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Old 20th September 2005, 07:41 PM   #1
sopapo is offline sopapo  Spain
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Default Why use pots? better opamps?

Hello,first of all,sorry for my bad english...
I wonder why is so spread the use of the potenciometers for control the audio signal and there is almost no developement for other systems to control the signal level in hifi or high end...

I mean that a audio signal goes into a pot with all the problems that it implies :bad contact between slider and carbon track,bad dinamic range (comparing to others devices),signal degradation in highs levels of attenuation,parasite capacity etc

threre are pot s like the DACT that have great performance but is in the same way and the intrinsic limitations are the same

so I ask why not to use with the potenciometer devices with more performance (noise,bandwith,dinamic range etc) like a good opamp (or discrete) in a certain configuration that the audio is not adverse affected by the pot?.....


In passive the best look like the secondary stepped transformer way.... it isnt?


Best regard
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Old 21st September 2005, 06:15 AM   #2
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I think I understand your question, but let me ask you:

How exactly do you propose controling the volume with opamps instead of potentiometers? Do you have a schematic (or could you explain it in more detail)?
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Old 21st September 2005, 12:15 PM   #3
anatech is offline anatech  Canada
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Pots are not that bad. Unless you mis-use them of course!. Transformers have an entire host of possible problems, they are less perfect.

-Chris
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Old 21st September 2005, 12:20 PM   #4
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Quote:
Originally posted by rtarbell
I think I understand your question, but let me ask you:

How exactly do you propose controling the volume with opamps instead of potentiometers? Do you have a schematic (or could you explain it in more detail)?
Actually, there are quite a few good VCA's (voltage controlled amplifiers -- Analog Devices comes to mind) in which you can control the gain with a DAC.
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Old 21st September 2005, 01:03 PM   #5
Previously: Kuei Yang Wang
 
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Default Re: Why use pots? better opamps?

Konnichiwa,

Quote:
Originally posted by sopapo
I wonder why is so spread the use of the potenciometers for control the audio signal and there is almost no developement for other systems to control the signal level in hifi or high end...

I mean that a audio signal goes into a pot with all the problems that it implies :bad contact between slider and carbon track,bad dinamic range (comparing to others devices),signal degradation in highs levels of attenuation,parasite capacity etc
Despite all these rather bad sides classic potentiometers WHEN BUILD APROPRIATLY AND UTILISED APROPRIATLY perform better, both objectively and subjectively compared to electronic attenuation solutions. Switched attenuators using resistive elements can be better or worse than the best classic potentiometers, depends on implementation.

Quote:
Originally posted by sopapo
so I ask why not to use with the potenciometer devices with more performance (noise,bandwith,dinamic range etc) like a good opamp (or discrete) in a certain configuration that the audio is not adverse affected by the pot?.....
Sadly, there is no such configuration. One of the better possible solutions is to use photoresistors, HOWEVER these things must be expensively selected for matching dark & light resistances or require very complex circuitry to gain a servo system that ensures the desired volume regardless of the optical resistors charateristic.

(hint, if you use the resistor to change both AC and an overlaid DC voltage you can use the DC to drive a servo which makes sure the DC attenuation follows a preset ratio, but adding DC you now need blocking capacitors which a normal potentiometer does without, so most of the time you merely swap one problem for another)

Quote:
Originally posted by sopapo
In passive the best look like the secondary stepped transformer way.... it isnt?
On that I am in complete agreement.... ;-)

Sayonara
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