400w Hi fi Mono Amplifier PCB 1 nos
Retail Price Rs 249.00
Offer Price Rs 189.00
Assembled and Tested 400w Amplifier Board
Retail Price Rs 1449.00
Offer Price Rs 999.00
This High power amplifier is liked by amateurs as well as professionals.
We revised the pcb 4 times so far based on customer feedback and our own testing.
The latest version is smaller in size and with metal tab connectors to support high currents.
For MOSFET version of this amplifier CLICK HERE
CLICK HERE to download 400 watt hifi amplifier circuit diagram
Input stage works as a transconductance amplifier ( voltage in - current out ).
This stage consist of Long Tailed Pair (LTP) made of Q1 & Q5, working as differential amplifier.
Input signal received at the base of Q1 is amplified and sent to VAS from collector. Negative feedback (NFB) received at the base of Q5 from output determines overall gain and balance of the amplifier.
Constant current is supplied to the LTP by Constant Current Source (CCS) made of Q2.
Collector currents of LTP transistors is balanced by Current Mirror (CM) made of Q3 & Q4.
In simple words input signal is amplified by the input pair Q1 & Q5 and sent to VAS for further amplification.
Voltage Amplification Stage (VAS)
As the name suggests, all the voltage gain of the amplifier is achieved in VA Stage.
The VA stage is Darlington (Beta Enhanced) which has better performance then single transistor VA stage.
Signal received from input stage at the base of Q6 is amplified via Darlington pair Q6 & Q9. Voltage amplified signal sent to the base of driver transistor Q11 from the emitter of Q9.
Constant current is supplied to VAS from CCS made of transistor Q7.
Biasing circuit is made of transistor Q8, which works as voltage divider. With preset RV1, base current of output transistors can be precisely adjusted.
Important to note that the biasing transistor Q8 must be fitted on the same heatsink along with output transistors to ensure thermal tracking and feedback.
Sample Video showing process of fitting amplifier board on heatsink.
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 pair of NPN and PNP output transistors.
Driver Transistors Q10 & Q11 work as buffers to prevent excessive loading of VAS and also provide input to the output transistor pairs of Q12, Q14 and Q13, Q15 respectively.
Thermal feedback via transistor Q8 is necessary to prevent output transistors from destruction by thermal runaway.
Zobel Network - made of R30 & C10, 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 load.
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Output power at various supply voltages -
Standard Test configuration for output power measurement -
PCB designed with thick copper tracks & large solder pads to facilitate straightforward placement and soldering of components.
* - Always use complementary NPN-PNP transistor pairs.