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. ;)

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

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.

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:

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.

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

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.

The Muffsy Phono Preamp is, and will continue to be an MM phono stage. Moving magnet and moving coil cartridges require different operational amplifiers, so a combination of MM and MC is not feasible at this size and price point. 

Until now, the only way to use the Muffsy with moving coil cartridges has been to use a step-up transformer or a separate head amp (of which there aren't many around). Now that's about to change!

The Muffsy MC Head Amp is a very high quality amplification stage that brings the MC signal up to MM levels, and it goes between your turntable and the Muffsy Phono Preamp (or indeed any MM phono stage).

The design goals for the Muffsy MC Head Amp have been:

• Dual mono topology
• Signal-to-Noise ratio above 70 dB
• Variable input impedance
• DC servo to eliminate input/output capacitors
• Gain of 24.6. 0.3 mV input gives 5 mV output / 0.5 mV gives 8.5 mV out
• Same great PCB quality as the other Muffsy products
• The Muffsy MC Head Amp will fit in a B0905 enclosure together with the Muffsy PSU
• Easy and understandable build documentation

I've been running the latest prototype with an Ortofon MC30 Supreme for quite a while now, and the Muffsy MC Head Amp is brilliant. It's absolutely dead quiet and offers the same pitch black silent background, the great soundstage together with the rich and revealing sound that the Muffsy Phono Preamp is known for.

Be on the lookout for the Muffsy MC Head Amp very soon. Here's some more information about the project from the very beginning: https://hackaday.io/project/12483-muffsy-mc-head-amp

The signal to noise ratio (SNR) compares the level of the audio signal to the background noise. An SNR of at least 65 dB is what's needed to have a completely silent phono stage. The Muffsy Phono Preamp's SNR, with OPA2134, comes in at 79.46 dB as shown below.

The measurement of signal to noise ratio can be a rather arbitrary affair. Some measure it as the difference between the noise and when the signal has 1% total harmonic distortion, while others compare it to a 0 dBV output. I've seen one manufacturer use 3 volts output as the reference point. With its 36 dB gain, it barely outputs a tenth of that with a normal MM cartridge connected.

For the Muffsy Phono Preamp, you'll get the signal to noise ratio as it is under normal use. This means that it will be referenced to an input of 5 mV, which is normal for a standard moving magnet cartridge. The output, at maximum gain, is then -2.54 dBV.

The measurement above shows the noise profile of the Muffsy PP-3 with OPA2134 operational amplifiers. The inputs are shorted in order to avoid picking up environmental noise, and the measurements are A-weighted. The graph is an average of 20 samples, instead of just picking "the best measurement".  

The red square shows the total noise power, from 20 to 20.000 Hz, which is -82.0 dBV.  The difference between the signal and the noise is then 82.0 dB - 2.54 dB. This gives a signal to noise ratio of 79.46 dB.

This is comparable to how commercial vendors  measure the signal to noise ratio, but here you can be sure that it is under normal operating conditions. That said, your cartridge will also create some noise of its own. When you connect your turntable to the Muffsy Phono Preamp, the actual signal to noise ratio will probably be around 77 dB.

It's worth noting that these measurements were done with the Muffsy Phono Stage powered by the Muffsy Power Supply. Both were housed in a B0905 enclosure with the Muffsy Back Panel, as described in the build instructions. The components were taken straight out of a Muffsy kit without any matching of any kind.

NOTE:

This modification is only intended for the Muffsy Phono Preamp together with the Muffsy Power Supply and Back Panel in the recommended B0905 enclosure. Before you try this, have a look at the other ways of eliminating hum.

Arno just completed building the Muffsy Phono Preamp, and was haunted by distortion. He decided to use the B0905 enclosure for shielding and ended up with a completely quiet phono stage.

Notice also how Arno connected the ground lugs of the RCA connectors in a star pattern. Great idea Arno!

He drilled a hole in the cabinet and connected a piece of cable from the ground screw to this hole.

The reason this works is that the Muffsy Power Supply has a completely floating ground. If you're using a power supply that connects directly to mains power, this solution might inject more noise if not done correctly.

You can see Arno's modification from a different angle in the above picture, and a larger version of his close-up below.