SF Bay Music Tech

2014/03/16

Noise Source Transistor — Conclusion

Filed under: analog2.0,tech notes — Gan @ 6:08 AM

DSC00098_2I have been working for a while to determine which transistor to use for noise source in noise generator.  I was using 2SC3311 which was obsoleted recently.

I did several tests, mainly by listening, and chose BC547.  The reasons are:

  • It has good taste as a noise source.  Easy to find sweet spots when using it with a filter and VCA.
  • Noise level was close to 2SC3311, so my previous design works with simple replacement.
  • Availability is good.
  • Unlikely to get obsoleted soon.

I started the test with listening “raw” noise without any modification and filtering.  However, it didn’t work well.  Many of the candidates sounds similarly.  However, I found characteristics of transistors are so different when I also used a VCF and a VCA driven by an envelope generator.

Also, it was hard to determine “which sounds better” when I conducted A/B comparison test.  So I changed the strategy and just played with synth using each candidates, and chose one I felt the most fun to play with.  Thus I gave up “measuring” eventually.

Demo using the chosen transistor.

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