Audio Volume Control with Resistor Switches

Posted on Jul 4, 2012

The traditional potentiometer is implemented with an electrical contact that slides over a resistive layer. An example of a well-known audio-grade potmeter is the Alps Blue. I still use this one myself. A high-end (good and costly) alternative is the rotary switch. This device consists of a series of discrete resistors and switches, of which always one switch is actually closed. Resistor-switch networks can offer advantages over the potentiometer such as: Improved quality of the electrical contact, in comparison with the slider. Improved consistancy between separate audio channels (stereo or multi-channel). Less sensitive to dust and wear.

Audio Volume Control with Resistor Switches
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Good audio attenuator rotary switches are made for instance by DACT. An impressive DIY rotary attenuator is here. It is special in using two decks of switches and two sets of resistors per channel. Nice switches and resistors are available for instance at Of course there are integrated circuits that implement a similar functionality, and where the mechanical switches are replaced by MOSFETs. See for instance National and Cirrus. Clearly such devices allow nicely compact solutions. However, for truly high-end audio, I do not trust the sound quality of such devices due to the non-linear parasitic capacitances in such switches. This page focusses on an alternative solution, using discrete resistors and relays as switches. While maintaining the advantages of the rotary switches, the relays offer improved options for remote control of the attenuation, and the solution becomes trivially extendible to handle multi-channel control. Furthermore, the use of small mass-produced relays promises great quality-for-money for DIY audio enthousiasts. This is an example of such a project. A nice design is dicussed in this diyAudio thread. Circuit Examples and Properties Below, different circuits are presented. To obtain concise drawings and a fair comparison, all circuits are constructed to provide (just) 16 volume levels, with steps of 1.5dB, and with an impedance level of about 100Kohm. Remind that for...

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