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Forum Home > Tips, Tricks and Tutorials! - Builder's Guides for GuitarPCB Boards! > Sticky: Capacitor Codes Chart + Capacitor Types for Pedals

Barry
Site Owner
Posts: 8793

A handy chart for keeping all your pFs, nFs and uFs in order! Enjoy!


Take notice in picofarads their is hardly any difference between values so you may substitute for values that are close. For example the difference between 100pF at .0001 and 470pF at .00047 is only .00037. That is not very much at all. For guitar pedals these are typically used as high frequency filters and often manufacturers will use whatever is most common in their supply cabinet.


For many capacitors it is worth buying small capacitor kits on eBay etc... for example you search a "Ceramic Capacitor kit" on eBay that contains values from 1pF all the way to 100nF at 20pcs each for $10 or less so it is pretty hard to beat. Many sellers have different assortments so it is important to see what assortment they have first.


The same is also true for higher value capacitors but there are many sources for those. I do like MMLC (which are also a type of ceramic capacitor) for their small size in the higher values and equal tone reproduction.



Right Click and Save As for a Bigger Printable version - Enjoy!




or if you prefer:




The Crash Course Advanced - A Beginners Guide to Effects Pedals Components, by Mod Billy, edited by Wilkie, as well as tweaked by Bruce R. and Barry is a must read.



March 26, 2010 at 10:23 PM Flag Quote & Reply

dcountry13
Member
Posts: 550

Read this thread......Some Great Info!

 

http://www.guitarpcb.com/apps/forums/topics/show/4055341

 

 

January 20, 2011 at 10:30 AM Flag Quote & Reply

Barry
Site Owner
Posts: 8793

When ordering Metal Film or Box Caps for pedals make sure they have a 5mm Lead spread.


Check the Datasheet before you buy them to determine the Lead Spacing.

This is what we use in all of our pedals when this type of Cap is called for.


1. Different companies use different labeling. 22nF = .022uF,  27nF = .027uF,  33nF = .033uF  etc...

2. Most capacitors have a "tolerance" of 10 - 20%, this means "stated value could be off by 10 - 20%."


Also note that under PCB's in the Menu bar above you should be able to find a Picture of a Populated Board to see what I am using in a particular build! Although feel free to use what you have in stock or will fit.

Click on the picture once for a normal view and then click on it again for a blow up view.


Voltage is critical to size not sound.

Use 16v to 63v for sizes that fit.



January 28, 2011 at 5:25 PM Flag Quote & Reply

Barry
Site Owner
Posts: 8793

The Crash Course Advanced - A Beginners Guide to Effects Pedals Components, by Mod Billy, edited by Wilkie, as well as tweaked by Bruce R. and Barry is a must read.

January 29, 2011 at 11:34 AM Flag Quote & Reply

Bruce R
Moderator
Posts: 1680

A member named Chumbox posted this question:


Tonnman

You once noted in a thread of mine you don't like using electrolytic capacitors in the audio part of the circuit and was hoping to get clarification why this is?


Tonmann's Response:

Electrolytic capacitors have many disadvantages compared to film capacitors:


They are polarized, which means that in order for the capacitor to stay "healthy", the positive lead should be connected to a higher voltage than the negative lead.  Although electrolytic capacitors will take some "reverse polarity" abuse, it is better to work with "healthy" capacitors.


They use an electrolytic paste for the dielectric (the insulation between the plates), the paste dries out with age making the capacitor degrade over time.  This paste also means that the capacitor uses ion transfer as opposed to electron transfer (film capacitors) plus the dielectric absorption is higher for electrolyics - this does several bad things.

Frequency delays - electrolytics are slower to react causing distortion at higher frequencies.

Noise - electrolytics produce more noise.

Non linear impedance (resistance) at higher frequencies.


Although much of this applies to high end audio amplifiers (frequencies up to 20kHz) rather than the lower frequencies (5kHz - 10 kHz) for guitar pedals, I couldn't say (because I've never measured) how  bad the effects are.  I take the approach that using components with better characteristics is preferable whether or not I can hear the difference,


I remeber years ago electrolytics had tolerances of +100%, -50%. A 22µF capacitor could be anywhere between 44µF and 11µF - not good for tone / EQ circuits.


Although manufacturing techniques have improved regarding tolerances, dielectric absorption, ESR, ESL etc, most audio grade electrolytic capacitors do not come cheap - check out the prices for Black Gate capacitors !!!


So even with all of the negative aspects, are electrolytics ever needed in the audio path of a guitar pedal ?



Looking at the above diagram let's take each capacitor in turn and look at the orientation and the frequency response.  We'll assume that we want to keep the frequency response flat at the lowest guitar frequency (84 Hz).


C1 - is orientated incorrectly ( a mistake in a lot of circuits) since there is no DC voltage from a guitar connected to the input and there is a DC voltage on the base of the transistor, C1 should be turned around.  BJT transistors have a relatively low input impedance (resistance), much lower than a FET or op amp.  To keep the bass response flat, C1 needs to be quite large - somewhere in the low µF range. An electrolytic is unavoidable unless you want to cut some bass frequencies.


C2 - orientated correctly.  An electrolytic is unavoidable - to get a good amount of gain at bass frequencies, the capacitor needs to be somewhere between 2µ2 and 22µ.


C3 - the orientation may be correct, it depends on the bias voltage at the collector of the transistor and the V ref voltage on the input of the op amp - measuring is the only way to tell.  An electrolytic is not needed, the input impedance of the op amp is very high, you could go as low as 22nF to keep the bass response flat.


C4 - orientation is correct.  The primary role of C4 is to prevent DC voltages from going to ground, this allows the bias voltage to be set correctly.  A secondary role is create a high pass filter ( attenuates bass frequencies).  The value of the capacitor depends on the choice of the resistors - an example may help:

Ignoring C4 for the moment, the gain of the op amp is the value of the resistor connected between the output and the -ve input divided by the value of the resistor connected from the negative input to the right side of C4 (you would also add one to the answer because it is a non-inverting amplifer).


If the resistors are 10k and 1k respectively, the gain would be 10k / 1k = 10 +1 = 11


If the resistors are 470k and 47k respectively, the gain would be 470k / 47k = 10 +1 = 11


Both gains are the same (it is the ratio of the resistors that determine the gain, not their values).


If we now take C4 into consideration, to keep the bass response flat, it's value would have to be about 4µ7 for the 10k / 1K resistor pair and about 220nF for the 470k /47k pair.


To avoid using an electrolytic capacitor with an op amp you would scale the resistors accordingly.


C5 - orientated correctly.  The capacitor value is determined by the pot value.  For a 100k pot, a value of 220nF will keep the bass response flat, for a 10k pot it's between 470nF - 680nF

 

 

 



So there are my resaons (plus some tips) for preferring film capacitors to electrolytic.

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June 17, 2012 at 10:32 AM Flag Quote & Reply

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