If you ran out of free input slots in your audio mixer, it's likely that you asked yourself how to merge two distinct audio signals into one.

One solution could be to buy a mixer with more inputs. Unfortunately if you are a cheap bastard like me, this is NOT an actual solution.

Lurking the net you probably found that "wye" or "Y" cables are NOT the answer to your question too... this is CORRECT. "Y" cables can be used to split a single signal in two, but not to merge two signals into one.

So, how can we manage this? Well, with a simple circuit here called "wye box".

Step 1: The Circuit

I realized a cheap wye box replicating the summing circuit in this great article HERE.

In particular, the circuit that merge two balanced or unbalanced audio singals into one (figure 1). Simple and effective.

Step 2: Components List

You are in the need for:

- 3x stereo 6.35 mm (1/4") jack panel mount female connectors

- 2x 470 Ohm resistors

- 1x 10K ohm resistor

- 1x ABS box/case

... some solder, a solder iron, some centimeter of cable, a drill.

You don't even need a perfboard for this.

I used a 5 x 8 cm case here, but it was a tight fit. Use a 7 x 10 instead ;).

This list is for a mono-to-mono summing box. I realized (see pics) a stereo version by simply doubling the lines (one for right "R" audio signals coming from the synths you want to merge, and one for left "L" signals) which uses double the components (except the shared ABS box); they are two identical, indipendent, circuits.

You can replace the 1/4" stereo female connectors with 1/8" stereo female connectors if you wanna save space or if your setup mainly use such connectors.

Please, pay attention while dealing with the drill: keep the rotating speed low, wear protective glasses and gloves. Safety comes first and a injury is a fun-killer.