Acoustic guitar with 2 pickups, but no internal mixer: what to do to make it mono?

Question

I have a custom Taylor Dan Crary guitar which has two pickups installed. One goes to the left, one to the right stereo channel.

One pickup is for the strings, the other for the body sounds (ie. percussion).

The current owner used a Y-cable to split the stereo signal into a separate left and right mono output, then plugged each output into his mixer, and there he could decide how the signals would be mixed.

I'm a street busker traveling with minimal luggage, and I need to keep my gear as little as possible. I have two inputs on my little PA system, one for my microphone, the other one for my guitar. I don't want to carry around an additional mixer. So I need a way to mix those two signals together into a single mono channel.

I have no idea about acoustic engineering, but I think it should be possible somehow to build a simple adapter which has:

• at one end a male 1/4" TRS stereo signal (to receive the two pickups' individual signals)
• and then merges it into a 1/4" female TRS mono at the other end

Preferably, it would offer a little control dial/knob so I could manually choose the wanted ratio.

I have a friend who knows to solder audio cables and such, he just doesn't know a lot about guitar gear, so it would be great to get some advice from you guys.

Another way to go could be the installation of a small mixer into the guitar's body. I don't like the huge plastic elements and displays of many modern guitar mixers; in fact, the Taylor's unobtrusive three little knobs are most appealing to me (while the Dan Crary in question doesn't have any of these at all).

So maybe there is even a small mixer that allows for what I need which would only have a single knob on the outside of the guitar body (I don't care too much where it would be... possibly directly next to the stereo output)?

Any help is highly appreciated. Thanks a lot. Josua

Answer 1

You can wire a TRS at one end to link the tip & ring, then to a regular 'guitar jack' TS at the other.

This is basically how a Rickenbacker stereo sums to the mono jack.

Lifted from Cadfael's collection of wiring diagrams (Google translate link to English)

Answer 2

Whether you build it or buy it, what you're looking for is called a "2-channel passive mixer". (Passive because it requires no power supply.) Even if it's not adjustable, it's still considered a "mixer" in an electrical sense.

It will be helpful to know more about the pickups in the guitar: Is the "strings" pickup magnetic? Is the "body" pickup piezoelectric? Are there any active electronics (i.e. does it need a battery?) If the pickups are of different types it will take more careful consideration (or at least experimentation) to get it right.

If both pickups are of the same type and approximately equal electrical characteristics, a passive mixer is very simple:

• If a fixed balance between the two channels is acceptable, you only need two resistors (which are small enough to fit inside the shell of a 1/4" TRS plug). Each resistor goes between one pickup and the output. These are commercially available as "stereo to mono summing cables" which have a TRS at the input, a TS at the output and resistors molded into the TRS shell. The commercially available products might not have resistor values that are suitable for the electrical characteristics of your pickups. (They're more often used for connecting stereo line-level signals like synths to a mono input like a combo amp.)
• A "balance" mixer could be as simple as a potentiometer wired between the two channels with the wiper connected to the output. This could even be mounted inline on a cable, close to the instrument end. Selecting the potentiometer value depends on the electrical characteristics of the pickups.

I found a commercial product that goes to the other extreme of complexity, flexibility and ruggedness for about $130. It's still completely passive.