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Old 2nd September 2008, 12:39 PM   #1
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Default passive attenuator

I would simply like to know why passive pots lack dynamics and bass?

This has been my own experience with them and I'd like to know what kind of distortion could cause such effects?
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Old 2nd September 2008, 01:27 PM   #2
juma is offline juma  Germany
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The eternal question, torturing mankind since the dawn of time

Impedance matching, dear professor, impedance matching !
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Old 2nd September 2008, 06:34 PM   #3
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ok well could someone explain the details of this to me?

what is impedance mismatch and how does it make the sound lacking in dynamics?
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Old 2nd September 2008, 06:55 PM   #4
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Quote:
Originally posted by Professor smith
ok well could someone explain the details of this to me?

what is impedance mismatch and how does it make the sound lacking in dynamics?

Please consider getting "The Art of Linear Electronics" by John Linsley Hood. It covers all the essentials about audio electronics, like filters, impedances, circuit theory, etc.

The book is now in reprint from Audioxpress: http://www.audioxpress.com/bksprods/BKSELEDES.htm

Also consider reading Nelson's prior articles on the ZEN line of preamps and amps. They are available on www.passdiy.com.

Both of these resources are a gold mine for learning!

-David
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Old 2nd September 2008, 06:58 PM   #5
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Old 2nd September 2008, 10:42 PM   #6
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Quote:
Originally posted by Professor smith
ok well could someone explain the details of this to me?

what is impedance mismatch and how does it make the sound lacking in dynamics?

well impedance mismatching is the theory that stands behind the maximum transferred power.
Now the theory says that a real generator with its internal resistance connected to a load transfers the maximum power to the load when the load has the same impedance of the internal resistance of the generator.
The power figure is, if i don't recall wrong, an upside down parabolic behavior (the maximum is Pgen/2).
As you can understand by varying the load connected to generator the ability of the system to transfer power varies accordingly.

How do we summarize this?
A passive attenuator's system obviously varies the impedance seen by the stage behind it as the volume position varies.
This leads to the problem of different adaptive conditions at different volume level positions and not all them will be the ideal one, of course.
As the dynamic might be defined as the ability of an amplifier to output power", you easily understand how this, of course, affects the above parameter.


Stated this, i like them both : active and passive volume control system.
I would personally try to make them both and see what i like the most.


Hope this helps.
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Old 2nd September 2008, 11:08 PM   #7
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Default Re: passive attenuator

Quote:
Originally posted by Professor smith
I would simply like to know why passive pots lack dynamics and bass?

This has been my own experience with them and I'd like to know what kind of distortion could cause such effects?
I don't know. There is no theory which adequately explains this, but there
is a common perception that this is so. Having the wiper see a high impedance
load seems to improve it.

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Old 3rd September 2008, 03:06 PM   #8
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What does reducing the current of the signal source do to the sound?

I have heard that this is what causes the lack of bass drive and dynamics, is this a myth?
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Old 3rd September 2008, 07:15 PM   #9
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Probably. It's a conclusion lacking context. I can probably come up
with counter examples pretty easily.
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