# Formula to a Impedance Controller

Discussion in 'General Electronics Chat' started by veenife, Mar 13, 2014.

1. ### veenife Thread Starter Member

Jan 16, 2014
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hey... in this video.... ( http://www.youtube.com/watch?v=r1yPMDHiRuc ) ... this guy is building an input impedance controller...
im curious to know how will that interact with a transistorized preamp??

i mean the controller goes in between microphone and the preamp... and it lowers the input impedance from the preamp... so i assume that in a way is connected in parallel ...

but is it in parallel with another resistor or in parallel with the transistor directly...???

also i would like to know how could i calculate the change on the input impedance once the controller (1kohm) is full opened??

2. ### alfacliff Well-Known Member

Dec 13, 2013
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why deo people listen to these things? "adding impedance in paralell increases impedance"? more like lowers it in the real world. qutting a pot across the input of a preamp will cause more change in level than impedance. impedance is complex, a mixture of reactance and resistance.
I know that impedance mismatch of micophones will change tone quality, a low impedance input with a high impedance microphone will sound tinny, and a high input impedance with a low impedance microphone will cause it to be bassy. but a 10 to 1 ratio? 1 to 1 is more proper.

3. ### veenife Thread Starter Member

Jan 16, 2014
42
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... hm... i dont know where did you get the increase part from... but yeah of course, the controller is lowering impedance!!!

but is that in parallel with the transistor directly... or what with is this controller interacting with???

also how to calculate the changes of this interaction???

4. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
the preamp is most likely isolated by a transformer or capacitor at the input of the preamp. the controller is putting a resistance in paralell with the input to lower the resistance, known in the video as impedance. this will also reduce the audio from the mic to the preamp.

5. ### veenife Thread Starter Member

Jan 16, 2014
42
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hm.. interesting... is any tweak possible on this project to actually change the impedance of the preamp instead of resitance??

so i guess the ohm´s law formula to parallel resistance will give me the answer for this interactiong... or???

6. ### alfacliff Well-Known Member

Dec 13, 2013
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429
the usual way to change the impedance of a preamp is to use a tapped transformer. there are transformers on the audio market to do this.

Jan 16, 2014
42
0