The following 700 words could not be found in the dictionary of 615 words (including 615 LocalSpellingWords) and are highlighted below:

0033uf   01pf   01uf   100pf   10n   10u   10uf   1pf   1uf   20cm   2f   3uf   470p   470uf   47uf   about   absorption   accuracy   across   act   actually   adhesive   advantages   Advantages   age   air   all   All   Allied   alter   alternating   aluminum   Aluminum   amounts   amplifier   amplifiers   Amundson   an   analog   Analog   Analoq   and   another   anyway   application   applications   applied   apps   Archive   Art   Asian   ask   associate   assume   at   attenuate   audio   Audio   audiophile   audiophiles   availability   Available   available   Avoid   avoid   aware   away   axial   axials   bad   Baker   Barbour   based   bass   battery   be   Because   because   become   becomes   behavior   being   below   best   better   between   bible   bit   bleeds   blocking   Both   brand   Buchla   build   But   but   by   Bypass   bypass   bypassing   called   Cambridge   can   cap   capability   capacitance   capacitor   Capacitor   capacitors   Capacitors   caps   care   case   catalog   ceramic   Ceramic   ceramics   Ceramics   certain   charge   checking   chemistry   chip   choice   circuit   circuits   Clark   coated   coating   coefficient   coil   come   comes   Common   companies   company   compiling   concentrates   concern   conclusion   conductor   conductors   confused   connected   consisted   consists   constant   constants   constructed   construction   contain   cost   couple   coupling   criteria   current   cylindrical   Damaged   dangerous   decoupling   Definitely   deg   degrees   Delivery   demanded   depend   describe   design   designer   designers   Devices   Dialog   dielectric   dielectrics   Dielectrics   differing   Digi   digikey   Digikey   digital   Dinner   diodes   directly   Disadvantages   disc   distortion   does   doing   Don   don   double   due   dust   East   effect   effects   electric   electrode   electrolytes   electrolytic   Electrolytic   electrolytics   Electronics   Electronote   energy   ensure   epoxy   equivalent   Eric   etc   European   even   ever   everywhere   example   exceed   excellent   excessive   exhibit   exist   expected   Expensive   expensive   extreme   extremely   Fairly   fairly   famous   few   figured   filled   Film   film   filter   find   fine   fix   Foil   foil   foils   following   Following   For   for   forget   formed   frequencies   frequency   from   funny   gel   generally   generically   get   given   Glass   glass   glop   go   good   Good   Grant   great   Great   greater   grouped   Guide   guidelines   had   happen   heard   heat   high   High   higher   Hill   Horowitz   hot   How   however   ideal   If   if   Illinois   impedance   impregnated   in   In   inches   include   index   induce   inductance   Inductive   industrial   inexpensive   Inexpensive   infamous   information   input   inside   insulator   internal   into   isn   Jar   jar   Jeff   just   Key   knock   know   known   languages   large   Large   leaded   leakage   leakages   leaking   leaky   less   let   Leyden   like   limited   Limited   limits   line   liquid   listed   little   ll   load   local   logic   lose   loss   lossy   Low   low   Made   made   major   make   makes   Manufacturers   manufactures   many   margin   Mark   material   Medium   metal   metallized   Metallized   Mica   mica   microfarad   microphones   might   military   mine   Mini   Miscellaneous   mix   Moderate   moderate   moisture   Monolithic   more   More   most   Most   mouser   Mouser   much   Music   my   Mylar   name   near   need   Nelson   never   new   Newark   next   non   note   Note   noted   now   odd   of   off   offenders   offer   official   often   oil   Oil   old   on   one   One   online   Only   only   Operable   operated   Operates   optimized   or   orientation   Os   Other   other   others   out   output   outside   over   overpriced   Page   paper   Paper   parallel   particularly   pastry   path   paths   Paul   peak   pennies   people   performance   Perry   phenolic   physical   Pick   picofarad   piece   piezo   pirated   pitfalls   place   plastic   plate   Plates   plates   polarity   polarized   polycarbonate   Polycarbonate   Polycarbonates   Polycarbs   polyester   Polyester   polypropylene   Polypropylene   polystyrene   Polystyrene   Poor   popular   positive   potential   power   powered   ppm   preamps   predate   present   Press   pretty   primary   problem   problems   processing   projects   prompt   prone   proper   provides   purposes   put   quality   quick   Quite   quite   range   ranges   rated   rating   readily   really   reason   recommendations   recommended   Reference   reference   referred   regarding   regulator   regulators   related   relatively   Relatively   remedy   replace   report   requestable   requires   reserviors   resist   resistance   resistors   resonate   retain   Rich   Richter   roll   rules   safety   same   schematics   Schreiber   searchable   second   See   self   selling   send   sensitive   separated   series   serious   shaped   should   signal   signals   similar   since   sinks   situation   size   slightly   small   Small   smaller   So   so   Some   some   sound   sources   specialized   specified   speed   Sprague   square   stability   stable   stack   stacked   step   still   stop   storage   strange   stuff   substantially   such   Such   suggestions   suitable   supplies   supply   synth   tabular   tack   taken   tantalum   Tantalum   Technology   teflon   Teflon   temp   tempco   temperature   temps   terminal   Tesla   than   Thanks   that   That   The   the   their   them   there   therefore   these   These   they   They   this   This   through   tight   time   timers   timing   tin   to   today   tolerance   Tony   too   toxic   transducers   try   tube   tuning   two   Typ   type   types   typical   typically   Umm   University   use   Use   used   Used   useful   users   using   usually   Usually   value   valued   values   Values   variable   variety   various   vary   versions   very   Very   vibration   Vishay   Vitamin   voltage   voltages   volts   volume   volumes   wall   want   was   waveform   website   well   Well   were   What   when   Where   where   which   Why   why   wide   Wide   will   window   wise   wish   with   work   working   workspace   worse   worst   wrapped   X7   ya   yeah   year   years   Yep   Yes   yet   you   your   Z5  

Clear message

E-Music DIY Reference Archive

The Capacitor Reference Guide

Q: What's a capacitor, anyway??

A: A capacitor consists of 2 metal plates separated by an insulator. More generically, a capacitor consists of two or more conductors separated by a non-conductor or 'dielectric'.

Q: Plates?? Dinner plates??

A: The first caps were the infamous "plate glass and tin foil" types used (still today) in high-powered RF circuits, like a Tesla coil. They consisted of an alternating stack of aluminum foil and a piece of window glass, about 20cm square. The odd foils were connected to one electrode, and the even foils to another like so:

Glass   ============
Foil 1  ******************
Glass   ============
Foil 2  ******************
Glass   ============
Foil 3  ******************
Glass   ============

The first relatively large cap was a jar with a metal coating on the outside and inside, the official name for which is a 'Leyden Jar'.

Q: How come mine are so small??

A: Technology has demanded ever smaller capacitors with differing dielectrics for various purposes. Manufacturers figured out that if you replace the plates with plastic film, you could roll capacitors like a pastry to make them smaller.

Q: So why so many types: Mylar, polyester, etc. etc.??

A: The types describe the "quality" of the film used. That's why most caps are grouped as:

  1. Ceramic
  2. Electrolytic
  3. Film
  4. Miscellaneous (like mica)

Capacitors are referred to by their dielectric material. Common types include plastic, ceramic, tantalum, mica, air, and electrolytes.

Q: Why do electrolytic caps have + and -?

A: Because the insulator used is a liquid (actually a gel), the chemistry of it requires one end to be more positive than the other, like a battery.

Some capacitors are constructed such that they have a greater DC leakage in one polarity. In the proper DC polarity they offer great amounts of capacitance in a small volume.

Q: Great, now I'm even more confused!! How do I know which one to use in a certain application??

A: Well, here are some rules to go by, listed by application (note: all values given are just typical suggestions):

BYPASS CAPS - Bypass cap recommendations may vary from designer to designer. The famous 0.1uf (microfarad = 10^-6) ceramic is a good value for audio supply bypassing; 0.01uf may be a little better if you mix higher speed circuits like logic on the same supplies. Values also depend on load and input impedance. Don't use the "disc" types if you can avoid it; use axial-leaded types. The reason is they are coated with epoxy and resist moisture. Also, they are much smaller. Do not forget to retain a 10uf or greater aluminum or tantalum electrolytic on circuits as well. They act as local energy storage reserviors when the DC supply is more than a few inches away.

AUDIO COUPLING CAPS - Used to AC couple an audio input. Use 0.47uf metallized polyester or polypropylene. Values less than this will attenuate bass frequencies.

VCF CAPS - Use polypropylene film.

VCO CAPS - Use polystyrene if you can find them (try Mouser); the one German company that makes the film will stop selling it this year!! Metallized polypropylene, and polycarbonate are also fine. See "What about polycarbonate caps?" below.

POWER SUPPLY CAPS - For the cap between the diodes and the regulator, use a cap rated to 105 degrees C. They are only slightly more expensive (pennies) than the 85 deg. C types, but much higher quality. For the output caps on 3-terminal regulators, use a 1.0, 2.2 or 3.3uf tantalum in parallel with an 0.1uf ceramic.

Following are some guidelines, listed by capacitor type:

CERAMIC CAPS - Low cost capacitors in the range from about 0.1pf (picofarad = 10^-12) to 1uf. Dielectrics can alter values with temperature (X7R, Z5U types), some are temperature stable (COG, NPO types), but some vary extremely with temperature. They exhibit lossy behavior and a little waveform distortion. Good for power supply bypassing and RF applications. Low self inductance makes them good for use as bypass in digital circuits. Avoid ceramics in the audio path.

TANTALUM CAPS - Moderate cost capacitors in the range from about 0.1uf to 470uf. They have polarized dielectrics and fairly small volume wise. They have a limited voltage capability; usually less than 50 volts. Good capacitors for supply bypassing but have some leakage current. Not recommended for decoupling or signal processing.

ELECTROLYTIC CAPS - Moderate cost capacitors in the range from about 0.1uf to 2.2f. They have polarized dielectrics and are used in a wide variety of voltages. Some types are optimized for decoupling and audio signal processing. Most have some leakage current. It should also be noted that electrolytic caps SHOULD NOT be used where the DC potential across the cap is substantially below the rated working voltage. Some people might assume that doing so provides a safety margin. But since the dielectric is "formed" by the voltage applied across the capacitor, they will lose capacitance when operated much below their rated voltage.

This is why voltage ranges are relatively small: 6.3, 10, 16, 25, 35, 50, etc. Pick the voltage rating the next step higher than the _peak_ voltage across the cap.

If you exceed the voltage rating for an electrolytic or let it get too hot it can EXPLODE!! Great care should be taken to ensure that this does not happen, as capacitors contain some pretty toxic stuff. Avoid a dangerous situation by double-checking the orientation of and the voltage across your electrolytics. Also, don't place electrolytics near heat sinks.

PLASTIC CAPS - (a.k.a. Mylar, polyester, polycarbonate, polypropylene, polystyrene, and 'metallized' versions.) These caps are stacked or wrapped (stacked - parallel plates, wrapped - cylindrical shaped plates) dielectric construction and may resonate at very high frequencies. Usually excellent for decoupling and bypassing of audio signals. Some types are better for audio than others (e.g. polypropylene). Values between 470pF and 10uF usually. Available in fairly moderate to large size volumes.

MICA CAPS - They are tight tolerance capacitors between 0.1pf and 0.0033uf typically used for RF coupling or bypass applications. Fairly expensive but useful for high frequencies. Fairly large physical size for their values.

AIR CAPS - Used for small values from 0.01pf to 100pf and usually variable capacitance types for RF tuning. Relatively large for their values and prone to dust leakages.

Q: What about Mylar?

A: Mylar, also called polyester, is to be AVOIDED!! Mylar is popular for ONE REASON: PRICE. They are not suitable for serious audio work. Mylar was the first film cap available (about 1953) and most 'old-timers' associate film caps to a Mylar cap.

Q: Why?

A: They have 2 problems: over time, they 'age'. They change their capacitance. The second problem is Mylar isn't that good of a film: it is "leaky" and the charge bleeds off. That's why in VCO's and S/H's a Mylar cap is the WORST choice you can make.

Q: What about polycarbonate?

A: This type is known for good performance (i.e. stable) over a wide temperature range. Polycarbs are used in similar applications as polyester caps. The Illinois Capacitor company makes a line of polycarbonate caps with temperature coefficient (tempco) of 50 ppm, similar to good metal film resistors. The primary concern for VCO timing caps is tempco. Polycarbonates are specified for Electronote VCO's. They are also specified directly on the schematics for Buchla VCO's.

Q: Are paper caps OK to use?

A: Paper capacitors predate Mylar by about 60 years. They are prone to leaking and other bad age-related effects, and are therefore not recommended. In case you want to experiment with "bad" capacitors, there are new paper-dielectric capacitors being made for the more extreme audiophiles. Audio Note is the major brand. Also, Sprague/Vishay still manufactures the old phenolic-impregnated-paper 'Vitamin Q' types. All very expensive, and very leaky. Definitely not recommended for time constants in VCOs or for temperature-sensitive applications.

Q: What about oil-filled caps??

A: Oil-filled capacitors still used in high-voltage AC applications. Some audiophiles build DIY tube amplifiers using oil caps to filter the high-voltage plate supply; users report that oil-filled caps have some major advantages over electrolytics, sound quality being one of them.

Q: Do teflon caps really exist?

A: Yes. Made by 2 companies at present. Used in very specialized military and industrial applications, and in overpriced audiophile tube preamps.

Q: Are there any strange capacitor-related effects I should be aware of?

A: All caps, particularly DC-blocking caps in the audio path, can become transducers, like microphones. A vibration may induce voltages due to internal "piezo-electric" effects. A knock on your synth's case, for example, may be heard through your amplifier. One fix is to put a glop of RTV adhesive over the capacitor. Ceramics and some plastic caps are the worst offenders; yet another reason to never design them into the audio path!! Some ceramic dielectrics are worse than others regarding this effect.

Q: Any other pitfalls to avoid?

A: Yep. A high-valued cap (electrolytic, tantalum) is often used to bypass relatively low frequencies. Such a capacitor, however, may not bypass expected high frequencies (based on the circuit's RC time constant for an ideal cap) because the equivalent series resistance (ESR) of these caps becomes excessive at high frequencies. The remedy is to parallel the capacitor with a small (0.1uf) high frequency cap.

Q: Where can I get more information?

A: If you care about this stuff you need the analog designers bible, "the Art of Electronics" by Horowitz and Hill, Cambridge University Press, readily available everywhere and pirated into most Asian and East European languages.

Q: I wish I had a quick reference I could tack on the wall next to my workspace!

A: Umm, yeah, funny you should ask...This data comes from Analog Devices' "Analoq Dialog" 30-2 from 1996. The data is tabular and concentrates on dielectric absorption (DA) criteria.



Typ. DA



Aluminum Electrolytic


  • Large values
  • High current
  • High voltage
  • Small size
  • High leakage
  • Usually polarized
  • Poor stability
  • Inductive



  • Low loss at high frequencies
  • Low inductance
  • Very stable
  • Available in 1% values or better
  • Quite large
  • Low values (-10nF)
  • Expensive

Monolithic Ceramic


  • Low inductance
  • Wide range of values
  • Poor stability
  • Poor DA
  • High voltage coefficient

MOS (on chip)


  • Good DA
  • Small
  • Operates at high temperature
  • Low inductance
  • Limited availability
  • Only small values

NPO Ceramic


  • Small case size
  • inexpensive
  • wide range of values
  • good stability
  • low inductance
  • DA generally low
  • Limited to small value



  • Good stability
  • Low cost
  • Wide temperature range
  • Large size
  • DA limits to 8-bit apps
  • High inductance

Polyester (Mylar)

0.3 to 0.5%

  • Moderate stability
  • Low cost
  • Wide temperature range
  • Low inductance (stacked film)
  • Large size
  • DA limits to 8-bit apps
  • High inductance (wrapped film)


0.001 to 0.02%

  • Inexpensive
  • Low DA available
  • Wide range of values
  • Damaged by high temps. +105C
  • Large case size
  • High inductance


0.001 to 0.02%

  • Inexpensive
  • Low DA available
  • Wide range of values * Good stability
  • Damaged by high temps. +85C
  • Large case size
  • High inductance

Tantalum Electrolytic


  • Small size
  • Large values
  • Medium inductance
  • Quite high leakage
  • Usually polarized
  • Expensive
  • Poor stability
  • Poor accuracy


0.003 to 0.02%

  • Low DA available
  • Good stability
  • Operable at high temp. +125C
  • Wide range of values
  • Relatively expensive
  • Large size
  • High inductance

Q: Where can I get good caps?

A: In the US, try Digikey ( has an online searchable index). Other sources include Allied, Newark, and Mouser ( Both Digi-Key and Mouser'll send ya a free catalog, requestable at their website. Delivery is quite prompt.

Q: What are the best types to use in DIY synth projects?

A: In conclusion:

  1. ceramic axials for bypassing
  2. metallized polyester or polypropylene for audio coupling
  3. polypropylene for all audio paths (VCF's, VCA's, etc.)
  4. polystyrene, polycarbonate, or metallized polypropylene for VCO's
  5. tantalum and ceramic for voltage regulators

Thanks go out to the following people for compiling this information:

Paul Schreiber, Mark Amundson, Rich Nelson, Jeff Baker, Paul Perry, Eric Barbour, Grant Richter, Tony Clark

References/Capacitor (last edited 2007-02-11 11:36:58 by TomArnold)