Electronics
Capacitors for audio
Possibly this should be on the Snake Oil page, for when it comes to what capacitors are required for hifi audio there is a fair amount of bunkum. OTOH, practical capacitors do introduce measurable non-linearites (due to fact that a real capacitor has series and parallel R, and series L), so some choices do make a difference: it is widely known that electrolytic types are best avoided in the signal path, and they need a small value non-electrolytic in parallel if used for decoupling. Also widely accepted is that polyester capacitors are inferior to other plastic film types. Esoteric circuits such as hifi valve amplifiers will use silver-mica capacitors and such like. With many valve amplifier designs the C values are smaller and electrolytics can be avoided completely in the signal path.
Several people have gone into this topic in some depth, and some have provided test results (some subjective, some objective) of high-end capacitors. Here is a list of web articles:
How to Pick Audio Capacitors - Max Pierson
Picking Capacitors - Walter G. Jung and Richard Marsh
Measured Differences Between Capacitors for Audio Applications - Conrad Hoffman
Audio Circle - My Capacitor comparisons - Jon L
The Great Capacitor Shoot-Out - The Vinyl Tourist
Capacitors - Darmowe Liczniki
Comparing electrolytic capacitors - Eric Juaneda, High End Audio
Capacitor Characteristics - Rod Elliott (ESP)
Capacitor Distortion Mechanisms - Stephan Großklaß
CapSite 2009 - endir
Capacitor Sound? - Cyril Bateman
The Sound of Capacitors - Steve
A passive role? Martin Colloms
Clarity Cap research
Capacitor Test - Humble Homemade Hifi
Do capacitors sound different? - Mark Wheeler
Several people have gone into this topic in some depth, and some have provided test results (some subjective, some objective) of high-end capacitors. Here is a list of web articles:
How to Pick Audio Capacitors - Max Pierson
Picking Capacitors - Walter G. Jung and Richard Marsh
Measured Differences Between Capacitors for Audio Applications - Conrad Hoffman
Audio Circle - My Capacitor comparisons - Jon L
The Great Capacitor Shoot-Out - The Vinyl Tourist
Capacitors - Darmowe Liczniki
Comparing electrolytic capacitors - Eric Juaneda, High End Audio
Capacitor Characteristics - Rod Elliott (ESP)
Capacitor Distortion Mechanisms - Stephan Großklaß
CapSite 2009 - endir
Capacitor Sound? - Cyril Bateman
The Sound of Capacitors - Steve
A passive role? Martin Colloms
Clarity Cap research
Capacitor Test - Humble Homemade Hifi
Do capacitors sound different? - Mark Wheeler
Resistor Calculators
1 or 2% 5-band resistors are the norm nowadays, and they are less tolerant than the old 4-band 5% types (this is a good thing). It does make reading R values harder, but there are calculators for this (there are dozens of these online). I like any that are fast (not all are), and allow you to get the colour code from a value of R, or vice versa. Here are links to a few:
Electronics 2000 (a good no-fuss 4 or 5 band calc - offers colour or value input)
Hobby Hour (offers both value -> colour, and colour -> value)
DigiKey (4,5, or 6 bands)
If you are caught off-line then there is Electron Helper. This also includes an Ohm's Law calculator.
Electronics 2000 (a good no-fuss 4 or 5 band calc - offers colour or value input)
Hobby Hour (offers both value -> colour, and colour -> value)
DigiKey (4,5, or 6 bands)
If you are caught off-line then there is Electron Helper. This also includes an Ohm's Law calculator.
Electrical myths
Ever found textbook explanations of how electricity works lacking (incomplete, illogical, ambiguous etc)? William Beaty decided to address this issue. His discourse WHY IS ELECTRICITY SO HARD TO UNDERSTAND? is an excellent tackling of this difficult subject (but not for the faint hearted - probably best not to go there until you are quite familiar with the usual pre-suppositions of electrical theory).
500 Series modules

It seems these 1 1/2 " wide vertical modules are back in fashion. This layout originates from telecommunications and broadcast equipment from the 70s / 80s. This format was adopted by a few audio engineering manufacturers in the 80s, before being overtaken by the idea of putting 2, 4, or even 8 devices into a single rack unit. Radial Engineering have reinvented the 500 series rack (as used by API) and call it the Workhorse. They have produced an open source specification so that (hopefully) any card can plug in and work properly. There is also an extension to the spec to allow for a mix buss in the sub rack.
Electronic Musician magazine have a roundup of 500 series racks here.
Electronic Musician magazine have a roundup of 500 series racks here.
Audio Kitsets
There are a few signal processor kitsets that have appeared on the market. They are mainly copies of vintage gear (SSL, LA4 etc). In the USA there is Serpent Audio, and in Australia there is JLM Audio. Hairball Audio do an 1176 clone kit. All three post overseas. If you are so experienced that you don't need a kitset then this site has some useful information. Also checkout DIY recording Equipment, who even include a U87 mic copy project.
If it is more a guitar amp you're after then Ceriatone are making clones of classic amps (Marshall, Fender, Vox etc). To get started with something simpler, you may prefer guitar stomp box kits from Mammoth or Bitsbox. Also checkout the Guitar Kit Builder site where there is a list of other suppliers, and the roundup of suppliers at Music Things.
For a simple synth kitset, try the MeeBlip digital synth.
If it is more a guitar amp you're after then Ceriatone are making clones of classic amps (Marshall, Fender, Vox etc). To get started with something simpler, you may prefer guitar stomp box kits from Mammoth or Bitsbox. Also checkout the Guitar Kit Builder site where there is a list of other suppliers, and the roundup of suppliers at Music Things.
For a simple synth kitset, try the MeeBlip digital synth.
AC Theory in a Nutshell
(AC THEORY FOR NON-MATHEMATICIANS)
1. For a resistive circuit the voltage and current are in phase and can be calculated using their RMS values in the Ohms law equations (RMS=0.707 Imax or Vmax).
2. For a purely capacitive circuit the voltage is behind the current by 90°.
In other words maximum current flows when the voltage is zero, and maximum voltage is when the current is zero.
3. Capacitors exhibit an electrical property called Reactance, which is defined as the ratio of the capacitor voltage to current. Note that this is different to resistance due to the 90° phase difference.
4. The capacitive reactance is frequency dependant due to fact that for a given voltage the charging time is reduced as the frequency increases.
The formula for this is: Xc = 1 / (2πƒC)
5. For a purely inductive circuit the current is behind the voltage by 90°.
As with the capacitor, maximum current flows when the voltage is zero, and maximum voltage is when the current is zero.
6. Inductors also exhibit reactance. This also varies with frequency as there will be more change of flux over time for a higher frequency. Therefore a greater back-emf is generated to oppose the current.
The formula for Inductive reactance is: XL = 2πƒL
7. Impedance is the total opposition to current in an AC circuit. It is comprised of Resistance and Reactance. Because of the phase difference of voltage and current in inductors and capacitors, the two cannot be simply added together.
The formula for impedance is:
1. For a resistive circuit the voltage and current are in phase and can be calculated using their RMS values in the Ohms law equations (RMS=0.707 Imax or Vmax).
2. For a purely capacitive circuit the voltage is behind the current by 90°.
In other words maximum current flows when the voltage is zero, and maximum voltage is when the current is zero.
3. Capacitors exhibit an electrical property called Reactance, which is defined as the ratio of the capacitor voltage to current. Note that this is different to resistance due to the 90° phase difference.
4. The capacitive reactance is frequency dependant due to fact that for a given voltage the charging time is reduced as the frequency increases.
The formula for this is: Xc = 1 / (2πƒC)
5. For a purely inductive circuit the current is behind the voltage by 90°.
As with the capacitor, maximum current flows when the voltage is zero, and maximum voltage is when the current is zero.
6. Inductors also exhibit reactance. This also varies with frequency as there will be more change of flux over time for a higher frequency. Therefore a greater back-emf is generated to oppose the current.
The formula for Inductive reactance is: XL = 2πƒL
7. Impedance is the total opposition to current in an AC circuit. It is comprised of Resistance and Reactance. Because of the phase difference of voltage and current in inductors and capacitors, the two cannot be simply added together.
The formula for impedance is:
8. Resonance.
As we have now seen XL increases with ƒ, and Xc decreases with ƒ. Therefore if a capacitor and an inductor are connected in series, at some frequency XL = Xc and as they are out of phase will cancel out. This is the resonant ƒ ; the circuit current is maximum and limited only by the circuit resistance (ie Z = R).
If the capacitor and an inductor are wired in parallel, at resonance the Z (and therefore V) is maximum. The circuit current will be minimum.
ƒ0 = 1/ [2π.sqrt(LC)]
Spice
Instructions for using B2 Spice, along with some example circuits.

spice_setup__circuit_examples.pdf | |
File Size: | 163 kb |
File Type: |
Studio Headphone Amplifier

Most studio headphone amps have too little power to provide the volume required by a rock band (1/2 deaf drummers etc). My solution is to use 20W power amp modules, and a distribution system to the studio via 100Ω current limiting resistors. Put RDL ST-CL1 limiters on the output of the amp so you don't deafen the band.
DIY lead tester

I designed this lead tester a few years ago for my students to build. I built a prototype, which I still use. As you can see it uses only a few components so it can be put together in an afternoon. As this tester will be used to sort out good leads from bad, make sure your soldering is reliable.