On the internet I came across a funny design: a discrete 741 operational amplifier. You can buy it at Adafruit, see the circuit also here:

Adafruit XL741 discrete 741 opamp
Adafruit XL741 discrete 741 opamp

The design contains the following parts:

  • 20 x transistors
  • 11 x resistors 
  • 1 x capacitor

I immediately started to consider whether it is possible to reduce this design to the original DIL8 package of the 741. This is indeed possible: you can see that the components fit on the PCB:

Discrete 741 operational amplifier in DIL8
Discrete 741 operational amplifier in DIL8

Discrete 741 opamp in DIL8
Discrete 741 opamp in DIL8

I don't have time to make it myself, so I want to make it a kind of competition. The big challenge is that mounting the components has to be done by hand and with my solder paste dispenser:

Solder paste dispenser
Solder paste dispenser

It's a terribly precise job, but with my dispenser you can handle parts like 0201.

The transistors must of course be very small, I am thinking of types such as the 2SC5658T2LQ with size VMT-3.

These are the rules:

Dimension 0.4" x 0.3".
Double sided PCB.
Components on topside.
The tin must be applied with my solder paste dispenser.
The application of the tin, placing the components and soldering must be filmed.
The opamp must be functional and tested well.
Use 8 castellated mounting holes.
Ball grid components are not allowed.

Who wants to participate in the competition?

I don't know yet how I'm going to shape the competition, let me know if you have a good idea.

IBM Solid Logic Technology

I discovered that discrete integrated circuits actually existed as early as in 1964. IBM made custom hybrid circuits using discrete, glass-encapsulated transistors and diodes, with silk screened resistors on a ceramic substrate, forming an SLT modul, see Wikipedia.

IBM Solid Logic Technology SLT 1964
IBM Solid Logic Technology SLT 1964

IMB SLT module in 1964
IMB SLT module in 1964

The dimensions are approximately equal to DIL8 by the way. In addition, they use a ball grid array, which apparently already existed also in 1964.

Other interesting projects with discrete transistors

MOnSter 6502


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