Changing the pot in a new Electroharmoix LPB-1?

[olddawg]

I'm using an LPB-1 for a volume boost for leads in an effects loop. It works great except that it is usable only in a very sensitive area within the first 1/4 turn of the pot. If you accidentally bump the damn knob the gain can be overwhelming. Does anyone have a suggestion or know of a mod? I do know this is a common issue. Not sure if doubling the value would do much.

[J M Fahey]

Schematic ?

[olddawg]

Schematic ?

Thanks for your response Juan. It's just a single transistor gain stage with a 100kA pot. I'm pretty sure the nano is the same. I don't want to change the transparency but make it more adjustable for the first half of the pot. I could change the total gain by changing the voltage divider network, but want to avoid that.

[Enzo]

If nothing else, replace the 100k pot with a 75k resistor over a 25k pot. voila, the pot only covers the first 1/4 of the original pot.

[olddawg]

If nothing else, replace the 100k pot with a 75k resistor over a 25k pot. voila, the pot only covers the first 1/4 of the original pot.

Thanks Enzo... That makes sense! I might try a 50k resistor and a 50k pot.

[Enzo]

You could also just try a different taper 100k.

[olddawg]

You could also just try a different taper 100k.

That was my first thought. Replace it with a linear taper.

[J M Fahey]

Thanks for your response Juan. It's just a single transistor gain stage with a 100kA pot. I'm pretty sure the nano is the same. I don't want to change the transparency but make it more adjustable for the first half of the pot. I could change the total gain by changing the voltage divider network, but want to avoid that.

Weird.
IF it's a true Log pot, setting it to around "4"(on a 0/10 scale) it's unity gain, meaning what comes in goes out unchanged.

So eithervthat pot is not Audio/Log or the preamp has some error and transistor is runni9ng full tilt.

Enzo's solution is right, but it *should* not be necessary.

To check pot curve, unplug the pedal, we need no power nor load nor signal through it, set it to "5"and measure resistance wiper to hot and to ground.

A Log pot should have roughly 90k mid to top and 10k mid to ground.
A Linear one will be roughly 50k/50k .

Please measure and post, before modding anything.

Just for the hell of it, re re confirm that it's actually wired as shown, as a typical voltage divider.

Maybe the schematic is fine (looks so) but the actual veroboard (or whatever you used) layout is not and wiper simply shorts output to ground.

Problem is, it will work, but in a crude way ... doing 90% of its job in the first couple points.

[olddawg]

Weird.
IF it's a true Log pot, setting it to around "4"(on a 0/10 scale) it's unity gain, meaning what comes in goes out unchanged.

So eithervthat pot is not Audio/Log or the preamp has some error and transistor is runni9ng full tilt.

Enzo's solution is right, but it *should* not be necessary.

To check pot curve, unplug the pedal, we need no power nor load nor signal through it, set it to "5"and measure resistance wiper to hot and to ground.

A Log pot should have roughly 90k mid to top and 10k mid to ground.
A Linear one will be roughly 50k/50k .

Please measure and post, before modding anything.

Just for the hell of it, re re confirm that it's actually wired as shown, as a typical voltage divider.

Maybe the schematic is fine (looks so) but the actual veroboard (or whatever you used) layout is not and wiper simply shorts output to ground.

Problem is, it will work, but in a crude way ... doing 90% of its job in the first couple points.

Juan.... This is a brand new off the shelf LPB-1 Nano. I think the problem is really in the way I'm using it as a clean boost in an effects loop and the send signal is a bit hot for it with unity at the zero point on the pot. I probably should have just built a passive attenuator stomp box but these LPB-1s are about as cheap as I could buy the parts. ($29 free shipping, no tax)They really are for instrument level signals, but don't clip with a line level signal. I used to have an original one back in the last century (the one with the switch and the plug). I didn't like it much for my amp at the time but I used to sneak it on the mains send from the board to the power amps in the house PA at a club we played. The club owner could never figure out why we were louder than the other bands, lol. Anyway, I digress. I have this new LPB-1 Nano as a clean boostin an effects loop to boost lead volume. It works fine... Just has a lot of gain in the loop and I have it turned down below a quarter rotation. The sweet spot is very sensitive. It's usable. Just a pain if you accidentally nudge the knob a hair. I'm going to make those measurements you have suggested just to quantify what is going on. A 100k linear pot may do the trick. If not Enzo's suggestion should definitely work.

[J M Fahey]

A linear pot will be worse

[olddawg]

A linear pot will be worse

Probably, I am dyslexic. Lol.