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As you've worked out, it is a result of the resistor pair, giving just a touch under 5V.
It is then used via various other resistors/diodes/capacitors, to feed the inputs to the opamps, and ensure that all signal processing happens at positive voltages, with the centre being the reference voltage. To fully understand it you need to understand each step of the process, and the signal at that step.
So starting with the input, you have an AC signal, that centres around GND (0V). The first thing it hits is a resistor and a coupling capacitor. The resistor is what defines your input impedance. It handles a mix of ensuring there is some load on the signal, reduces noise, avoids static build up, and couples the AC signal to GND.
Now with an AC signal coupled to 0V, it means it's continually moving between positive and negative voltages, and handling both positive and negative voltages would introduce a lot of extra complexity into the circuit. So what the coupling capacitor does, is instead of the AC signal being coupled to 0V, it couples it to your reference voltage via the 510K resistor, so instead of the signal moving between say -0.5 to 0.5V, it's now moving between 4.5V and 5.5V (assuming Vref is 5V, and your capacitor is perfectly coupling the signal - which it won't!)
This then means that you can do whatever signal processing/manipulation you want using only positive voltages.
However, because you're now using the reference voltage as your signal centre point, everything has to work from that reference voltage.
And then finally, before leaving the pedal, the signal passes through another coupling signal, where the signal is then coupled back to GND.
All the components have arrived from Bitsbox and I've made a start assembling them onto the breadboard. Progress is a bit slow because of the following:
I also learnt about why a diode is used for polarity protection, and when to use a diode in parallel to the voltage supply, when to use a Schottky diode in series, about forward voltage drops, and how a bridge rectifier works (that's bloody clever that is). Woo, get me... ;-)
Oh yes, I also learnt about the importance of putting a "load" across your 9v battery when taking multimeter readings. That diode got bloody hot when strapped directly across the battery terminals. ;-)
It's been useful for all sorts of stuff outside of pedal building too.
Oh, and can anyone recommend good wire strippers for single core 22 AWG wire (breadboard wire)? I'm currently using a cutting knife and my fingernails, and it's doing my head in. ;-)
Automatic strippers, that only cut on two sides, aren't any better than a pair of side cutters or Stanley knife, where solid core is involved. Off course it depends on the exact insulation, as some will strip easier than others.
But this style would probably work just as well if they cover the right wire size - https://www.ebay.co.uk/itm/Automatic-Cable-Wire-Stripper-Crimper-Crimping-Tool-Adjustable-Plier-Cutter/253073025632
The breadboard layout is clearly not the best, but this is really the first time I've done this for a proper circuit, and, hey, it works.
It's the Timmy circuit above, and it doesn't sound too bad. :-)
Lessons learnt:
So, for me, this was a successful proof of concept exercise. I've proved that I can get it together to buy and assemble the components, interpret a schematic and make the thing work.
And now I need to think about how to make this permanent. Options:
- Veroboard it together and re-use my components and buy pots, switches and an enclosure
- As option (1) but locate a PCB. But this might use onboard pots and I'd need to be careful with drill holes
- Buy the whole goddam kit and solder it together (like this one)
And for being such a clever dick and putting together my very first breadboard pedal I'm going to drink a lot of wine. ;-)Rather than put jack sockets on the breadboard it's easier to have a couple of jack sockets with wires soldered to them so you can make contact with the breadboard circuit easily .... likewise with pots
Personally I tend to build on veroboard from the off with every joint soldered. It's less prone to bad connections and you very quickly learn how to build compact sensible layouts.
For prototyping I use a lot of salvaged electronics from all kinds of broken radios, speakers, mains adapters ... if you get some braid a decent solder sucker you can harvest pretty much any through hole component easily and it;s not that hard to do SM
Here's a little vid I made showing the build of a Tubescreamer by harvesting the opamp and passive compnents from an old computer speaker and a tablet power supply
One of the cheapest options for wire is 6 core alarm cable. When you remove the sheaf you have 6 colours of wire and I like to stick to a coloured system that makes fault finding easier like this
Red : + Volts
Black : - Volts
Green : Ground
White : signal in
Blue : signal out
Yellow : signal control function
Your gonna pay more buying from Bitsbox, some of the components are 4 times the price I pay for common pots. opamps and caps
Happy building in 2018 and keep reporting the progress
Right, I want to get this built onto a proper PCB or Vero and into an enclosure... :-)
Looking at the circuit Veroboard be fine, not complicated enough to warrant a PCB
Quick question to the pedal builders - if I use a vero board how do I fix it in the enclosure, or can it just float around inside?
I was trying to post a picture but imgur isn’t working tonight either the site or the app. The second pedal down on this post is on vero and the board is being held in place by the cables to the pots. Vero works it’s fun and is the ultimate in DIY but for neatness I do prefer a pcb and board mounted pots.
http://thefretboard.co.uk/discussion/114178/getting-back-into-building-new-update#latest
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_76_77&products_id=361
One interesting general observation - I was surprised that my trial breadboard build wasn't noisy at all. I was expecting that with all those wires and connections the circuit might have picked up noise. But it's very clean (for an overdrive, that is).