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Audio Volume Relay Attenuator with IR Control

Audio Volume Relay Attenuator with IR Control

Compact and simple circuit: just 5 tiny relays implement a 32-step logarithmic stereo attenuator. The 32 steps of 1.7dB together span a 54dB attenuator range. Only a single IC controls and drives the circuit. An IR receiver allows remote control. The device can learn and store your favorite key codes.
The controller currently understands the popular Philips ‘RC5’ protocol, as well as the newer RC6 protocol. A JVC protocol is under test. The PCB supports audio input channel selection next to volume control. This is fine to implement a small passive pre-amp, but of course allows a combination with your favourite active buffer/pre-amp.

The PCB has an output ‘serial control’ to connect to ‘slave’ boards. The ‘slave’boards are actually the same PCBs with a few components omitted. Together this creates a multi-channel input select and volume control, for 5.1 or 7.1 sound, or for stereo audio with balanced (XLR) connections. The ‘serial control’ reliably sends the new relay state, not just increments.

The circuit implementation targets high-end audio applications, with its relays and PCB space for somehwat larger audio-grade resistors. As net result, this cicruit is not as cheap as some other solutions with -for instance- a motorized potmeter.

The circuit does not create clicks/glitches in the audio output signal while making volume steps, due to carefully switching relays ‘off’ before others ‘on’. However, you can clearly hear the mechanical activity of the relays. If you don’t like that, relays are not your solution.

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