Before You Begin Construction

PLEASE NOTE:

• Make sure you have time to construct the kit. If you are stressed, building the kit will not be very rewarding. And it often leads to mistakes.
• Familiarize yourself with the instructions before you start building the Muffsy Phono Preamp.
  
• Take the time needed to double-check component values and placements.
• Even if you're not using the Muffsy Power Supply, Back Panel or the B0905 cabinet, the information given here will serve as inspiration for your build.

Illustrations Explained

The picture below is a larger version of your printed circuit board. For each step, this will be used to show you which components you will be adding to the board.

This picture shows you where you are in the build process. It also shows what each component looks like, and it will contain special instructions or information.

Step 1: Check the Kit Contents

Before you start building, check that you have all components and familiarize yourself with the kit. Here's a list of the kit's contents:

*) Previous versions of the kit has 4 of each the 300 and 2k2 ohms resistors.

All resistors are 1/4W, metal film, 1% tolerance.

Note:

This high quality printed circuit board has plated-through holes. Do not attempt to drill the holes to make them larger, doing so will destroy the board. The four mount holes, one in each corner, may be drilled to size.

Step 2: Solder the Resistors

There is a total of 30 resistors that go onto the printed circuit board.

The resistors are bidirectional, meaning that you don't have to worry about which way they are oriented.

It's recommended that you measure the resistors before you put them in place, and make absolutely sure that the right resistors go in the correct positions.

The picture below shows all the standard resistors soldered in place. The resistors in the kit are Multicomp MF25, 1% tolerance temperature coefficient of ±50ppm/°C.

Note the two input resistors marked on the picture below. The previous version of the board has 2k2 ohms resistors, newer ones have these replaced with 300 ohms.

Step 3: Solder the DIL Sockets

These are the sockets for the operational amplifiers. They will make it easier to replace the small chips later on if you should want to. Soldering the sockets will also make sure you don't overheat the operational amplifiers when installing them.

The orientation is very important for these two sockets, get it wrong and you will be confused about which way to mount the operational amplifiers. There's a notch in the socket that matches up with the picture on the printed circuit board, as shown in the pictures below.

Using a piece of masking tape to hold the sockets in place might be a good idea.

Step 4: Solder the DIP-Switches

These four DIP-switches are here to adjust the input impedance and overall gain of the phono stage.

It is absolutely essential that you get the orientation right. If you don't, adjusting the features of the preamp will be very difficult and confusing.

Use a piece of masking tape to hold the switches in place while you solder.

Step 5: Solder the Ceramic Capacitors

There are four ceramic capacitors on the board, surrounding the op amp sockets. You don't have to worry about the orientation of these capacitors, I like to place them so that the text is showing.

Step 6: Solder the Wima Film Capacitors

There are eight Wima MKS2 capacitors in all.

Start with the six capacitors in the RIAA equalization filter before you continue to the two output capacitors. They are bipolar, so orientation is not significant. I still like to place them so that the text is visible.

Make sure that the right value capacitor is mounted in the right spot. The four 68 nF and the two 47 nF capacitors are very similar in size.

Note that the PCB has space for two different sizes of output capacitors, 5 and 10 mm lead spacing. One of the legs must be towards the center of the board, and the capacitors must span the "-||-" symbol. The pictures below explains this.

Step 7: Solder the Electrolytic Capacitors

The four 22 uF electrolytic capacitors must be oriented correctly, or there's a chance they will go up in smoke.

The board shows a plus (+) symbol, this is where the longer leg of the capacitors will go. The capacitors have a white band with several minus signs (-), this side has the shorter leg. This minus side goes downward when the board is oriented as shown on the pictures.

Step 8: Optional - Solder the Input Capacitors

For some very special setups/cartridges, you may need some additional input capacitance. If you do, mount these two capacitors now.

It is very likely that you won't need them, and they are not included in the kit.

Step 9: Assemble the Back Panel

NOTE:

Use these instructions if you bought your kit on 2016-11-13 or later. If your kit was bought earlier, please follow these steps instead.

Get the four RCA connectors, two red and two black. Some of the parts are not needed, these are the ones you want:

Take the four RCA connectors and put the plastic shims on them:

• PLEASE NOTE:Do not put plastic shims on the back of the panel, the RCA contacts and the ground screw are connected through the exposed metal on the back to form the grounding.
• The plastic shims on the front can be left out, you will find that the connectors are easier to tighten with the shims though.

Mount the two RED connectors in the top holes, and the two BLACK connectors in the bottom holes:

Insert the ground pads on the top two connectors and fasten them with a nut. Fasten the bottom connectors with nuts only.

It's a good idea to use a couple of wrenches to make sure the RCA connectors are tightly fastened. If they are loosened and twisted around, you could snap or short the signal cables connected on the back of the connectors.

PLEASE NOTE:

These connectors are electrically connected together inside the back panel, do not use the plastic shims on the back. If you do add these shims, you will get humming and poor sound quality.

Mount the ground screw and fasten it with a nut. Add the shim and the knurled thumb nut:

Mount the power connector. The hole is not centered, make sure it is towards the top of the board. Fasten the power connector with the nut that comes with it:

Click the power button in place. Make sure the "1" is on top:

Your back panel is now done. Here's how the backside looks when it's finished:

Step 10: Build the Power Supply

Follow the build instructions for the power supply, but DO NOT solder the screw terminals. We'll get to the audio and power connections next.

PLEASE NOTE: Make sure that you don't exceed the maximum voltage of your operational amplifiers. The Muffsy Power Supply delivers +/- 15 volts, which is fine for the op amps delivered with the kit. Others, like some of the Burson discrete operational amplifiers, max out at +/-12 volts. (Have a look here if you need to change the Muffsy Power Supply's voltage.)

Step 11: Audio and Power Connections

Cut two pieces of the shielded audio cable, approx 7-10 cm long. Strip the wires like as described below:

• First wire: ~4 cm on one end, and ~3 cm on the other end
• Second wire: ~3 cm on one end, and ~1.5 cm on the other end

When you're done, the cables will look like this:

Twist the shielding (the exposed outer wire) and strip about 0.5 cm from each of the red and white wires like so:

Take the first cable (with 3 and 4 cm stripped) and hook it up the 4 cm end to the two screw terminals with two inputs.

• First screw terminal: White cable to the left and shield (exposed cable) to the right
• Second scew terminal: Red cable to the right

You will now have a cable with two screw terminals on it, like this:

Make sure that the cables are securely tightened to the screw terminals. Solder the screw terminals to the output on the Muffsy Phoho Preamp with the wires facing INWARDS:

Take the second cable (the one with 3 and 1.5 cm stripped) and connect the 1.5 cm end to a screw terminal with three inputs.

• The red cable goes in the left hole
• The shield (exposed outer wire) goes in the middle hole
• The white cable goes in the right hole

Solder this screw terminal to the input of the Muffsy Phono Preamp, with the wires facing INWARDS:

Cut three pieces of wire, red, black and blue to about 8-10 cm, and strip about 0.5 cm on each end:

Connect these three wires to the screw terminal with three inputs.

• Red cable goes in the left hole
• Black cable goes in the middle hole
• Blue cable goes in the right hole

I advise you to braid these cables tightly to prevent interference. Do make sure that the cables are securely tightened in the screw terminal:

Solder this screw terminal to the power output of the Muffsy Power Supply with the cables facing INWARDS:

Connect another screw terminal with three inputs to the end of the braided cables:

• Blue cable goes in the left hole
• Black cable goes in the middle hole
• Red cable goes in the right hole

Make sure that the cables are tightly secured in the screw terminal and solder this screw terminal to the Muffsy Phono Preamp power input with the cables facing INWARDS:

Cut a piece of red wire, ~3 cm, and strip 0.5 cm from each end:

Solder this wire between the bottom of the back panel's power button and the L-shaped terminal on the power connector.

PLEASE NOTE: Take care not to apply too much heat to the connectors on the power button. The plastic will melt otherwise.

Cut two pieces of wire, red and black, approx. 15 cm long. Strip 0.5 cm off the ends of the cables:

Solder the black cable to the top of the power button, and the red cable to the bottom terminal of the power connector.

PLEASE NOTE: Take care not to apply too much heat to the connectors on the power button. The plastic will melt otherwise.

Twist these two cables tightly to prevent interference and connect them to a screw terminal with two inputs. The orientation does not matter:

Solder the shielded input signal cable's 3 cm end to the RCA-connectors on the back panel. They are the two in the middle. The red cable goes on top, the white on the bottom and the shield (exposed cable) to the ground lug of the top RCA connector:

Solder the shielded output signal cable's 3 cm end to the outer RCA connectors on the back panel. The red cable goes on top, the white on the bottom and the shield (exposed cable) to the ground lug of the top RCA connector:

Solder the screw terminals with two inputs (the one that comes from the power button/connector) to the Muffsy Power Supply's input. Make sure that the cables are secured to the screw terminal, and that the cables are facing INWARDS:

Step 12: Mount the Muffsy Phono Preamp in the B0905 Cabinet

Mounting the Muffsy Phono Preamp in the B0905 cabinet couldn't be easier. Just slide the cards into the grooves of the cabinet, starting with the Muffsy Power Supply

Please Note: 

This can be a tight fit. Pushing the screw terminals inwards while sliding the boards in place will help.

There is some variations in the quality of the B0905 cabinets. Sometimes the walls are bent ever so slightly inwards. It is quite okay to file off some plastic from the outside of the screw terminals to make the boards fit.

Continue with the Muffsy Phono Preamp. Make sure that you don't put to much strain on the cables, or they could come off:

Screw the back panel in place, using the provided scews, and you're done!

Step 13: Mount the Operational Amplifiers

Whether you have ordered the OPA2134, NE5532 or decided to use some other operational amplifiers, they have to be mounted in their sockets.

Carefully bend all the pins of the operational amplifiers inwards, so they are more straight. Insert them into their sockets, making sure they are oriented correctly. The notch on the operational amplifiers matches the notch on the sockets.

PLEASE NOTE: Make sure that you don't exceed the maximum voltage of your operational amplifiers. The Muffsy Power Supply delivers +/- 15 volts, which is fine for the op amps delivered with the kit. Others, like the Burson discrete operational amplifier, max out at +/-12 volts. (Have a look here if you need to change the Muffsy Power Supply's voltage.)

Step 14: Adjust the Input Impedance and Gain

The final step is to set the input impedance and amplification level on the Muffsy Phono Preamp.

Input Impedance Settings

The switches to the left, the ones with four settings, are used for setting the input impedance. The default setting is to set switches 2 and 3 to on, which will give you 47k ohms.

Please note that the input impedance switches must be set. Setting all the switches to OFF will make the Muffsy Phono Preamp sound awful. Do also make sure that the settings are identical on both switches.

With 47k ohms as a starting point, the general rules are:

• Higher values will give more treble
• Lower values will give less treble

Follow this chart to select the right input impedance:

Selecting the Gain

The gain settings are controlled by the to switches to the right, the ones with two settings.

The gain settings are really different volume presets. This allows you to match the cartridge on your turntable with your amplifier. Make sure that the settings are identical on both switches, or the volume will be different on the left and right channels.

Setting switch 1 to ON, and switch 2 to OFF will give you 40 dB of amplification, which is a good starting point. Go to a lower value if the sound is too loud, and a higher value if the sound is too low. Use the table below to choose the right gain setting for your system:

Troubleshooting

Can't get your Muffsy Phono Preamp to work? Bring out your multimeter and do some tests:

• Troubleshooting the Muffsy Phono Preamp and Power Supply

Humming can be a sign of grounding problems:

• Eliminate Hum

Congratulations, You Have Built the Muffsy Phono Preamp

Here's a few parting words before you enjoy your new Muffsy MC Head Amp:

• The Muffsy Phono Preamp is only to be used with moving magnet (MM) or high output moving coil (HOMC) cartridges
• For low output moving coil (LOMC), pair your Muffsy Phono Preamp with the Muffsy MC Head Amp
• Connect the cables from your turntable to the input of the Muffsy Phono Preamp and make sure the ground cable is connected at both ends
• Tell all your friends, family, colleges and random strangers on the street about your Muffsy, and write about it on the forums you subscribe to
• An honest review on Tindie is always greatly appreciated. Do contact me first in case you have any complaints though, and we'll make sure your phono preamp is working to your satisfaction