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§ 3.8 - AC-coupled 8 Channel Stereo Mixer

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Before you attempt this build, please:

This will help ensure that you will have the best possible experience, resulting in a build that works the way you expect it to.

This Mixer Block build is an AC-coupled, unity-gain, line-level, eight-channel, stereo mixer.

To power this with the Power Block, use the +/- 12 regulated Power Block build.

Tip: Unity gain (zero gain) is important here. This is because if all eight inputs to one of the op-amp channels reach 1.23 volts, in phase, all at once, then at unity gain the mixer will produce a 9.84 volt output level. This would be highly unlikely, but it is always at least possible.
If the mixer were to be built with more gain, then the output voltage would get too close to the op-amp's power supply rails (typically +/- 12 VDC), and distortion would result.
  1. C1—C2: .1 uF ceramic capacitor
  2. C3—C4 optional: ceramic capacitors, only needed for op-amps that require compensation
    TLO-72 and TLO-82 op-amps do not require compensation.
  3. C5—C20: 2.2 uF ceramic or other non-polarized type capacitor (see frequency response calculator)
  4. C21—C22: 10 uF ceramic or other non-polarized type capacitor
  5. R1—R18: 10 k-ohms 1/8th watt resistors
  6. U1: TLO-72 low-noise op-amp, can substitute TLO-82, or similar. Observe polarity. An IC socket is strongly recommended.
  7. Install 3-pin jumper J1 — use .100 inch (2.54 mm) header pins; do not close
  8. Install 2-pin jumper J2 — use .100 inch (2.54 mm) header pins; do not close
  9. Install 2-pin jumper J3 — use .100 inch (2.54 mm) header pins; do not close
  10. Install 2-pin jumper J4 — use .100 inch (2.54 mm) header pins; do not close
  11. Connectors, quantity 4, optional: 5.08mm (.200 in) Spacing, 2-pin PCB Mount Screw Terminal Blocks
  12. M3 mounting hardware, 4 mount points
Tip: If you would like to DC-couple the outputs while retaining the AC input coupling, place jumper caps across J3 and J4.
See also:Recommended Tools
Mounting to Wood Surfaces
Mixer Block Parts Sources
Wiring to Terminal Blocks


AC-coupled 8-channel Stereo Mixer, Build Guide


Mixer Block Schematic

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