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Old 27th May 2008, 11:07 AM   #1
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Default Looking for Balanced attenuator ideas

Hi Guys,

please help me in finding schematics for balanced volume attenuator.

Thanks!
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Old 27th May 2008, 11:41 AM   #2
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is it working? (attachment)
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File Type: jpg att_xlr.jpg (10.1 KB, 361 views)
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Old 27th May 2008, 12:22 PM   #3
Dan2 is offline Dan2  South Africa
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to my understanding, a balanced line has 2 signals, exactly the same but out of phase by 180deg, so that any common interference is regected by the amp

cartman, if that doesn't work im sure a stereo pot (dual pot) on the hot and cold lines should work.
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Old 27th May 2008, 02:35 PM   #4
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Quote:
Originally posted by Dan2


cartman, if that doesn't work im sure a stereo pot (dual pot) on the hot and cold lines should work.

Do you mean this? (attachment)

...by the way, this is not logical/likeable for me, because in this case I loose the "Ground independence"

What do you think?
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Old 27th May 2008, 08:28 PM   #5
forr is offline forr  France
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Hi Cartman,
A variation of your first drawing is the inclusion of two identical precision resistors in the signal wires and then a variable resistor between their ends, no reference to ground. It is used, I think, by Morgan Jones and Erno Boberly.
However, according to D. Self who designed mixers, your second design is to be the prefered one (the pots are supposed well matched) because it has a better common mode rejection. Common mode voltages are not rejected by the first solution.
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Old 27th May 2008, 08:41 PM   #6
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Thanks Forr for you reply...

by the way, I would like to build a passive balanced preamp with my just stereo (dual) stepped ladder 10K attenuator....

What is the best solution?

Which benefit is the more important?

1) "no reference to ground"
2) "Common Mode Voltage Rejection"

As I know, the balanced signal is great why there is independence of ground. Is it true?
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Old 28th May 2008, 03:26 PM   #7
Dan2 is offline Dan2  South Africa
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as far as i know, common mode signals (interference) are usually a problem with very long wires, so if you put the attenuator pretty close to the amp (mixer) it should be ok.


i have never put an attenuator on a balanced line so i can't really help too much more
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Old 28th May 2008, 03:36 PM   #8
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by cartman

by the way, I would like to build a passive balanced preamp
with my just stereo (dual) stepped ladder 10K attenuator....
Hi,

That is not possible without input and ouput transformers.

/sreten.
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Old 28th May 2008, 08:40 PM   #9
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Quote:
Originally posted by Dan2
...
i have never put an attenuator on a balanced line so i can't really help too much more
Thanks Dan2!
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Old 28th May 2008, 08:42 PM   #10
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Quote:
Originally posted by sreten


Hi,

That is not possible without input and ouput transformers.

/sreten.
Thanks Sreten!

...and if I would have 2pcs stepped ladder 10K attenuators? (1 dual per each channel) can I use it? (w/o transformer)
If so, how I can connect?

thx!
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