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Under Saddle Tone Control


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ok, i've got a buddy with a takemine flat top that wants to be able to plug in and wants volume and tone control and budget is a big issue. i'm an lr baggs dealer and i have an older RTS II in stock which doesn't have controls..it's an undersaddle ribbon transducer with an active end pin preamp.

you can no longer buy the soundhole volume and tone control add on from baggs but their guy said he'd send me a diagram of how to add a regular volume pot..he did and it works fine. but i still need tone control.

so here's what i've done so far..i've added a 10k volume pot (their suggestion) with three wires..removing a solder blob on the preamp board exposes two terminals which receive the wires from one outside lug and the inside lug on the pot. a ground wire goes to another spot on the preamp board and to the other outside lug of the pot. so far so good. volume works great.

i then added in a tone pot runing a wire from the outside lug to the hot lug of the volume pot. i put a .005 cap on the center lug and a jumper from there to the ground on the volume pot. basically just like wiring up a single coil and in my head this should work but doesn't. i tried another 10k pot first with no luck and then a 250k pot and still no luck.

any thoughts or suggestions? i've tried a couple of different value caps but nothing works. i'll drink a beer..ok, two beers in honor of the first one of you that can tell me why this doesn't work and if there's a way to make it work. :D


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Sounds to me like it would be easier (and less prone to weirdness) to run a post-preamp tone control - I'd try wiring that 10k pot/.005 cap as currently configured between hot and ground on the output (but that's just me). You might also find that a larger cap, maybe as large as .22, might work better. Since you're only getting 3dB of rolloff at 3.2KHz with the tone all the way down (and 6dB per octave above that), you're probably not having much audible effect on the guitar signal. For comparison, active EMGs use a 25K pot and a .1uF cap, for a corner frequency of only 63Hz (over 6 octaves lower than your current configuration). HTH

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i was hoping you'd show up. :D

i'll try that..wiring it post preamp. it's certainly not working now..maybe the larger cap is all it needs..i'll let you know.

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well i've discovered two things about this: the original configuration that i had works..just wiring the tone pot to the inside lug and the ungrounded outside lug gives me some tone control.

and i don't know why but i got nothing until i tried a 1meg pot. i tried a 10k, a 250k and a 500k with no luck. a .1 cap is the largest i have in the shop at the moment and that with the 1 meg pot gives me a bit of control. i'm going to order some larger value caps and see what happens.

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