Hifi Preamps for your Record Player

By: skrodahl | September 26, 2016

UPDATE:

Since only one extra resistor value is needed to get the higher impedances, it's been added to the kit. Now you can choose between these two options.

The input impedances on the Muffsy MC Head Amp can be changed to your liking. To help you find the right values, here's a nifty input impedance calculator.

Muffsy MC Head Amp - Default Input Impedances

You can play around with the values for R1, R2 and R3, and the calculator will show you what the input impedance choices will be. With all the switches set to OFF, the input impedance will be equal to R3.

The picture shows the values that are included in the kit.


PLEASE NOTE:
The resistors R3 MUST be installed, or you risk that the Muffsy MC Head Amp won't function.

Here's a suggestion for other component values, if you need a bit higher impedance:

Muffsy MC Head Amp - Alternative Input Impedances

By: skrodahl | September 21, 2016

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!

You can now build your own MC Head Amp

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.

By: skrodahl | September 18, 2016

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

Category: News 

Tags: muffsy, vinyl, moving coil, mc, head amp 

By: skrodahl | September 18, 2016

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.

By: skrodahl | September 12, 2016

Wondering how the Muffsy MC Head Amp measures? Look below for the numbers.

  • Topology: Dual mono
  • Gain: 24.6 dB
    • 0.3 mV input = 5 mV output
    • 0.5 mV input = 8.5 mV output 
  • Input impedance: 47 - 100 ohms, in four steps
  • THD: < 0.1 % *)
  • THD+N: < 0.6 % *)
  • SNR:  71.8 dB, referenced to 0.5 mV input @ 1 kHz
  • Frequency Response: +0.0 / -0.1 dB (20-20.000 Hz)
  • IMD (ITU-R): 0.001 %
  • DC Offset: < 0.1 mV
  • Dynamic range: > 110 dB, referenced to 0 dBV output
  • Power requirements: +/- 15V at < 50 mA
  • PCB Size: 84.0 x 59.4 mm / 3.3 x 2.3 in

*) The inherent noise in my signal generator is too high too accurately measure the THD and THD+N. I'm looking at how to solve that. The numbers are too high, both should be well below 0.1%, but I've added my measurements for reference anyway.

Check here for more details on the measurements.
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