the role of the capacitor in music

the capacitor

capacitors

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:

SymbolNameEquivalence
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.

Filters

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.

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Texas Could Vote to Secede From U.S. in 2023 as GOP Pushes for Referendum

Texas Republicans are pushing for a referendum to decide whether the state should secede from the U.S.

A typical middle-aged male Texan waving the America flag with his fat gut hanging out
Texas Republicans are pushing for a referendum to see if the state should secede from the U.S. Above, Kenny Wolfam open carries a pistol and wears a “Trump 2020” t-shirt while counter-protesting a “Moms Demand Action” protest at Buffalo Bayou Park in Houston, Texas on June 17, 2021.
The New York Stock Exchange on Wall Street.

The demand for Texans to be allowed to vote on the issue in 2023 was one of many measures adopted in the Texas GOP’s party platform following last week’s state convention in Houston

Under a section titled “State Sovereignty,” the platform states: “Pursuant to Article 1, Section 1, of the Texas Constitution, the federal government has impaired our right of local self-government. Therefore, federally mandated legislation that infringes upon the 10th Amendment rights of Texas should be ignored, opposed, refused, and nullified.

Texas Republicans are pushing for a referendum to see if the state should secede from the U.S. Above, Kenny Wolfam open carries a pistol and wears a “Trump 2020” t-shirt while counter-protesting a “Moms Demand Action” protest at Buffalo Bayou Park in Houston, Texas on June 17, 2021.

In another section on state governance, the platform states that Texas Republicans want the state Legislature to pass a bill in its next session “requiring a referendum in the 2023 general election for the people of Texas to determine whether or not the State of Texas should reassert its status as an independent nation.

The myth that Texas can secede from the U.S. continues because of the state’s history of independence, according to The Texas Tribune. Texas declared independence from Mexico in 1836 and spent nine years as its own nation before becoming a U.S. state. Texas then seceded from the Union in 1861 before being readmitted following the end of the Civil War in 1870.

The U.S. Constitution makes no provision for states to secede and in 1869, the Supreme Court ruled in Texas v. White that states cannot unilaterally secede from the Union.

“If there was any constitutional issue resolved by the Civil War, it is that there is no right to secede,” the late Justice Antonin Scalia once wrote.

Still, modern secessionist efforts have continued in the state for decades—and calls to secede tend to become louder when a Democrat is a president, according to the Tribune.

It’s not clear how popular the effort is among Texans, but the Texas Nationalist Movement’s website claims almost half a million Texans support its work to “make Texas an independent nation again.”

The movement’s efforts have been promoted by Texas Republicans. Last year, state Representative Kyle Biedermann introduced a bill that called for a “Texit” referendum, which was endorsed by Texas GOP chairman Allen West. The bill ultimately failed.

The bill was rebuked by lawmakers on both sides of the aisle, with Republican state Representative Jeff Leach branding it a “disgrace to the Lone Star State” and the “very definition of seditious.”

As well as the issue of a referendum, delegates also voted on more than 270 platform planks as the convention closed on Saturday. The votes will be tallied and certified in Austin, but it is rare for a plank to be rejected, party spokesperson James Wesolek told The Tribune. He has been contacted for additional comment.

Texas Republicans also approved a resolution declaring that President Joe Biden was “not legitimately elected,” signaling the continued support for former President’s baseless claims of widespread fraud in the 2020 presidential election.

The Texas GOP’s new party platform also called for full repeal of the Voting Rights Act of 1965.

Other planks also indicated a further shift to the right for the party, giving prominence to culture issues. The platform describes homosexuality as “an abnormal lifestyle choice,” and also declares that the party opposes “all efforts to validate transgender identity.

The platform also calls for a total ban on abortion and “equal protection for the Preborn.” Abortion is currently prohibited after around six weeks of pregnancy in Texas, but an imminent ruling from the U.S. Supreme Court could overturn the decision in Roe v. Wade that guaranteed abortion rights nationwide and trigger a law in Texas making abortion illegal.

The new Texas GOP platform also states that the education system should focus on “imparting essential academic knowledge, understanding why Texas and America are exceptional and have positively contributed to our world, and while doing so, also offer enrichment subjects that bless students’ lives.”

It calls for students to learn about the “Humanity of the Preborn Child,” including teaching that life begins at fertilization. It also demands that the state legislature pass a law prohibiting the teaching of “sex education, sexual health, or sexual choice or identity in any public school in any grade whatsoever.”

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Scientists have discovered what causes Resting Bitch Face

Image without a caption  By Caitlin Gibson

But there was one big difference, she added. FaceReader, being a piece of software and therefore immune to gender bias, proved to be the great equalizer: It detected RBF in male and female faces in equal measure. Which means that the idea of RBF as a predominantly female phenomenon has little to do with facial physiology and more to do with social norms.

February 2, 2016 at 10:00 a.m. EST

Queen Elizabeth has it. So does fashion designer Victoria Beckham. And actress Kristen Stewart — poor thing, she’s practically the poster girl.

Among the slew of pop culture icons said to be afflicted with so-called Resting Bitch Face (alternatively known as Bitchy Resting Face), the vast majority are women, though Kanye West is among the male examples. All of them have been mocked by Internet commenters for having a certain unintentional expression when their faces are not in motion  — a look best described as vaguely annoyed, maybe a little judgy, perhaps slightly bored.

Since the RBF meme took over the Internet in 2013, fueled by a viral mock-PSA about “Bitchy Resting Face,” legions of people have identified the dreaded phenomenon in celebrity listicles, in their own social circles, even in the mirror.

RESTING BITCH FACE EXAMPLE BITCH FROM THAT STUPID VAMPIRE SHIT. FAGS.

the QUEEN BITCH HERSELF: Kristen Stewart of “Twilight” fame, often considered the poster girl for RBF

So Jason Rogers and Abbe Macbeth, behavioral researchers with international research and innovation firm Noldus Information Technology, decided to investigate: Why are some faces seen as truly expressionless, but others are inexplicably off-putting? What, exactly, makes us register a seemingly neutral expression as RBF?

“We wanted this to be fun and kind of tongue-in-cheek, but also to have legitimate scientific data backing it up,” Macbeth said.

The researchers enlisted Noldus’s FaceReader, a sophisticated tool engineered to identify specific expressions based on a catalogue of more than 10,000 images of human faces. The software, which can examine faces through a live camera, a photograph or a video clip, maps 500 points on the human face, then analyzes the image and assigns an expression based on eight basic human emotions: happiness, sadness, anger, fear, surprise, disgust, contempt, and “neutral.”

To establish a baseline, Rogers and Macbeth first had FaceReader assess a series of genuinely expressionless faces. Those expressions registered about 97 percent neutrality, Macbeth said; the remaining three percent included “little blips of emotion”  — a touch of sadness here, a hint of surprise there, but nothing significant.

Then they plugged in photos of RBF all-stars Kanye West, Kristen Stewart and Queen Elizabeth. Suddenly, the level of emotion detected by the software doubled to six percent.

One particular emotion was responsible for the jump: “The big change in percentage came from ‘contempt,’” Macbeth said.

And how exactly does a piece of software measure contempt in a face?

It’s in subtle signals, like “one side of the lip pulled back slightly, the eyes squinting a little,” Rogers explained.

Or: “It’s kind of a tightening around the eyes, and a little bit of raising of the corners of the lips — but not into a smile,” Macbeth suggested.

The cues are understated, yet the machine detects and interprets them the same way our human brains do, she said. “Something in the neutral expression of the face is relaying contempt, both to the software and to us.”

Consider actress Anna Kendrick, who has publicly bemoaned the effect of RBF on her life.

“When she was younger, directors would say, ‘Why don’t you smile more, you need to smile more, you don’t seem like you’re very happy,’” Macbeth said. “That’s something that’s expected from women far more than it’s expected from men, and there’s a lot of anecdotal articles and scientific literature on that. So RBF isn’t necessarily something that occurs more in women, but we’re more attuned to notice it in women because women have more pressure on them to be happy and smiley and to get along with others.”

Worried that you might have RBF? Now you can find out for sure. After publishing their results in October, Rogers and Macbeth invited members of the public to submit their own faces for analysis. Guys and gals alike are welcome to email photos of their most “neutral” facial expressions to jason@noldus.com, and FaceReader will tell you if you’re actually expressionless — or if you and the Queen have RBF in common.

Image without a caption

Caitlin Gibson is a feature writer at The Washington Post. Since joining The Post in 2005, she has contributed feature stories, essays, long-form enterprise and local news to the paper and The Washington Post Magazine.

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A Unique Anatomy Study by a Student of Fine Arts

A drawing / sketch / illustration of a human skeleton posed kneeling with hands together and looking upward, either praying to God or begging, perhaps both; hand drawn or sketched on paper or parchment with charcoal or graphite; in juxtaposition with a typical anatomical study done by a student of fine arts for figure drawing or medical illustration.

-Patrick Scheidegger
human skeleton praying to God hand drawn or sketched on paper or parchment with charcoal or graphite in juxtaposition of a typical anatomy study done by a student of fine arts for figure drawing
bone to pick when you don’t have a nose ?

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Russians laugh at nuking New York City

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