Citation 12 MOSFET Power Amplifier

FEATURES

1. Design reference to the Harman-Kardon Citation 12 classic power amplifier circuit as blueprint and circuit modified as reference to Nelson Pass
2. Maximum output power can reach 75W for 8 ohm output loading
3. High precise MOSEFT IRFP240
4. Built-in voltage regulating circuitry, come with Nichicon Muse for power filtering capacitor
5. This kit use WIMA 0.1uF/400V as bypassing capacitor and Dale resistors

6. PCB dimension: 10mmx14mm, 2.5mm thickness and 2oz copper

Optional: Toroid Transformer T200 200W (for two channels)

ASSEMBLY GUIDE

1. Assembly all the components according to the schematic and part list (which can be downloaded in this page)

2. Open the bypass jumper J3, J4, J12 and J13 before switch on power.

3. Apply two 27V AC to J1 and J2. ~33V DC is obtained for the filtering capacitor C1, C3, C5, C7, C9 and C11 and ~-33V DC is obtained fo the capacitors C2, C4, C6, C8, C10 and C12. This step is to ensure the power supply block work well.

4. Remove the power supply and discharge the capacitors (short by a 10ohm/2W resistor to ground). Open the bypass jumper J3 and J4 and short the J12 and J13 by wires, power supply is now in series with the 10ohm/2W resistor to limit its maximum current supply to the circuit in case of any components burnt out (This step important!). Also, large heat sink is required to drain out the heat generated by two power MOSFET. The MOSFET is very hot, dont use figure to touch it!

5. The R16 and R21 is used to measure the biasing current of the output stage (high biasing current mean high output driving current and hence higher output power). At the beginning, the resistor trimmer RV1 is set so that the biasing current is as small as possible to prevent burnt out of MOSFETs due to high current (turn it until it reach the most anti-clockwise position)

6. Turn on the power supply. Disconnect the power supply when you see any smokes, lighting or smell any burnt. Ensure the resistor trimmer is set in the correct position.

7. Measure the voltage across the 10/2W resistors (J3 and J4), the biasing current can be calculated by the following equation:

I = V/ R = V/10

Gradually turning the resistor trimmer VR1 until the biasing current I reach to 75mA - 100mA (V=1V). Again, higher biasing current, higher output power, but I=75mA is suggested. (Disconnect the power supply if see there is any smokes)

8. Short J3, J4, J12 and J13 by wires। Everything is finished and enjoy it!