Wednesday, 31 March 2010

Audio attenuator

I know, I know - everyone is wondering when I'm going to pop a cap in the aerosol of Silly String. I'm still waiting for the Great Hairy Leader to lend me his vidcam. I want the best possible footage for your delectation. More news soon...

The project for March did actually take place. The Hairy One needed an audio attenuator to balance line-out from a sound desk to mic-in on his video camera, so he could record some live gigs without unwanted background noise. A bit of Googling turned up schematics for a suitable mono attenuator. The Secret Laboratory adapted the design to produce a stereo attenuator for the purpose, constructed entirely from salvage. This is recycling at its best.

The R1s are 10K and provide the bulk of attenuation. The R2s are 1K and serve to sink optional power from the camera input to ground, fooling it into thinking it really is dealing with a powered mic (you lose a bit of signal here as well but, hey, attenuator - there's a clue in the name). The C1s are 104 ceramics. You could use almost any similarly rated ceramic caps here - all they are doing is making sure that no DC power gets from the camera to the desk. This model provides approximately 21dB attenuation.

I really wanted to etch a custom board for this project but, when I sketched in on paper, it looked like three strips of Veroboard, so I built it on three strips of Veroboard.

I put phono plugs on the desk end (line-out) and a single 3.5mm stereo jack on the camera end (mic-in). Worked a treat.

I wanted to post a photo here but the device was needed on the night in question. I'll post a photo as soon as I get the device back.

1 comment:

  1. Would it work for me? I have the attenuation span of a fish.