0 to -12dB Attenuator in 0,5dB steps !
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 4th June 2003, 10:54 AM #1 Junoman   diyAudio Member   Join Date: Jun 2003 Location: Frankfurt 0 to -12dB Attenuator in 0,5dB steps ! Hello, i need some help regarding passive preamp/attenuator calculation/construction. IŽd 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
 5th June 2003, 06:50 AM #2 Taco   diyAudio Member   Join Date: Nov 2002 Location: Chicago I have used this page to calculate my stepped attenuator. http://www.quadesl.com/attenuator.html
 5th June 2003, 08:41 AM #3 Junoman   diyAudio Member   Join Date: Jun 2003 Location: Frankfurt 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
 5th June 2003, 09:53 PM #4 fdegrove   diyAudio Senior Member     Join Date: Aug 2002 Location: Belgium 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, __________________ Frank
 6th June 2003, 09:50 AM #5 Junoman   diyAudio Member   Join Date: Jun 2003 Location: Frankfurt thanks, but i need some advice how to do this ! best regards Junoman
fdegrove
diyAudio Senior Member

Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
 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 .
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Frank

 6th June 2003, 06:14 PM #7 Junoman   diyAudio Member   Join Date: Jun 2003 Location: Frankfurt 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
diyAudio Moderator Emeritus

Join Date: Jun 2002
Location: U.K.
Quote:
 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
diyAudio Senior Member

Join Date: Aug 2002
Location: Belgium
WAKING UP THE NEIGHBOURHOOD...

Hi,

Quote:
 That could cause a shock late at night
Yep.
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Frank

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