Attenuator impedance?

[Vogue]

Firstly sorry if the question is stupid ... but just starting my DIY hobby in electronics area. So please help me.

If you have a 10K attenuator, and ad to resistors of 250K one from input to output and one from output to ground, what vil the actual impedance of the attenuator with the resistors be - and how do I calculate this.

Vogue

[Steve Eddy]

You mean like this?



se

[AndrewT]

Hi,
whether the circuit is as SteveEddy has drawn or not, it would help if you told us the Zin (input impedance) of the next stage and also the Rs (source impedance) of the preceeding stage. These both affect the effectiveness of the attenuator.

If you can find out what capacitance is in the cables feeding in and out the attenuator and installed in the next stage input circuit, it would help?

[Jan Dupont]

You can calculate it using Ohms law, however the Zin will vari when turning the pot.....
What's this circuit used for ???

[BlueWizard]

First let's wait and verify that Steve Eddy's drawing is actually what is intended.

Second, to Vogue, instead of giving us a hypothetical circuit, why don't you tell us what you are trying to accomplish, then let us discuss possible solutions.

I'm wondering if you aren't trying to create your own constant impedance L-Pad?

If we assume the potentiometer in Steve's diagram is linear, that is 50% turn is 50% resistance, then when set to the top, instead of 10k ohms, the Output sees 9,615 ohms, when set to 50% the effective resistance is 4,902 ohms, when set all the way to the bottom, the output sees 0 (zero) ohms and the input sees 9,615 ohms.

Again, if we assume Steve's drawing is correct, and we assume that for some reason this is actually what you want to do.

Maybe you are asking simply as a point of curiousity, it that true, as others have said, it is simply a matter of Ohm's Law. However, if you are trying to accomplish something specific, tell us what that is, and I'm sure we can help you.

If you are trying to create an attenuator that presents a constant impedance, let us know. That's actually easy to explain and easy to obtain.

Steve (the other Steve)/BlueWizard

[anechoic]

>_in--250k----------->10kPOT_(wiper)---->250k---out_>
____GND____________GND______________GND


I think (but not sure) he means the R on the input is before the 10k pot
and the R on the output is after the 10k pot
both 250k's go to GND
see my lousy diagram above

[Vogue]

Well the idea is to improve the sound - if the resistors are good. I really dont understand why ... but the calculations match my own one.

The attenuator is going to be used in a DIY passive preamp - or in a modification of an old preamp I have. If used as modification, then I need to match the old values of the preamp's attenuator - on average ... but in my own project i can do what i like



Sorry not an expert ...

Vogue

[Sonusthree]

Hi,
As Andrew has said, It would be helpful to know what the passive preamp will be between.

Output impedance of the source and input impedance of the power amp would be useful if available.

Regards,
Martin

[Vogue]

Now you are beeing too practical ... My EAR899 amp does have some demands ... but however this was in some sence a theoretical question.


Vogue

[Sonusthree]

Originally posted by Vogue
Now you are beeing too practical ... My EAR899 amp does have some demands ... but however this was in some sence a theoretical question.


Vogue

Are you happy with the Ohms law explanation then or do you require further clarification?

Regards,
Martin.