C18Q1 Learn electronics and build a pedal

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PhiltrePhiltre Frets: 448
edited December 2017 in Making & Modding
So, my challenge is:
  • to have a deeper understanding of electronics (as I mentioned in my other thread)
  • get all the components together, breadboard, multimeter, etc
  • study the schematics and choose a pedal to prototype
  • build the pedal on a breadboard and understand what's going on
  • build the pedal on a PCB or vero board in an enclosure

So far, I've made quite a bit of progress as I've studied a few electronics books, got some components and tools from Bitsbox and put together some basic circuits on a breadboard. Heck, I even made a power capacitor discharge cable, some flashing traffic light LEDs, and I know what a 555 and decade counter chip does, and ohm's law! And now I'm learning about op amps.

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  • PhiltrePhiltre Frets: 448
    edited December 2017
    Oh yeah, apparently, the theme of this challenge is "(Santa didn't bring it so) I had to make it myself". OK, so Santa didn't bring me a Timmy pedal so I will have to make it myself. :-)
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  • PhiltrePhiltre Frets: 448
    It's the first day of the C18Q1 challenge and I have the 'flu. Nevertheless, I will continue. Bleugh...

    So, I've decided to build a Timmy clone based on the schematic I found online. The initial aim is to put this together on a breadboard, with the simplest of offboard components - i.e no footswitch, no LED, in and out jacks wired loosely, and trim pots for the 4 pots because I can't be arsed to have dangling wires. Initially, that is. I want to be able to experiment with different value components and types of capacitor and understand what each thing does, rather than just blindly cobbling it together. Actually, it might be interesting to also try something else for the dual op-amp IC, the JRC4559. Any suggestions?

    Later today I'll order some components from Bitsbox. Still not sure what type of non-polarised caps to use - I understand the use of electrolytics, but for the decoupling caps there's polyester film, multilayer ceramic, polybox, polypropylene...not sure which to use.
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  • Adam_MDAdam_MD Frets: 2529
    edited January 1
    Try a lm1458 ic Paul C used to offer that as an option in the Timmy.  A good old jrc4558 will sound good too.  

    As for the caps at pedal voltages if they’re good quality you’re unlikely to hear much difference between them if they’re the same value.  Some cheaper ceramics will just introduce noise so make sure you use NPO ceramics.  Most pedal builders tend to use poly box or NPO/COG MLCC caps because they sound good, are quiet and they’re the right size.

    When I was starting out and ordering caps based on the right value without paying attention to size or power rating I accidentally ordered some massive buggers which I wasn’t able to use.  

    Now i order 5% poly box film caps with a 5mm pitch for all nf values, NPO/cog ceramics/mlcc with a 2.5mm pitch for pf and mini electrolytics for uf with a height of 5 or 7mm to give me as much room to fit everything in an enclosure as possible.  Electrolytics can get very tall if you’re not paying attention when ordering them and  fitting anything over 11mm in a 1590b enclosure is a real challenge.  

    Good luck with your exploration it’s a very addictive but fun hobby.  
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  • PhiltrePhiltre Frets: 448
    Adam_MD said:
    Try a lm1458 ic Paul C used to offer that as an option in the Timmy.  A good old jrc4558 will sound good too. 
    Yep, I've put both of those on the components order.

    As for caps, I'm a bit confused why there's a mixture of different types used in a project. I'm ordering my components from Bitsbox and they have  a Timmy kit - https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=280_281&products_id=2046 but the caps they specify are mixed:
    • 1x 47nF Polyester Film
    • 1x 10nF Polyester Film
    • 1x 39nF Polyester Film
    • 2x 1uF Multilayer Ceramic
    Why not all Polyester Film? Or all Multilayer Ceramic?

    Good luck with your exploration it’s a very addictive but fun hobby.  

    Cheers!


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  • Adam_MDAdam_MD Frets: 2529
    edited January 1
    The 1uf mlcc has been picked due to the size vs the 1uf film cap.  This one is 10mm tall and quite wide though I’d still rather use a film cap than the MLCC from bitsbox because I don’t know what the tolerance or dielectric is.  Stick some of these on your order too so you can experiment.  

    https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_76_77&products_id=361

    I’d also use one of these instead of the 100pf ceramic disc in that kit.  It will have a tighter tolerance and less noise.  

    https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_75_318&products_id=2218
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  • PhiltrePhiltre Frets: 448
    Bitsbox sell cap kits. Would it be worth getting one or both of these?:

    Multilayer Ceramic Kit https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_286&products_id=1992

    Polyester Polybox Kit https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_286&products_id=1994
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  • Adam_MDAdam_MD Frets: 2529
    I bought both of those when I started and only used the poly boxes I still have the mlcc caps in a box somewhere.  Honestly if you’re buying ceramic for audio purposes you need to get some which are NPO or COG dielectric.  

    I replaced the ceramics in my early bitsbox builds with NPO ceramic caps and the difference was huge they had a lot less noise and sounded much better definitely less harsh.  
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  • m_cm_c Frets: 238
    Adam knows better about audio usage than me, but in general the type of cap depends on the application.

    Electrolytic are typically polarised (I.e. they have a + and -, get them wrong they'll most likely leak or go bang), but they get used because they give you the most capacitance per volume, however they're not the most efficient type capacitor. They're typically used where you need lots of capacitance, and if you need lots of smoothing, you'd pair them with a ceramic capacitor (Electrolytic will handle low frequency voltage ripple, whereas the ceramic will handle any higher frequency ripple).

    Polyester are probably the most bulky in terms of capacitance per volume, but they are non-polarised, and very good at handling varying frequencies.

    Ceramic again usually fall in between polyester and electrolytic, but there are different types.
    The only time I've used ceramic, is for filtering on SMD PCBs, as they're nice and durable for reflow soldering, compared with other types.

    It's probably worth having a read of this discussion - https://electronics.stackexchange.com/questions/69919/ceramic-vs-film-capacitor-which-one-is-preferred-in-audio-circuits

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  • PhiltrePhiltre Frets: 448
    OK, I'll pop a couple of NPO 100pf and the Polybox kit onto the order. Thanks for advice!
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  • PhiltrePhiltre Frets: 448
    For reference this is the Timmy schematic:


    timmyver3wj0
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  • m_cm_c Frets: 238
    If you want to see how different values can affect things, look into SPICE (Simulation Program with Integrated Circuit Emphasis - yes I just had to google for the correct name!).

    I've played with LTspice in the past - http://www.linear.com/designtools/software/ but a quick search has turned up an online simulator - http://www.partsim.com/simulator#

    What they let you do, is take the likes of that timmy circuit, create a model of it, and the see how it reacts to different signals. Although aimed at testing circuits before you make them, it is actually a very good learning tool, as it lets you see what's going on, and how changing components affects the output.

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  • Adam_MDAdam_MD Frets: 2529
    edited January 1
    Philtre said:
    For reference this is the Timmy schematic:


    timmyver3wj0
    Have a look at the amp 11 and jan Ray schematics as well they’re only a few components different from the Timmy you might as well breadboard those as well while working on the Timmy.  



    http://tagboardeffects.blogspot.co.uk/2013/03/vemuram-jan-ray.html?m=1
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  • Adam_MDAdam_MD Frets: 2529

    m_c said:
    If you want to see how different values can affect things, look into SPICE (Simulation Program with Integrated Circuit Emphasis - yes I just had to google for the correct name!).

    I've played with LTspice in the past - http://www.linear.com/designtools/software/ but a quick search has turned up an online simulator - http://www.partsim.com/simulator#

    What they let you do, is take the likes of that timmy circuit, create a model of it, and the see how it reacts to different signals. Although aimed at testing circuits before you make them, it is actually a very good learning tool, as it lets you see what's going on, and how changing components affects the output.

    Thanks @m_c I’ve never seen that before thanks for sharing I’ll have a play with this later.
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  • PhiltrePhiltre Frets: 448
    Have a look at the amp 11 and jan Ray schematics as well they’re only a few components different from the Timmy you might as well breadboard those as well while working on the Timmy. 

    I'm on it! Cheers.
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  • Danny1969Danny1969 Frets: 3214
    The thing that irks me is the insistence of pedal guys drawing the bias circuit separately like it's a power supply ..... 2 resistors acting as a potential divider is just biasing the non inverting input at half the supply, just draw this bias in with the circuit ... 

    Almost every overdrive I've ever seen is basically an opamp with clipping diodes in the negative feedback loop so if you build a basic non inverting config and run 2 wires from pin 7 and pin 2 (on dual opamp as used in most pedals) you can experiment with different diodes and the gain without having to solder things in and out of the circuit board just by connecting the diodes and gain pot \ fixed resistor between these 2 wires 
    www.2020studios.co.uk 
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  • PhiltrePhiltre Frets: 448
    Danny1969 said:
    The thing that irks me is the insistence of pedal guys drawing the bias circuit separately like it's a power supply ..... 2 resistors acting as a potential divider is just biasing the non inverting input at half the supply, just draw this bias in with the circuit ...
    I'm no expert (yet!) but is this a thing that comes from the way valve amp schematics are drawn?
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  • m_cm_c Frets: 238
    Philtre said:
    Danny1969 said:
    The thing that irks me is the insistence of pedal guys drawing the bias circuit separately like it's a power supply ..... 2 resistors acting as a potential divider is just biasing the non inverting input at half the supply, just draw this bias in with the circuit ...
    I'm no expert (yet!) but is this a thing that comes from the way valve amp schematics are drawn?

    It's just to do with neatness. If you look at the Timmy diagram, the Vref output from the bias circuit is used in 3 different places.
    If you didn't draw it separate, then you'd have a few extra wires linking things, which would make it look cluttered. Plus by keeping it separate, it clearly identifies where the Vref actually is, and where it is being used.

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  • PhiltrePhiltre Frets: 448
    What is a "Vref" and why is it needed? Is it a positive or negative supply? From my (limited) knowledge the two resistors act as a voltage divider to create a smaller voltage (5v I think in this case).
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  • Danny1969Danny1969 Frets: 3214
    Philtre said:
    What is a "Vref" and why is it needed? Is it a positive or negative supply? From my (limited) knowledge the two resistors act as a voltage divider to create a smaller voltage (5v I think in this case).
    Opamps are designed to run from a duel supply, like +15 - 0 and -15V  ... a pedal only has a single +9V to run from so  basically by biasing the non inverting input halfway of the 9V we can pretend +4.5 V is 0V and then block the DC on the output with a cap


    www.2020studios.co.uk 
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  • PhiltrePhiltre Frets: 448
    Danny1969 said:
    Philtre said:
    What is a "Vref" and why is it needed? Is it a positive or negative supply? From my (limited) knowledge the two resistors act as a voltage divider to create a smaller voltage (5v I think in this case).
    Opamps are designed to run from a duel supply, like +15 - 0 and -15V  ... a pedal only has a single +9V to run from so  basically by biasing the non inverting input halfway of the 9V we can pretend +4.5 V is 0V and then block the DC on the output with a cap
    OK, but the opamp still needs a +9v supply to pin 8 and negative ground to pin 4, right?
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  • m_cm_c Frets: 238
    Vref is a reference voltage.
    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.

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  • Danny1969Danny1969 Frets: 3214
    edited January 1
    Philtre said:
    Danny1969 said:
    Philtre said:
    What is a "Vref" and why is it needed? Is it a positive or negative supply? From my (limited) knowledge the two resistors act as a voltage divider to create a smaller voltage (5v I think in this case).
    Opamps are designed to run from a duel supply, like +15 - 0 and -15V  ... a pedal only has a single +9V to run from so  basically by biasing the non inverting input halfway of the 9V we can pretend +4.5 V is 0V and then block the DC on the output with a cap
    OK, but the opamp still needs a +9v supply to pin 8 and negative ground to pin 4, right?
    Yes, if you imagine we connect 8 to +9V and 4 to ground THEN we bias pin 3 at half the supply of 4.5V. Now our guitar signal which is an AC voltage can either swing our opamp upwards from 4.5V to near the 9V or negative from 4.5V towards ground. The only downside is we now need to block the permanent 4.5V on the input and output of our circuit from interfering with other devices in our chain, so we use caps on the input and output which block the 4.5V DC but allow the AC signal element to pass through
    www.2020studios.co.uk 
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  • PhiltrePhiltre Frets: 448
    edited January 1
    Great explanation @m_c and @Danny1969 - thanks! Wizs all round!
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  • PhiltrePhiltre Frets: 448
    edited January 3
    Quick progress update.

    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:
    • My eyesight isn't as good as it used to be and these components are bloody tiny and fiddly
    • Figuring out the best way to lay out the components on the breadboard
    • The breadboard I have is cheap, and some of the contacts are are a bit dodgy and stiff

    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. ;-)

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  • Adam_MDAdam_MD Frets: 2529
    Philtre said:
    • My eyesight isn't as good as it used to be and these components are bloody tiny and fiddly
    Get a magnifying lamp I have a daylight one which has been one of the best pedal building purchases I've made. I used to get really bad headaches if I'd spent a long time working on a pedal but that stopped once I grabbed a lamp with decent magnification.  

    It's been useful for all sorts of stuff outside of pedal building too.  
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  • PhiltrePhiltre Frets: 448
    Adam_MD said:

    Get a magnifying lamp I have a daylight one which has been one of the best pedal building purchases I've made. I used to get really bad headaches if I'd spent a long time working on a pedal but that stopped once I grabbed a lamp with decent magnification.  

    It's been useful for all sorts of stuff outside of pedal building too.  
    I tried a round magnifier once but I couldn't handle the the curvature of the glass, things looked distorted. Can you get flat ones?

    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. ;-)
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  • m_cm_c Frets: 238
    For solid core wire, the best option is manually adjustable wire strippers. The type with two V-shaped jaws, with a screw to set how close the V's get, as that way you're cutting the insulation at 4 points.

    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.
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  • PhiltrePhiltre Frets: 448
    edited January 4
    Success! And it worked first time. :-)

    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. :-)

    Image1


    Lessons learnt:
    • Trim pots save space, but it's a bugger if you want to play with the knobs
    • Ditto for the DIP switch - difficult to access
    • I need to come up with a better solution for offboard sockets and pots
    • Breadboarding can potentially lead to more errors as the connections can be sketchy

    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:

    1. Veroboard it together and re-use my components and buy pots, switches and an enclosure
    2. As option (1) but locate a PCB. But this might use onboard pots and I'd need to be careful with drill holes
    3. 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. ;-)
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  • Danny1969Danny1969 Frets: 3214
    Well done @Philtre ..... that's good progress and a lot learned

    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 :-1: 

    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 


    www.2020studios.co.uk 
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