linear vs log pot

[swal]

i am building a distortion plus. the pedal works except there is no distortion, just clean sound. the volume works but the drive pot does nothing. the instruction asked for a 1m linear, but all i had was a 1m log. could that be causing no distortion? when I turn the drive pot there is no change in the sound at all. all the help would be great thnks

[RDV]

Well, that ain't it!

RDV

[swal]

anyone know what it might be pls help

[RDV]

Check the debugging page in the links above you, and follow the instructions. If you can't give more info, people here can't do much for you. Like, which schem, what method of building, part substitutions, etc.

RDV

[RDV]

Assuming you have sound at all, make sure that you 1 meg pot is going to ground. Also pinout of whichever OA you used is also very important.

RDV

[swal]

Ive gone through debugging and cant find what is wrong,  I am using the tonepad.com layout with a 741 oa and ger 1n34a diodes for clipping.  ihave the pot attached too the ground on my board and too the in jack ground. and the pedal is working as a great volume pedal right now.

[RDV]

Ah, more info! You say the drive does nothing? Not even changing the level?

Do you have pin 1(of the 1m pot) attached to the circuit, and 2 & 3 attached together and then to ground?

RDV

[swal]

the drive pot makes no change to tone sound or level at all. and 1 is hooked up to board and 2+3 are together to grnd.

[Fret Wire]

If you look at the schematic, lugs 1 & 2 are tied together and grounded, and 3 goes to the ckt. Actually, it doesn't matter ckt wise, if 3 or 1 goes to ground, as long as lug 2 is tied to whichever lug goes to ground. The only difference would be if the pot worked forwards or backwards.
If you are using their pcb, that board has a pad for each pot lug.

Do you have the diodes correctly orientated?

[swal]

diodes are ok i took them out and switched them aroung to double check and also put new ones in, no difference.  i dont know if this would help but when i unhooked the 1m drive pot and just left all three wires hanging unconnected there was no difference just the clean tone and i could change volume with the 10k level pot.  there is no difference if i have the pot attached or just have the wires hanging loose :?

[Fret Wire]

Is this a perf or pcb? Are you using one of their suggested wiring layouts?

[swal]

made it with blue press and peel and im am using the wiring from tonepad. ive checked over the wiring 20 times it is ok.  i have built a couple pedals allready. normal if there is a problem the pedal doesnt work at all, i have never had a pedal that is working, but not working at the same time. it makes debugging frustrating and all most impossible :cry: . if i cant find out what is wrong by wensday ill just strip it and start over.

[Mark Hammer]

The linear vs log distinction is NEVER, I repeat, NEVER the reason for something not working.  Never has been, never will be.  The circuit doesn't "know" what the taper of the pot or trimpot is, only the user does.  The circuit sees precisely the resistance it sees when the control is at rest.  Only the user knows how it got there and how much more it can move.

The only reason that taper is important is when there is a need to distribute the amount of change that twisting the knob produces in a particular way.  For example, if there is a dire visual need to know where the "middle" is (e.g., a treble cut/boost circuit, or a dry/wet blend control, or a left/right pan control), then a linear-taper pot is called for, sine that tends to assure that there is as much resistance on one side of the wiper as on the other when the wiper is set to the midpoint of rotation.  Use of a log pot would still allow the circuit to "work" but all the treble boost might be squished into a few degrees of knob rotation and the "middle" might be somewhere around 3:00 (using a 7:00 to 5:00 rotation, with 12:00 the physical midpoint).  Under those conditions, your treble boost stops being an adjustment and starts to behave like an all-or-none control - not what you were aiming for.

Log pots are always used when one is adjusting volume, since logarithmic change is what our ears detect.  They are also used for any sort of level mixing control where the intent is to reduce/control the amount of something from some maximum.  So, for instance, if you made an octave-down box, you'd use a log pot to adjust how much octave-down is mixed in with the straight signal.

There are some instances where the taper chosen would depend very much on what things are important to the user.  For instance, some people like to use slow speeds on tremolo and rarely aim for faster speeds.  As such, being able to dial in finer distinctions in slowness is important to them, but not fine distinctions at the fats end.  Other people it is the opposite.  Then there are those who want reasonable diability across the entire range of speeds available.  Although the LFO in the tremolo will work regardless of what the pot taper is, each of these people will likely want a different taper than the other one will.

[phillip]

For the Distortion +, OD250 and Ross Distortion I actually like the way a linear taper pot responds as the volume control...the Ross Distortion actually came with a 50K linear pot as the volume control.

Since those three circuits, and other similiar circuits, have a pretty low output when using certain clipping diodes (especially Germanium) the linear taper pots will allow more output sooner in the rotation of the pot since the resistance increases and decreases smoothly, unlike an audio pot which increases slowly at first, then starts to increase very rapidly, moving all the more useable output level to farther in the rotation.

Phillip

[swal]

I am using a linear for the volume and it works nicer then a log.  But, I am just going to take the circuit apart and put it on a large prf brd and getting it working there then put it onto the board.  There must be something wrong with the board. I accidently grabed the hole bottom off the board and it worked. I noticed when i pinch the top of the oa and the bottom of the board it works  it works perfectly :? The board has turned into a mess im just going to start over again. thnks for the help guys, i most likely made some stupid mistake that ill notice when i rebuild the brd.

[phillip]

If it worked when you pressed down on the IC, then it sounds like either a broken trace on the board or a bad solder joint that only made contact with the copper trace when it was pressed down.

Phillip

[swal]

I am almost for certain it is a bad trace i could go through the circuit with a dmm, but i was just looking at the generalsite and i like that board ten times better.  I ll use that layout and start from scratch.  this is my first failure and i dont like it, i think ill enjoy breaking the brd apart when i take all off the parts :evil:

[Fret Wire]

One thing that can save time and headaches, is to check the board very carefully with a magnifying glass after you etch it. You may find broken traces that you can't see normally with your eyes. It happens more than you think. Then, give it a check with a DMM. That's why I never leave the resist on a board, it can hide a bad trace. You can have a perfectly good looking board, then remove the resist from the traces, and find a small break.