the role of the capacitor in music

the capacitor


In the realm of passive components, capacitors are second only to resistors in ubiquity. They are everywhere, in almost every electronic device you will ever come across. So it’s no surprise that capacitors are an integral part of audio circuits in general, and guitar effects specifically.

What makes capacitors so important? Well, they can be used to perform some very important functions:

  • DC Blocking:Capacitors pass alternating current (AC), but block direct current (DC)
  • Coupling: Capacitors are used in between various stages in audio circuits
  • Filtering: Capacitors are key elements of filters, such as a tone control
  • Smoothing: Capacitors are used to smooth out ripples and noise in power supplies
  • Timing: Capacitors are used to set the timing of circuits such as low frequency oscillators
  • Storing: Large value capacitors are used to store up energy. For example, the flash of a camera typically uses a capacitor to store and quickly discharge amount of power

Units of Measure

As with all passive components, you need to have a basic understanding of units of measure when working with capacitors. Capacitance is measured in Farads, named after English physicist Michael Faraday. A value of 1 Farad is actually quite high, so we use sub measures as follows:

μFmicro1,000,000μF = 1F
nnano1,000nF = 1μF
ppico1,000pF = 1nF

If you are like me, the concept of base 10 arithmetic is wildly advanced and causes your head to hurt. So I invariably turn to the awesome online and downloadable calculators from http://www.electronics2000.co.uk for doing unit conversions.

Capacitor Types

Although capacitors come in an almost bewildering array of types and sizes, no need to worry. The majority of capacitors in guitar effect designs fall into three types:

  • Electrolytic: Usually for large capacitance values, typically 1μF and above. These are usually polarized, meaning there are positive and negative leads.
  • Film: The most commonly used types, typically in the range of 1nF to 999nF. These are non-polarized and can go in either way.
  • Ceramic: Used for smaller values, typically from 10pF to 999pF. As with Film capacitors, these are non-polarized.

With these basic types in minds, let’s learn a bit more about each.

Voltage Rating

One of the most common questions about choosing capacitors is voltage rating. Different capacitors are rated for different voltage ranges. The best rule of thumb is to choose a capacitor with a voltage rating that is at least twice the operating voltage of your circuit. So if you are building a circuit that runs of 9 volts, choose capacitors with ratings of at least 16 volts.

Electrolytic Capacitors

Electrolytic capacitors are visually distinguished by their ‘can’ form factor. They are commonly used in power supply filtering and decoupling applications. They are usually polarized which means that they have a positive side and a negative side. (See “Non-Polarized Electrolytics”below).

Electrolytic capacitors come in several physical configurations:

axial capacitorsAxial: There are leads coming out either end of the cap. Typically mounted parallel to the board.
radial capacitorRadial: Both leads come out of one end. Typically mounted vertical to the board.
snap-in capacitorsSnap-In: For larger electros, not recommended for DIY stuff because they lack the long leads that make it easy to fit them to a board.
smd capacitorsSMD: Surface mounted device, which are designed to be assembled/soldered by automated devices. Not so user-friendly to human solderers.

The polarity of the electrolytic capacitor is almost always indicated by a printed band. Additionally, the positive lead is usually longer.  

When working with electrolytic capacitors, here are a few things to keep in mind:

  • Polarity: Most electrolytic capacitors are polarized. Hook them up the wrong way and at best, you’ll block the signal passing through. At worst (for higher voltage applications) they’ll explode.
  • Getting Shocked and Possibly Dying: This is not usually a concern for low-voltage stompbox applications, but for high-voltage circuits, especially tube amplifiers, big electros can hold a charge for quite a while. Before you open up anything that plugs into the wall, google capacitor discharging and approach with caution. See ;Capacitor Fires and Explosions” below.
  • Radial vs. Axial:To maximize the real estate on a PCB, you’ll almost always want to use radial leads. When you order caps, get the radial ones. If you order Axial by mistake, it isn’t hard to bend the leads so as to mount them in a radial, upright configuration.
  • Non-Polarized Electrolytics: To further confound you, electrolytics are made in non-polarized versions. These are rarely used. The only place I’ve seen them is on either side of the first opamp stage in the Tube Screamer.

Ceramic Capacitors

ceramic capacitors

Ceramic caps are typically used for lower capacitance jobs. Values are usually in the picofarad to low nanofarad range. They are ugly looking, and that is about as technical as I’ll get on the whole ceramic vs. film caps debate.

Most folks cannot discern an audible difference between the two types in common stompbox use, so you’ll have to try for yourself. A good rule of thumb is to remember that from an electrical engineering standpoint, film capacitors are generally preferred over ceramics in audio path applications. Ceramics are non-polarized and usually supplied in the radial lead configuration.

The Great Tantalum Debate

Tantalum capacitors were popular in the eighties in stompbox designs like the Ibanez Tube Screamer and various MXR and DOD designs. The primary benefit of tantalums is that they offer a higher range of capacitance values in package that is physically smaller than electrolytics.

Like electrolytics, they are polarized so you’ll want to get the direction right. Tantalums are *very* susceptible to polarity inversion. In other words, if you hook one up backwards you might as well throw it away–there is a good chance it is cooked.

Do they sound better? Do they sound different? The answer is a definitive yes. No wait, that’s a definitive no. There are many opinions about tants, so I really cannot offer you anything definitive on this subject. I can however, share some of the feedback and comments I’ve heard and read.

  • Replace place all electrolytic caps in the signal path with tantalums for a smoother sound.
    Some folks hear more “grit” and treble with tantalums. Some hear a smoother sound.
  • Replace the .022 tantalum in your tube screamers with a poly film part for better sound, others claim the original part is integral to the true tube screamer sound.
  • Some folks claim tantalums are not as reliable as electrolytics, but this may be mostly due to older composition and packaging types uses in decades past.

As always, your mileage will vary. But this is one of the most wonderful areas of stompbox design–there are so many variations, we’ll probably never get bored. Try the variations yourself until  you find your ideal sound.

Capacitors on the Fringe

There are various esoteric or rare capacitor types that pop up from time to time.

Tropical Fish Caps

These are vintage poly film capacitors that use color codes to denote the capacitance value. Very rare nowadays and expensive too. Some builders like to use them in vintage circuits,especially wah pedals.

The Wima Audio Black Box Audio Cap

Rare, elusive and really expensive. I don’t have much info on these, but some audiophile people swear by them.

Wet Tantalums

Most tantalum caps are of the dry-slug variety. This means that they are composed of dry tantalum powder. Wet-slug tantalums on the other hand use gelled sulfuric acid. For more mojo, I wonder if wet-slug tantalums would be worth trying. Although they are typically used for high temperature and voltage applications, one has to wonder…

Audiophile Parts

In the world of DIY audiophile building, a great emphasis is often placed on capacitor performance. As a result, there are a number of manufacturers of high-end (and expensive) capacitors. I’ll leave the subjective vs. objective argument to the reader. But it does make sense to point out that guitar effects, especially in stompbox format, are not designed to be audiophile devices.

Which Type Should I Choose?

As with all component types, there are pros and cons for each type. In general, the choice of capacitor type will be made for you, either by the author of the schematic you are using, or by the simple factor of capacitance value. In other words, the schematic will specify electrolytic or film by the symbol used. That makes the choice easy.

But what about when a specific type is not specified, only the value is shown? In general, you look at the value specified, and choose the type appropriate for that value. Other factors may influence your choice of capacitor type, particularly in audio circuits. So I’ve include benefits and drawbacks of each type.

Capacitor TypeTypical Value RangeSchematic SymbolBenefittsDrawbacks
Electrolytic>= 1μF
Higher capacitance values in smaller packages, Reasonable priceLeakage is higher than most types, service life: Electros typically don’t last near as long as other types. This is typically why tube amps need to be re-capped after a number of years. Tolerance is not great: most passive electronic components have a tolerance rating which denotes how close to the part is to the actual printed value. Tolerance for electrolytics is abysmal, in the 20-40% range, but for stompbox applications, this doesn’t matter.
Film1nF – 999nF⎯||⎯̇Low leakage and they last a long timeLarger values are inordinately physically large
Ceramic1pF – 999pF⎯||⎯InexpensiveFilm caps are usually preferred to ceramic caps where audio performance is a key design factor

Capacitors on Schematics

Here’s what capacitors look like on schematics:

What about Variable Capacitors?

One of the first questions I had when I started building stompboxes was “I have variable resistors (potentiometers) all over the place. Why don’t I have variable capacitors?” The answer is that they are limited to a very small capacitance and are quite expensive too. As such, they are not practical for stompbox usage.

Here’s a trick to simulate a variable capacitor, especially useful for tone control applications. Attach two different capacitor values to a potentiometer–moving the wiper then sends more or less of the signal to one of the caps thereby changing the frequency response.

Capacitor Fires and Explosions

Like other components, capacitors can explode, burn, and/or stink when they are voltage-abused. Here are some fun fire and explosion pictures. Note that many capacitors were harmed during these experiments.

Some builders have intimated that tantalum capacitors smell the worst when on fire. This is a very useful piece of engineering knowledge to have.

The Application of Capacitors in Stompboxes

So now we are familiar with the basics of capacitors, how can we use them in stompboxes? In a surprisingly large number of ways actually.

Power Supply Filtering

In the context of stompboxes, power supply is a low voltage (usually 1.5-18 volts) direct current. The battery is a pretty ideal power source for stompboxes. As long as the battery isn’t dying or depleted, it doesn’t fluctuate wildly or introduce DC ripple into the equation. So if you are running solely on battery power, you really don’t need to worry much about filtering.

Power supplies, like the ubiquitous unregulated black wall warts on the other hand aren’t so ideal. If you are sure that your stompbox design will only ever see external voltage as supplied by a nicely regulated and filtered AC adaptor, then you don’t need to design in filtering. But in the real world, such assurances are not available. You have to assume that at some point you (or the person you build stompboxes for) will plug in a cheap nasty Szechuan special and noise and nastiness will result.

Of course, it is interesting to note that many stompbox schematics will include no filtering at all, and for the majority of uses, that is actually ok. Filtering really becomes an issue when your circuit is presented with a crappy power supply or fluctuating “crazy Ivan” mains voltage.

A wall wart uses a transformer to step down the mains voltage to a pedal friendly 9-11 volts or so (for a 9v adaptor) and then converts AC into DC using a 4-diode bridge rectifier. The rectifier flips all the waveform swings of the AC voltage but still results in some “ripple” in the DC waveform. Ripple equates to noise in your circuit. The simplest way to get rid of this ripple is to tack a largish-value electrolytic cap from the power supply to ground to smooth things out. For most stompbox designs, this works just great. Let’s look at an example.

Here we simply add a 100uf polarized electrolytic from the power supply line to ground to reduce ripple:

Finally, there is an additional electrolytic on the bias voltage (C3) which smoothes out the bias supply.

A parting note on caps in power supplies. For amplifier circuits, you’ll see big electrolytic cans in the power supply section that you don’t see in stompboxes. These act as “reservoirs” of current to handle short spikes in power demands from the amplifier and to smooth out the available pool of current.

The Input and Output Caps

Almost every stompbox design has these two caps. As we talk about these, keep in mind the following schematic of the Electro Harmonix LPB booster (I’m using this one because it has input and output caps and is about as simple a circuit as you can find.)

The input cap (C1), if you haven’t already guessed, is attached at or very near the input. The purpose of the input cap is to form a high-pass filter, in conjunction with a resistor (here the R2 part). It also acts to stabilize the rest of the circuit from the input which is usually a guitar, bouzouki, or another pedal. The key point here is:

The value of the input cap directly controls any frequency attenuation that happens before the signal hits the main effect circuitry.

Now on to the output cap. In our schematic above, that’s the C2 value. The output cap serves two purposes. First, like the input cap, it can serve as part of an RC network to attenuate or pass certain frequencies. If you want the full frequency range, a value from 100nf to 1uf can be used. The output cap also serves to remove any direct current from the signal. Remember that our stompbox designs almost all run on direct current–we want to be sure none if it escapes from the output jack, so an electrolytic cap will do the job nicely.

Input and Output Capacitor Values from Various Classic Stompbox Circuits
CircuitInput CapOutput Cap
Ibanez Tube Screamer.027uf film10uf electrolytic
ProCo Rat22nf film1uf electrolytic
Boss DS-1.047 film1uf electrolytic
Dallas Rangemaster.005uf.01 uf film
Dallas Fuzz Face2.2uf electrolytic.01 uf film

Let’s say you are building a treble-booster–you would want to attenuate any low frequency content before it hit the amplifier circuit. So you would put in a lower value input cap to accomplish this. The Dallas Rangemaster, perhaps the most famous of all treble boosters, has an incredibly small .005 uf cap.

Another great example of the effect of cap values on frequency response isa href=”http://folkurban.com/Site/LofoMofo-724.html”>Tim Escobedo’s LoFoMoFo. Look at the very small values for the input, output and shunting caps (R1, R3 and R2, respectively). These parts conspire to remove pretty much all the bass content of the input signal:

Alternatively, let’s say you want the majority of the useful frequency content to be passed through–in this case you would use a larger value cap, say 100nf-1uf. A rule of thumb is that a 1uf capacitor, input or output, will allow all guitar frequencies to pass through.


Variable Low-Pass Filter

Here we use a small value cap (500pf up to 50nf is a good range for experimentation) wired in the signal path of a circuit. If the pot’s wiper is at the full open position (no resistance) the signal will bypass the cap and go straight through. But as the resistance is increased, more signal will pass through the cap which will attenuate higher frequencies.

Another way to implement a low pass filter is to used a potentiometer in series with a capacitor to ground. This type of configuration can be spliced into the signal path of a circuit, but it should be noted that there is some signal loss. This is the case with all such passive circuits. Usually, there is a gain stage after a passive tone control to boost the signal lost in the passive section. For example, look at the last transistor stage in the Big Muff Pi circuit: it’s function is to make up for the signal loss in the preceding tone control.

Smoothing Diode Clipping

You can add a small-value capacitor in parallel with a diode clipping arrangement to smooth out the high-end of the clipping. This is a somewhat interesting area for experimentation.

Capacitors for Timing

Another common use for capacitors is to control the time interval of a circuit. For example, in a low-frequency oscillator, a capacitor is used in conjunction with a potentiometer to set the frequency. Our first example is a simple LFO based on the 40106 Hex inverting Schmitt trigger. The combination of C1 and VR1 set the frequency:

Next, we have a classic 555 basic monostable oscillator. In this configuration, the frequency is set by a combination of R1 and C1.

How to Build Your Own DCR Measuring Tool

Let’s build one of my favorite DIY guitar tools that I use daily in my shop. I’ll show you two versions and then explain how to put them into action.

Welcome back to Mod Garage. After receiving numerous requests to show more DIY tools for guitarists, today we’ll explore one of my favorites. For years I’ve used this one in the shop daily and I’m sure you’ll love it. It’s cheap and easy to build, but very effective for analyzing circuits of electric guitars and basses without opening the electronic compartment or lifting the pickguard. It’s a kind of adaptor or extension to measure a pickup’s DC resistance (DCR) from outside the guitar. After building one, we’ll discuss how to interpret the measurements.

The DCR of a pickup is by far the most common parameter you can read when reading pickup descriptions and often it’s used as an indicator of the output. The reason for this is that it’s easy to measure, but, sadly, it doesn’t tell us anything about a pickup’s output nor its tone. To quote pickup designer Bill Lawrence: “DC resistance tells you as much about a pickup’s tone and output as the shoe size tells you about a person’s intelligence.

I’ve written about DCR as a pickup parameter in detail and you can read about it in “Mod Garage: Demystifying DCR.”

DCR is not a primary parameter in pickup design. It’s simply the result of the type and gauge of the pickup’s wire, the number of turns, and other parameters like the winding pattern, etc. But it isn’t completely useless, and we can use it as a good reference point for analyzing pickups both inside and outside a guitar or bass circuit. All you need for this is a digital multimeter (DMM). You don’t need an expensive calibrated precision DMM—any entry level DMM will work. You can get a simple digital DMM for $10, but if you want to invest in a better device, it can’t harm.

The easiest way to analyze a pickup is outside a circuit. Simply set your DMM to ohm and connect the two pickup leads to your DMM. If your DMM doesn’t have an auto-range function, set it to 20k ohm. Now you’ll get the DCR reading for your pickup. You can compare it to the factory specs of your pickup and it should be close. If your DMM shows “infinite” or “overload,” you know the pickup wire is broken. Let’s say your pickup should read 7k ohm, but yours reads around 2-3k ohm. Your pickup likely has a short circuit somewhere in the winding. Used this way, the DCR is always good to quickly check if a pickup is alive or not.

To quickly analyze a guitar or bass circuit with one or more pickups, you first need to build the DIY adaptor tool this column is about. There are two different versions, and you don’t need much for this:

  • Version #1: This is the quick and dirty version. You need a standard 6.3 mm straight mono plug (the same type on all your guitar cables), some wire of your choice (preferably in two different colors), and two insulated alligator clips.
  • Version #2: A more elegant version that you can also use with a scope if you have one. You need the same parts as for version #1, but instead of two alligator clips, you need two 4 mm banana plugs, and the two wires need to be longer than what you’d use for Version #1.

So, heat up your soldering iron and let’s get to building version #1.

  1. Solder one piece of wire to the HOT terminal of the mono plug and another one to the GROUND terminal. I prefer a red wire for the HOT and a black wire for the GROUND terminal (Photo 1).
  2. Solder an insulated alligator-clip to each end of the two wires, preferably a black one to the black wire and a red one to the red wire. Ready!

Version #2 is built the same way, but, instead of alligator clips, you solder a 4 mm banana plug to each end of the two wires, if possible, also in black and red. The two wires should be long enough that can place your DMM and/or scope at some distance from the guitar. In Photo 2, you can see version #1 on the top and version #2 on the bottom.

The difference between the two versions is that with version #1 you put the plug into the output jack of the guitar, connecting the two probes of your DMM to the alligator clips: the black probe of the DMM goes to ground (black wire) and the red probe goes to hot (red wire) as seen in Photo 3. With version #2, you need to remove the two probes from your DMM, plugging the two banana plugs directly into your DMM or your scope, also seen in Photo 3.

Both versions work equally well. Version #2 is just easier to operate when you also want to use the adaptor for a scope.

For a quick check, you can also directly touch the hot and ground terminals with the probes of your DMM, but you need both hands or a second person for this if you want to play around with the controls or the pickup-selector switch.

Now we can easily check four things with this tool, assuming everything is connected the way it should be and your DMM is set to ohm and auto-range or the 20k ohm scale if your DMM doesn’t have an auto-range mode:

  1. Do you receive a reading on your connected DMM? If not, check if the volume pot is fully opened. Do you receive a reading now? If so, close the volume pot completely and see if you still receive a reading. No? Perfect, you just proved that the volume pot is alive and well.
  2. With a fully opened volume pot and a reading on your DMM, slowly turn down the volume and watch the reading on the DMM. If you receive some crazy reading, chances are good there is a treble bleed network on your volume pot. If the reading slowly goes down to zero, you know that there is no treble bleed network on the volume pot, and you can check if it’s an audio or linear volume pot (plus the taper it has, if it’s an audio pot). Let’s say we have a 500k volume pot. When you close the volume pot halfway and receive a reading around 250k, you know it’s a linear pot. An audio pot, depending on its taper, will result in a much higher reading on the first 50 percent of the volume pot. If you read 500k until the volume pot is almost fully closed, this means the pot has a 90:10 audio taper—exactly the kind of volume pot you don’t want to have. If you read something around 300k in the middle of the volume pot, you know it’s a 60:40 audio taper.
  3. If the volume pot is fully opened and you don’t receive a reading on your DMM, chances are good that your output jack is broken, not connected, or connected incorrectly. Please make sure there is no activated kill-switch in the circuit that can also cause this “problem.”
  4. Turning the tone knob(s) will make no difference in the reading you receive. If you receive a slightly higher reading with a tone pot fully opened compared to when it’s closed, you know it’s a no-load tone pot.

There is a lot to discover from just the outside of any guitar or bass. So, now let’s see what we can measure from outside the instrument starting with a Telecaster with a 4-way switch. The readings in all examples are the readings I received with guitars I had in the shop, but they can be different in your instruments:

  • Bridge pickup only: 5.85k ohm
  • Neck pickup only: 6.76k ohm
  • Both pickups together: 3.18k ohm
  • Pickup selector switch in position #4: 12.30k ohm

The readings for both pickups are within the factory specs and are in a typical range for a vintage-flavored Telecaster pickup set. With a reading of 3.18k ohm for both pickups together, you know that both pickups are in parallel. With the reading of 12.30k ohm, you know that both pickups are in series with each other.

Here is the simplified math behind these readings:

  • Series connection: DCR pickup #1 + DCR pickup #2
    • In our example, it’s 5.85k + 6.76k = 12.61k ohm, which is very close to the reading of 12.30k we received. The missing 0.31k ohm are eaten up by the resistance of the pots and the tolerance of your DMM. For this test, I chose the cheapest DMM I could find in the shop. A calibrated high-quality DMM will have much less tolerance.
  • Parallel connection: (DCR pickup #1 + DCR pickup #2) divided by four
    • In our example, it’s 5.85k + 6.76k = 12.61k ohm divided by four = 3.15k ohm, which is very close to the reading of 3.18k ohm we received.

Now let’s repeat this with a standard Stratocaster:

  • Bridge pickup only: 7.07k ohm
  • Middle pickup only: 5.88k ohm
  • Neck pickup only: 5.70k ohm
  • Bridge + Middle pickups together: 3.26k ohm
  • Neck + Middle pickups together: 2.94k ohm

All three pickups are within the factory specs of this Strat. We have a slightly hotter bridge and two vintage-flavored pickups. The two in-between positions are in parallel.

Lastly, let’s try a vintage PAF-loaded Les Paul:

  • Bridge pickup only: 7.77k ohm
  • Neck pickup only: 7.09k ohm
  • Both pickups together: 3.74k ohm

Both PAFs have the typical vintage DCR and are in parallel in the middle position.

by Dick Wacker – PREMIER GUITAR

Raspberry PI Robot Kit

Build ya a sexbot!

Raspberry Pi 3 Robot Kit from SunFounder
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  • Raspberry Pi Model 3 B
  • Motor/Servo driver board
  • Use included visual programming code (Dragit) or Python
  • 8 channel RPi GPIOs and 5 analog ports for sensors and actuators
  • Text-to-Speech and Speech-to-Text capable
  • Lead Time: this product takes approximately 30 days to arrive.


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HOW TO: make a wireless camera from shit round the house

Got an old cell phone laying around pretending to be a paperweight? SURE YA DO! Round up your old phones and watch the video. It’s mildly entertaining and easy.

No one is safe: “This tiny $30 device can break into your car and home.”

hack home security systems with this cheap electronic pussy device / cum

This super-small piece of electronics can hack into your car and home, and it requires only $30 to make. Not everyone wants to accept this simple truth, but that doesn’t make it any less real: hackers outpace security advancements. When it comes to both online security and real-world security, hackers have already devised 10 new tools by the time security researchers come up with an effective way to block one old tool. As a result, no one is ever truly safe — and a new device recently shown off by a well-known security researcher is yet another example of just how vulnerable we really are.

Online and offline security expert Samy Kamkar took to Defcon 2015 to show off a tiny device he calls “Rolljam.” The device is as shockingly simple as it is devious and brilliant, and it can be used to break into just about any car. Worse yet, it can even be used to break into a target’s home.

Rolljam is a tiny series of circuit boards with three in-built radios, Wired reports. It works by using two of the radios to jam the wireless signal sent out by a car’s keyless entry remote, while the third radio reads the code that was transmitted by the remote, which is then stored on the device.

Keyless entry devices use a system of rolling codes to prevent hackers from stealing them wirelessly and reusing them at will. Once a code is used a single time, it cannot be used again — and therein lies the brilliance of the Rolljam device.

Since the device blocks the signal from a car’s key fob while it is being transmitted, the unique code never reaches the owner’s car. The next time he or she presses the unlock button, a new code will be transmitted and it will successfully unlock the car. But that first code was never actually used, so the Rolljam can then transmit it at a later time and it will successfully unlock the target car.

Kamkar’s device was used to successfully unlock cars made by Nissan, Cadillac, Ford, Toyota, Lotus, Volkswagen and Chrysler, and it also worked perfectly with a number of garage door openers, potentially giving the user access to a target’s home