“The Road to Your Complete DIY Equipment” 2024 Second Edition - Build the Ultimate Power Supply Yourself: Creating an Active Servo DC Supply

Man, it's hot out there, isn't it?
The perfect way to spend a summer day is sweating it out indoors, building gear to refine your sound.

As I briefly mentioned before, the number one piece of gear I want all you effects pedal enthusiasts to build is this: A DC power supply for your effects pedals.
This summer, let's finally break free from power supply noise.

So, today's topic is a DC power supply for effects pedals.
It's called an "active servo DC supply."

Simply put, it's an AC/DC adapter.
In other words, it's a handy little device that converts household AC 100V to DC 9V or 12V for your effects pedals.
Now, you might be thinking, "I can buy one of those for super cheap, why bother building it myself?"
But once you build this, you'll see just how much power supply noise is coming from your pedalboard.
I want you to experience the power of an active servo for yourself.

Enough talk, let's take a look at the circuit.
...Here it is, a good old-fashioned hand-drawn schematic, messy but full of character (lol).

To avoid switching noise, I first used a transformer for the main voltage conversion.
After rectifying it with a diode and stabilizing it with a 3-terminal regulator, I used an operational amplifier (OP-AMP) to dump any noise components in the power supply to ground.

In fact, this circuit is well-known in the Japanese audio community.
It is a power supply circuit that was only used in high-end amplifiers developed by Matsushita Electric (Panasonic, Technics).
Even without using an OP-AMP, it would be sufficient as a power supply for effects pedals, but to further reduce noise, I deliberately used an OP-AMP to extract and remove noise components. It's a truly remarkable circuit.

Now, as always, let's start selecting the parts.

First, the transformer.

Let's find a transformer that meets the following conditions:
To create a DC 9V voltage, use a transformer with a 12V to 15V output. To create a DC 12V voltage, use a transformer with a 15V to 18V output.
Calculate the available output current at 60% of the transformer's stated output current.

Example: A 12V 1A transformer can create a 9V 600mA power supply.
Example: If you need 500mA at DC 12V, you need a transformer with at least 15V 0.8A output.

Next up, the rectifier diode.

For this voltage and current range, a Schottky diode is the best choice for sound quality.
I highly recommend the 31DQ04 from Nihon Inter.
I dare say that there is no other diode that can maximize sound quality.
Some people choose diodes with barely enough voltage and current ratings, but this is extremely dangerous.
As a rule of thumb, choose a diode with twice the voltage rating and three times the current rating.
In other words, the 31DQ40 can be safely used with a voltage of 20V and a current of up to 1A.

3-Terminal Regulator

Although they are currently in very short supply, you should try to find NJM7809 (9V) or NJM7812 (12V).
They are highly reliable and unlikely to cause dangerous situations.
They can handle up to 1.5A of current, but in reality, the power consumption of a single effects pedal is quite low.
It's usually around 100mA at most, so this regulator is perfectly fine. Adding a heat sink will give you even more peace of mind, but it's not necessary.

And the heart of the active servo is the OP-AMP "NE5534".

This can also be replaced with "JRC5534D" or similar.
Be careful not to mistakenly purchase the 5532, as it is a dual OP-AMP.

Finally, the electrolytic capacitors.

There aren't any capacitors that I would say are particularly outstanding these days, but as long as you choose unused, fresh ones made in Japan, you should be fine. Personally, I think Nichicon or Elna are good choices.

Now, for the resistors, this time I'm going to be specific.

Considering that they'll be used in a power supply circuit, metal film resistors are the obvious choice. However, resistors have current noise, and given the purpose of this project, I've determined that KOA's 1/2W class metal film resistors are the best option.
They are easily available, affordable, and made in Japan, so they won't hurt your wallet.

And here's the list of parts you'll need for this "Active Servo DC Supply":

Power transformer:

Japanese-made, no center tap, 0V-15V output.

Output current: 0.5A.

We recommend Japanese-made transformers to minimize voltage fluctuations due to current consumption.

Schottky diodes:

Nihon Inter 31DQ40 x 4

If unavailable, 31DQ60 x 4 (with thicker leads) can be used.

3-terminal regulator:

NJM7809 (for 9V) x 1

NJM7812 (for 12V) x 1

Choose one of these.

Electrolytic capacitors:

I personally recommend Nichicon (Moe).

2200uF/12V~15V (for 9V)

2200uF/15V~25V (for 12V)

220uF/voltage rating according to the output voltage above.

10uF/voltage rating according to the output voltage above.

Resistors:

KOA metal film resistors 1/2W

33KΩ x 1

1KΩ x 1

OP-AMP:

NE5534 (NJM5534 is also acceptable) x 1

Ceramic capacitors:

33pF x 1

222pF x 1

That's all for the parts.
First, please get these!! ...To be continued.