Dist+ pot ?

[csmatt45]

hello folks,

I am using a 1m linear pot for the gain on my dist +. I'm having the problem with all of the gain being bunched up at the end because I can't get a reverse log pot. I read "the secret life of pots" at GEO, but I got lost in the algebra a bit. I'll get it eventually, but for now, what is the easiest way to spread out the gain, by altering my 1M lin pot. I know I'll end up with a smaller K pot, but I'll sacrifice a bit of gain if thats the trade off. can some help me with this in, "dummy" terms, like: "put a XX resistor betweem lug 3 and 2 and a XX between 2 and 1".

thanks as always...

matt

[Mark Hammer]

Only about 100k of that pot's range is actually useful.  That's why you need an "exotic" taper.  Save yourself some trouble and just stick a 100k log pot in there.  All the settings you want are in that 100k.

[csmatt45]

thanks Mark.


Just for sake of saving my $3 bucks, how would you fake it with the 1M if you had to?

best,

matt

[Pushtone]

My GGG D+ gain pot works smoothly, but backwards.
I just settled on the counter-clockwise rotation with the 1M lin.

I'll try that 100k pot thing, thanks (again) Mark.

I think I'll dedicate my next D+ to you.
How's the Hammer+ sound?

[Mark Hammer]

thanks Mark.

Just for sake of saving my $3 bucks, how would you fake it with the 1M if you had to?

best, matt

Note that there is a difference between voltage division, where the ratio between what's on one side of the wiper and what's on the other is a big part of what matters, and simple variable resistance, where the absolute value of the resistance is what matters.

When you start sticking parallel resistors along with an existing pot, the absolute resistance will necessarily change since two parallel resistances will never be greater than the smaller resistance of the two.  You will certainly be able to get a bunch of different tapers or rates-of-change, but you lose the overall absolute value of the pot.  So, yes, you can get closer to a reverse-log taper on your initially 1M pot, but it won't be 1M when you're done with it.  That's why the simplest thing is just to use a smaller value log pot (assuming you have one sitting around) and just wire it up "backwards".  In this case, "backwards" means that the resistance achieved gets larger as you turn clockwise.  This will have the effect of reducing gain in a clockwise direction.  Counter-intuitive, obviously, but it's reverse-log, requires no math and doesn't require special orders.

[csmatt45]

I know I'll lose the 1m value (see my first post), but I'd rather the pot work in traditional (clockwise=more gain) and have my pot's taper be a little funky, and a lesser value, than 100k log backwards. The way it is now I can deal with, I would just like it a little better if possible.

the other factor is the way the pot was put in (i'm still learning), it's easy to access the lugs, but would be a pain in the butt to remove the pot. I'd have to unglue my standoffs etc...lesson learned.

thanks,

matt

p.s. sorry to be a nag but, I'm still wondering, if you were stuck on a desert island with only the 1m a handfull of resistors and a dist+. What would you do to make it "a little" better.

[Mark Hammer]

I'll be an apologetic nag too  .  The reason why people NEED a reverse log taper pot for the Distortion+ is because it is poorly designed and has to compensate for that poor design.  As noted in the earlier posting, all the interesting things it does happen in the last 50-100k of rotation, so the pot needs to be a reverse log taper so it can hurry up and get there.  Otherwise, as you correctly noted, most of the pot's rotation seems to do nothing.  Right now, it's like a boring family trip where where you drive 5hrs sr=tuck in the back of the car, until you get to some fabulous ice cream place, then turn around and drive 5hrs back home.  People want the reverse log because it allows you to "gun it" and cover the 5hr distance in less time.  But why not just move in down the street from the ice cream place?

Right now, you and everyone else who builds the darn thing are struggling with the fact that you've got this little puny bit of pot rotation where you go from fairly little boost to full tilt.  You want to spread that out.  If you have a 1M pot, spreading that out requires a special taper.  If you declare that the 900k of generally unused resistance is disposable and only use the last 100k, most tapers will seem to be perfectly adequate and allow enough "dialability".

This is not sloppy seconds or a cheap substitute for what you *really* want.  This IS what you really want.  If you want proof, do the math.  The gain is equal to the 1M feedback resistor plus the 4k7 and pot value, divided by the 4k7 and pot value.  When the pot is at full resistance, that's 2.0047M/1.0047M, or just sliiiiiiiiiiigghtly more than x2.  Turn the pot down to half its resistance, and the gain is now given by (1M+500k+4k7)/(500k+4k7)=2.98.  Turn it down to 3/4 max resistance and the gain is now 1.2547/.2547 = 4.93.  Trust me, with a gain of around 5, you're NOT getting any distortion...and you've used up 3/4 of the available resistance in the pot.  This is precisely why the original used a reverse-log pot...to get the stupid part over with quickly.

If you were repairing an original script one, and you needed to flawlessly replicate everything on the original so you could fetch vintage bucks at a guitar show, fine go with a 1M reverse log.  But if you're just making yourself one, just do what will make it sound good.  IMHO, a 100k linear will probably be fine.  Alternatively, a 250k with a 220k fixed resistor in parallel will yield something that covers only the interesting part of the 1M and gets through the least interesting parts of the remaining 117k.

The place to put the fixed resistor is between the wiper and the lug you rotate towards.  If the shaft is facing you and the lugs are pointing down, that would be the one on the right.  Run the wires from the wiper and rightmost lug to the board and away you go.

[petemoore]

  I've chosen to eliminate that pot [actually just replaced it with a HF rolloff pot], I decided that the rolloff tone available @ guitar volume is thick and cleaner enough that it's otherwise uninteresting character makes it a nice easy alternate place to find tonewise when gettting from Heavy Dist to something 'less.
  Instead I've incorporated a HF rolloff Cap/Pot, this is handy when re-adjust to higher/lower volumes.
  Otherwise I always used whatever 100k or so there.

[mac]

I decided for a 250K linear. At max gain is about 4. Or if you are not going to use the clean sounds, use a 100K linear. Gain at max is about 10 and the less tricky than the 250K.

if you speak some spanish see www.pisotones.com

mac