Attenuator impedance? - Page 2

Vogue · 7th July 2007, 12:33 AM

Well ... I might not be happy ... but I guess that it’s hard to overlook that law.

But anyhow I needed to be sure that I calculated correctly – as I see it, the resistors only make small changes to the impedance

I will report about the progress i make...

Vogue

BlueWizard · 7th July 2007, 08:09 AM

Well, first and foremost, IF Steve Eddy's diagram is correct then the circuit really does nothing.
Since the fixed 250k ohm resistors are more than 10 times any value that the potentiometer can deliver, they really have no effect.

As my math shows instead of 10k, you simply have 9,615 ohms which is only a 4% difference and is probably within the design error range of the potentiometer.

And, for the record, when I was young and first studying electronics, I considered the same circuit, sure I was on to something, but in the end, it does nothing of any significance.

Again, you have only give us the vaguest idea of what you are trying to accomplish. How is what you are trying to do any different than a plain old level control, and why couldn't it simply be done with a normal 10k Pot to ground?

What is the input impedance of you power amp, and what is the output capability of your pre-amp. As long as the Pot is 1/10th to equal to the input impedance and is within the current capability of the pre-amp out, your in the clear.

Knowledge is power, the more knowledge we have available to understand the problem, the more we can apply our knowledge to the solution.

Steve/BlueWizard

Vogue · 7th July 2007, 11:57 AM

Sorry about the lack of info ...

My power amp EAR899 has a input impedance of 47k ohms. My CD players output impedance is not known to me (SAT CDFIX).

Vogue

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7th July 2007, 12:33 AM	#11
Vogue diyAudio Member Join Date: Oct 2005	Well ... I might not be happy ... but I guess that it’s hard to overlook that law. But anyhow I needed to be sure that I calculated correctly – as I see it, the resistors only make small changes to the impedance I will report about the progress i make... Vogue

7th July 2007, 08:09 AM	#12
BlueWizard diyAudio Member Join Date: Jun 2007	Well, first and foremost, IF Steve Eddy's diagram is correct then the circuit really does nothing. Since the fixed 250k ohm resistors are more than 10 times any value that the potentiometer can deliver, they really have no effect. As my math shows instead of 10k, you simply have 9,615 ohms which is only a 4% difference and is probably within the design error range of the potentiometer. And, for the record, when I was young and first studying electronics, I considered the same circuit, sure I was on to something, but in the end, it does nothing of any significance. Again, you have only give us the vaguest idea of what you are trying to accomplish. How is what you are trying to do any different than a plain old level control, and why couldn't it simply be done with a normal 10k Pot to ground? What is the input impedance of you power amp, and what is the output capability of your pre-amp. As long as the Pot is 1/10th to equal to the input impedance and is within the current capability of the pre-amp out, your in the clear. Knowledge is power, the more knowledge we have available to understand the problem, the more we can apply our knowledge to the solution. Steve/BlueWizard

7th July 2007, 11:57 AM	#13
Vogue diyAudio Member Join Date: Oct 2005	Sorry about the lack of info ... My power amp EAR899 has a input impedance of 47k ohms. My CD players output impedance is not known to me (SAT CDFIX). Vogue

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