Kunthrandum 3.2 - opamp based extremely low distortion audio power amplifier<

Kunthrandum ver. 3.2 - opamp based
extremely low distortion audio power amplifier

Fig.1 : Kunthrandum schematic diagram
NOTICE: This project now have some Major updates.. including the PCB design.. I'll post it here as soon as it gets finished.. DO NOT FOLLOW THE ABOVE GIVEN DIAGRAM... ITS OUTDATED. please come back later...

Please read this also... (That will help speeding up things..)

Description:

Kunthrandum is an extremely low distortion audio power amplifier. According to the LTspice simulation results, this circuit produces 0.00001% Total Harmonic Distortion at full power output with the opamp LT1810 from Linear Technology. It is a simple straight forward design with two opamps in the input stage to solve the non-linearities in the class-AB MOSFET power output stage. The quality of the output is highly dependent on the opamps used, the better the opamp the better the waves at the output will be. There are many good opamps available arround to taste with this circuit.. try Linear Technology LT1810, LT1469, LT1122, Analog Devices AD8599, AD823, Burr-Brown OPA2134 etc.

When you are turning it on for the first time... do it like this:

Set the 'quiescent current adjust' preset to the middle (not zero).
Connect voltmeter across one of the MOSFET source resistors.
Connect input to ground and output to a dummy load of 8ohm(1/4 watt) resistor.
Turn on the power supply. (always use fueses..)
Adjust the 'quiescent current' voltage so that meter reading is between 30mV-100mV. (ie. 30mV / 0.5ohm = 60mA)
Wait 5-10min for the amp to heat up and check whether the current is stable. If it is increasing rapidly, lower the preset.
Set the current somewhere stable above 100mA (depends on your heatsink size).
If the dummy survives with no damage, the amp is ready to test with a speaker.
Keep the meter connected and play some music... and watch the readings as long as u can.

Quiescent currents between 100mA and 250mA is better, a big heatsink and a strong power supply is highly recommended. Go for higher quiscent currents if you can provide forced air cooling. When the output current is below quiscent current the amp works in class-A region, and produces extremely low distortions, reaching near the op-amp specifications. I've been able to set the quiescent current as high as 800mA with a cooling fan attached to the heat sink.

Note: In an amp with +/-50v power supply, when the output is at 10V :

the voltage across the MOSFET is 40V.
current though the circuit = 10/8 = 1.25A
power to the load = 10 x 1.25 = 12.5W
power dissipated at MOSFET in the form of heat = 40 x 1.25 = 50W ...!
at 25V it reaches the maximum, 78Watts... heat.

I'm utter much sure that I won't be the one to enjoy the real quality of this amp.. when there is someone else to try building this amp.. and as he/she have reach to much better components than I use here.. most importantly the one via which it all comes out... the speaker system... :)

Components List:

R1 = 2k2
R2 = 22k
R3 = 1k
R4 = 33k
R5,R6 = 100k
R7,R8 = 10k
R9,R10 = 2k2
R11,R12 = 10k
R13,R14 = 470
R15,R16 = 100
R17,R18 = 100

R19,R20 = 0.22
R21,R22 = 0.47
R23,R24,R25 = 10k
R26 - R30 = 2k2
R31 = 100k
R32 = 1k

C1,C2 = 47uF
C3 = 0.47uF
C4 = 47uF
C5,C6 = 220pF
C7 = 0.1uF
C8 = 470uF

D1,D2 = 1N4148
Q1,Q4 = BC548
Q2,Q3 = BC558
Q5 = IRF9630
Q6 = IRF630
U1,U2 = TL072
U3,U4 = TL072

Reference:

1. International Rectifiers HEXFET Application Notes.

Tips:

1. Use fuses wherever they are needed..!
2. Try high quality opamps like Linear Technology LT1810, LT1469, AD8599, AD823 or OPA2134.
3. Minimize lead and track lengths of decoupling caps to reduce noise.
4. Use polyester caps in parallel to electrolytic coupling caps.
5. Use thick wire for power and speaker lines.
6. Do not operate this amp near seismographic monitoring stations.
7. Keep coming back to this site to check for updates or corrections.
8. Pleeease Donate. And feel free to e-mail me.

Thanks to Linear Technology LTspice... which with kunthrandum is developed.