Building directions
Build in small pieces and then test
The experience solder everything in no particular order but if the board is hand soldered, then wait to the big electrolytic caps to the last.
The less experenced is recommned to divide the completion in steps.
Test supply voltage is +- 15 V.
Reference voltage
Solder Q1, Q3, Q5, R4, Q6, Q4, Q2, R1, H1-H4, R14, R15, Q17-Q20.Then apply +- 15 volts. Measure that you have 0.6 volts between base and emitter on each transistor. Measure across R14 and R15, should be 1.0-1.2 V (= 500 µA). The total current of the LED bias should be 1.0-1.2 mA.
PNP emitter follower
Solder R7, Q7, Q9, R9 and Q11. Turn on the power. Tie the input to ground. Measure that the emitter voltage to ground at Q11/Q12. Should be 0.60-0.65 V. Measure the voltage across R7. Should be 0.60-0.65V. Voltage across R9 = 25-27 mV.
NPN emitter follower
Solder R6, Q8, Q10, R8 and Q12. Tie the input to ground. Turn on the power. Measure that the emitter voltage to ground at Q12. Should be 0.60-0.65V. Measure the voltage across R6. Should be 0.60-0.65V. R8 = 27 mV.
Remove the short to the input. Measure the voltage over R1. Should be less then ±500 mV. This is a random voltage due to the ratio between the current gain Hfe in Q11 and Q12
Output stage
Solder Q15, R11-R13, Q16. Tie the input to ground. Turn on the power. Measure the output voltage. Should be ± 0-10 mV's. Measure the voltage across the R11-R13. Should be 20 mV. Load the output with 1kohms. Measure now the same thing.
Big bang method
Start in this order, most practical. Start with small parts then finish with big caps and wires.
- Transistors, the small ones SOT23
- Resistors
- Capacitors, not the electrolytic ones
- Transistors, the big ones SOT223
- Then continue with the high electrolytic caps
- Wires