This is a SynthCard format project that allows you to supply power to the rest of your SynthCard modules and will accept virtually any signal source, allowing you to attenuate or amplify anything to get it into your SynthCard modular.

Supplies

You'll need the SynthCard Input & Power PCB.

This format is flexible and very DIY, so you may want to diverge from the parts I use. But to follow along with what I'm doing here, you will need:

The PCB
2 x mono (can be stereo if you want) 1/4" phone jacks like this
1 x DC power jack sockets like this
2 x (or 4 x if you want to use 3.5mm phone cables for patching) Thonk style mono jacks
1 x TL074 or similar op amp
1 x AMS1117 adjustable voltage regulator in SOT223 footprint like this (secret: you can use any voltage in this circuit and it'll still be adjustable)
1 x 1K box style multiturn trimmer
2 x 100K potentiometers, sealed vertical box-style (I used 1M pots in this build)
1 x 220uF or 100uF electrolytic capacitor

Step 1: Little Voltage Regulator

The large tab of this part connects to a bit of PCB that's designed to be a very small heatsink, so it will need a bit of extra heat to get solder to melt onto it. Solder the tab down first, then get the three legs.

Step 2: Add the Trimmer and Capacitor and Potentiometers

I used a 100uF capacitor here instead of the 220uF specified by the silkscreen. The more uFs the better, as long as the capacitor can physically fit and the voltage isn't lower than 75% of what you're planning to use as power.

Also, you can see the potentiometers installed.

The potentiometer set the gain of the output amplifiers. The silkscreen specifies 100K potentiometers, but you may choose, as I have done here, to use 1M potentiometers instead, for ten times the possible gain. The input resistor is 1K, so with a 100K potentiometer, the possible gain is 100, but with a 1M pot, the possible gain goes up to 1,000 which is probably more than you'll need but hey why not?

Okay reminding myself of the circuit, using a higher value potentiometer will increase the noise in this circuit, since the full resistance of the potentiometer is being used.... blah blah do what you want LOL

Step 3: More Parts!

Here you can see the TL074 quad op amp added, along with the Thonkiconn jacks and the DC power jack. Oops, I don't have a picture of the 1/4" phone jacks being added.

The Thonkiconn jacks and the 1/4" jacks are directly connected to each other. So don't use them to mix signals besides just the two channels.

But then, turn over the PCB and solder everything in!

Step 4: Pins!!!

I've chosen to use pins and female wires as patch cables for my SynthCard modules. If you want to do this as well, you'll need to use output pins where you can also choose to put more Thonk jacks.

It can be a challenge to get single pins held straight in the PCB while soldering. I use poster putty (BluTak etc) to hold them. Move quickly and you won't burn it too badly.

The pair of power pins stick DOWN from the PCB. Do it like in the picture because next up? SynthCard brick time!!!

Step 5: SynthCard Bricks

You can print your own SynthCard bricks using this file here. Grab a DIP-8 socket (leaf spring type, not the machined ones) and bend four of the pins over like in the picture.

Solder a bit of wire to the pointed-together socket pins. This will carry the current and ground from card to card.

The DIP-8 socket gets shoved into the SynthCard brick like pictured. It might take a bit of effort to get it seated properly, but then hopefully it's there to stay!

Step 6: Whee!!! Ready to Go Also, Calibrating the Voltage

Hurl your new SynthCard onto the bricks like in the picture!

I forgot to get a picture of adjusting the power.

If you're using 5V power from the USB-C input, you won't need to adjust the voltage. But if you're using a different source of DC power, you'll want to choose a voltage and turn the trimmer until you've got that power.

If you don't have an easy way to check voltages, this board can help. There's two little LEDs on the board that gradually light up and get to the "mostly-on" brightness when the output voltage reaches the indicated level, about 5V and about 12V. At 9V the first LED is fully bright and the 2nd LED is quite dim.

Some SynthCard circuits might require no more than 5V to run safely, but all M4TM SynthCards will be able to tolerate 12V and more. This is a flexible, wild-west synthesizer format that anybody can develop for, so make sure your modules will play nicely with whatever voltage you choose.