this mixer combines several sets of stereo audio inputs into a single stereo output. each input has a separate volume control for left and right channels.
Ingredients:
R1 - (2 per stereo channel) 220 K
R2 - (2 per stereo channel) 100 K Audio Taper Potentiometer (radio shack #271-1722)
R3 - (2) 2200 ohm
R4 - (2) 4700 ohm
R5 - (2) 10 K
R6 - (1) 100 ohm
C1 - (2 per stereo channel) .47UF Ceramic Capacitor 50V (radio shack #11298320)
C2 - (2) 470UF 35V Electrolytic Capacitor (#272-1018)
C3 - (2) 220UF 35V Electrolytic Capacitor (#272-1017)
C4 - (2) 22UF 35V Electrolytic Capacitor (#272-1014)
Q1 - (2) MPF102 Field-Effect Transistor (#276-2062)
Q2 - (2) MPS3904 NPN Transistor (#276-2016)
1 SPST Switch (#275-634)
1/4" Phone Jacks (2 for output + 2 per stereo channel) (#274-252B)
1 small PC board (#276-158B)
1 9V DC power supply (i used a casio keyboard AC-5 from best buy)
optional -
radio shack sells a 12V LED with a small resistor attached to it, which can be used as power indicator. the red lead will go to the switch and the black lead with resistor goes to the ground.
all of these parts should be available from local electronics stores. i had to order the .47UF caps from radio shack since they didn't have any in the store. the volume potentiometers had long posts, so i used a Dremel tool to cut them to a shorter length. be sure to wear a mask to avoid breathing in metal dust when cutting the posts. the mixer shown in the pictures was rack mounted and is made of wood. since all jack barrels are grounded, you could use an aluminum panel (available from PAIA). this mixer can be expanded to any number of inputs simply by adding more components. each stereo input will require 2 phone jacks, 2 pots, 2 resistors, and 2 capacitors. the total cost for a mixer with 8 stereo inputs will be around $50 USD.