Monday, 5 September 2016

Klon 3v3 Clone: Schematics and PCB layout

Klon 3v3 Clone Schematics

Klon 3v3 Clone schematics have been implemented using Eagle CAD. Op-amps used are TI LME49721, they are low-distortion, low-noise Rail-to-Rail Input/Output that can be powered between 2.2 and 5.5V. Passive values, resistors and capacitors have been changed to adapt to the power supply change from 9V to 3.3V, many of them have been multiplied by 3 and some of them adjusted to achieve a similar signal in all op-amp stages. Top gain potentiometer series resistor has been splitted into R4 and R5 on both sides of the potentiometer to avoid the low gain value obtained when this potentiometer is set to minimum. filter components around bottom gain potentiometer have been obtained by multiplying by 3 the original values.
Clipping diodes D1 and D2 are 1N34A germanium, they are not part of the BoM since they cannot be found through big distributors, specialized guitar pedal shops can stock them.
Gain resistors R7, R19, R23 have been tuned during simulations to obtain a similar saturation to original circuit on each stage, and then tweaked again on real circuit by ear. Note that values that appear in the BoM are those used on simulations and are lower than the final used values.
1nF capacitor C24 has been added for better circuit stability.

The 9V to 3.3V DC-DC converter is an integrated step-down controller TI TPS62122 in a tiny WSON-6 package. R29-R30 resistors set the FB reference voltage to get 3.3V on the output. A 22uH L1 inductor is required for the switching regulator. Switching frequency is as high as 800kHz, far from audible frequencies, but an additional LC filter, L2 100nH, C22 1uF has been added to reduce output ripple. recommended C19, C20 input output decoupling capacitors have been added to input and output respectively.

Mid 1.65V reference voltage for op-amps bias is generated by LM4041 reference voltage IC.

FB1-FB2 BLM31PG121SN1L are 120ohm ferrites to filter input and out signals respectively

9V input power supply is filtered using CF1 Murata NFM3DPC223R1H3L 22nF EMI filter.

D3 is an input power protection for inverted voltage.

The Klone 3v3 Clone BoM can be found on this link. Please review it before buying the components. Components used are SMD 0402 whenever possible.
Klon 3v3 Clone Eagle CAD Schematics

Klon 3v3 Clone PCB layout

Circuit has been implemented on a 54 x 54 mm 2-layer PCB that fits into a 1590B enclosure. 3.3V power supply is routed as a plan on top layer, and GND is routed as a plan on bottom layer.
Klone 3v3 Clone PCB layout: Top layer
Klone 3v3 Clone PCB layout: Bottom layer

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