0 to -12dB Attenuator in 0,5dB steps !

[Junoman]

Hello,
i need some help regarding passive preamp/attenuator calculation/construction.

I´d like to feed my disk (vinyl) cutting lathe with the direct signal
output of my D/A converter unit without any active preamps if this is possible.

Output of the D/A is at 0dBFS(digital) +12 dBu output which lets the record cutting lathe cut a record with +12db.
i need to attenuate in 0.5dB steps down to 0DB. that means 24 steps would be perfect. maybe more.

i also like to pick the signal before or/and after the attentuator for my monitor matrix without affecting the signal.

could anyone help me designing this or tell me how i calculate the
resistor network. i am very bad in maths !

The Attenuator btw. must work with 4 channels (2 x stereo) with minimum tolerance (0.1dB) between the cannels.


best regards

Junoman

 

[Taco]

I have used this page to calculate my stepped attenuator.

http://www.quadesl.com/attenuator.html

 

[Junoman]

thanks for your reply and link.

i calculated a list.

10kOhm, 24 Steps in 0,5dB steps.

But at the switch setting (the last) 23-24 the output resistance is
only 157Ohms whic is a little to low i think !

greetings

juno

 

[fdegrove]

Hi,

For this particular application you are best served by a constant impedance attenuator.

Take a look at series type attenuators, not the shunt types.

If the fact that you have several resistors in series as you attenuate bothers you, than simply calculate each step as the sum of all previous ones and you're done.

Cheers,

 

[Junoman]

thanks,

but i need some advice how to do this !

best regards

Junoman

 

[fdegrove]

Hi,

but i need some advice how to do this !

Meaning you need advice on the formula to use for the calculation of the resistor values or on how to hook them up?

Here's a basic series att. where more Rs are seried as you attenuate, I would use it slightly differently in that I summ the values preceding my next step.
Only disadvantage is that now have to switch in and output as you move.

A picture of the classic series attenuator:

If you need the formula, let me know. I'll try to type it in.

Also keep in mind that if you use 24 positions of a 24 position switch you won't have an end stop .

 

[Junoman]

Hi Frank,

thanks for the help.

yes i would need the formula. also the output Resistance should be not that low when highest attenuation is selected.
steps should be 0.5dB. 24 stepts. first step bridged.

best regards and thanks

andreas

 

[dhaen]

Also keep in mind that if you use 24 positions of a 24 position switch you won't have an end stop .

That could cause a shock late at night

 

[fdegrove]

WAKING UP THE NEIGHBOURHOOD...

Hi,

That could cause a shock late at night

Yep.