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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

741SE
741SE

By the way, the LM741, which dates from 1967, is totally outdated. Today's opamps operate from a single supply voltage of a few volts and have a rail-to-rail input / output. The circuit of the LM741 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 LM741 operational amplifier in DIL8
Discrete LM741 operational amplifier in DIL8

LM741 circuit
LM741 circuit

Discrete LM741 opamp in DIL8
Discrete LM741 opamp in DIL8

I don't have time to make it myself, so I make it a 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.
  • You ust use  VMT-3 like transistors
  • 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.

Who wants to win €250?

The first person who take up the challenge and carry it out successfully will receive €250 from me. To participate, please contact me.

High-density PCB

This project falls into the category high-density PCB, I think you need 0.1mm traces.

Example high density HDI PCB
Example high density HDI PCB

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

Discussions

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