OFF-BOARD WIRING: Positive Ground

A short guide to off-board wiring for positive ground effects.  It's not as complicated as it's sometimes made out, but I do get that it's confusing.  If you want all the details, head over to the tech section of Amplified Parts - it may hurt your brain by the end, as it's very detailed.

Note #1:   Positive ground effects are not the same as positive centre DC power jacks.  People often confuse the two.  

However, I have heard that some people do reverse the DC jack polarity for their positive ground effects, as they prefer the switching when a battery is involved.  For me, this is just one more complication that should be avoided.  

Note #2:   Apart from the battery-only option, these all need a good quality isolated power supply to work (no daisy chaining with negative ground effects).  

I use a Voodoo Labs Pedal Power 2 Plus that I picked up second-hand.  It's great, but it's not the most lightweight or modern supply - if you travel internationally, you'll probably want a lighter fast switching supply that can automatically handle variations in supply voltage (220-240v vs 110-120 etc).

POSITIVE GROUND GUITAR EFFECTS - DC ONLY

Often just a DC jack on its own is fine - there are a lot of benefits with this approach.  No batteries for one (obviously), mono jacks are fine and you gain space in the enclosure.  

This is my preferred approach for anything that will live on my board.  Note that the DC jack is wired in the normal manner and the polarity of the LED is reversed.  Simple right?

DC WITH BATTERY

Sometimes people want both options, which is understandable, but I'm not really into it.  

It's not obvious, but two switches are now working in the circuit above.  One in the DC jack, and the stereo input jack.  

DC switch:  When the DC jack is plugged in, it breaks a connection between the two positive terminals, so the battery is now out of the circuit.

Input jack switch:  V+ is connected to the ring of the stereo jack.  The circuit can only be powered up once a jack is inserted, connecting the ring (V+) to the sleeve (ground).

JUST BATTERY - OLD SCHOOL, NO LED

Possibly the easiest option, if you don't mind changing batteries occasionally and can remember to unplug a guitar lead.  There is no cleaner power supply than a battery, although they are kind of an environmental disaster.  Without an LED, they will last about a year or so in fuzz pedal.   Some folks also swear that batteries sound better and only use carbon types.  

WHAT ABOUT DC INVERTERS?

Yes, you could just add a DC inverter, but then it's no longer a positive ground effect, is it?  As far as the rest of your pedal chain is concerned, it's a regular negative ground effect.

I rarely do this, as I mostly use 0.15" vero board for vintage-style circuits.  The hole spacing doesn't match the inverter IC and being a bit of a purist at times, I don't like the look of it.  I've also had issues with dodgy ICs and high-pitched noise at times.  It can work well and heaps of people do it, it's just not for me.

VERO: Getting Started Building DIY Guitar Effects - Vero Layout Guide

I've had a few questions lately via Instagram about some basics on my vero layouts - while this doesn't cover everything, I hope it helps clarify a few things for people just starting out. 

Essentially, my vero layouts are functionally the same as many others, the key differences being the use of colour coding, and they usually have less text as a result of this.  I more than make up for the lack of text on the layout with my ramblings on the blog posts.  Components on the layout are scaled to physically match the size of the components that I use.  

GUITAR FX VERO LAYOUT GUIDE

ADDITIONAL GUIDES

Techniques

Tools

Off-board wiring (stomp switches)

WIRE: Hook-up Wire for Vero Construction

22AWG and 24AWG are what most pedal builders use, but depending on where you live, these values may not be readily available from your local store.  Of course, online is always an option, but shipping a bunch of heavy copper reels can be expensive.  

22AWG and 24AWG are not available in the most common electronics stores in Australia (Jaycar and Altronics).  21AWG and 26AWG are the nearest available size stocked locally.

WHAT SIZE HOOK-UP WIRE TO USE FOR PEDALS?

As mentioned above, 22AWG or 24AWG are your best bet.  Anything larger than stranded 21AWG will probably not fit in a standard vero board.  Also, keep in mind the size of the lugs on a 3PDT switch and the DC jack that are quite small.

Thinner than 26AWG starts to feel a bit sketchy - not recommended.  As the wire gets smaller, I find it harder to solder and it feels like it will break off.  Specs for voltage and current start to get a bit on the low side too.

Note the sizes below, which are limiting factors.

Standard vero:  

• ~1mm holes (0.9mm)
• 2.54mm pitch (0.1 of an inch)

Vintage style vero:   

• 1.4mm holes
• 3.8mm pitch (0.15 of an inch)

Stomp Switches

Now this will vary a little, but as a reference, Alpha 3DPT have 2.3mm x 1.1mm holes.  I have seen some specs for 0.9mm wide holes.

AMERICAN WIRE GAUGE (AWG) SIZES

AWG sizes specifically relate to solid core wire - the equivalent stranded wire will be slightly larger. Wire thickness decreases as the AWG number increases.  

21AWG

• 0.723mm in diameter
• 0.412mm square in area

21AWG can take more current / voltage than any pedal will ever need.  This is often sold as medium-duty general use hookup wire (available at Altronics).  This gauge is getting into amp building territory.

22AWG

• 0.644mm in diameter
• 0.326mm² in area

24AWG

• 0.511mm in diameter
• 0.205mm² in area

26AWG

• 0.44mm in diameter
• 0.129mm² in area 

26AWG is often sold as light-duty hookup wire. It’s still quite OK to use considering the low voltage and amperage requirements of your average guitar pedal.  Not my favourite - I think it’s a bit fragile.

If you’re in Australia, this is one of the options on reels at Jaycar and it’s what comes in the little bags of pre-cut wire.  Strangely Jaycar lists what appears to be the same cable sold by the metre as 25AWG.  Altronics also has a huge range of colours in 26AWG sold by the metre or reel. 

STRANDS

Apart from the gauge of wire, there’s normally a reference to the makeup of the wire - how many strands and their thickness.  The same wire gauge can be made up of a number of different strand configurations.  More strands = more flexibility.  Common strandings are 7, 13, 19 & 27. 

Example using 24AWG Alpha specs

1 x 0.51mm (solid wire)

7 x 0.20mm

19 x 0.13mm

Strands can also be described in AWG, with the first number being the number of strands, and the second number being the AWG size.  

7/32 = 7 strands of 32 gauge wire.  This is the same as 7 x 0.20mm

METRIC SYSTEM

The metric system for wire size is relatively simple - it's the cross-section of the cable in square millimetres and also the number of strands of wires, with their diameter in millimetres.    Where it can get a little confusing is when only the stranding is listed.

Using 24AWG as an example, these are all the equivalents using just standing: 1/0.5,  7/0.2,  19/0.12,  30/0.1

INSULATION TYPES

There's a range to choose from, depending on your budget and what kind of look that you're going for.  I stick with plain old PVC, mainly due to price.

Cloth

• Vintage looks
• Have to take some care not to end up with ragged-looking ends when cutting it to size
• Can't use regular wire strippers

PVC (Polyvinyl chloride)

• This is the standard insulation found on most products - lots of builders use PVC
• Can be melted with a soldering iron if you take too long - max heat is ~100C
• Flexible enough for decent positioning 
• Cheap, readily available, does the job

MPPE (Modified Polyphenylene Ether)

• Similar to PVC, but lighter and more eco-friendly as it can be recycled
  

PTFE / TEFLON (Polytetrafluoroethylene) 

• Usually rated for harsh environments, often military spec cable
• Rated for higher temperatures - almost double that of PVC 
• Harder than PVC or silicone - slightly stiffer, harder to strip
• Three times the price of PVC

Silicone

• Rated for higher temperatures than PVC 
• Very flexible - more so than PVC or PTFE
• Softer than other insulators - less hard-wearing
• Almost four times the price of PVC
• Generally, a really nice hookup wire to work with, but it comes at a high cost

CONDUCTOR MATERIAL:  COPPER VS ALUMINIUM WIRE

Always copper.  Aluminium is the cheaper less conductive alternative.  Often really cheap wire is copper-clad aluminium.  

TINNED VS UNTINNED WIRE

Tinned wire has a coating applied to the copper strands before they are combined into a cable (usually tin or silver).  Tinned wire is more resistant to corrosion, and as such is easier to solder.  

Does this mean you don't need to tin before soldering?  Yes, you still should tin tinned cable - confusing yeah?  Tinning cable sticks the individual wire strands together, which reduces the chances of a rouge hair-thin wire touching something it shouldn't on your board.   Tinning is not essential, but it is often very helpful.

PRE-BONDED WIRE

This is a wire that in addition to a tin coating on the individual strands, the entire cable has been heated so that the tin flows and bonds the strands together  OR  once the cable is formed from raw copper wire, the cable is given a topcoat of tin.  

It does make the cable a little stiffer, and you don't need to tin the wire, as this has already been done for you.  24AWG pre-bonded is a go-to cable for a lot of people.

As shown below, with bonded wire the individual conductors form one solid piece.

With regular wire, the individual conductors can be easily separated

DECIPHERING CABLE REELS

Sometimes looking at labels on reels can be a bit confusing - but once you know what you're looking at, it's not so hard.  As an example for this reel of Alpha 5854/7 wire:

24 AWG (7/32) SPC
.010 (.25MM) PFTE INS
MIL-W-16878/4 TYPE E 200C 600V

First line:        AWG, Strands, then conductor type (SPC = silver plated copper)

Second line:   Insulator thickness and type

Third line:      Further specifications which in this case is a Military spec, including max temperature and voltage.  If you see Type E on the cable, it's a good cable.  

VERO: How to Mount Vero in Pedal Enclosures

THE PROBLEM WITH VERO / STRIPBOARD LAYOUTS

As much as I like a bit of vero (clearly), vero is not meant for commercial-scale production, at least in the modern sense.  Unlike PCBs, where pots and switches can all be mounted on the board, thus providing a convenient way to hold the board in the enclosure, vero layouts are almost never designed this way.  This brings us to the issue at hand - I've built it, now how do I make it stay put in the box, or how do I know this thing will be reliable?

Vero, or stripboard layouts are often laid out by folks like me, with small size often being the main driver of the layout, without any consideration for anything else.  What is rarely seen on layouts is space for mounting points, or any indication of how it should be laid out in an enclosure with pots, jacks, switches etc.  Sure, we all like to do our own thing, but it's kind of hard to work out when you're just starting out.  I know when I was starting out, boards were jammed in enclosures in any way possible, usually with a lot of excess wire.  As long as it worked and I could close the lid, I was happy.

SO WHAT TO DO?

Well, kind of obvious - secure the vero board to the enclosure properly.  The board is literally full of things that you don’t want touching the enclosure, switches or any other conductors.

HOW TO MOUNT VERO IN A GUITAR PEDAL ENCLOSURE?

Standoffs

This is my preferred method.  Self-adhesive plastic standoffs are pretty handy - but you will need to check if there's space on the layout for a few holes and that there is enough room in the enclosure once the pots and switches are in (which should happen first, in my opinion).  If there isn't enough room, see if there's room to add a couple of rows or columns to the vero layout for mounting holes.

Standoffs come in many different shapes and sizes, usually with a plastic snap to lock them in place, or a small screw.  Naturally, if you are using the metal screw type, make sure that the screw isn't shorting the conductive strips on the vero board.   Of course, there is the bulletproof method, of screwing the standoff all the way through the enclosure, but this is a little harder to do and can limit space for graphics on the front.

This is a small point-to-point board - a single screw was enough to secure it.  In retrospect, I should have used two.  

Plastic standoffs on each end of a D*A*M Fuzzsound worked well

Glue

Quite a few people use hot glue guns to secure boards, and it works, but good luck if it ever needs repair.

Tape & Velcro

Thick double-sided tape and velcro also does the job.  At least with Velcro, you can remove it for repair, but something about velcro in a pedal bothers me.

Gum

No not that type of gum.  This is a suggestion from a comment left on the post (thanks Brain).   There's a sticky gum/gel specifically designed for sticking down boards, but you can still remove them later (with a bit of effort).

https://guitarpcb.com/product/gum-wadz-pcb-mount/   

LAYOUT PLANNING

I normally look at the vero layout, pots, switches and enclosure size before starting the build.  This way I can get a feeling for how I might finish, before I start.  Kind of frustrating to have something in mind, only to find that it was never going to fit after building the circuit.  I learnt this the hard way, maybe more times than I care to admit.

After I've built and tested the circuit (with ample wiring already on the board), I double-check that everything fits, by first adding the jacks, switches and pots to the finished enclosure.  Then drop the board in, to confirm the initial plans are still valid.  

I usually wire up the jacks, stomp switch and LED first - then I attach the circuit to the enclosure, and cut the cable to size, and solder connections as required.

Another method I sometimes use is to create a cardboard wiring jig, and do most of the work there, before transferring to the proper enclosure.   This just provides a bit more room to move, as some enclosures can be a little cramped to work in, and it works out about the same in terms of final product.

How bad does the cardboard jig look?   This is the Revox A77 preamp that I put in a wedge enclosure.

WHAT TO AVOID WHEN MOUNTING CIRCUITS IN PEDAL ENCLOSURES?

Now I think I've done nearly all of these things at one stage - so no judgement if you have too.

Try not to:

• Wrap it in electrical tape, sure it works, but what a mess

• Stick it in a plastic component bag

• Do nothing and hope for the best / won't the wires just hold it where it should be?

 

POWER: DC Power Filtering

REDUCING NOISE ON DC POWER FOR FX PEDALS

When looking at a guitar pedal schematic, you're really looking at two circuits that overlay each other, sharing resources, and working together.  There's one for the AC signal and one for DC power.  

We use capacitors to block DC, and let AC signals pass - this is called coupling, and you will see it everywhere on circuits used for audio.  Capacitors are also used to store power and create filters.

What is noise on a power supply?

Noise on a power supply can come from various sources, and essentially it's an unwanted signal on the DC supply.  It can be present in your home wiring, radiate from other electrical devices, or be left over ripple from the conversion from AC to DC in an external pedal power supply. 

DC has no frequency, as it's a flat line (0hz), so it's blocked by capacitors.  Adding signal (noise) to DC is like having another source of AC entering the circuit, that can move past the capacitors blocking DC, and join your guitar signal.  We don't want this to happen - especially for high gain circuits. 

How can noise be reduced?

The most common way used in guitar effects is by decoupling the power supply and adding a low-pass filter.  This, used in conjunction with a high-quality external power supply, will go a long way to reducing noise.

Decoupling is very similar to coupling, but now the capacitor is used to ground AC signals, letting DC pass by the capacitor.

If noise appears on the DC line, hopefully, most of it will be taken care of by the decoupling capacitor.  Remember AC signals see capacitors as shorts - DC sees them as a blockage or break in the circuit.

Adding a 100ohm resistor with the capacitor forms a low pass filter with a cut-off of around 16hz - this helps filter out additional noise in the audible range.  Keep in mind that the filter cut-off frequency is not a hard wall.  It’s really a gentle slope, so this doesn’t eliminate all noise,  but it can definitely make a big difference.  

Sometimes a 100n ceramic capacitor is added, which helps with high-frequency filtering - this is specific to ceramic caps, don't use a poly cap.  At one stage, I didn't believe that this would work, as in theory it's just adding a little extra capacitance - that is until I heard the results on a breadboard.  One on particular circuit, the results were audibly very apparent.

Quite often 100n capacitors are also placed as close as possible to V+ and V- of ICs to help reduce noise. 

There's a good chance you will also see something like this on schematics - it's the same thing as above, but with a voltage divider to provide a bias voltage at half the supply.  Bias voltage is often required for ICs, but I will not go down that rabbit hole here.  

Quite often, a smaller capacitor is used, as much of the work has been done with the one that comes before it.  The 100k resistor also forms a low pass filter with the 47u capacitor, with a cut-off frequency of 0, so there's not much point of having anything bigger.   Even if the voltage divider used 10k resistors and the capacitor was 10u, the cut-off frequency would be a very low 1.6hz

Battery Power 

Now, if you really want to avoid any power-related issues - use batteries.  A battery is about the purest supply of DC you will find.  I often test with my pedals with a standard DC power supply and a battery just to see what's happening with noise.

They are terrible for the environment, so most people do not use them for this reason. Some manufacturers don't even have it as an option - for my builds I only ever add battery snaps to vintage builds that are positive ground.   

There are rechargeable battery packs on the market specifically made for pedal supplies these days.   I have not tried one, but they are probably worth a look.

POWER: Polarity Protection

POLARITY PROTECTION FOR GUITAR EFFECTS PEDALS

Guitar pedals are full of components, some of which are so sensitive to voltages of the wrong polarity that they will explode - electrolytic capacitors in particular.   Exploding caps is not good.  

And to really start at the beginning, the wrong polarity means V+ and ground (or V-) have been swapped the wrong way around.  This usually happens due to people using random 9v adaptors, not realising that most effects run off centre-negative adaptors.  

Vintage pedals were designed to run off batteries, so you never see polarity protection on schematics - try and connect a 9v backwards.

How to protect circuits?

There are several ways to protect polarity.  I'll start with the most common two and describe some pros and cons for each.

Both methods below rely on a key characteristic of diodes - they only let current flow in one direction. On schematics, this is the direction that the triangle in which the diode symbol is pointing.   

Diode across the power supply (parallel)

The diode sits across V+ and grounds with the cathode (negative side) facing the positive voltage.   Some people are really quite vocally opposed to this method, but you will see it used by some major builders.

V+ can't travel through to ground, as the diode prevents this from happening - but if the polarity of the power supply is reversed, the diode acts as a short between V+ and ground, protecting the circuit.

• Allows maximum voltage to pass through to the circuit

• While it protects the circuit from damage, it essentially short circuits the pedals power supply to do this - it could damage your pedals external power supply, if the power supply has no short-circuit / reverse voltage protection

• Does not protect against overvoltage.  i.e.  plugging it into 24v when it can only take 9v

• 1N400X series diodes are commonly used.  A 1N4001 is rated to 50v, which is plenty for our purposes.

Diode in series with supply voltage

Being in series with the power supply means that current has to travel through the diode, and being a diode it only lets power through one way.  So it's a really simple way to solve the problem.  

• There will be a voltage drop matching the forward voltage of the diode used, which is why 1N5817 Schottky diodes are seen so often, as they have a lower voltage drop compared to a 1N4001 (about 0.6v with a normal diode, and 0.3v with Schottky)

• Does not have any impact on external power supplies

• Does not protect against overvoltage.  i.e.  plugging it into 24v when it can only take 9v

CAPACITORS: Capacitor Basics for Pedal Builders

Capacitors can be pretty complex things, given that they are passive components.  There are plenty of in-depth discussions and explanations out there, but this is not one of them.  This is intended as a primer for anyone just starting out building, who wants to know a little more about capacitors, but doesn't like looking at equations and doesn't have an interest in physics.

This handy video on youtube also covers capacitors really well in a simple way, but not so much in the context of the guitar.

Capacitors are also one of the most argued-about components in existence when it comes to anything audio-related, or at least in some circles.  Capacitor X should never be used, Capacitor Y will change your life.  We've all heard it.  

CAPACITOR BASICS FOR DIY GUITAR PEDAL BUILDERS

SO WHAT ARE CAPACITORS ANYWAY?

The capacitors that you will find in guitar effects are made from two conductors, separated by some form of insulator (called a dielectric).  

The conductor can be a thin foil or an electrolyte (guess where the name for electrolytic caps comes from).  

The insulator can be almost anything - including air....  Common insulators include ceramic, glass, plastics (polypropylene, polystyrene, polyester), paper and mica - which also helps explain the names given to different types of capacitors.

Note that the two conductors are separated - there is no physical connection between the two.  Capacitors work by building up an electric field and transfer or store electrical energy via this field. 

Unlike their friend, the resistor, capacitors are more complex in how they work.  Where a resistor has a set resistance, the resistance of a capacitor, which is called inductance, varies greatly depending on frequency - they pass very high frequencies with ease and block very low frequencies.  

Their ability to block low frequencies is why they are used as coupling capacitors.  DC voltage is basically a flat line (hopefully), which is 0Hz.  You can't go any lower than that.   Transformers are an alternative to coupling capacitors, but they are big, heavy and expensive by comparison.

TYPES OF CAPACITORS

There are quite a few different types of capacitors available, with many opinions on the internet regarding which ones sound the best - or that they all sound the same. 

These are some of the most common types of capacitors and where they might be found. 

Electrolytic Capacitors

• power supplies for decoupling and filtering DC ripple

• large values for coupling capacitors (usually once values are over 1 or 2uF)

Ceramic Capacitors

• filtering high-frequency DC ripple

• small value capacitors, usually less than 1nF

Film Capacitors (any type)

• coupling capacitors, usually between 1nF and 1 or 2uF

• filters for AC signals

Note:  Multi-layer ceramic capacitors range from very low to quite high capacitance and are often used for a range of different purposes.

CAPACITOR POLARITY

Some capacitors have polarity - electrolytic and tantalum in particular.  There are electrolytics that are non-polar, which are marked 'NP'

Ignoring polarity on a power rail will result in a small pop, followed by a dead capacitor and a short circuit.

A common question on social media and forums is about replacing a polarised electrolytic caps with a different type of capacitor - the answer is yes, you can.  Pretty much the only reason electrolytics are used, is that they are smaller and cheaper than other types for the capacitance required.  A 100uf film capacitor would be gigantic and expensive, so electrolytics are used.

CAPACITORS IN GUITAR EFFECTS CIRCUITS

Typically, capacitors will fulfil one of these roles, and sometimes a couple at once.

Coupling Capacitors

Coupling capacitors join different sections of circuits while blocking DC voltage from the previous section.  They carry AC signal - so they are usually in the signal path.

• AC signal passes

• DC voltage blocked

Decoupling Capacitors 

Decoupling capacitors are used in DC power supplies and are not in the signal path.  Decoupling capacitors may also be distributed around the circuit - different sections may have their own decoupling capacitors.

• Reduce DC ripple

• Remove AC noise by providing a path to ground

• Isolate sections of the circuit in terms of DC power supply

• Supply current quickly without affecting other areas of a circuit

A lot of vintage effects do not have decoupling or any kind of filtering, or very minimal amounts if it is present.  They were designed to run on batteries, so this was never really a consideration.  When building vintage circuits, unless you plan on using only batteries, add modern filtering and polarity protection.  

High and Low Pass Filters

Capacitors form high or low-pass filters when paired with a resistor or an induction.  Most commonly with resistors in guitar effects pedals.

• Power filtering to reduce DC ripple (a decoupling capacitor can also be part of a low-pass filter)

• Equalisation provided by filters (a coupling capacitor can also form a high-pass filter)

Coupling capacitors often form high-pass filters in circuits, especially if they are placed before pots or bias resistors - basically, any resistance going to ground after the coupling capacitor will form a filter.

In the example below, which just happens to be a Big Muff, the input capacitor (C6) is a coupling capacitor, blocking DC from entering from another source or leaking out from the DC bias voltage applied to the base of the transistor (Q1).  One of the resistors in the bias network is after the coupling capacitor and goes to ground (R10).  

A 100nf cap with a 100k resistor forms a high-pass filter, which works out to be around 16Hz - of course, there are a lot of other things happening to the signal; I'm only using these two components as an example.  

The output capacitor is also a coupling capacitor, which forms another high-pass filter with the Sustain pot, which will be variable (pots are variable resistors).  The graph shown is only in relation to the 100n/100k RC filter; it is not the frequency response of the Big Muff booster stage.    

CAPACITOR VALUES

Capacitance is measured in Farads - and the annoying thing about farads is that one farad is a truly gigantic amount of capacitance compared to the actual size of capacitors commonly used, so we end up measuring them in microfarads (uF) which is one-millionth of a farad, nanofarads (nF) which are one billionth, and pico-farads (pF) which is one trillionth.  

This makes the math a bit more interesting, with any equation requiring farads.  I generally avoid math where possible by using online calculators.  

So a garden variety capacitor can be listed as 0.01uf, 10nf, or 10,000pf, which causes a bit of confusion when you are just starting out.  

CAPACITOR MARKINGS

Electrolytic capacitors are easy to read, as they always have the capacitance and voltage clearly marked.  Smaller capacitors are a bit harder to read, as there's less space for printing, so manufacturers resort to number codes.

If there are only two digits listed, you can take this value as the capacitor's value in pF.  If there are three, then you have a multiplier to factor in.

The additional number tells you how many zeros to add to the first two.  So 101 = 100pF, 102 = 1,000pF and so on.   

Get the magnifying glass out for small MLCC caps

CAPACITOR TOLERANCE

Not unlike resistors, capacitors are also built to certain tolerances, which also relates to price.

Further to the number code mentioned above to determine capacitance value, if there's a letter at the end, the letter indicates tolerance.  example:  101J = 100pF 5% tolerance

Common tolerances are;

F    1%

G    2%

H    3%

J    5%        (common for MKT caps)

K    10%

L    15%

M    20%    (common for electrolytic caps)

N    30%

Z    +80%, -20% 

CAPACITOR VOLTAGE RATING

All capacitors have a voltage breakdown rating, which is often printed on the capacitor; sometimes this is in the form of a code.  

Exceed the voltage breakdown rating, and the capacitor will become conductive.  Note the point above about the two conductors in the capacitor being separate, well that's not quite the case when voltages are exceeded.  

As a general rule, the voltage rating of a capacitor should be double what it will encounter in the circuit.  This is usually only an issue with electrolytic capacitors, as they have a low voltage rating when compared to other types of capacitors.

Can you replace a capacitor with one of a larger voltage rating?  Yes, you can.  It makes no difference, as the capacitance is still the same.  

Can you go smaller?  Yes, so long as it still meets the double the expected voltage rule.  Example:  replacing a 100v cap with a 50v cap in a 9v circuit is not going to be a problem.

Voltage codes (Max operating voltage);

1A    10V

1H    50V

2A    100V

2T    150V

2D    200V

2E    250V

2G    400V

2J    630V

3A    1000V

STRAY OR PARASITIC CAPACITANCE 

Capacitance can be formed by accident, which is where terms like parasitic or stray capacitance come into play.  Thinking about what a capacitor is - two conductors separated by an insulator (including air), well that's practically every component placed on a board, including the off-board wiring.  

Veroboard is just strips of conductors running directly next to each other, separated by an insulator.  It's basically a big flat capacitor with really low capacitance.  I've read reports that there are about 13pf between tracks, on a 300m length board, which works out to about .2pf per hole.   That's pretty small - most multimeters can't even measure that low.   

Components also have internal capacitance, which you will see listed on transistor datasheets.  Again, it's usually pretty small.

So the question is just one of does it matter?  Is the capacitance enough to cause problems?

WHAT IS LEAKAGE & DOES IT MATTER?

Leakage is not a physical substance leaking out of a capacitor (although that's also bad), it usually refers to DC leakage in a coupling capacitor.

Capacitor leakage can cause the dreaded switch pop, which is partially the reason why a resistor is often paired with an electrolytic capacitor on inputs/outputs.  The resistor provides a path to ground for DC to drain.  

All electrolytic capacitors leak to some degree.

SHOULD I SPEND MORE ON FANCY CAPACITORS?

If it makes you happy, yes.   Just don't spend too much...  if it's marketed as audio grade you will probably pay too much, if it says audiophile, you're about to be massively ripped off.  

Also worth noting is that many vintage pedals were built with really cheap parts.  You don't hear of anyone pulling caps out of their vintage pedals to replace them with new audiophile versions (at least, I hope they aren't).

 

WHAT ABOUT VINTAGE OR NOS CAPACITORS?

Will it sound better?  Probably not, but they can look cool, especially if using carbon composition resistors.  Given a choice between grey vs red with stripes...   I prefer the latter.  I have a range of different NOS caps, largely based on looks.  I also have a large stock of regular MKT and greenies that I happily use.  

Just don't buy vintage or NOS electrolytics, as they can actually dry out or physically leak over time.  Paper in oil can often have issues.

Again, don't pay too much for them.  It makes me sad to see people paying excessive amounts of cash for vintage ceramic capacitors to "upgrade" their new Strat or buying bumblebees for their Les Paul copy to get that magic tone.  For a period-correct restoration of a vintage instrument, fair enough, I'd probably do the same.  Dropping a $50 cap in your Squier? That's maybe not the best use of your money.

CAN YOU HEAR A DIFFERENCE?

So this is where things might get more controversial - people make all sorts of claims about capacitors and their sound.   Different types of capacitors do have different properties, which might affect the sound in different circumstances, but is a guitar pedal one of those circumstances, and is there really much difference anyway?

Things to consider;

• Capacitor tolerance - tolerance can vary quite a bit, up to 20%.  So even changing two capacitors of the same type might actually result in a slightly different sound.  As an example, in a filter, it will change the roll-off frequency, resulting in an audible difference.

• Listening conditions - to make a proper comparison, listening conditions need to be identical, as does the sound source.  Example:  next time you are playing the guitar, just turn your head away from the amp a little.  Sounds different, right?   Sit in a different spot - sounds a little different right?   See where I'm going...   

• Confirmation bias - so you've just dropped a bit of cash on fancy caps.  You've read that they sound better, and someone on youtube was raving about them.  When they finally arrive in the post, and you get a chance to try them out, you actively try to hear something different about them.  Subconsciously, you may hear what you want to hear.   This is why double or triple-blind tests are used in scientific studies.  It removes unintended bias from results.   

• What is the capacitor actually doing - is the cap actually in the signal path?  No, you can't hear an electrolytic cap in the power supply.   Should you put a good cap there?  Sure, you want a good quality cap that will last and perform well.

• Have you ever bought an album only to return it after discovering that cheap ceramic capacitors were used in the vintage Big Muff used on a track?  Yeah, probably not.

And if you want to hear a bit more about capacitance, inductance and impedance, all relative to guitars - Kingsley explains a great deal in this video on That Pedal Show.  

RESISTORS: Basics for Guitar Pedal Builders

Everything listed below is about guitar pedal builds and is not intended cover all possible uses of resistors.  It's an incomplete and general reference intended for someone just starting out building pedals.   So if I have missed particular properties or information, it's because I either don't understand them or it's irrelevant for this purpose.   

RESISTOR BASICS FOR PEDAL BUILDERS

All fixed resistors are made from a combination of conducting and non-conducting materials (insulators).  

The ratio of the two materials determines the resistance level, measured in ohms.  

In other words, if a resistor has a high amount of conducting material compared to non-conducting material, it's a lower-value resistor.  Electrons easily flow through the resistor, as resistance along their path is low.  

If the opposite is true, and there's a lot of non-conducting material in the resistor compared to conductors, then it's a higher-value resistor.  Electrons now have a harder job of passing through the resistor; therefore, resistance is high.

What do resistors actually do?   As mentioned above, they provide resistance to the flow of electrons, which controls current (sometimes called intensity).  Current is measured in Amperes, usually shown as I in equations.  So thinking of current as intensity when I is used as the symbol can be handy.  

In very broad terms, resistors are used to control the intensity of the current going to other components in the circuit.  Current relates to voltage and power as shown in Ohms Law, so as well as controlling current, resistors can also control voltage to components.  Resistors are also used to set impedance, divide voltages and form filters with their friend, the capacitor.  I'm sure they do more, but we'll keep things simple here.

CARBON COMPOSITE RESISTORS

The magical resistors make everything sound vintage right?  Well, they at least look the part, and that's the only reason I use them in a build.   

Pros:  Look vintage/period correct.

Cons:  Expensive, can be hard to find, tend to be large compared to other resistors, technically higher in thermal and current noise than other resistors.  Tolerances are usually 10% or 20% and are not very stable.   

Here's an interesting link with a summary of studies on carbon composition resistors over the decades.  It will not be good news if you like carbon composite resistors.  Incredibly inconsistent and noisey is my one takeaway.

CARBON FILM RESISTORS

Carbon film appeared after carbon composition resistors and is still widely used today.  Nothing wrong with carbon film at all.

Pros:  Look vintage/period correct, very cheap and accessible.  Tolerances are good

Cons:  Technically higher in thermal noise than more modern resistors (but again, you probably won't hear this in your build)

1W Carbon Film Resistors

METAL OXIDE RESISTORS

Metal oxide came after carbon film, so the next technological progression.  

Pros:  Technically better than carbon comp or film.  Some amp builders like these for their ability to handle high power and surges.

Cons:  Not as readily available as metal and carbon film.  Perhaps a little more noise than metal film.

1W Metal Oxide Resistors

METAL FILM RESISTORS

Metal film is an improvement on metal oxide, so technically a better resistor than any other standard resistor available and is considered the standard by most people.

Pros:  Cheap and accessible, technically very low noise, and high tolerances - usually 5% or better.

Cons:  Can be easier to damage with power surges.

RESISTOR VALUES

At first, the available values might seem very random, but there is a system to this.  The standard is the E24 series - and there are many different series in the E standard, but let's not go there.

Resistors are spaced in values so that one resistor in series, does not overlap with the next in the series, when tolerances are considered.

For every value resistor that you can find, there are others available in multiples of 10, 100, 1,000 etc.  example:

33ohm        3.3k        33k        330k        3.3M

So when trying to trace a circuit, you know you are probably not reading a resistor correctly if you come up with an odd value, not in the usual series.  Custom resistors are available but rarely used in guitar effects (likely due to cost and being pointless).

RESISTOR MARKINGS

Resistor values and tolerance are designated by colour codes, which are the coloured bands on the resistors.  

READING RESISTOR VALUES

The coloured stripe closest to one end is the first stripe.   Read left to right from the first stripe.  The last stripe is always tolerance.

Some resistors are easier to read than others, especially four-band resistors using a gold or silver band for tolerance.  It's really obvious where to start and there are only three colours to consider.

I won't list the colours etc, here, as while I remember most of them now, I still use an online calculator occasionally to double-check.  There's plenty out there, just google it and bookmark a favourite.

RESISTOR TOLERANCE

Resistors come in various tolerances, ranging from plus/minus 20%, 10%, 5% and 1%.  Tolerance is how far from the stated resistance value the resistor might be.  It doesn’t mean they will be 20% off; it just means they might be.

In a guitar pedal, 5% tolerance is fine.   Even 10% is not going to be a big deal in many cases.

Smaller tolerances can be found, but they're expensive and unnecessary for anything related to guitar effects. 

Most resistors, especially metal film will measure quite close to their actual value.  Vintage carbon composite resistors, on the other hand, can be a bit off - they can drift in value over time.   

RESISTOR POWER RATINGS

Resistors come in a range of power ratings, measured in Watts - 0.125 W, 0.25 W, 0.5 W, 1W, 2W etc, and once we see larger values, they start getting into wire wound and specialised resistors, which are not used in small signal circuits.

Quarter to half watt are commonly used for pedal building.  Don't buy big resistors for mojo value, as they generally don't fit a board designed for regular-sized resistors.  But suppose you are doing a mojo build with fancy axial or tropical fish capacitors. In that case, normal quarter-watt metal film resistors can sometimes look out of place (at least in my opinion).   

Unlike resistance & tolerance, power ratings are not marked standard resistors.  If you have an unknown resistor, you must guess based on size.  

Exceed the power rating, and you will have a dead resistor (it will overheat and burn).  Kind of odd that they never list power on the resistors, as the result of mistakes is a dead resistor / possible circuit damage.