Befaco Quad-T Assembly Manual

Quad-T assembly manual:

This module has four equal parts (four oscillators type twin-T), the drawing of the PCB is intentioned for an easy
assembly procedure by symmetrizing two groups of oscillators taking the central axis by normal, and themselves
symmetric around the line at 45º and 135º respectively. On this way once you find one component in one of the parts is
easy to find his simile on the other tree portions. Finally in the middle we can find a transistor amplifier who can
saturate the audio signal, on this way we can produce natural percussive sounds (avoiding saturation) or a more
aggressive sounds by increase the level of the sum at the amplifier input.

Part list:

Resistors:

Cant. Value Code Name on PCB

8 2K2 Red, red, red gold R3, R11, R50, R55, R8, R21, R40, R53

4 2M Red, black, gren, gold R9, R19, R42, R52

1 3K3 Orange, orange, red, gold R30

4 6K8 Blue, gray, red, gold R1, R22, R38, R60

4 10K Brown, black, orange, gold R6, R10, R51, R58

4 22K Red, red, orange, gold R14, R18, R43, R48

5 47K Yellow, purple, orange, gold R13, R29, R31, R32, R49

12 100K Brown, black, yellow, gold R5, R7, R15, R17, R24, R25, R36, R37, R45, R46, R54, R56

1 110K Brown, brown, black, orange, brown R33

4 270K Red, purple, yellow, gold R2, R12, R47, R59

1 470K Yellow, purple, yellow, gold R28

Pots:

4 5K 502 blue R16, R23, R39, R44 – multi-turn potentiometer

4 200K ó 100K 204 ó 104 white or black R20, R26, R34, R41 – 1 turn potentiometer

Condensers:

Cant. Value Code Name on PCB

1 560pF n56 or 561 C4

4 1uF 1uF C7, C8, C27, C28 (electrolytic check polarity before

2 2,2uF 2.2uF C17, C18 solder it, long leg = + )

4 10nF 103 C6, C10, C25, C29

12 330nF 330n C5, C9, C11, C16, C19, C24, C26, C30

The ones labeled as: C1, C2, C3 - C13, C14, C15 - C20, C21, C22 - C32, C33, C34 (rounded by a white box) are the
determinant of the tune of each sound, we will put here a PIN in order to choose the tune of them.

Actives:

9 BC546A Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9 – transistor, put them according to the drawing on PCB
1 LED3MM D1 - LED diode, check polarity, long leg = +

Electro-mechanical:

1 Sw1 Slider switch (on/off)
1 X1 3.5mm jack socket

In the middle of the PCB we will put the CR2032's clip, in bottom over the spots the six rubber feets.

The blue pot adjust the 'release' of each sound, this release also depends on the pitch, so if you want to change the pich
after you will need to adjust again the desired release.

The procedure for release adjust is the next: connect an amplifier (and his speaker) to the Quad-T, touch the sensor like
if you want a regular percussive use, you should hear a 'click' every time as you use the sensor, if not use the volume
(black or white pot) until you hear it, now turning the blue pot the 'click' will become more in tune for every turn until it
oscillate permanently, go back a bit, the exact point depends on the individual taste. After this we can adjust the amount
of distortion in the amplifier stage by turning the volume (black or white pots), note that the volume adjust also changes
the release as a normal response of this kind of circuit.

The condensers supplied for the tunning is this:

C1,C2 3,3n
C3 4,7n - higher pitch

C14,C15 15n
C13 22n

C20, C21, C32 33n

C22 100n
C33, C34 27n – lower pitch

Finally with the spacers screws and nuts we will put the plastic cover on top

Note: the sensor is a resistive piece, is based on the conductive capacity of the skin, this is very changeable from person
to person, in some cases the sensor wont be able to sense you at all, if is your case you can moisture (not wet) a bit you
finger before play. It also work with 'piezo' sensors, can be attached very easy to the provided pads in the left and right
and they will be sensitive to pressure. Also a 3V gate or trigger will make the circuit works.