Individual string pickups through a passive (in guitar) mixer circuit - what resistor values?

[Clintoncraft]

I started a project 9 years ago that has just been sitting since I don’t have the knowledge base to solve a problem I’m having:  I have wound pickups for individual strings on a project guitar.  I want to be able to mix these pickups from both of two pickup positions into a one-both-one, two channel output (so I can send the output from any string to one of two amps, or both).  I built in a passive mixer with resistors in series with the pickup output into the 3 way switches to isolate the pickups from each other, but I was, and still am operating from relative ignorance to the value of these resistors that would work.  When I built it, the output is super low, so I’m wondering if my idea is failed at the outset, or whether it’s just a question of using the wrong resistors.  Any help in progressing my question to the point it’s understandable to you knowledgeable folks, and even to the point it’s successful would be greatly appreciated.  Thanks in advance.

[MiKro]

On 11/20/2021 at 11:45 AM, Clintoncraft said:

I started a project 9 years ago that has just been sitting since I don’t have the knowledge base to solve a problem I’m having:  I have wound pickups for individual strings on a project guitar.  I want to be able to mix these pickups from both of two pickup positions into a one-both-one, two channel output (so I can send the output from any string to one of two amps, or both).  I built in a passive mixer with resistors in series with the pickup output into the 3 way switches to isolate the pickups from each other, but I was, and still am operating from relative ignorance to the value of these resistors that would work.  When I built it, the output is super low, so I’m wondering if my idea is failed at the outset, or whether it’s just a question of using the wrong resistors.  Any help in progressing my question to the point it’s understandable to you knowledgeable folks, and even to the point it’s successful would be greatly appreciated.  Thanks in advance.

Welcome to PG,

What you have appeared to do is similar to what Boss/Roland did on the GK series pickups for midi. Since these are a single string pickup, less windings are available therefore less output. First look at summing boards. These will give you some idea how to mix and match the signals. Also you will most likely need a pre-amp of some sort. Another avenue to look at is Cycfi research and there Nu pickups and  there Nexus electronics, this may give you an idea as well.     There website is here      Cycfi Link.

I hope this helps.

MK

[curtisa]

The issue with passive mixing is that it tends to be lossy, so unfortunately you'll be stuck with the summated output being significantly less than the individual signals you're trying to mix. The situation gets worse the more signals you want to mix together as each source cross-loads the other down. In passive mixers this is usually resolved by adding a recovery amp to the output of the mixer to make up for the loss. Guitar pickups have typically high source impedance so the effects are much worse than trying to passively mix, say a couple of synths or some pedals together. What about adding some kind of clean boost pedal to the output to bring it back up to a respectable level?

The ideal solution would be to employ active mixing using an opamp in a virtual earth configuration, which would eliminate all the major issues with mixing the pickups. Based on your description of how you want each pickup to behave it sounds like you could probably adapt a left-centre-right mxer circuit. It's the sort of thing that could be done on a small bit of perf board using a single chip and a dozen or so resistors. Provided you're not averse to installing a 9V battery into the guitar and doing a little bit of custom circuitry maybe explore this as an idea?

Have you tried just connecting one of your pickups directly to an amp (without going through any mixing) to see how it compares to a regular pickup?