I have build a dual power supply for an analog synth (see image below).

enter image description here

The input source is a 12 VAC - 1.7A adapter. It is based on the Wall Wart power supply from Music from Outer Space.

Now I would like to include a 5V output to drive one or more Arduinos. If I expand the power supply with a voltage regulator (LM7805) in parallel with the LM7812 regulator, would this work?

enter image description here

I expect that the LM7805 regulator will be less efficient as it has to bring the voltage down from 12V to 5V and will produce more heat. Therefore, I've attached all voltage regulators to heat sinks.

Might it be better to exchange the LM7805 linear voltage regulator with a switched voltage regulator? The advantage being that it is more efficient and produces less heat, while the noise might increase. I do not intend to use batteries, so efficiency is less important, and I expect that the Arduino will not take much current.

An additional question: Have I placed the fuses F1 and F2 at the correct position in the circuit?

  • \$\begingroup\$ Use a switching regulator for the 5V, not a 7805. \$\endgroup\$
    – user16324
    Mar 3, 2021 at 18:24
  • \$\begingroup\$ run it from the +12v rail instead of the unregulated voltage; less waste heat. DON'T use an SMPS for an analog music circuit, that's just sacrilege. \$\endgroup\$
    – dandavis
    Mar 3, 2021 at 20:01
  • \$\begingroup\$ NB. I've changed the circuit diagrams so that the first one reflects the dual power supply I have now. @Transistor pointed this out in the first answer. \$\endgroup\$
    – Dieudonné
    Mar 3, 2021 at 22:17
  • \$\begingroup\$ @dandavis You're just moving the heat to the +12V regulator. \$\endgroup\$
    – pipe
    Mar 4, 2021 at 2:26
  • \$\begingroup\$ @pipe; right, but presumably that's already heatsinked in the design. \$\endgroup\$
    – dandavis
    Mar 4, 2021 at 5:27

2 Answers 2


enter image description here

Figure 1. OP's original circuit, since removed.

You haven't copied the power supply from Music from Outer Space correctly.


simulate this circuit – Schematic created using CircuitLab

Figure 2. You can't always get what you want. This time you're lucky.

Your arrangement in 1(b) has no ground reference between the supply and your capacitors. The voltages will be all over the place.

1(a) will work.

One fuse will suffice. Add it on the upper winding output. That way it provides protection should anything happen on the diodes or smoothing capacitors.

enter image description here

Figure 3. The RS 78xx series switching regulator.

There are a variety of three-pin 7805 replacements which have a built-in switching regulator in a package a little bigger than the 7805 1 A version. Use those for efficiency. e.g. RS K78xx series.

  • 3
    \$\begingroup\$ Switching noise might annoy an audiophile, but maybe use a 6.5V DC DC and clean it up with a 5V regulator \$\endgroup\$
    – Voltage Spike
    Mar 3, 2021 at 18:49
  • \$\begingroup\$ The 5 V is for a few Arduinies, according to the OP. \$\endgroup\$
    – Transistor
    Mar 3, 2021 at 18:50
  • 2
    \$\begingroup\$ Before omitting the capacitors ask yourself, "What do I know that the manufacturers don't?" The capacitors are required to stabilise the regulator and preventing it from oscillating. \$\endgroup\$
    – Transistor
    Mar 3, 2021 at 22:00
  • 1
    \$\begingroup\$ It's more than that. The switcher may be relying on one or both capacitors to actually work and prevent it going into oscillation. \$\endgroup\$
    – Transistor
    Mar 3, 2021 at 22:18
  • 1
    \$\begingroup\$ It wouldn't affect the 12V rails, they would also be regulating. \$\endgroup\$
    – Voltage Spike
    Mar 4, 2021 at 16:06

a) To protect against capacitor failure, delete F1 and F2, and use a single fuse ahead of D1/D2.

b) Since efficiency and size are not factors, I vote for the linear 5 V regulator. Note that most small buck regulators require external input and output capacitors. Also, "proper" grounding techniques are very important for conducted noise control, but they vary widely depending on the physical arrangement of the components. KISS.

  • \$\begingroup\$ So would you say that a linear regulator is less efficient but is better noise-wise? \$\endgroup\$
    – Dieudonné
    Mar 4, 2021 at 13:52
  • \$\begingroup\$ Yes. Both halves of that are almost universally true. \$\endgroup\$
    – AnalogKid
    Mar 4, 2021 at 14:05

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