150 watt QC AMPLIFIER USING NPN POWER TRANSISTORS

---

New version of our 150 watt Hifi Quasi Complementary ( Only NPN Power Transistors ) Amplifier. 

More Robust Drivers and Improved PCB Design.

Compatible Power Transistors - 2SC5200 / 2N3055 / 2N3773 / TIP35C / NJW0281G

• High Output  -  150 watt Max  Dynamic output power .
• Very Low Distortion - 0.01% Total Harmonic Distortion at 60 watt power output.
• Speaker usability - 4 & 8 ohms, 50 watt to 200 watt speakers can be used with this amplifier.
• Broad supply voltage -  ±18 volts to ±35 volts DC supply working range. 
• Standard components - All components used are available online or at your local electronics store. 
• No SMD components - Only through hole components used, making soldering and replacement hassle free.  
• Cost effective - This amplifier can be made in a fraction of cost compared to similar amplifiers available in market. 

                                                                       Click Here  to download 150 watt amplifier circuit diagram 

Input Stage  

Input stage works as a  transconductance amplifier ( voltage in - current out ).

This stage consist of Long Tailed Pair (LTP) made of Q1 & Q5, working in differential mode. constant current flows from Constant Current Source (CCS) made of Q2, collector current of LTP is balanced by Current Mirror (CM) made of Q3 & Q4.

In simple words input signal is amplified by the input pair Q1 & Q5, current amplified input signal is sent to VA Stage for voltage amplification.

Voltage Amplification Stage ( VAS )

As the name suggests all the voltage GAIN of the amplifier is achieved in VA Stage.  

VAS of this circuit is Darlington ( Beta Enhanced ) so low GAIN transistors can be used.

Signal received from input stage is amplified via Darlington pair Q6 & Q9. Constant current flows from CCS made of Q7. 

Biasing circuit is made of Q8, preset RV1 is to adjust output stage biasing voltage. 

it is important to note that the biasing transistor Q8 must be mounted on the same heatsink along with Output transistors to ensure thermal tracking. 

In simple words signal received from input stage is amplified by Q6 & Q9. voltage amplified signal is sent to output stage.

Output Stage ( OPS )

This circuit has Class B output stage, so each half of the signal is amplified by each  NPN output transistors.

Driver Transistors Q10 & Q11 work as buffer to prevent excessive loading of VAS as well as to provide input to the output transistors Q12 and Q13 respectively.

Output Topology is Quasi Complementary with Baxandall Diode, thus NPN transistors are used as power output devices.

Thermal feedback via transistor Q8 and correct bias voltage adjustment via preset RV1 is necessary to prevent output transistors from destruction by thermal runaway. 

 Negative feedback via R11 to the base of Q5 ensures overall amplifier performance and stability. 

Zobel Network -  made of R24 & C9 provides protection against high frequency oscillations.

In simple words signal received from VAS is given to the output transistors via driver transistors. output transistors conduct high current to drive the speakers in accordance with signal.

• 3 Stage Class AB amplifier 
• INPUT -  Long tailed pair with Constant current source and current mirror
• VAS - Darlington VAS with biasing control preset, biasing transistor mount on main heatsink.
• OPS - Quasi complementary NPN transistor power output Pair.

• Input Sensitivity - 500mV to 3V ( Peak to Peak)
• GAIN - 26.8dB  ±0.1 dB 20 - 20 KHz
• AC Stability -  720 KHz
• Noise at Output - 135nV/Hz1/2

  Power output at various Supply Voltages -  

• 12v - 0 - 12v  = 20 Watt 
• 18v - 0 - 18v  =  40 Watt 
• 24v - 0 - 24v  =  80 Watt (Recommended)
• 35v - 0 - 35v  =  150 Watt (High heat )

  Standard Test configuration for output power measurement - 

• 2SC5200 transistors
• 1Khz Sine wave input signal
• 4Ω 800 Watt Load Resistors

• Type of PCB  - Single sided, Glass Epoxy FR-4 Grade A  
• PCB Size - 99 mm x 70 mm (3.9 inch x 2.7 inch ), pcb Thickness - 1.6 mm.
• Thickness of copper on PCB - 35 micrometer 

PCB designed with thick copper tracks & large solder pads to facilitate straightforward  placement and soldering of components. 

     Transistors  

• Q1, Q2, Q5 - 2N5401, MPSA92, MPSA93

• Q3, Q4, Q6 - 2N5551, MPSA42, MPSA43

• Q7                   - BD140, MJE350, 2SA1220,

• Q8, Q9          - BD139, MJE340, 2SC2690, 

• Q10               - 2SC2073, 2SC4793, TIP41C, MJE15028-30-32

• Q11               - 2SA940, 2SA1837, TIP42C, MJE15029-31-33

• Q12, Q13       - 2SC5200, 2N3055, 2N3773, TTC5200, 2SC5200N, NJW0281G, TIP35C

            * - Always use complementary NPN-PNP pairs.