25 June 2012

DIY Stepped Attenuator Volume Control

The latest project to be added to the site is a DIY passive volume control which is made using a switched attenuator.  A stepped attenuator operates by switching to different resistors at each of switch settings.  The benefit of a stepped attenuator is that it can use low noise metal film resistors making them quieter than typical hot formed carbon and conductive plastic potentiometers.  The volume control uses a stereo 100k 24-position stepped attenuator which comes fully assembled for $18US from 8 Audio-Mall.  The attenuator uses 1% precision metal film resistors on a "make before break" multi-position switch.  A photo of the stepped attenuator is shown below. 

stereo 100k  24-position stepped attenuator
stereo 100k  24-position stepped attenuator
The stepped attenuator is housed in a small wooden enclosure with aluminum top and bottom plates.  A knob, RCA jacks and a 4 Pole Double Throw (4PDT) switch round out the DIY volume control.

DIY Stepped Attenuator Volume Control
DIY Stepped Attenuator Volume Control
Matt reports that he is pleased with the results of the stepped attenuator volume control as it is significantly quieter than any of the carbon and conductive plastic potentiometer he has used.  The attenuator was measured to have a noise figure which is about 26dB lower than a typical PEC hot molded carbon potentiometer of the same value.  For full project details, see the DIY Switched (Stepped) Attenuator Passive Volume Control project page.


More DIY Volume Controls

2 comments:

  1. You can't just design a circuit where the noise of the pot doesn't matter?

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  2. The bigger benefit of a stepped attenuator is precision; pots don't track very well between channels, and it's not possible to optimize the curve to fit your needs.

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