Hifi Preamps for your Record Player

By: skrodahl | May 13, 2019

A very simple, but useful PCB. A power supply for the Muffsy Relay Input Selector (or anything else that can be powered by 5V DC/1A):

Muffsy Input Relay Selector - 5V
Breakout Board for the MeanWell IRM-05-5 PSU

The MeanWell IRM-05-5 takes an AC input between 85 and 265 volts, or a DC input between 120 and 370 volts and converts it to 5 volts DC at a maximum of 1 ampere.

This open source PCB project created in Eagle lets you add input and output cabling, as well as providing mounting holes for the PSU. Download it here:

The project contains the schematic, the board, and the gerber files (and also the .cam file to generate your own gerbers).

By: skrodahl | May 02, 2019

While there are lots of quality kits for preamplifiers, I have never really found a decent way of adding more inputs to a preamp. The existing ones are either of dubious quality, spec'ed like a spaceship, or both.

So I decided to make my own input selector. With relays. And an ESP-32 module! A year, and four revisions later, you can buy it on Tindie for $69.

The entire project is fully open source, no strings attached.

So what is it?

It is a programmable input selector for preamplifiers, the size of a Post-IT note, with:

  • Four stereo inputs
  • One stereo output
  • Mute
  • Mains power on/off through a solid state relay control
  • Break-outs for all ESP-32 pins

It's controlled by a rotational encoder and IR remote, and you get the great build instructions that you've come to expect from a Muffsy kit.

Muffsy Relay Input Selector - Kit
Muffsy Relay Input Selector - Kit Contents

The PCB, all onboard components, ESP-32, rotational encoder and IR receiver are all included in the kit. You also get the fully functional software for it, as well as the Eagle project files for the PCB.

The benefit of using an ESP-32 is that you can program it yourself, and use other functions like touch sensors, Wifi and Bluetooth.