LED

Capacitance Calculator

Here's a handy capacitance calculator.

http://www.calculator.org/property.aspx?name=capacitance

Balanced vs unbalanced

 An unbalanced audio path has two conductors. One carries the audio signal and the other is the shield/ground. There is nothing at all wrong with an unbalanced signal but at times can be susceptible to picking up interference from radio frequencies or electromagnetic fields that cause noise and buzz.

A balanced signal has three conductors. It relies on a sum and difference principal.
Sum and difference is the combining (summing) of two signals that are out of phase from each other. Whatever doesn’t cancel out is what you’re left with (difference).
When two identical signals of identical amplitude (volume) are combined and one is 180 degrees out of phase from the other you have complete cancellation of that audio. However, if one of those signals is a different amplitude, you don’t get complete cancellation. And it’s this principal that makes a balanced audio path work.
The output from a balanced piece of gear will have the audio signal on pin 2 (hot). That same signal will be present on pin 3 (cold) however that signal is at a lower amplitude than the signal on pin 2. The shield/ground will be on pin 1.
When the signal reaches a balanced input, the signal on pins 2 and 3 are combined with either pin 2 or pin 3 (usually pin 3) out of phase. If that cable happens to pick up interference along the way, it will be on all pins, in phase together and at the same amplitude. When it gets to the input, pins 2 and 3 are combined out of phase and any signal exhibiting the same amplitude (the noise) will cancel out completely. Since the audio is at different amplitudes, it doesn’t cancel out and you’re left with the difference: clean audio!
As for the mics, most all are designed with a balanced output and should be plugged in to the balanced input of a microphone amplifier (pre-amp)
Plugging a mic into an unbalanced input won’t ruin anything but mics generate a very low level signal that needs lots of gain to bring it up in level. Amplifying a signal that much benefits from the noise canceling of a balanced connection

Tube stuff

Here's a nice diagram and cool explanation of signal flow through a common tube circuit.

http://www.el34world.com/charts/currentflow.htm

Video on biasing a Sound City L-B 50. By connecting one end of your multimeter to the centre tap of the output transformer and the other to pin 3 of the output tube. Read the current here. Should be around 42mA.

http://www.youtube.com/watch?v=PYuFsZhFIe8

Great site and forum for vintage gear

http://vintageamps.com/

Simple circuit to switch between tube rectifier and solid state rectifier in a tube amp.

Tubes 101

A tube amp works by letting 2 different types of voltage pass in 2 different directions, while not letting the 2 pass the same way together. The guitar signal which is a low AC voltage goes from the input jack toward the speaker output (getting bigger along the way) while the high DC voltage that powers the tubes runs back in the reverse direction often along the same connection points that serve as stage inputs for the AC signal.

Signal runs straight to pin 2 of the input tube (12AX7).
Pin 2 is known as  the Grid.
Pin 1 is the output which is also known as the Plate.
The flow of electrons from grid to plate increases gain.
Pin 3 is the cathode. This determines the operating level.

Parts

Came across this link while searching for a 7 pin headphone volume pot for a Vestax DJ Mixer.
Might come in handy

http://www.potentiometers.com/

http://www.potentiometers.com/SeriesP140.cfm

http://www.ebay.ie/itm/10-Potentiometer-pot-10kAx2-stereo-audio-log-7-pins-CD-mixer-Zeck-/330918401757?pt=LH_DefaultDomain_186&hash=item4d0c4616dd

NAD C325BEE Repair

This is a picture of a NAD C325BEE stereo amplifier that came in for repair. The 

Amplifier Fan Control

Automatic cooler fan for ampifiers

http://www.circuitstoday.com/automatic-cooler-fan-for-amplifiers

Free Wheeling Diode

http://www.control.com/1026147908/index_html

Another Fan control circuit

http://sound.westhost.com/project42.htm

Comparator video tutorial

http://www.youtube.com/watch?v=y0Q0ERSP24A

Electronics forums

Here are some interesting forums about music and electronics. Lots of good info here.

http://music-electronics-forum.com/activity.php?s=83f284281a5e9faac798355a729c6aa1

http://www.electronicspoint.com/

http://www.audiokarma.org/

www.diyaudio.com/‎

www.diyrecordingequipment.com/‎

Safety first!

Here is an isolation transformer. Been meaning to get one of these for the workshop.

http://radionics.rs-online.com/web/p/safety-site-transformers/4368798/

http://en.wikipedia.org/wiki/Isolation_transformer