An update on my electronics projects (by )

One of the challenges of being a massive nerd - who loves learning complicated technical skills - is that it can sometimes be hard to find new skills to learn. Thankfully, analogue electronics has provided me with a rich vein to mine; it's full of things that take some work to master, yet offer the opportunity to create interesting and useful things.

So, after the success of the Polyp Mixer (in which I learn how to use op-amps and to manage impedances within a circuit) and the trickle charger (in which I gained experience with basic power electronics), I am currently working on a... thing. I don't quite know what to call it, but I'm going with the working title of "microphone pre-amp". And my goal with this (other than to end up with a working microphone pre-amp) is to master the class A bipolar transistor amplifier.

The Goal of the Microphone Pre-Amp

So, the Polyp Mixer sits on my desk, mixing the audio output from my two PCs, and with two spare channels - one of which I intend to connect to a radio transceiver in future, the other being spare for random laptops or listening into audio circuits I'm working on (such as the microphone pre-amp, as it happens). This means I can listen to all of these devices through my nice amplifier and speakers. I can even plug headphones into the amplifier if I want to.

But, when I talk to people in video calls, I am using the nasty little microphone built into my USB webcam - and I can't feed that audio to the other computer, nor to a transceiver or anything. Rather than have a plethora of microphones for everything, I'd much rather have a single microphone that just feeds microphone-level signals to all of my devices.

So, the first goal of the pre-amp is to have a box that has a microphone in socket on the front, so I can plug in a microphone, and a bunch (let's say 4: two computers, a transceiver, and a spare, matching the mixer) of microphone-level outputs on the back to feed into my devices' microphone inputs.

However, this is complicated by the fact that different microphones produce different signal levels (of the pile I've tested, I've seen signals from 5mV to 100mV peak-to-peak). Normally I'd deal with that by adjusting "mic gain" controls on the inputs to everything, but it would be simpler if I had a "mic gain" knob on the pre-amp to adjust for different microphones, and then all the downstream devices can have their mic gains set to a constant level.

But not every device has a mic gain knob, because some things are meant to be plugged into custom-made headsets rather than arbitrary microphones. So, as well as the front-facing "mic gain" knob to adjust to different microphones, I could also do with "mic level" output knobs next to each output on the back, so each can be tweaked to read the same volume.

Also, if I switch microphones, I'd like to be able to get the level right before talking into my devices - so it would be nice to have a mute control and a level meter. I can mute the outputs, talk to see the level meter deflect, and adjust the mic gain knob until it's just hitting the maximum and not going over it. (This is why vu meters always have a green bit and a red bit; you're supposed to adjust levels until they're using the green area nicely but not going into the red area). So, I need a mute switch and a level meter.

Some microphones have a really tinny frequency response, picking up high frequencies much better than low frequencies. It would be nice (and fun!) to be able to compensate somewhat for this. I can't quite stomach building full spectrum analyser, but a classic James-Baxandall tone control circuit would be a fun addition.

Some of my microphones have a push-to-talk button; it might be nice to be able to feed that into the pre-amplifier, and have it drive the mute control. So, the mute switch really needs three settings - audio on, audio muted, and do-whatever-the-input-push-to-talk-socket-asks-for. And an LED showing the current output status, so I can tell if it's working when in external-push-to-talk mode.

A radio transceiver needs to know when I push-to-talk so it can transmit, so there also needs to be a push-to-talk output socket on the back.

Oh, and finally - I have a few headsets, with a microphone and earphones, so it would be nice if the thing also contained a headphone amplifier with a line-level input and output, so it can be connected between the mixer and my amplifier, and save me from running a long cable down from the headphone socket on the amplifier. So stick a headphone output and a headphone volume knob on the front for that, too.

At first I wanted to put a number of different sockets on the front, so I can just plug headsets directly in - an Android TRRS socket has lines for a mono microphone and stereo headphones, and the Kenwood/Baofeng headset socket has mono microphone, mono headphone, and push-to-talk. But in the end I decided it would be simpler to just have separate headphone and microphone sockets like on a PC, and a 3.5mm mono push-to-talk socket, and buy or make adapters from other standards to those three jacks. I managed to find a TRRS->dual TRS splitter on eBay, and made my own Baofeng->headset, microphone, and PTT lead (using two five-ohm resisters as a passive mixer to mix the stereo headset signal into a mono one). Having these adapters also gives me the flexibility to connect Android or radio headsets to computers, or connect a radio headset to a smartphone.

In other words, this thing has accumulated some feature creep, through a bunch of weakly interconnected features! The most questionable of these is including the headphone amplifier - but it does feel convenient to be able to plug a headset into a single box, and as the mixer is conveniently situated on my desk while the amplifier proper is a bit more of a reach away, it would be messy to be running a headphone cable extension back; headset splitter adapters only have ten centimetres or so of lead, so the microphone and headphone sockets do need to be close.

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One, Two, Three… Blast Off (by )

Gloucester Story Telling Cafe May the 4th 2023

Before covid we were running a story telling night called The Moving Story Telling Cafe but it was derailed and not just by covid - we sadly lost one of our trio to cancer. So last month we relaunched but this time without the Moving - The Folk of Gloucester have kindly offered us a permanent home and also house one of the other Legacy projects of Chloe The Midnight Story Teller... The Story Telling Library.

Last month was a special launch and opening of the library with lots of guest story tellers who all knew Chloe personally - that means the this month is going to be the first actual Gloucester Story Telling Cafe and it happens to fall on May the Forth. One of the reasons the three of us... Chloe, Jane and myself worked so well was that we are unashamedly geeks but perhaps not so obviously geeks to those with narrower ideas of what a geek is. We love our sci-fi and fantasy and I had a request from the Gloucestershire Poetry Society to have an event that geeky poetry would be welcome... well how could we resist such a set up.

So we are blasting off with a Starwars joke and a sci-fi author whizz reading a poem from their sci-fi novel!

Chris Hemingway The Future  published in 2016

Chris Hemingway is a poet, prose writer and musician from Gloucestershire. His book “The Future” was published in 2016 and was described by Cheltenham Poetry Festival as ‘darkly witty, like “The Man Who Fell to Earth “ meets “The Office”’. He has also had published two poetry pamphlets ‘party in the Diaryhouse’ and ‘paperfolders’. That’s a lot of ‘p’s’…

I have used a picture of my dad dressed up an explorer of space when he was a little boy - my Granddad took arty pictures and with my Nanny loved to make outfits for my dad and I am so lucky that copies of this one still existed in Australia and that a cousin kindly sent a copy to me.

Doors open at 7 on May the 4th 2013 at The Folk of Gloucester 99-103 Westgate Street Gloucester, Gloucestershire, GL1 2PG

There is a cafe and bar. Entry is free but we will have a pay what you want pot out!

We are open to all story telling types from traditional to memoirs, to flash fictions, to novel extracts, to oral and of course narrative poetry!

Our Moto is "story telling for all/everyone" and as such not only do we have some fab guests lined up as well as music but we have an open mic were we would love people to come and share. Open mic slots are a max of 10 minutes.

This is the years itinerary - first Thursday of every month except January as lets face it - it is nearly always going to be too close to New Years Eve for most people and I can't be dealing with that!

Gloucester Story Telling Cafe 2023 dates

Here is the Facebook event for tomorrows: One Two Three... Blast Off! and May the Forth be with you!


I am very excited about where this is all going - Story Telling and Gloucester have a long history and I hope a longer future!

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