The opamps are TL074 and TL072. I don't know why I picked a 4558 there. Like I said, need to work on Eagle.  :lmao:

Buffering the Vref is something that needs to be done. I was thinking a small regulator might work, but that would take up more space. Freeing up the other opamp would help. My intention there was to isolate the tone section from the volume, but realistically that doesn't matter much.

The phase shift may be an issue. I found flipping the wire on one pickup improved the blending a bit. Should just make one input stage inverting. Possibly the LP side, since I might need to tone down the gain on it a bit.

Here's the schematic. It's basically two unity gain Sallen-Key filters, a highpass for the bridge and lowpass for the neck. I will admit, the concept is not mine. The guy who will be using it asked how to do it and I ended up making it.

I found that using one pot for blending works better than a dual. Perhaps I should have buffered Vref, since the opamp inputs sit a bit below 4.5V.


Personally I prefer discrete. I find it easier to work with. At small signal level, emitter/source degeneration suffices for biasing. This is supposed to be a more 'hi-fi' tone, so I went with opamps. Might make a transistor version too. It'd probably come out smaller, knowing my layout skills.  xP

Also, I really need to play with Eagle more...

It's basically a highpass for one pickup and a lowpass for another followed by a mixer. If anyone wants a schematic I can post one. I went with dual rails so it could be DC coupled, and I prefer not to use virtual grounds for some reason. :loco I'd go for a switch on one of the pots, but since I'm making it for someone else I figured automatic switching would be easier for them.

I can do it with single supply, which is what I've settled on. Thanks for the suggestions though. I've been messing with different switching arrangements and mechanical is really the simplest in this case.

Thanks. That is the simplest solution, and most likely the best way to go about it.

I've digged around for ideas on this, but haven't seen anything fully suitable yet. I'm designing a preamp to put in a bass guitar. It's set up to use a bipolar supply. Standard switching arrangement is to run the negative battery cable to the ring lug. Since I'm using a bipolar set up (caps and resistors between each rail, ground in center) I can't use the negative to ground. I'd have to have a switch on one or both rails that closed when something gets grounded.

I've seen one of RG's schematics using a PNP transistor, but that's made for a voltage doubler chip that only uses the positive rail. I found when trying it the rails were not anywhere near to equal voltages.

Would a relay work for this?  Also, I think the reason the PNP didn't work is because the resistors were in parallel with the voltage divider on the positive rail only, so it offset one side to a wrong value. If I used an equal amount of resistance from the negative rail to ground, would that balance the rails? Or maybe use an NPN to switch the negative rail as well?

I'm sure it's possible. I've heard that the Mike Pope preamps use stereo jack switching and a bipolar supply. My only other option is to use a switching jack, but those are rather expensive for the kind I need (normally open), so I'd like to do it on board. What would work?