Friday, February 08, 2013

Passive low-value audio pads

I've often had to knock up audio attenuators to make music gear (which is typically +4dBu for zero level against 0dBu for broadcast) and my usual m.o. is to approximate everything around a 10k potentiometer; typically 100ohm sending impedance, 10k ohm terminating impedance and an H-network for balanced lines and a T-network for unbalanced. You can find numerous examples online.

So - all credit to my colleague Matt for saying "..no, no - let's do it properly";
So, for a variable 1.5 -> infinite pad you need Z1 and Z2 at 390 ohms and a 5K potentiometer. 

Blow me down, the 5k pots arrive with their wipers at the centre position and all six that I've made so far have been bang on 2dBs at that centre point. It pays to be precise.

1 comment:

brig said...

I have had some success with the Neutrik's range of NTE1 and NTE 4 transformers for attenuation and interfacing.

I have a page here which goes through some of the basics.

http://iweua.com/Applications/Audio.html