Hifi Preamps for your Record Player

Build the Muffsy MC Head Amp MH-1

The Muffsy MC Head Amp kit comes complete with all on-board components. Read these instructions carefully before you start building, then follow each step when building the kit.


You can also have a look at the schematics for the Muffsy products under the Modify It page.

Connecting the Muffsy MC Head Amp

This is how you connect your Muffsy MC Head Amp when you're done building it:

How to Connect the Muffsy MC Head Amp

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 MC Head Amp.
  • 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.
  • Do perform the tests in Step 16, so you don't risk damaging your head amp.
  • It's not recommended to use batteries to power the Muffsy MC Head Amp.

Ready? Here we go!

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:



 Quantity Component
 1 Muffsy MC Head Amp, Printed Circuit Board
 2Resistors 0.25W, 47 ohm
 2Resistors 0.25W, 100 ohm
 2Resistors 0.25W, 150 ohm
 4Resistors 0.25W, 220 ohm
2Resistors 0.25W, 300 ohm
 2
 Resistors 0.25W, 750 ohm
 2
 Resistors 0.25W, 100k ohm
 4
 Resistors 0.25W, 1M ohm
 2
 Film capacitors, 330 pF
 8
 Ceramic capacitors, 0.1 uF
 4
 Film capacitors, 1 uF
 2
 Operational amplifiers, LT1115
 2
 Operational amplifiers, OP177
2
 Electrolytic capacitors, 100 uF
 1
Four-way DIP-switch
4
8-pin DIL sockets
 1
Screw terminal, 3 positions
 1Sticker with alternative impedance values
30 cm / 1 ft  RVVP 2x0.2 shielded audio cable

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 18 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.


  • Before you solder the resistors, consider if you want to change the input impedances using the resistors included in the kit. Here's how you can do that.

 
Default Input Impedances
 
Alternative Input Impedances

  • See the picture below for where to place the resistors, depending on which input impedance scheme you have chosen. Apply the included sticker if you decide to use the alternative impedances:

 
Resistor Values - Input Impedances
 
Sticker with Alternative Impedance Values

All orders after 2016-09-28 are shipped with resistors that will let you choose between these two input impedance schemes. When you're done, you will end up with either 2x 220 ohm or 2x 300 ohm resistors that are left over.

  • You may want to lower the gain. Replace the 47 ohm resistors with 82 ohm (not included in the kit) to get 5 mV output from a 0.5 mV cartridge. The default setup gives:
    • 0.15 mV input = 2.5 mV output
    • 0.3 mV input = 5 mV output
    • 0.5 mV input = 8.5 mV output.

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.

 
Standard resistor values - Click on the picture for a bigger version
 
Resistor values - Alternative impedances

The picture below shows all the standard resistors soldered in place. The resistors in the kit are Multicomp MF25, 1% tolerance with a temperature coefficient of ±50ppm/°C. They are very fit for the job, and you should not have to worry about replacing them with more audiophile resistors.

Step 3 - Solder the DIL Sockets

These are the sockets for the operational amplifiers, and there are four of them. 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 four 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.


Note that the text beneath the DIL sockets refers to the operational amplifiers that will be mounted later.


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

Step 4 - Solder the DIP Switch

This four-way DIP-switch is here to adjust the input impedance of the head amp.


It is absolutely essential that you get the orientation right. If you don't, adjusting the features of the head amp will be very difficult and confusing. The text "ON DIP" goes towards the top of the board and the numbers "1 2 3 4" go towards the bottom, as shown in the photo.


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

The input impedance can be set between 47 and 100 ohms, or between 50 and 300 ohms (alternative resistors) in four steps, according to the tables below (and the text on the board itself).

The safest choice is to set the impedance to 100 ohms, unless you know exactly which impedance your cartridge needs.

 
Muffsy MC Head Amp - Default Input Impedance Settings
 
Muffsy MC Head Amp - Alternative Input Impedance Settings

Step 5 - Solder the Ceramic Capacitors

The eight ceramic capacitors shown in yellow in the picture below are up next.


They don't need to be oriented in any special direction. It's a good idea to mount them with the text outwards though, so that the values are visible.

Step 6 - Solder the 330 pF Capacitors

These are Wima FKP2 polypropylene capacitors. There's two of them, one for each channel. Mount them as shown on the pictures below, orientation does not matter.

Step 7 - Solder the 1 uF Capacitors

These four larger capacitors are Wima MKS2 polyester models. There's four of these capacitors. Orientation does not matter, although it looks nicer if they're all mounted the same way. These pictures show where the capacitors go.

Step 8 - Solder the Screw Terminal

The kit contains one screw terminal with three inputs that connects to the power supply. There is space for screw terminals on the signal input and output, but these really should be soldered directly to the board in order to avoid introducing noise into the circuit.


Solder the screw terminal as shown in the pictures below.

Step 9 - Solder the Electrolytic Capacitors

These two electrolytic capacitors form the power supply decoupling together with the ceramic capacitors in step 5.


Please make sure that they are mounted correctly, or they can go "poof". The longer leg goes in the hole marked '+', the shorter leg (which has the white strip with the '-' symbols) is oriented to the left, when the board is seen as it is below. The second picture shows how it should look when you're done.

 Step 10 - Connect the DC Power from the Power Supply

Build the Muffsy Power Supply, but DO NOT SOLDER THE SCREW TERMINALS.

Cut three pieces of red, blue and black cable, 7 to 10 cm long. Strip about 5-6 mm on each end:

Fasten the three cables in the screw terminal in this order:

  • Left (+VE): RED
  • Middle (GND): BLACK
  • Right (-VE): BLUE

Braid the three cables, as that will shield from interference:

Mount the screw terminal on the Power Supply board, with the cables facing inwards: Solder the screw terminal to the Power Supply board:

Connect the cables to the MC Head Amp's screw terminal in this order:

  • Left (+VE): RED
  • Middle (GND): BLACK
  • Right (-VE): BLUE

Step 11 - Connect the AC Power from the Power Supply

Cut two pieces of wire, red and black, 7 to 10 cm long. Strip the ends about 5-6 mm:

Fasten the two cables in the screw terminal, orientation does not matter, and twist the cables tightly:

Mount the screw terminal on the Power Supply board, cables facing inwards, and solder the screw terminal to the board:

Solder the two cables to the Muffsy MC Head Amp board. It does not matter which cable goes where:

 Step 12 - Assemble the Back Panel

Your back panel may be delivered with a piece of gray wire. This wire can be used for manually connecting the ground between the connectors. This wire can safely be tossed away.


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. Do not use plastic shims:

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 13 - Wire the AC Power from the Back Panel to the MC Head Amp

Cut a piece of red wire, approx 4 cm. Strip about 5-6 mm from each end:

Solder this piece of wire between the bottom pad on the power button, to the top pad (the L-shaped one) on the power connector:

Cut two pieces of wire, red and black, 7 to 10 cm long. Strip 5-6 mm from each end:

Solder the black cable to the top pad of the power button and the red cable to the bottom pad of the power connector:

Twist the cables tightly and solder them to the MC Head Amp board. It does not matter which cable goes in which hole:

The Muffsy MC Head Amp power cabling is now done!

Step 14 - Connect the Audio Input and Output

Take two pieces of shielded cable, 7 to 10 cm. Strip 3 cm from one end and 1.5 cm from the other:

Twist the shield (the thin outer cables) and strip 5-6 mm from the red and white cables. Do this on each end:

Now solder the longer ends of the cables to the connectors on the back panel. The red goes on top, the white on the bottom and the shield on the ground pad:

Do the same with the other cable as well:

These cables will line up with the INPUT and OUTPUT marked on the MC Head Amp board. Solder as this:

  • Right: Red Cable
  • Middle: Shield
  • Left: White cable

Step 15 - Mounting the MC Head Amp in the Enclosure

The Muffsy MC Head Amp is now fully assembled, all that's left is to slide it into the enclosure, and fasten the panels:

Step 16 - Testing the Muffsy MC Head Amp

Testing the Muffsy MC Head Amp before using it is essential. If these tests are not successful, it's very likely that you will damage the operational amplifiers.


You will need a multimeter capable of measuring both AC and DC volts for these tests.

Do Not Use Battery Power - Make Sure All the Voltages are Correct

The OP177 operational amplifiers are there to make sure that there is no DC offset on the signal. If there is only +15 volts or -15 volts, it will work very hard to correct this, frying your LT1115 operational amplifiers in the process.


If you're using batteries, this can happen if only one of them runs out of power. This is why you're discouraged from using batteries to power your Muffsy MC Head Amp, and why you need to be 100% sure that the voltages are correct.

Inspect your Printed Circuit Boards

Before you go ahead, you should visually inspect the circuit boards.

  • Make sure all the components are mounted, and that the orientation is correct
  • See if all component leads are soldered, and check for bad solder joints or shortcuts between the joints
  • Cut all leads underneath the boards so that they are flush with the solder joint
  • Check that no leads on either sides of the boards are touching each other
  • Double-check all the connections between the boards and to the back panel
  • Don't let the bottom of the boards, or the component leads touch the enclosure

Remove the Operational Amplifiers

If you have installed the operational amplifiers in their sockets, please remove them. The purpose of this test is to make sure that they're not being damaged.

Turn the Power to OFF, and Connect the AC Adapter

Turn the Power ON

This is your very first test. Turn the power button ON, and touch the components on the Power Supply to check that they don't get hot.


If any of the components get hot to the touch, there's something wrong with your power supply or cabling. Remove the power adapter immediately and check the power supply board for errors.


If the components stay cool, move on to the next step.

Measure the Muffsy MC Head Amp Board

  • Take out your multimeter, turn it to VOLTS DC and place the BLACK PROBE on the middle screw on the screw terminal
  • Place the RED PROBE on each of the "+15V" and "-15V" spots marked on the picture below, and check the voltage
  • The voltages are never exactly 15 volts, but they will be very close
  • If the voltages are correct, you can move on to installing the operational amplifiers
  • If the voltages are incorrect, repeat the inspection again
  • If you can't find anything wrong from the inspection, look below for more options

Troubleshooting

These are the errors you can get:

  • All the tests show ZERO volts
  • All the "+15V" test points show ZERO, or very close to ZERO volts
  • All the "-15V" test points show ZERO, or very close to ZERO volts
  • The test points show some other voltage

Make sure you have an AC power adapter:

  • You should use a power adapter from 15 to 18 volts, and it needs to have AC output, usually marked "AC to AC", "AC/AC" or using the symbol "~"
  • If the power adapter says "AC to DC", "AC/DC" or has the symbol "=", it is a DC adapter and needs to be replaced with an AC adapter

Check that the power supply is getting power:

  • Set your multimeter to VOLTS AC, and measure across the input screw terminal on the power supply (marked in the picture below)
  • The voltage should be at or above what it says on the AC adapter
  • If you measure zero volts, change your multimeter setting to VOLTS DC
  • If you measure either +15 volts or -15 volts DC, or more, you are using a DC adapter. Replace it with an AC adapter
  • If you still measure zero volts, check the wiring from the power connector, through the power switch, through the AC traces on the Muffsy MC Head Amp and to the power supply
  • If the connections are okay, make sure that your AC adapter is working

  • If the power supply is getting AC-power, and the output power is missing or wrong, you need to go back and inspect your board. Make sure that the orientation and placement of the components are wrong. Things to look out for is placement of voltage regulators, and orientation of diodes and electrolytic capacitors. Check that all the solder joints are okay, and that there are no short circuits anywhere.

Support

If you have gone through all the tests and the troubleshooting, and your Muffsy MC Head Amp still isn't working, please contact me so we can find and fix the problem together.

Mount the Operational Amplifiers

Before you mount the operational amplifiers, disconnect the AC adapter and turn the power switch to OFF. If you don't, the op amps may be damaged.

There are four operational amplifiers in the kit. Two marked LT1115 and two marked OP177. The LT1115s do the amplification and the OP177 make sure that you don't have any DC in your signal.

Mount the operational amplifiers in their sockets, as shown in the picture below. The sockets and operational amplifiers have a notch that correspond. Mount the op amps carefully in their sockets without bending any of the legs, and check that the orientation of each chip is correct. Mounting them wrong will most likely damage them.

Connect the AC adapter and turn on the power, while touching the LT1115 operational amplifiers.

If the LT1115 op amps get really hot, disconnect the power immediately, and go through all the tests again. The LT1115 operational amplifiers will get a little bit warm when the head amp is powered on, but they should not be burning hot.

Congratulations, You Have Built the Muffsy MC Head Amp!

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

  • The Muffsy MC Head Amp is only to be used with low output MC (LOMC) cartridges
  • Connect the cables from your turntable to the input of the Muffsy MC Head Amp, and make sure the ground cable is connected at both ends
  • The Muffsy MC Head Amp does not apply any RIAA correction, it needs to be connected to an MM phono stage, like the Muffsy Phono Preamp
  • 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 head amp is working to your satisfaction