Active filters

http://www.simonbramble.co.uk/techarticles/active_filters/active_filter_design.htm I came across this page while I was looking for a page that gives comparison among various types of active filters. Cool.  You can compare by yourself using LTSpice.  
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Matching Transistors, 2SC1815 or 2N3904

You need to use well matching transistor pairs to make a good quality transistor ladder VCF. Above is the classic methodology to find matching transistor pairs.  I tried this procedure with 2SC1815 and 2N3904 I have.  Next version of Analog2.0 boards will support the both types of transistors, so I wanted to know how different they are in VCF perspective. Here is the result: The result shows that 2N3904 has less variability. This comparison might not be fair since my 2SC1815 transistors are very cheap ones purchased from Akizuki-Denshi, so these might have different quality control in manufacturing than usual retail transistors.  But at least I learned following: 2N3904 is…

Gerber File Viewers

There are choices of free Gerber file viewers out Internet.  I’ve tried some so I’ll take notes for archival purpose.

I decided to use GC Prevue btw.

Analog2.0: Noise&Mixer and LFO Board Update

　 Analog2.0 boards update work is in progress.  I've done with the Noise&Mixer board and the LFO board.  Besides the transistor lead position fix that is the main purpose of the update, I'm putting a couple of mod points on every board, like Easter eggs. On the left is the Noise Generator & Mixer board.  On the right is the LFO board.  
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How to Convert Sampling Rate with Java

This worked for me. http://stackoverflow.com/questions/2276027/converting-the-sample-rate-on-the-fly-when-reading-a-wav-file-into-a-samples-arr You can convert by applying AudioSystem.getAudioInputStream to an AudioInputStream object, and you get another AudioInputStream as the result.  Here is the sample code of the part: AudioInputStream inStream = AudioSystem.getAudioInputStream(soundFile); AudioFormat outDataFormat = new AudioFormat(8000.0f, 16, 1, 2, true, false); AudioInputStream outStream = AudioSystem.getAudioInputStream(outDataFormat, inStream); In order to make above code work, we need following two extensions.  Without these extensions, we get exception on the execution above. http://www.tritonus.org/tritonus_share-0.3.6.jar http://www.tritonus.org/tritonus_remaining-0.3.6.jar
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More on Semiconductor Switch

Continued from yesterday’s article.  Here are the switches I compared.

Mechanical Push Switch (Tactile)

You hear click noises.
[audio:https://gaje.jp/blog/wp-content/uploads/2011/12/tactile.mp3|titles=tactile]

Relay

There are occasional pop noises.
[audio:https://gaje.jp/blog/wp-content/uploads/2011/12/relay.mp3|titles=relay]

Analog Switch

Not bad but click noise intermittently happens.
[audio:https://gaje.jp/blog/wp-content/uploads/2011/12/tactile.mp3|titles=analog_sw_chat_cancel]

 

JFET Switch

 The most stable so far.
[audio:https://gaje.jp/blog/wp-content/uploads/2011/12/JFET.mp3|titles=JFET]

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Charge Pump with Arduino

Right: charged, left: normal 5V drive

A charge pump is a circuit that boosts DC voltage.  I tried to make a charge pump using Arduino to enhance power supply for a blue LED.  A blue LED typically has higher forward voltage.  Some ones go to 4V, so 5V-supply processors are slightly powerless to drive it.  Thus a charge pump helps to enhance blue LED brightness.

As you can see in the photo above, charged one is brighter.  The supply voltage was increased to 8V in this case.