I am trying to make a PCB for the attached schematic (mixer.jpg). Rather than run on 2 9V batteries, I would like to plug it into the wall using a +9 / -9V DC power supply.

Do I need both diodes and capacitors (D1, D10, C21, and C22 in the attached mixer schematic 1.jpg) near the power supply? Or do I only need 1 of each (D1 and C21) as in mixer 2.jpg?

Not sure if both diodes and both caps are necessary when batteries aren't involved.

Thank you for your help!


mixer schematic 1.jpg

mixer schematic 1 p 2.jpg

mixer schematic 2.jpg

mixer schematic 2 p2.jpg

  • 1
    \$\begingroup\$ I don't see any part designators in your 1st schematic. Are you referring to the 1N4002 diodes and 47uF caps? \$\endgroup\$ – brhans Jan 10 '19 at 21:41
  • 2
    \$\begingroup\$ Your second and third images are identical, and neither of them shows the power supply section. \$\endgroup\$ – duskwuff -inactive- Jan 10 '19 at 21:53
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    \$\begingroup\$ I'd be interested to know what you think the gain is for the input op-amps? \$\endgroup\$ – Jack Creasey Jan 10 '19 at 23:28
  • \$\begingroup\$ Please edit and fix the bottom two images. As it is, we don't know what you are asking. \$\endgroup\$ – Edgar Brown Jan 10 '19 at 23:58
  • \$\begingroup\$ Sorry about that.... the 2nd page of the schematics has now been added. To clarify, I would like to know if I need two 1N4002 diodes and two 47uF capacitors if I am using a +9V / -9V adapter rather than batteries. These components are next to the battery inputs on the original schematic. I'm fairly sure my interpretation using one diode and one capacitor is wrong, since it would short the ground to the negative rail. \$\endgroup\$ – xYx'oO Jan 11 '19 at 14:35

Assuming you're talking about the parts across the battery inputs, you should have the electrolytic capacitors to provide some extra reservoir capacitance near the circuit.

The diodes are optional, but they might save your day if you ever get the power input connected in reverse, most likely they would protect the op-amps from destruction.

If it's possible that one of the supplies could be present and the other not, you should have the diodes as they will prevent the capacitors from being reverse biased and possibly damaged.

| improve this answer | |
  • \$\begingroup\$ Thank you, Spehro! I have added the second page of the schematics and a comment which hopefully clarifies my question. Since I will only have 3 wires soldered to the PCB from the power supply (rather than two batteries with +/- terminals that can be accidentally put in backwards), I don't know if both diodes and both capacitors serve a purpose, or if you only need one of each. \$\endgroup\$ – xYx'oO Jan 11 '19 at 14:43
  • \$\begingroup\$ Maybe I'm misunderstanding, but It looks like your -9V is connected to ground. That won't work. \$\endgroup\$ – Spehro Pefhany Jan 11 '19 at 15:14
  • \$\begingroup\$ I do believe the version with one diode and one capacitor is incorrect. How about the version with two diodes and two capacitors? And if I only need one diode and one capacitor, how should I correct the schematic? Thank you for your help. \$\endgroup\$ – xYx'oO Jan 11 '19 at 19:11

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