Building directions

Patch for board Revision 0.

The new boards have unfortunately two errors.

Top side

Top side patch

The base of Q9 needs to be connected to the base or collector of Q5.

Solder side, bottom side

 Solder side patch

The base the collector of the Q6 needs to be connected to the base of Q10. The pcb is seen from the bottom side.

Building instructions for the prototype boards

Since the board isn't debugged yet, build in small pieces and then test

Test supply voltage is +- 15 V.

Reference voltage

Solder Q1, Q3, Q5, R4, Q6, Q4, Q2, R1, R2, R3. Then apply +- 15 volts. Measure that you have 0.6 volts between base and emitter on each transistor.

PNP emitter follower

Solder R7, Q7, Q9, R9 and Q11. R5, a tin blob. Tie the input to ground. Measure that the emitter voltage to ground at Q11. Should be 0.6V. Measure the voltage across R7. Should be 0.6V. R9 27 mV.

NPN emitter follower

Solder R6, Q8, Q10, R8 and Q12. Tie the input to ground. Measure that the emitter voltage to ground at Q12. Should be 0.6V. Measure the voltage across R6. Should be 0.6V. R8 27 mV.

Output stage

Solder Q15, R11-R13, Q16. Tie the input to ground. Measure the output voltage. Should be i mV's. Measure the voltage across the R11-R13. Should be something. Load the outout with 1 kohms. Measure now the same thing.

This design is very easy to build. You should start with all low SMD parts. Solder in the electrolytic caps at last. For this solder job I recommend a good pair of tweezers. I use a type especially made for SMD. With this pair of tweezers I get a very good grip. You must also have a soldering iron with a small tip but.

Make sure if you want the class A circuit or not, Q13, Q14, R14, R15. Determine also if you want any of the R1, R2 or R3 resistors. If you don't want the input filter just short R5 with tin or a small wire.

Start with all low SMD parts

• Resistors
  Transistors
  Capacitors, not the electrolytic ones
• Then continue with the high electrolytic caps
• Wires

Check the finished amp

Apply voltage and check the output voltage. Measure the DC voltage at the output. It should be the specified offset voltage, a couple of millivolts.

Measure the quiescent current.

The whole buffer is ready.

Good luck and happy listening.