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.

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.

Behold the new Muffsy Phono Preamp!

It'll be available on Tindie, very soon. Actually, it is available: https://www.tindie.com/products/skrodahl/muffsy-phono-preamp-kit/

What's New?

These are basically the same circuits as before. The focus has been on making the build experience even easier than before, and improve noise prevention.

• The op amps are OPA2134 and LM4562
• SNR improved by 2.9 dB, from 79.4 dB to 82.3 dB
  
• No screw terminals facing the side walls of the enclosure
  
• The AC power cables do not cross the input
  
• The DC power cables do not cross the output
• The AC and DC power connectors line up on the PP-4 and PSU boards
• The signal inputs and outputs line up with the RCA connectors on the back panel
• The grounding scheme is redesigned to avoid ground loops
• The input impedance switches are grouped together
• The gain switches are grouped together
• The back panel has a ground pad in one of the corners, to ground the cabinet
• The back panel now has gold pads and the golden "M" logo
• The power supply now has the golden "M" logo
• There's room for heat sinks on the power supply voltage regulators (if needed)
• The solder pads for the screw terminals are beefier
• The mounting holes have been increased from 2.8 to 3.0 mm
• The board width is approx 0.5 mm narrower for a better fit in the B0905 cabinet
• The board's corners are even more rounded to make it easier to insert into the B0905 cabinet

Built-in Grounding of the Enclosure

One prime example of the thought that's gone into this new version is the fact that the back panel connects to the enclosure for improved grounding and shielding from noise:

Crisp, Clear Pictures

I've put my new lightbox to good use, and produced some really nice pictures for the instructions.

Here's one of the new photos compared to the corresponding old phono. Judge for yourself:

Thanks

This new version of the Muffsy Phono Preamp couldn't have been created without the (without exceptions) enjoyably long and fruitful email conversations with so many people. Keep using the contact form.

A special thank you goes to the loyal customers who helped me test the prototypes and provided valuable feedback, you know who you are. ;)

While I've been sharing a lot of my work on muffsy.com, I've never really clarified how my view is on people using my work (or derivates of it). This is now changing.

I've decided to release all of my content (barring a few exceptions) under the Creative Commons Attribution 4.0 International license.

What does it mean?

It means that everything on muffsy.com, except where specifically stated, is open source. You have the right to:

If you're going to use any of the content on muffsy.com, you will have to adhere to these conditions:

• Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
  
• No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.
• You do not have to comply with the license for elements of the material in the public domain or where your use is permitted by an applicable exception or limitation.
  
• No warranties are given. The license may not give you all of the permissions necessary for your intended use. For example, other rights such as publicity, privacy, or moral rights may limit how you use the material.
  

There are also some conditions for muffsy.com to follow. Most notably is that the shared information must be in an open format. The only possible violation to this are my Autodesk Eagle design files. They can be used, but not always processed, by the free version of Autodesk Eagle. They can also be opened and edited (although not always perfectly) in the open source tool KiCad.

What are the exceptions?

The only exceptions to the Creative Commons on muffsy.com is for a few of my PCB designs, mainly variants of those that I'm currently selling. They are free for personal or non-commercial use, but you cannot use them commercially without my approval.

At the time of writing these are the only exceptions:

• https://www.muffsy.com/blogs/post/Make-Your-Own-Muffsy-PCBs
  
• https://www.muffsy.com/blogs/post/Make-Your-Own-Muffsy-Power-Supply
  

If not stated otherwise, everything is free to use as described above. That's right, text, pictures, schematics, design files. The lot!

YouTube user Blake G has posted a couple of vinyl-rips using the Muffsy Phono Preamp onto the video site. Although YouTube probably alters the bitrate, you can still get an idea on how the Muffsy Phono Preamp performs in his setup. His setup, btw, is:

• Turntable: Sony PS-X500
• Cartridge: Empire 999ve/x
• Phono Stage: Muffsy PP-3
• Line In: Behringer UCA202

Here are the links to Blake G's two rips:

• Bruce Cockburn - Hills of Morning
• Nickel Creek - 21st of May

This project is freely available, and you can have the boards produced yourself. That's not for everyone though, so I've decided to sell the PCBs for the BSTRD on Tindie.

The Bill of Materials on hackaday.io has been greatly improved, and even contains a Mouser shopping cart for all parts except the tubes, tube sockets, LED resistors and transformers.

After a lot of testing, ordering of components, assembling kits, more testing and writing build instructions, the Muffsy MC Head Amp kit has finally launched!

If you're looking for a way to use low output MC cartridges with your Muffsy Phono Preamp, or any other MM phono stage, look no further! Get it on Tindie today for only $79!

One very important requirement before launching the kit was to have a section in the build instructions on testing the circuit before you power it on, and troubleshooting the head amp if the tests fail. That all came together last night, and then it was just a matter of opening the gates at Tindie.

The build instructions for the Muffsy MC Head Amp contains every step from start to finish, including customization, testing and troubleshooting, all in one single page. This makes it easier to build than ever. And remember: If you don't know how to solder, EEVBlog's videos will get you going  in no time at all.

It's done, it's built, it's the first of its kind, it's plugged in, it sings! 

No hiccups, no artifacts, it just works. It's playing the 40th anniversary "Crime of the Century" by Supertramp right now.

Sweet :)

This does mean that, with some effort, the kit will be ready in about two weeks. The kit is available as of September 21st!

Also, the build instructions are very close to finished, I'm still writing the part about testing to make sure your head amp works before plugging it in.

http://www.muffsy.com/build-the-muffsy-mc-head-amp-mh-1.html

That's right, the MC Head Amp made it to the front page of HACKADAY, which is a great honor!

Unfortunately, there's some confusion in the article and in the comments that I would like to address here.

The Article Mixes the Phono Preamp and the MC Head Amp

The article shows the Muffsy MC Head Amp and the Muffsy Phono Preamp.

• The Muffsy MC Head Amp is a high quality gain stage that makes it possible to use an MC cartridge with an MM Preamp.
• The Muffsy Phono Preamp is a phono stage that applies RIAA equalization to the signal and amplifies it so it can be used with your stereo's input.

The HACKADAY article lists the specifications for the Muffsy Phono Preamp, which is why it goes on explaining variable gain and RIAA equalization.

Some of the Comments are Critical to the Project

Instead of tackling each comment, here's some more info on the Muffsy MC Head Amp:

• It amplifies very low signals, typically between 0.1 and 0.5 mV, to between 3.5 and 8.5 mV.
• With signals this low, (1/1.000th or less of the signal from a DAC or CD player) the noise plays a very significant role. There are only a handfull of op amps that can handle this task, I chose the LT1115.
• Sockets are used for the op amps, so that they can be replaced if anything goes wrong. It also used to avoid overheating the op amps when they are soldered in place. That makes sense for a DIY project. Leave them out if you are confident that you don't need sockets.
• There is confusion whether or not the PCB has ground planes. Rest assured, it does.
• The kit comes with shielded cables that share the ground. That's why it's only three inputs/outputs. Left, right and shared ground.
• A DC Servo does add capacitors in the signal path, even more of them than when using output capacitors. It's just another way of removing the DC component in the signal. This particular design even limits the bandwidth, starting the attenuation at just above 100 kHz.

So, why did I go for an op amp based head amp then?

• Because it's a kit, one that can be built by people who have never tackled DIY electronics before.
• Op amp circuits are easier to build, the result is very predictable.
• It works with the existing Muffsy power supply, no need to design more components.
• Discrete (transistor) based circuits can be better, but require matching of transistors and tuning after installation.

Summary

The Muffsy MC Head Amp performs wonderfully. It is completely silent, it has a very low noise floor and it does not add coloration to the sound. The sound signature of your MM phono stage will be what you hear when using the Muffsy MC Head Amp.

The Muffsy Phono Preamp measures and performs along the lines of really expensive solutions, but costs only $79. The circuit is much simpler and easier to build. If you enjoy making your own equipment, this project is for you.

Great care is taken to remove all sources of interference. The kit is complete, there's no question marks or missing pieces, which gives you a fully working product when you're done building it, and you won't get better quality PCBs or components anywhere. Use the recommended enclosure, and you don't have to do any metal work, the circuit boards slide into the grooves of the cabinet and the back panel completes it with all switches and connectors.

You may have noticed that the Muffsy MC Head Amp is on its way. UPDATE: It's already here!

Here's why you might want one for yourself.

The basic purpose of a head amp is this:

• To use a low output MC (moving coil) cartridge with your existing MM (moving magnet) phono stage.

An MC cartridge typically has 1/10 of the signal strength of an MM. The signal from your MC pickup will be amplified by the head amp to a level that can be handled by the phono stage you already own. It does so without adjusting the RIAA curve. But why?

As it turns out, there are a number of reasons:

• Your favorite phono stage or amplifier only has MM input
• The quality of the MC input on your phono stage or amplifier isn't good enough
• A step-up transformer is too expensive
• Your current MC phono stage lacks the settings you need
• You want to try what MC cartridges are all about, without having to buy a new and expensive phono stage

The MM and MC cartridges behave quite different. The best topology for low noise with MM is not the same as that for MC. In short: MM cartridges need low current noise and MC cartridges need low voltage noise, but an amp can only have one of those. If there's one input stage on your MM/MC phono stage, you can be relatively sure that it is optimized for only one of them. Most likely moving magnet. A dedicated head amp ensures the best sound quality at all times. Now you can use your vintage amp, tube phono stage or any other MM phono stage with an MC cartridge.

If you have found the phono stage of your dreams and it only has MM input, you will need a head amp or a step-up transformer in order to use an MC cartridge. Step-up transformers range from expensive to very expensive. That's not to say that phono stages or head amps don't, but they can be had for less money. Look no further than to this site for proof of that.

If you're on the lookout for a DIY MC head amp, the Muffsy  MC Head Amp is among the simplest and best options out there. And I'd wager it'll be the cheapest as well. It is extremely easy to build, can be had with both a power supply and a back panel, and does not require any drilling or enclosure modifications of any kind. 

Every care is taken to ensure the very best sound quality, and to avoid all noise and distortion. It measures and sounds excellent, and you get the satisfaction of building your own hifi gear.

Stay tuned for more in-depth information about the Muffsy MC Head Amp.

While we're waiting for the Muffsy MC Head Amp, here's a sneak peek of the new back panel for the B0905 cabinet.

There are a lot of considerations to make when dealing with the very low output from an MC cartridge. Noise and interference should be avoided in all parts of the design, and that's why there's a new back panel available.

The back panel for the Muffsy Phono Preamp uses pieces of wire to manually ground the RCA connectors and the ground screw. For MC, these could in certain circumstances act as small antennas, so best get rid of them. As you can see from the above picture, there's copper exposed around the holes for the connectors. These will make contact with the connectors, and there are copper traces beneath the black coating that connects them together.

Not only is this better suited for low level signals, it's even much easier to build.