DaveP's Attenuators

[letterbeacon]

I find the way DaveP lays out his attenuators very easy to understand - here's an example of his one for his BA-6A:

What sort of attenuator is this? A T Pad? What's the best way to calculate the values if I wanted to build something similar on a 6 position rotary switch?

Thanks.

 

[user 37518]

From what I'm looking at, it looks like a simple U pad.

 

[Rob Flinn]

Not a T pad.  It's like using a stereo pot in a U pad config but instead of the tracks of the pot you have 2 resistor ladders.

 

[letterbeacon]

So, if I'm after a 600r attenuator, as long as each leg adds up to 300r then it'll work?

Are there any advantages/ disadvantages of a U pad over a T pad?

 

[user 37518]

So, if I'm after a 600r attenuator, as long as each leg adds up to 300r then it'll work?

Are there any advantages/ disadvantages of a U pad over a T pad?

In a U attenuator you have 3 or 4 resistances, 2 of them to a common point like in your circuit, if you want a 600r output, you need that the Thevenin resistance be 600 ohm, not only making 2 of them 300 ohm, in other words you need to consider the shunt aswell as the series resistances in the calculation for output impedance. For 600:600 attenuators check the book "Handbook for sound engineers " by Ballou