Hifi Preamps for your Record Player

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.

By: skrodahl | October 16, 2018

Several people have been in touch lately with questions on how to modify the PCB into something it isn't right now. Popular requests are balanced inputs and/or balanced outputs, and DC servo on the outputs.

The PCB itself doesn't really lend itself to any of the modifications above, but you could always try doing add-on boards or roll your own from the open source freely available schematics.

An explanation of the Muffsy Phono Preamp PCB layout can come in handy for such alterations. And wouldn't you know, here it is:

Muffsy PP-4 PCB Layout
The Muffsy Phono Preamp PP-4 PCB Layout

Modifications you can do are changing the input impedance and altering the variable gain. I'm also happy to announce that the gain calculator has been updated to show the output voltage and voltage gain:

Muffsy PP-4 Gain Calculator
Muffsy PP-4 Gain Calculator

Finally, if you want to make major modifications, a way of simulating the circuit would really come in handy. Well, here's the Muffsy Phono Preamp LTSpice simulation file.

Muffsy LTSpice Simulation
Muffsy Phono Preamp LTSpice Simulation

By: skrodahl | June 15, 2018

It's become evident that I need a better solution for photographing my projects. So I went out and bought some surprisingly cheap LED panels:

LED Panel
LED panel, (c) MIA Worldlight

But then I had no idea on how to build this into a suitable light box. So I spent the time buying suitably sized vinyl backdrops and some clamps from the UK based eBay seller photogeeks11. I can't thank the seller enough, small sized vinyl backdrops are very hard to find. They are also of excellent quality.

 
Black backdrop
Black backdrop, (c) photogeeks11
 
Mini clamps
Mini clamps, (c) photogeeks11
 
White backdrop
White backdrop, (c) photogeeks11

My first lightbox...

The first lightbox was three pieces of scrapped wooden planks. Just to hang the backdrops from. The two side LED panels leaned against the planks, and I managed to somehow balance the top LED panel long enough to take one picture. Then it all crumbled and fell to the floor. (Nothing broke, luckily.)

My first lightbox
My first lightbox

It did produce one good picture before the whole construction fell apart though. Keep in mind that this is taken using my Galaxy S7 Edge with default settings.

My first lightbox picture
My first lightbox picture

Rethinking the lightbox (the one that didn't fall apart)

Since I wasn't in the mood for having my (albeit cheap) LED panels crushed, I set out looking for alternatives to scrap wood. I finally found some nice square aluminum tubing and plastic joints.

 
 
 

With the building material in playce, I brought out my trusty old (and very dull) hacksaw and started construction. Here's the result:

 
Second lightbox, partly assembled
Second lightbox, partly assembled
 
Second lightbox, fully assembled
Second lightbox, fully assembled

The plastic joints had to be hammered into the tubing, and I was a bit worried that I would never be able to disassemble the light box (it's big, and I don't have that much space). Luckily, the plastic sort of shaved off. Using the hammer, I was able to take it apart.


While still a very snug fit - which is good, the lightbox is nice and stable - I'm able to pull the tubes apart so I can store the lightbox when it's not in use.

Pictures, or it didn't happen!

Well, I have only one picture. It's of my B&O IcePower module, on white vinyl backdrop.


This picture is also taken with my Galaxy S7 (the system camera is now on a tripod in front of the light box). I had to change exposure, and do some post-editing though. 

IcePower 125asx2
IcePower 125asx2

I think that's quite a beautiful result. Now that I have the system camera mounted, I've finally found my lightbox solution.


It wasn't exactly cheap though, it came in at just above US$ 300. It's tailor made to my needs, which is why we all do the DIY-thingie in the first place. Right?

Update: Picture taken with the system camera

Here's the Muffsy Back Panel photographed with my Sony Alpha 5000 with a Minolta MD Rokkor 50mm f/1.7:

...and the camera itself:

The Sony Alpha 5000, with its 20 megapixel APS-C sensor, is really great as a manual camera. It's got no viewfinder or fancy autofocus, so I wouldn't use it to shoot sports pics. Or outdoors, due to the relatively dim LCD monitor...


The range of vintage lenses that can be used with the Sony Alpha (E-mount) cameras is almost endless, since there are adapters available for most lenses. Check out the YouTube channel AdaptedAlpha to see lots of examples of older lenses being used with the Sony E-mount cameras.