Analogman sunface DIY clone #2

As I was curious, I decided to build another analogman sunface with the NKT275 red dot transistors I got. However, whereas my first Sunface used a veroboard, I decided to use a PCB. The layout I used for this was conceived by Scruffie, and uses a voltage inverter with a MAX1044. A very ingenious system allows you to switch the power off when you unplug the input jack, very useful with 9V battery. However, as the enclosure I used was quite small (1590B from Hammond), I did not have space left for a battery so I decided to go full power supply. Which is also more practical for a pedalboard stompbox that you are not going to move a lot. And with the voltage inverter, any 9V boss like power supply is perfect! I used a 3PDT PCB. It is very practical, and most of all, really really neat looking. I really paid attention to the wiring this time and try to make the cables as short as possible. I am really happy with the result, it is really nice looking inside.
I decided to make a simple yet classy look with an aluminium faceplate and a laser engraved logo. The logo were engraved by HPM laser, very helpful and affordable! On the faceplate, I drilled the holes for three potentiometers and I engraved letters (I painted the letters with black ink after engravement). F = fuzz, V = volume and B = bias of course. I am really happy with the result.

As I was planning to sell it, I also got some "boutique kit accessories" like a small cotton bag I got on amazon and stickers that I got from Moo. Used this link to have a 10% discount: http://uk.moo.com/fr/share/#8srxpd .

 

HOW DOES IT SOUND?

I made a small video to test my camera. It is not the best sounding demo ever (I do not have the gear necessary to record proper demos...) but it can give a quick idea of how the pedal is sounding. Do not mind the string noise please! I will remake a proper video when I will have a bit more time. For me, this guitar pedal sounds very good, plenty of low end, and very sensitive to the guitar volume knob.

HOW DOES IT WORK?
It is the same circuit as the Sunface, with the bias knob. I already wrote a post about the Sun Face circuit, you can find the Fuzz Face circuit analysis here. The PCB follows the same layout.
However, the power supply section is modified to accept a +9V classic power supply (finally!). For that, it uses a MAX1044 integrated circuit, which can invert the supplied voltage. Here is the schematic that we can find on the datasheet:

Just a few words about datasheets: they are like ID for components. You can find datasheets on the supplier's website (for instance Wima if you are looking for the Wima MKP2 capacitor's datasheet). All the characteristics of the component are written in the datasheet. Thus, it is really useful to look for the datasheet if you miss something about one component (exact size for PCB, max voltage...)

The voltage enters the chip through the V+ pin (number 8), and goes out inverted through the number 8 pin. The pin number 3 is connected to the ground, and a 10uF capacitor is connected between the cap+ (connected to the + lug of the cap) and cap- (Guess which side of the cap ^^). A 10uF is connected to the ground near the output voltage.

The power supply can be also a bit improved with a simple layout that you will find in many stompboxes. It is present in Scruffie's layout (without the 0.1uF capacitor)

 

The diode connected to the ground protects the circuit from polarity inversion. Indeed, the diode only let the current goes through in one direction (following the arrow of the scheme of the diode). So if we plug a classic center negative power supply, the ground will be 0V, and +9V will be +9V. No current will go through the diode. However, if we plug a center positive power supply (which can happen with fuzz faces that usually need center positive power supply), the ground will become +9V, and the voltage will be the ground! In a normal context, this would damage the components, and specially the transistors... However, here, the current will go through the diode straight to the +9V (ground), avoiding such trouble (quite annoying with NKT275 transistors, which worth almost 30 euros!)

The 100 ohm resistor, combined with the 47uF and 0.1uF capacitors eliminate all the residual oscillations that come from the power supply. Indeed, when the current is converted from alternating to direct, some ripples can still be there. As the capacitors only let the alternating current go through them, the alternate current will go to the ground instead of parasiting the circuit and generating "hum" noises! The different values of the capacitors are here to eliminate high and low frequencies of alternating current.

In the end, with this simple layout, we get an input voltage more stable (less noise), and a protection if someone plugs in the wrong power supply (center positive instead of negative). Which can happen with Fuzz Faces!

I hope that everything is clear! If not, post a comment!

To go further:
Geofex from +9V to -9V: an ingenious system to use the battery only when a jack is plugged in.