Assemble your feed me mk3 fuzz

You just bought a new feed me DIY kit? Congratulations, this kit will allow you to learn more about the working of one of the most famous effects, while having the satisfaction to assemble the pedal yourself!

The Feed Me is inspired by a famous circular fuzz pedal from the 60s. But with a lot of customisation, this kit allows you to experiment with different settings and additional components to create a unique fuzz. To match the original model, or to move away from it for fat, modern sounds, or optimized for smooth clean up, or to go into gated fuzz area.
In this article, you will learn how to assemble your Feed Me kit, step by step, while learning how it works and the purpose of each component of the pedal.

before starting to assemble your feed me kit

technical documents

If you are familiar with Do It Yourself with your effect pedals, you will find everything you need in this downloadable document.
If you’re just starting out, the rest of the article is really made for you, so hang in there! Download this document anyway, you will need it to move forward and understand the rest of the events. Then you’ll see it’ s very useful.

leave your soldering iron on for 2 minutes before we start

The assembly of a FX Teacher kit has nothing to do with what you have already found on the net. Indeed, we have developed our own method to assemble your PCB, step by step, and to constantly check its proper functioning! And yes, we are committed to the infallible, but you also have some work to do so.
So, in order for you to understand all the tricks we’re going to ask you to do, I suggest you to start by devouring all of our tutorials, if you haven’t already done so.

Here they are, in order:

Disclaimer : If you’re in trouble with a step or you don’t understand something, we will be happy to help you. For this, leave a comment with your request on this blog post. This project is even so DIY, so it is up to you to make your own decisions and responsibilities, and to check what you are doing before going ahead. You will be answered as soon as possible and this answer will allow other readers to go forward. Don’t be surprised if your comment doesn’t appear immediately, we have to validate it to avoid spam from certain robots. To recap, no emails, no chat, no calls regarding DIY, only requests on comments section please. Otherwise, it’s unmanageable for us.
Please also check that your request has not been treated, also that your tensions are good and that you have followed all the steps 🙂
If you feel that you need to be coached, you can join one of our masterclasses, they are made for you ! 😉

assemble the feed me kit

first bag: the power supply

electronic diagram analysis

the power supply

The diagram starts with the 9V supply going into D1, which acts as a reverse polarity protection. Then we find R9 and R10 which, in parallel form a single resistor of 340Ω. We decided to use two resistors in parallel to make a 1/2W resistor, so that the resistor doesn’t get too hot if the BURN pot is at 0. This resistor will form a low pass filter with E2 and F6, cutting at 1Hz. It therefore only allows the DC voltage to pass, removing any fluctuation or noise that may come from the power supply.
The VA point is the output of the power supply circuit, which supplies the rest of the circuit with a filtered voltage. There is also the LED, with R11 limiting the current, connected to the footswitch.

the crack circuit

In the power supply, there is also the crack circuit, which will lower the supply voltage of the circuit, for a gated fuzz effect similar to a dying battery. When the CRACK switch is activated (to the right on the schematic), R7, R8 and the BURN pot are grounded, making a voltage divider with R9 and R10. The BURN pot allows you to vary the supply voltage from 0 to 3.8V, for more or less velcro fuzz.
When the CRACK is disabled, the circuit is supplied with 9V producing a rich, wide-open fuzz, and resistor R4 is connected to the effect output, attenuating the signal to balance volume differences.

bom and assembly

We start the assembly with bag 1. You can first check that you have all the components.

First of all, let’s make a little reminder about the components, in this bag you have an electrolytic capacitor and a diode, which have a polarity to respect.
For the capa, the + is drawn on the board and it corresponds to the longest leg. Then, for the diode, there is a grey ring drawn near one of the legs, the same ring is represented on the PCB.
For the potentiometer and the toggle switch, you must be careful to put them in BOTTOM, on the other side of the board. The toggle switch must be straight, so that the board fits easily into the case at the last step.

name	value	type	quantity	side	comment
R7	47Ω	resistor	1	top	yellow-purple-black-gold-brown
R11	100Ω	resistor	1	top	brown-black-black-black-brown
R8	220Ω	resistor	1	top	red-red-black-black-brown
R9, R10	680Ω	resistor	2	top	blue-grey-black-black-brown
R4	22kΩ	resistor	1	top	red-red-black-red-brown
F6	100nF	film capacitor	1	top	–
E2	470uF	electrolytic capacitor	1	top	pay attention to the direction
D1	1n4001	diode	1	top	pay attention to the direction
BURN	B5kΩ	potentiometer	1	bottom	put on the other side of the board
CRACK	SPDT on-on	toggle switch	1	bottom	put on the other side of the board

expected result and test

Once bag 1 is soldered to the PCB, your board should look like this. You also need to solder the two black and red wires that will be used to supply the board.

Then, for testing, supply the board with the FX Teacher kit, then simply place the multimeter between the GND and SUPPLY pads, to check that you have the correct voltages.

settings	voltage on supply pad
crack switch on low position	8,32V
crack switch up and burn potentiometer at maximum	3,58V

second and third bag: the fuzz

electronic diagram analysis

The circuit has few components, but it can be quite complicated to understand without explanations. We will therefore decipher it progressively, starting from the input and going to the output, to understand the purpose of each component.

input stage circuit

The FEED allows you to adjust the input level for more versatility than the original model. Lowering the FEED allows you to go in at a lower level to optimize clean up with the guitar’s volume control. Increasing it brings in more input level, for more saturation and sustain. At maximum, it allows the circuit to oscillate, like a famous 5-knob fuzz, thanks to the feedback resistor R5.
Then F3 acts as a coupling capacitor to eliminate the DC content and allow only the audio signal to pass through. But it also acts as a high pass filter with R5, cutting off anything below 7.2Hz. We chose a cut-off frequency below the audible threshold to keep as much bass as possible, but by lowering the value of F3, we can cut some basses, for a more punchy and screaming fuzz.

gain stages

Then there are two successive gain stages with Q1 and Q2. To begin the analysis, the influence of R5 in the circuit is ignored first.

The first stage is a common emitter configuration: by connecting the emitter of Q1 directly to ground without a resistor, the gain of this stage is huge, saturating the signal.
R6 sets the gain and bias of Q1. In pure theory, the optimal bias is at VCC/2 = 4.5V, but here the 33k value gives a much lower bias, producing a very asymmetric clipping which is typical of fuzz, for a more pleasing musical result.
On the second stage Q2, the gain is lower, being equal to (R3+BIAS)/FUZZ. The FUZZ trimpot therefore varies the gain of the second stage, producing hard clipping.

There are also three capacitors. C1 and C2 are Miller’s capacitors, connecting the base and the collector of the transistors to avoid high frequency noise and interference, which the circuit could pick up because of its huge gain. To avoid the fuzz that picks up the radio!
F1 is used to attenuate some of the high frequencies, and adds a warmth similar to what you might get using germanium transistors.

Finally, resistor R5 generates a feedback loop, reinjecting a part of the output signal to the input of Q1. This technique reduces the overall gain of the circuit, and above all allows the circuit to compensate for any variations in gain and noise, for a more stable fuzz. But by lowering its value, it also allows the circuit to enter into self-oscillation, for feedback effects controllable with the guitar volume. The FUZZ trimpot also allows you to control the level of the signal reinjected by R5, also affecting the overall gain of the circuit.

output stage

As the voltage gain of the circuit is huge, if we connected the output directly to Q2, the output volume would be way too high and unusable. So we take the output in the middle of a voltage divider formed by R3 and the BIAS trimpot, lowering the signal to the correct volume.

Next we find a bandpass filter formed by F2, R2 and F5. The F2 capacitor allows to cut the bass, and it is thus on this capacitor that we will act with the BASS switch and the terminal block. A value of 220nF lets all the basses pass, but a smaller value will cut the them. F2 also acts as a coupling capacitor, once again to eliminate the DC signal.
F5 cuts the high frequencies. The basic value of 100nF lets almost everything pass, but a higher value will cut the highs even more. Finally, the LEVEL potentiometer adjusts the output volume of the pedal.

bag 2 bom and assembly

We can start assembling bag 2, which contains the first half of the components for the fuzz circuit. Again, pay attention to the polarity of E1, and also the orientation of transistors Q1 and Q2.

About the trimpots, sometimes the value is clearly indicated, but sometimes it is not. If it is not indicated, there are always 3 digits that allow to determine it: the first two indicate the value, and the last one the exponent, or the number of zeros you have to add to read the exact value. For example, for the Feed Me, 102 means 10×10^2 = 1000 = 1kΩ, and 203 = 20×10^3 = 20000 = 20kΩ.

name	value	type	quantity	side	comment
R3	1,2kΩ	resistor	1	top	brown-red-black-brown-brown
R6	33kΩ	resistor	1	top	orange-orange-black-red-brown
R5	100kΩ	resistor	1	top	brown-black-black-orange-brown
C1, C2	100pF	ceramic capacitor	2	top	–
F1	33nF	film capacitor	1	top	–
F3	220nF	film capacitor	1	top	–
E1	22uF	electrolytic capacitor	1	top	pay attention to the direction
Q1, Q2	BC108	transistor	2	top	pay attention to the direction
FUZZ	1kΩ	trimpot	1	top	–
BIAS	20kΩ	trimpot	1	top	–

expected result and test

Once this step is finished, this is what your PCB should look like. We’ll go directly to bag 3, then we’ll do the tests and adjustments at the end of this bag.

bag 3 bom and assembly

Pay attention to the orientation of the terminal block, the holes for the capa must be pointing upwards, so that the capa fits in the empty space in front of the terminal block. Also pay attention to the toggle switch and the potentiometers, which must be placed in BOTTOM, on the other side of the board. The toggle switch must be placed straight, so that the board can be inserted into the enclosure without any effort.

name	value	type	quantity	side	comment
R2	100kΩ	resistor	1	top	brown-black-black-orange-brown
R1	1MΩ	resistor	1	top	brrown-black-black-yellow-brown
F5	100nF	film capacitor	1	top	–
F2	220nF	film capacitor	1	top	–
BASS	DPDT on-on	toggle switch	1	bottom	put on the other side of the board
FEED	B100kΩ	potentiometer	1	bottom	put on the other side of the board
LEVEL	A500kΩ	potentiometer	1	bottom	put on the other side of the board
CAPS	terminal	terminal block	1	top	pay attention to the direction
CAPS	6,8nF	film capacitor for the terminal block	1	–	screwed into the terminal block

expected result and adjustments

At the end of this step, this is what your board should look like. If everything is good, then we’ll proceed to the trimpot adjustment!

For the settings, take a small screwdriver and your multimeter. We start with the FUZZ trimpot, just turn it all the way up, that’s how the fuzz works the best! The gain can be controlled with the FEED and the volume of the guitar, but you can always lower it later if there is too much gain for you.

For the BIAS trimpot, set the CRACK toggle switch down, and insert the voltmeter between the BIAS and GND pads. Then turn the BIAS trimpot until the voltmeter measures 5.1V. This is the bias setting for the original Feed Me sound, and it is usually between 2h and 3h on the trimpot.

sound check

After the trimpot adjustments, you can do an audio test before putting the kit in the enclosure, to make sure everything works. There are special holes for the alligator clips of the FX Teacher kit, these are the footprints with the octagonal pads. You have the pads to connect the two grounds, the IN and the OUT.

If you want to go deeper into the analysis and understand how the Feed Me modifies the guitar signal, you can also connect the FX Teacher kit to your audio interface and visualize the output signals with Audacity, you have all the details here.

dynamic response with the feed setting

A first analysis to show the influence of the FEED on the dynamics of the fuzz. The blue signal is the input signal, a sine wave that increases in amplitude to simulate a progressively stronger attack. The grey signals show 3 output measurements, with the FEED almost at minimum, at noon, and at maximum.

With the FEED turned down, we can see that the fuzz reacts extremely well to dynamics: with a soft attack, the output signal is almost unchanged and still looks like a sine wave. With a harder attack, the signal saturates and clipping occurs, resulting in a square signal.
When the FEED is increased, the signal saturates even on soft attacks, which makes the signal less dynamic and more compressed.

the gated fuzz with the crack switch

We use the same input signal in blue, with an increasing amplitude, then we visualise 3 signals in grey. The first one with the CRACK off, then the two others with the CRACK on, and the SMASH at maximum and then at half.

When CRACK is activated, the circuit is underpowered, changing the bias of the transistors. The result is a sharp cut-off on one of the two half-waves of the signal, causing a very asymmetrical clipping. With a soft attack, the signal doesn’t have enough amplitude to pass through, causing this gate effect with limited sustain, and the very asymmetric signal is at the origin of this typical velcro fuzz sound.
SMASH turned down, the supply voltage is reduced even more, accentuating the gated fuzz effect.

the bass switch and bandwidths

Last analysis with the frequency response of the pedal. The BASS switch will allow you to modify and cut the low frequencies, to go from a rich and fat fuzz to a punchy and bright fuzz.

Switch at the low position, the terminal block is disabled and a 220nF capacitor soldered on the PCB allows all the bass to pass through. Switch on the upper position, the capacitor mounted in the terminal block will change the cut-off frequency, smaller values cutting off more bass.

final assembly

Does your board work perfectly? Congratulations, we can finally move on to the final step! You can also check out this article for more details on the assembling process.

The footswitch terminals

First open the true bypass bag, to get the male pins connectors. Don’t worry about the rest of the bag for now, we’ll install the footswitch at the end.

Be careful, we made a little update of the footswitch. If you have an old version, you must have two rows of 4 male pins, but if your model is recent, you must have a single 2×6 pins male connector, as shown in the next two pictures.

Place the pins on the TOP side of the PCB as shown in the picture, inserting the shorter side into the board, leaving the longer side exposed. Then solder them straight and flat on the board.

the audio jacks

Start by soldering the IN and OUT jacks, but don’t solder the power jack, we’ll do it when we put the board on the enclosure.

For the input, the black wire already soldered on the board goes on the bevelled side of the jack. Then solder the white wire between the TIP of the jack and the IN pad of the board. And finally a black wire on the RING of the jack, as on the picture. This configuration allows to disconnect the power supply of the circuit by isolating the ground if no jack is connected to the input of the pedal.
For the output, we only connect a green wire to the TIP, which goes to the OUT pad of the board. No ground wire, it already runs through the metal enclosure, and so we avoid a ground loop that could pick up noise.

insert the board into the enclosure

Once the jacks are soldered, it’s time to put the board in the enclosure! Check the washers and nuts before inserting the board, you should already have a nut screwed on each potentiometer, so that they are at the same height as the toggle switches. Everything else will be used to assemble the pedal.
You can insert the board into the enclosure, then fix it, by putting a washer and a nut on the pots, and only a nut on the switches.

Before screwing the IN and OUT jacks, we will first solder the power jack. Leave it screwed to the case, otherwise you won’t be able to put it on once soldered. The red wire goes on the longest lug, then the black wire on the other one, and solder directly into the enclosure.

Finally, you can screw the IN and OUT jacks, with one washer and one nut per jack.

the bypass

You are almost finished! You can now assemble the true bypass kit. Again, the pcb of the footswitch has been updated, so follow the correct steps depending on the model you have. If you have a footswitch with a 2x6pins connector, go directly to the “assembling the bypass, new kits” step.

assembling the bypass, old kits

Pay attention to the orientation, there is a footprint for each component on the correct side, the footswitch and the resistor are not on the same side. For the footswitch, the horizontal lines indicate the orientation of the pins. Insert the footswitch in the small pcb as far as possible and straight, as on the picture on the left.

Finally, once assembled, place the true bypass kit into the pedal, leaving a nut on the footswitch. Pay attention to the direction, the resistor of the true bypass must be pointing downwards, and once in place, the pins must pass through the pads on each side of the true bypass kit. Then screw the footswitch to the enclosure to hold it in place, then you can finally solder the pins!

assembling the bypass, new kits

For the pcb of the new footswitch, you still have the footprint that indicate the position of the footswitch and the resistor. Be careful to respect the direction of the pins of the footswitch, there are horizontal lines on the footprint that indicate the orientation.

For the footswitch, this time you just have to push it in just a little, so that it is raised and the pins are leveled with the other side of the pcb, like on the pictures.

You can then solder the resistor, the 2×6 female connector, and the footswitch, making sure that everything is straight.

Finally, you just have to insert the white plastic washer and the first nut on the 3PDT, then you can insert the bypass into the pedal, fixing it to the enclosure with the second nut you have left!

you have just finished assembling your feed me!

You’ve finally done the assembly of your Feed Me! Now all you have to do is plug it and check that everything is working properly. Then experiment with the settings, and the 3 extra capacitors supplied to place in the terminal block, to change the bass response of the pedal!

name	value	type	quantity	comment
CAPS	4,7nF	film capacitor for the terminal block	1	screwed into the terminal block
CAPS	10nF	film capacitor for the terminal block	1	screwed into the terminal block
CAPS	22nF	film capacitor for the terminal block	1	screwed into the terminal block

We hope that everything went well for you, and if you have any problems or questions, you can post them in the comments below. Maybe you can find some help by reading them, or ask your own question.
Have fun with your new fuzz, and see you soon for new kits!