The idea had not gone any further — the technology he was trying to use was not quite right for it — but it was something he might look at again "one day".
This time, the keen musician created a project called Varying Valve Voltage that allowed guitarists to still have a great valve sound but at lower volumes. It won several awards at the Otago Science Fair in August.
In the guitar world, it was common for players to turn their valve amps up to "insane volumes".
The reason for that was to achieve power tube distortion. That was a type of natural overdrive that came from overloading the vacuum tubes which provided most of the amplification.
That was a distortion of the second harmonic which sounded good to most people's ears. However, the volume was an issue.
Karl had an idea he could built an amplifier and include some circuitry to reduce the plate voltage without reducing any other internal voltages as a form of power attenuation. That meant a guitarist could still have the great valve sound but at lower volumes.
He now had an amplifier to use when recording with his band and a nice amplifier to play with at home "without disturbing the neighbourhood too much".
It was about year 9, when he was really getting involved in music, that he made some guitar pickups. Things had become more complicated as he learnt more about electronics.
He plays in a band called Saurian, whose genre was rock although that was in a "really broad way". The band played gigs and was also making some recordings.
"We don't have one style. If we like what's going on with our songwriting, that's what we play."
He was the guitarist and singer — "and everyone's tech". He started guitar lessons when he was 5.
"I don't remember the full reason I wanted to play guitar. I think it was from when I was about 3," he said.
Karl will leave school at the end of this year but had not yet decided what he wanted to do. "I want to do something to do with electronics and music. That's about as far as I've gotten. I'm still working on what I'll do next."
He had enjoyed doing some work in his school holidays for Perreaux, the Mosgiel-based firm which designed and manufactured niche audio equipment.
As for his inventions, he had even made microphones out of old phones — "they sound a little bit low-fi but that's pretty cool".
Meanwhile, Oscar McCartney created a pest trap, Trapduino 4000, that notified the user when it caught a pest, by sending out a radio signal when the trap had been triggered.
His father, John, said the family was involved with KAPOW — Keeping Arthurs Point's Original Wildlife — a group which was formed in August last year.
Oscar was very keen on "building stuff" and was seeking a project, so it seemed an ideal fit.
