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Practically Speaking Stories about real engineering – by Jake Rothman Audio doubt and workshop woes I said I wouldn’t do it, but here we are. I’m writing a column about not being able to write my column. If those who write for The Times do it, why can’t I? It has all come to this because I have no electronics lab and am utterly bereft. I’m all packed up ready to move to Craven Arms, a railway junction town (named after a pub that’s since closed) in the middle of nowhere, or Shropshire, if you’ve ever heard of it. However, I’m now in limbo because the buyers have gone cold, like my iron and scope. The library is also packed: 22 boxes of A4 ring-binders weighing 12kg each in the hall. 90% of the information in them is not online and never will be since no one is going to scan it. I could just pull stuff off the ’net and make an article out of that, but we all know that’s a con. Anyone could do that. The rest of the workshop, weighing in at around three tonnes, is in the garage. I just hope the concrete floor doesn’t give way! It used to hold a four-by-four, so I might get away with it. So all that’s left for now are some old memories; I hope none are libellous. Tele-phoney One of my first weekend jobs, around 1982, was at a film broadcast equipment supply company in the West End of London. I mainly made leads and did repairs and servicing. As usual, things came in completely trashed. I had a pair of Beyer DT48 headphones that had been run over by a forklift truck and were completely mangled. “A few tweaks should do it,” the customer said. I ended up making an entirely new pair from spare parts and old headphones. I think the bill cost £5 less than a new pair at £150. They came in a few weeks later trashed again, covered in sticky latex rubber solution holding clumps of somebody’s hair. The top-notch mixing desks we supplied used to have Penny and Giles conductive plastic faders. In those days, it was normal to replace individual parts such as wipers, bushes and tracks. One unit from the sports room came back a few times with oddly pitted tracks and wipers that had gone green. There was also white powder in the bottom tray, which I dumped in the bin. I told a senior technical guy about this, and he seemed strangely upset about the missing powder! Oh, the naivety of youth. Sticky situations Here’s one to remind you of how one musician can destroy a company employing several good electronic engineers, so beware if you are designing for the non-technical. It was early 1986 in Camden Town. I was a test engineer at a company making a leading-edge guitar synthesiser that could be played like a real guitar. Making one had always been the ambition of the decent CEO. It had a MIDI output that controlled a lovely polyphonic analog synthesiser built around Solid State Music (SSM) chips. They were a significant improvement of the Curtis chips that were popular at the time. All the circuit boards were top-notch surface-mount assemblies built by an avionics supplier in Reading. Even the guitar neck enclosed a long SMT board with LEDs denoting the positions of the frets. The frets were called SCI, or semi-conductive intelligent. This was basically a cermet* pot track with a signal across it so that a particular string and its position could be sensed to allow for pitch bending. The six strings were also scanned to sense which ones were depressed. Another clever trick was to separate the strings in the bridge position for strumming and picking, which made it easier to play than a normal guitar. I’ve always believed the best interface between man and electronics is the analog potentiometer, so the cermet frets seemed the right way to go, and they played beautifully to us engineers in the lab and the studio. That was, until – you’ve guessed it – musicians started playing it live on stage. They pressed so hard that the ceramic frets cracked, and some even fell off! I remember frantic weeks trying to solder on new frets and trying to get them to the exact height the musicians expected. I remember being scowled at by Kate Bush’s technician, while never even getting a chance to see her as she looked around the company. Worse was to come, as the guitars then did crazy solos on stage all by themselves, making even Steve Vai seem slow. This was a result of random triggering as sweat rolled down the misaligned fretboard. None of us in the lab realised that musicians sweated so much when they got into a frenzy. After all, we never did while looking at our scope traces and clean, dry circuits. It was such an innovative piece of technology that it won a British Design Award for industry, with our CEO being presented with a trophy by the Duke Of Edinburgh. On his return, he wound the company up. It’s a sad story, with around a million pounds burnt. I left with a Weller soldering iron and a few tubes of SSM 2024 filter chips. Ghosts in the machine Many musicians are superstitious, and some recording studios were built in Victorian, supposedly “haunted” buildings. As bored studio maintenance engineers in the days of tape, we used to play nasty tricks on some paranoid clients. One we used to like doing was laying down a half-hour track while they popped out for a few minutes. We did it at very high tape speed, using sources that would spook the ghost-fearing client when played slowly at the correct speed. One ended up being mixed in, but I felt it would be cheeky to ask for a royalty. * cermet refers to a ceramic strip glazed with a glass, metal and frit mixture, giving a stable and hard-wearing resistive element. 26 Practical Electronics | February | 2025 Another dodge was directed against arrogant old producers who claimed to have the hearing of a 20-year-old. We would mix in a 13kHz tone, which they couldn’t hear. Old producers use spectrum analysers now, so they would see through this. I even installed a big calibrated knob labelled FHS (Faux Harmonic Synaesthesia) in a mixer that did nothing, but some clients were convinced that it sounded better when set to a precise position! Strange solutions There was intractable hum in one Islington studio, I checked every Earth connection, cable shield, everything; no luck. After several coffee breaks, I gave up; nothing was making sense. For inspiration, I went exploring, going into the basement to look at the reverb chamber and tape archive. In the dry, dusty basement, I noticed an odd thick-gauge Earth wire going into the corner. Kicking the dust away revealed an Earthing rod where the ground was completely dry. I was suddenly overwhelmed with a desire to urinate, and reckoned I wouldn’t make it back upstairs, so there was the possibility to solve two problems at once. For low hum, it is essential that the main ground reference at the mixing desk has a low im-pee-dance. I never told them what I had done; I just issued an invoice for a day’s diagnostics and a big bag of copper sulphate crystals. I recommended that they water the rod with copper sulphate solution every few months. Silly puffs and fluff I had one mixing engineer who always seemed to destroy the monitor speakers with too much bass, tearing the cones from their lead-out wires. I came up with the idea of putting a small pile of talcum powder at the back of the reflex ports. If he overdid it, puffs of white “smoke” would appear and warn him of an additional invoice. I got found out when I inadvertently used perfumed talc. In 1989, I moved into lecturing where the main hazards were political rather than electrical, but loads of funny things kept happening. One of the first classes I taught was “Electronics for Guitars”, where the ambient IQ was rather low. I said to a student that he could check if his 9V PP3 batteries for the pedals were okay by just touching the terminals on his tongue. The next day, I was having a nice cup of tea in the canteen and I heard a funny sounding “yelp”. It was the student, jumping about with an unusual-looking battery stuck to his tongue. We later found out it was one of the new lithium batteries that had just come out for smoke alarms. These had much greater current capability than the old zinc-carbon types! I had one guy from Bolton who used to hold solder in his mouth, saying it gave him an “extra hand”. I gave him some advice about lead poisoning, shocks and looking like a prat, but he still kept doing it. One day, the inevitable happened – there was a huge thump and the power tripped. He had been soldering the back of an IEC socket, which was plugged into the mains, before being flung into the side of a big filing cabinet. It left visible dents where his skinny hip bone and shoulder had hit, looking like something out of a Tom and Jerry cartoon. Just after that, a student cut himself with a scalpel. Luckily, the lab technician had gone home, so I duly wrote up just the scalpel incident. The next day, she asked about the dents because the filing cabinet’s “Health and Safety” drawer was stuck solid. We all kept quiet. These days, I file a risk assessment for everything I say or do. Musical masochism I still shudder when I see what musicians do to equipment. They break pot shafts off, bend 5mm-thick rack panels, leave snapped-off jack plug remnants in sockets and enthusiastically test for liquid ingress. One connected a 33V HP printer power supply in reverse polarity to a 9V DC powered DAC, reasoning “well, it’s the same plug, innit”. I think engineers designing electronics for railways have the worst of it, though. Some drivers have been known to bash a plug into a socket with diesel trains. Apparently, there was some problem with the height of the control couplings between BREL vs Metro-Cam designs. Enclosed track-side equipment has to survive the contents of a toilet being discharged over it. The moral is that electronic engineers tend to be too kind to their creations when testing. Give it to somebody who’s drunk and doesn’t know the difference between a volt and a jolt! PE Fluffy bunnies Most furry objects found in sound engineering are microphone windshields. However, we used to pretend there were also extra uninvited guests. Small speakers under floors and in walls were always a good Halloween trick. A few speakers fed with a bit of judicious microphone scratching switched around would send some into a frenzy. I worked with one prissy lecturer who was terrified of rodents, so we built a hidden pulse-generator driving a little “squeak” tone burst into a piezo disc. The beep was so short and infrequent that the matchbox-sized unit was never found. Near misses When teaching practical electronics, there was always a risk of accidents. Any incidents had to be written up in an accident report book. Occasionally, some students did things that were unbelievable. Practical Electronics | February | 2025 27