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.
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.