How much total attenuation???

[Zero Cool]

I found a program that will allow me to calculate the steps for a series attenuator. but it requires i enter a number for the total attenuation.


How much attenuation is required for a typical stepped series volume control? This will be placed between a CD player and a Power amp.

 

[AndrewT]

Hi,
aim for between -60db and -80db.

But if you never listen to quiet music a smaller range may do, -40db to -60db.

You can also set the first step at -20db (or even higher) if you have a sensitive system that tends to have a high attenuation during all listening sessions.

 

[Zero Cool]

thanks i will give those numbers a shot.

How would i calculate the total resistance of a standard pot for comparison???

 

[AndrewT]

Hi,
it will usually be between 10k and 100k.

You would not calculate it.
Just measure it if the labeling is illegible.

 

[Zero Cool]

Oh i meesed up, i MEANT to say, how would i measure the total attenuation of a pot for comparison.


Zc

 

[AndrewT]

Hi,
most pots will go down to completely off (-infinitydb).

Very few audio taper pots are accurate by the time they get to -60db, the balance starts to wander to and fro as you adjust the attenuator. At -80db they are usually hopeless.

It is to improve this balance problem that some use a dual linear pot.

Then we are in a different ballpark when we go to stepped attenuator. You can easily achieve +-0.1db and even ten times better with selection, both in balance and absolute terms.

 

[davidsrsb]

You need to allow for input level variation, which can be as much as 20dB between an old cassette deck and a CD player, so 40dB is too small

 

[rephil]

Hello Zero Cool,

the attenuation of the pot is 20 log (Rmeasured / Rpot).

Example : the pot is Rpot = 10 Kohm, you measure Rmeasured = 100 ohm at the cursor (between cursor and ground) and so you get

20 log (100 / 10000) = -40 dB

Regards

rephil