at "the secret life of pots", but didn't quite understand the diagrams  . I'll have another look and hopefully it might make more sense.

Thanks again.

David.

[Joe Hart]

I am in the UK. I had already looked at "the secret life of pots", but didn't quite understand the diagrams  . I'll have another look and hopefully it might make more sense.

Welcome!!

Let me boost your confidence a bit. I have two college degrees (so I'm not a complete idiot), been messing with electronics as a hobby since high school (so I'm not a exactly a newbie), and I still feel like I'm barely grasping LOTS of concepts here! I've found that as you understand little bits and pieces, other little bits and pieces suddenly make sense. In other words, feel free to read "The Secret Life of Pots" a dozen times, but don't stress out if you don't understand it all. Ask intelligent questions and just try to understand enough to complete the project you're working on, because a couple of weeks later, those two weeks' worth of learning will enable you to understand a little more! If that makes sense!

Anyway, welcome and enjoy!!
-Joe Hart

[KazooMan]

Anselmo107

Do you have a simple meter to measure the resistance?  If not, this is one tool you definitely must have for this hobby and you can get a simple digital multimeter that will do just fine for very little money.

OK, so now you have  (or already had) a meter.  A good way to understand these sort of things is to actually give them a try.  Take a linear pot that you have on hand and a suitable resistor.  Measure theresistance of the pot by itself as you turn the knob from stop to stop.  You should get readings from zero through the total resistance (of vice versa) and it should be linear (ie. 25% at 1/4 turn, 50% at mid-way, etc.).  Now add the resistor as you think it should be based on your understanding of the diagram.  No harm here, you can always get both parts back.  Measure the resistance again.  You should see the effect of the added taper.  Try both the normal audio and reverse audio taper types.  Try a resistor of a higher value to see the effect. 

I'll bet you will understand this much better after you give it a real world try and can correlate your parts on the bench to the diagrams at RG's site.

[Joe Hart]

Measure theresistance of the pot by itself as you turn the knob from stop to stop.

I like to use a knob with "1-10" on it (like a guitar knob). That way I can actually get readings somewhat equidistant from each other. Another way to do it is to mount the pot on a piece of cardboard or something and then write in numbers to simulate the "1-10" scale of a knob. That way you can say: when it was on "3," the resistance was "X," now with the added resistor, the resistance on "3" is "Y." This may be overkill, but I think it's a little more reliable and "scientific."
-Joe Hart

[lopsided]

hi, not sure if it helps, but good explanation can be found here: http://www.diystompboxes.com/smfforum/index.php?topic=70732.0 (look for zyxwyvu first post the C case)
also, most of the time the exact taper does not affect the functionality, it just affects the way it feels. In other words, maybe just try a linear 10K pot and see if you can set tone with that one.

Jakub

[anselmo107]

Hey guys, Thanks so much for all of your replies, I might try and do what KazooMan said and use a meter to see the changes. Like you say I will probably learn quicker by actually doing it! Thank you Joe Hart, for your reassurance, your advice is good  . Also thank you for that other link, it looks very useful! If I can't seem to do it still, after trying all of the above I might just try and use a 10k linear and see how that is. Once again, thank you all very much for your help and advice. I will let you know how it goes!

Thanks again.

David.

[Joe Hart]

Thank you Joe Hart, for your reassurance, your advice is good  .

No problem. This is a great forum with some really great people on it! Just remember to ask the right questions. You'll get much more help if you DO NOT ask questions like: "how do I build a Fuzz Face?" Rather ask: "I breadborded a Fuzz Face using so-and-so's schematic/layout and the transistor voltages are blah-blah-blah and I'm not getting any output, any ideas?" I think that's the best advice for a new member on this forum. And, again, there are many great people here more than willing to help! Enjoy!
-Joe Hart