[Homemade Quantum Computer NMRQCP] Soldering the Op-Amp

*Original Japanese version is available here.

 Hello! I'm a KOSEN student taking on the challenge of developing a quantum computer using a homemade Earth's Field NMR (EFNMR) system.

Now that the test verification on the breadboard has been successfully completed, this time I'm finally sharing the process of "full-scale board implementation (soldering)"! I gave shape to two circuits at opposite extremes: a polarization circuit that passes a large current, and a receiving circuit that handles minute signals.

1. Controlling High Currents! Implementation of the Polarization MOSFET Circuit

First is the switching circuit for passing a large current to the coil. I implemented it on a double-sided through-hole glass universal board (B type 2.54mm pitch, 95x72mm).

For the main switching element, I placed an "N-ch power MOSFET 2SK4017(Q) (60V 5A)".

What I paid the most attention to was surge (back electromotive force) countermeasures. To prevent the circuit from being destroyed by surges generated from the coil, I soldered a "Fast Recovery Diode 20NFA40 (400V 2A)" to the back of the board, piled on plenty of solder, and wired it with "thick lines" to withstand high currents.

Also, I used UL1007 heat-resistant vinyl insulated wires (AWG18 red and black) for the power line, and as a safety measure against a potential short circuit, I perfectly incorporated a flat fuse holder and a 5A flat fuse in series on the positive side of the battery connection.

2. A Battle with Microscopic Parts... Implementation of the Analog Receiver Circuit (Op-Amp)

Next is the implementation of the ultra-low distortion, ultra-low noise operational amplifier "AD797BRZ" for amplifying the extremely weak FID signal.

Because this IC is a Surface Mount Device (SMD) chip and as tiny as a grain of rice, it cannot be plugged directly into a breadboard or universal board. So, first, I carefully soldered it onto a base called a "DIP conversion board" to process it into an easy-to-handle state.

[Sad News] Soldering the Op-Amp: I Never Want to Do It Again

Here is some realistic advice (or rather, a complaint) from me to fellow electronic hobbyists.

Soldering this op-amp was absolute hell because the part and the pin spacing were way too small.

The trick I learned after trying is to "melt just a tiny bit of solder, put it on, and let surface tension attach it." If you try to pour the solder in normally, you will definitely fail at first and it will stick to the adjacent pin (create a bridge).

Therefore, it is highly recommended to prepare a "solder wick" to absorb excess solder. If I hadn't had a solder wick, I would have been completely stuck.

I'll be honest. Anyway, I absolutely never want to solder an op-amp ever again (lol).

Although I gained some trauma, seeing the hardware take shape like this makes it finally feel like a quantum computer, which is really exciting!

• Daily experiment notes and code: Available on my GitHub repository (nmr-qc-project)
  
• Real-time development scenes and oscilloscope waveforms: Posting on X (formerly Twitter)
  

If you are wondering things like "Will it really work?" or "How do you generate waveforms?", please bookmark this blog and follow me on X!