Tuesday, 20 October 2020


 This story is third hand, so there are probably some inaccurate details – like all my other stories.

My brother recently changed jobs and he needed to buy himself a new laptop. He's a mechanical engineer, his old job was something to do with oil rigs, his new one swimming pools. His new job required CAD software so he had to buy a laptop with massive RAM and a huge GPU. I'm sure most of my readers can already see where this is going... it sounds like a gaming PC. That is exactly what he bought, and he now turns up to business meetings looking like he's a pro-gamer. I don't actually know anything about the laptop, but I'd like to think that it has a wild coloured (or super low albedo matt black) case, grotesque angular design, giant cooling vents and a brightly illuminated logo on the outside. Lets hope that the keyboard has individually programmable coloured LEDs, that the WASD keys are made from a different material, and that the membranes are certified for 100,000 cycles.

Richard "I hope he starts playing KSP" B

Wednesday, 14 October 2020


 This weekend I had houseguests from out of town. We went to admire a little corner of Dartmoor and I was reminded of something that happened in my childhood.

I think I was probably about 10 or 12 and I was swimming and playing in the river at Cadover Bridge. An unattended toddler fell from the river bank and ended up face down in the water. I recognised that this was important and that I needed to act quickly. I swam as strongly as I was able to the stricken toddler and even though I was nearly out of my depth I grabbed it and lifted it clear of the water. Not long afterwards the mother noticed what had happened, ran to the river's edge shouting, and grabbed her child from me. I was frightened and disturbed by the harsh way she acted and hurt that there wasn't even a word of thanks.

Looking back I can imagine that she was upset and that the welfare of her child was her main concern, but my overriding memory of the event is that I was cross and upset at how harshly I had been treated. Some time later, probably only a quarter of an hour the family approached my mother and I with effusive thanks and I was bought an ice cream. I'm pretty sure that I accepted it with bad grace.

Richard "One star. Would not rescue again." B

Sunday, 4 October 2020

Impedance mismatch

 There is a long running joke in product development that the software team will fix the hardware errors in software, and more rarely that the hardware team will fix the software errors in in hardware. In the distant past I did something similar, but it was a temporary workaround. The software guy was on leave, and we couldn't register any of these prototype devices with the PCs because (I seem to remember) the sense of an interrupt line was inverted. I wired in a switch and an inverter just to keep us working.

This weekend I did fix what I consider to be a software fault in hardware.

Back in the day, when I was working for my favourite boss I had to research some ORM solution. He also came from an electronics background and he warned me that I wad going to find the term "impedance mismatch" and that it was going to annoy me. He was right.

My mum is very forgetful, so her radio needs to behave exactly as the radio she had 20 years ago did. It's hard to get one with physical preset buttons, but not impossible. It needs to connect to the amplifier and speakers which she's already familiar with, but the one we found has a headphone output, not a line level output. Domestic line level is 1v peak to peak into something like 100kΩ. Headphones are normally a few hundred ohms. If you want to plug an ipod, mobile phone or suchlike into an amplifier, it's normally good enough to just turn the headphone volume to maximum and connect it to the input on the amplifier.

My mum's new radio doesn't have a real volume control, it's a dial which goes round and round and sets the volume in software. When the radio boots up it sets the volume to the last setting, unless the last setting was > 50%, in which case it uses 50%. This is far too quiet and meant that my mum would have had to wind the dial around every time she turned the radio on. It was a procedure she struggled with and didn't seem likely to accept.

I set about building a converter which would connect the headphone output (all amps and no volts) to the amplifier input (1 volt and no amps). It couldn't be something with a power supply because that would also need to be switched on and my mum would forget.

On stage you often need the opposite. Let say there's a keyboard with a normal line out, but you want to run that signal 10s of meters across a (electrically) noisy stage and connect it to a mixing desk which is expecting a microphone (µA of current in a push-pull circuit and no volts). The humble DI box does that exact conversion for you. DI stands for "Direct Injection" because you are injecting the signal straight into the desk without having to use a microphone.

These days DI boxes are usually active devices, taking the power needed to run a little op-amp from the 48v that the desk offers to the microphone in case its a condenser (capacitor) mic that wants to charge one of its plates. In the old days, or if you were cheap when you bought your desk, or if you've got some naughty mics that won't tolerate the phantom power, then you have to use a passive DI box. A passive DI box is nothing more that a matching transformer with a centre tap on the low impedance side in a sturdy box. Of course I own some passive DI boxes, and their ratings are surprisingly close to what I needed. 600Ω on the desk side, 50kΩ on the instrument side. I just need to connect a pair of them back-to-front between the radio and the amplifier.

I do sometimes use my lounge for sitting around and watching the tv, but here it is configured for electronics work:


Heatshrink to stop the cables from tearing apart:

Several layers of heatshrink so that the chuck type strain relief can grab the tiny little headphone cable:

This is the finished cable:
And this is the contraption:


To answer your questions:
Yes, it worked very well thank you.
No the microphone plugs aren't made by Neutrik, they're cheap copies cut off from a snake I own.
Yes, it is rather cumbersome.

Richard "XLR" B

Sunday, 27 September 2020

Challenge Accepted

 During the height of lockdown I was working from home, I was bored and I was making a lot of video calls. I came to find it rude when the people I had to talk to had crappy audio on their computers and they had a lot of hum/buzz/echo/background noise or were hard to understand. During one meeting I said to my colleagues how much I liked talking to the gamers because they always have really good headsets. One of these guys explained that he was just wearing headphones as he didn't like a head-worn mic. From just outside frame he pulled a massive (presumable broadcast quality) mic on an anglepoise stand.

I used to run sound for various bands and have enough audio equipment scattered around the house to put on a small music festival. I said "Challenge accepted" and spent the night putting together a system of stands, mic and headphones that would look equally impressive for my meetings the next day.

These two flight cases contained most of what I needed.

This is a battery powered mic preamp to bring the level up to something that the computer could deal with. I didn't have enough space to use an actual mixing desk.

This is what I was talking on for my meetings the next day. The mic is actually a bass drum mic, but it deals with speech and (tenor) vocals very well. It's in a stand that's designed for the stage so it's far to heavy and sturdy to be convenient. The headphones, while excellent are also ear defenders so it is quite oppressive to put them on

Richard "telephony" B

Monday, 21 September 2020


 I received this lovely message last week from a friend of mine. "Welcome to the joyless but effective world of South Korean motoring".

My old Citroen Nemo was written off following an accident and the insurance company took it away. My only other car is a loud and uncomfortable open top sports car, so shopping for a replacement was somewhat trying. I wanted to try an estate car, and ended up choosing a Hyundai i40. It's 8 years old, but even so, it's so low spec that it's laughable:

  • 16" wheels.
  • AM/FM Radio with CD player.
  • Leather gear knob.
  • Electric windows.
  • Adjustable wing mirrors.
  • Heated rear window.

That said, everything works (except the lock on the fuel door), it's smooth, quiet and easy to drive. It's also exceptionally boring.

Richard "Joyless but effective" B

Friday, 11 September 2020


 This weekend I took my boss with me to a track day. I'm trying to make a favourable impression on him to improve my chances of getting a demotion.

It was an odd day. The driving was arranged in sessions with the same group of cars each time. There were several long stoppages, but all for breakdowns rather than crashes. A turbocharged Westfield (why such a thing exists I have no idea) made a loud bang and briefly produced a large orange ball of flame. It then span off the track dropping an entire sump of oil on a fast corner. When it was pushed back into the paddock large components were dangling from the engine bay and scraping along the tarmac.

I did my best to correct the ratio of breakdowns to crashes. Towards the end of the day we were told that we would get just one more 30 minute session, but that we would be allowed to make a driver change in the pit lane. I was in a well maintained and trustworthy car, but I needed to determine when I had been driving for 15 minutes. I don't know how long it takes to look down at one's watch, but when I looked up again I found that I was completely off line and heading off the track, full throttle, at about 80mph. I remedied the situation without incident, but I didn't impress my passenger.

Richard "No lap timing" B