AMZ Mosfet Boost Trim Pot

[dave neuleib]

Can't figure out how to install 100K trim pot for R2. There are 3 holes in the board, all in a row, with 2 of them hooked together and the other one is seperated on the trace from the other 2. The trimpot has 3 lugs forming the shape of a triangle. When I check resistance values of the  2 lugs in line = 100k, the other 2 possibilities = the sum of 100K divided between both lugs. Here is where I am lost??? I can't even describe how I think it should be hooked up, but can somebody draw or explain to me how??  Thanks  Dave

[squidsquad]

The connections that don't change when the wiper is moved would corrospond to the outer lugs (100k) on a regular pot.
That leaves the wiper..which should change (when connected to either outer lug) as the trimmer is turned.
Your are using it as a variable resistor.  With the wiper shorted to either outer lug...the resistance to the remaining lug will be *tunable*.

[aziltz]

i think he's saying the trimmer doesn't fit because the holes are in a row.

[dave neuleib]

I can make it fit---- please confirm my thoughts-- the trim pots outside legs read 100k when shorted---I can connect the other lead to either one of these outside legs-- then connect these to the board(it does not matter which direction). The board has 3 pads for the trimpot connections and 2 of the pads are connected-- so they actually are connected if you could get them to fit in the 3 pads. It DOES NOT matter which direction I install the trim pot.

[aziltz]

as the other guy said, its only being used as variable resistance, not a voltage divider. so you could infact clip one of the outer legs, and simply insert the middle and outer lug.  since its a trim pot, orientation isn't so bad.

[dave neuleib]

I have a issue with the 5k pot---- the schematic shows grounding the wiper to one side also. My question is does it matter which outside lug of the pot I connect the wiper to--- will the pot work backwards if I connect to the wrong side??  Thanks  Dave

[mills]

It does work, but the boost comes on really suddenly if you wire it backwards.  There's a much more gradual increase in volume with it wired correctly.

[dave neuleib]

How can I tell which way is the right way??? Dave

[squidsquad]

It does matter...since it's a triangle...you have 3 choices.  Two of those choices are fine = wiper to one lug or wiper to the other lug.
But you do not want to accidentally clip the wiper...and use only the outer lugs.  That won't work.  That's why you need to be sure of your lugs.

[squidsquad]

Clip your meter on any 2 lugs...turn the trimmer...if the resistance changes...you have a wiper...but still don't know which.
Now leave the clip on one lug...and move the other clip to the other lug.  If resistance changes...you've found an outer lug...and the clip you didn't move is the wiper.
If you get a reading of 100k no matter how you turn...your clips are on the 2 outer lugs and the that leaves the wiper.

[dave neuleib]

I have the trim pot issue solved and the pedal completed----however the 5K reverse pot works backwards.  Full Volume=Full Counterclockwise      Lowest Volume= Full Clockwise    As you look at the back of the pot as it is installed in the pedal, the wire going to the gain pad on the board is on the right lug, the center lug is jumped to the left lug, and the left lug to ground. Is the backward issue related to the reverse pot or just wired wrong.  Thanks  Dave

[squidsquad]

*Reverse* refers to the taper of the pot...not the direction of rotation. 
So...swap wires to make it work in the usual direction.

[aziltz]

nevermind.  i'm stupid.   

[dave neuleib]

No I'm stupid!! Which wires do you change??? Just the outside or the outside and the wiper??  I just don't like changing wires any more than I have to.  Thanks    Dave

[MikeH]

If your control is working in reverse you just need to swap the outer lugs of the pot.

[dave neuleib]

Leave the jumper wire from wiper to outside lug as it is currently?  Dave

[dave neuleib]

Let me rephrase that--- leave the jumper wire from the center lug to the outside lug as is (yes or no)  and also switch both outside wires from side to side. Will this take care of the problem.  Dave

[MikeH]

Since it is simply a variable resistor, meaning increasing resistance does one thing, and decreasing it does another, we just need to reverse the directions in which the resistance changes, (if the pot is linear that is).  This can be done by swapping the 2 leads of the pot that go to the board.  We can also reverse the pot function in this case by changing which outer lug the wiper is tied to.  Think about it; If lugs 2 and 3 are connected, than resistance will increase as the pot is turned toward lug 3 (clockwise in my mind).  If we switch it and connect lugs 1 and 2, than resistance will decrease as we turn the pot clockwise.

If the pot is non linear, (log, rev log, W, etc) one of these scenarios will work perfectly, and the other will cause the pot to function properly but the taper will be reversed.  Unfortunately, I don't know off the top of my head which you'd want in this scenario.  Hmmm... perhaps this was no help at all afterall. 

I guess I'd say, If the taper feels right as it is now, but it just works in reverse, swap the leads at the board, otherwise switch the wiper.  And if that screws up the taper, at least you'll know what to do then.

[dave neuleib]

 Mike  Thanks for the info but I was hoping somebody could tell me definitley ( I hate to resolder) ---- anybody got a schematic of how to wire the  C 5K  gain pot on AMZ Mosfet Boost??  Dave

[MikeH]

Resoldering is an everyday part of stompbox making... you'd benefit if you learn to love it.