[23 August 2020] I recently found myself on Noel's Retro Lab Youtube channel and, having a slight interest in retro computers, I found myself watching a video where Noel diagnoses and repairs a noise distortion problem on a ZX Spectrum +3 (I used to have one of these) [link to video].

His process was easy to follow and he did an excellent job of not only showing the problem area on the board (although it looked fine), but he compared it to the circuit diagram, and then isolated the audio amplifier section and illustrated that part on its own.

Here are those three stages:

Circuit diagram showing the path of the audio output from the Sound Chip,
through the amplifier circuitry, and out through the video port.

Simplified ZX Spectrum +3 Amplification Circuit

Noel further explained that this is a Single Stage Amplifier. I can see the similarities between this and my previous Science Fair amplifier project which also featured a single transistor (unlike the first more complex one which used three). There is also a noticeable absence of a transformer.

"A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. It can be designed to "step up" or "step down" voltages and works on the magnetic induction principle." - Google

From this I assume this conversion is carried out prior to the circuitry illustrated above. The common ground, as i guess it would be termed, is also omitted from this simple diagram.

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[25 August 2020]

Today I turned to a book I have called Starting Electronics by Keith Brindley. It says:

[We] can still only guess at what [electricity] is. It's actually impossible to see electricity: we can only see what it does...

This statement reminded me about the topic of gravity in the book I recently re-read called Einstein's universe.

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