Replacing Volume pot in EA Trem with Resistor

[cheeb]

Hi guys,

I'm building the GGG EA Trem and I want to leave off the volume pot and just solder in a resistor across there at unity volume. I know the obvious thing to do is go ahead and wire in the pot and measure what resistance I'm at when I hit unity and go from there, but I'm lazy and I don't want to have to work for my knowledge. (haha just kidding, don't kill me!) I really just figured that since I'm at work and can't experiment right now anyway, somebody has to have done this before and can tell me what resistance I'm looking at to get unity, and whether or not this is a viable option. Thanks!

[John Lyons]

One man's unity is another man's...er....too loud/quiet

It will take you longer to solder in the resistors than it will take to measure them.
And longer still to desolder the ones you put in that didn't sound right because you
used someone else's reccommendation for the values. 

john

[cheeb]

Haha okay, you got me. That's what I get for being lazy. I'll just measure it off the pot then.

So I'm thinking all that's necessary is like (hypothetically) a 10k resistor from the circuit out to the switch and that's it, right?

[RickL]

Nope, the volume pot is wired as a voltage divider so you're going to need two resistors totalling 25k  with the output to the switch taken from the junction of the two resistors. I'd be tempted to just use a 25k trim pot in place of the volume pot and adjust it  to taste. There's not a lot of room but you might be able to mount it on the edge of the board between the pads marked V3 and 9V. You'll have to run a bit of wire from V1 of the trim pot to one of the ground pads.

If you don't have a 25k trim pot a 20k or 50k will probably work okay.

[John Lyons]

Rick is right.
A voltage divider/volume pot is only one resistance when full up or full off.
Example: If you have a 10k pot set in the middle what you have schematically are two resistors, two 5K resistors with the output taken from the juction of the two (which is the wiper) .
When you find the volume setting you like you will have a top resistance and a bottom resistance to measure.
Don't mix those town up or you will get the opposite of the volume you want (unless the setting is exactly in the middle...not likely)

john

[cheeb]

Cool. Thank guys. A trim pot hasn't even crossed my mind. I'm putting this together for a friend and a trim pot would be better than a set value anyway in case he changes gear or something. I didn't realize the volume control was a voltage divider instead of an attenuator or variable resistor. I still have a lot to learn about circuit observation.