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I'm looking to use a CD4051B multiplexer as a digitally-controlled switcher for audio signals.

The audio is coming from the HP / BP output of a voltage-controlled filter in a synth. The signal output is about 3v peak-to-peak. The mux select will be controlled by 5v TTL logic.

I only have supply voltages of 5v, 12v and -12v in my synth.

I'm finding the datasheets for the 4051 rather vague - has anyone had any success powering these chips with +/-12v bipolar power? (the -12v supply going to Vee)

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I suggest to have the audio signal centered at 6V and power the 4051 with GND and 12V (it works with voltage supply up to 15V) and use a simple level shifter from 5V TTL to 12V (either inverting as shown in the diagram below or non-inverting; whatever suits better) for the logic signals.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Are C1 / R1 / R1 providing the audio signal bias to 6v? Also, why is R3 connected to select pin bus? \$\endgroup\$ – CarlosTheJackal Aug 24 '17 at 8:06
  • \$\begingroup\$ Yes, R1, R2, C1 are for 6V biasing. R3 is a pull up-resistor that provides a +12V H-level (required if the 4051 is operated with Vdd=+12V). (This is needed for all digital logic inputs but shown only for one line). \$\endgroup\$ – Curd Aug 24 '17 at 9:46
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The CD4051 is specified at rail to rail voltages from 5v to 20v. This is not enough to power directly from +/- 12v, but it is not necessary to have balanced rails, so powering the device from +5v and -12v will meet the required voltage range, see figure 9 of the TI data sheet.

This will allow direct coupling of voltages swinging about ground, with no need to AC couple. It will also allow logic control to be done with 0-5v, without a level shifter from the logic (simple or not!)

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Thanks! I'll try this when I get home from work tonight.. \$\endgroup\$ – CarlosTheJackal Aug 24 '17 at 8:07
  • \$\begingroup\$ +1 that's better than my proposed solution; as the 405x have level converters integrated that allow using it for analog signals below digital GND. \$\endgroup\$ – Curd Aug 24 '17 at 10:14
  • \$\begingroup\$ @Curd yes, I thought so too, using it like it's meant to be used usually wins out over adding lots of extra components, and shifting the signal unnecessarily. I added a diagram to show the reduced number of components. Were you thinking of doing anything with your answer that reflected that? \$\endgroup\$ – Neil_UK Aug 24 '17 at 13:51
  • \$\begingroup\$ @Neil_UK: No. I looked at the datatsheet in detail (concerning the internal level converter for digital signals to use it with analog signals below digital GND) only after I've seen your proposal. \$\endgroup\$ – Curd Aug 24 '17 at 14:08

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