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Passive monitor controller input output impedance meaning
Passive monitor controller input output impedance meaning
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Old 21st December 2017, 09:23 AM   #1
Zaharescu Mihai is offline Zaharescu Mihai  Romania
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Join Date: Dec 2017
Location: Bucharest
Default Passive monitor controller input output impedance meaning

I hope I'm not flooding the forum with simple questions, if I do please let me know.
I'm having trouble understanding the input and output impedances from the specifications of the Nanopatch+ manual [1].
I always thought that a passive monitor controller was just a collection of synchronized potentiometers on hot and cold wires. This would mean that if set at maximum volume it would act as a direct connection and if set at 0 it would be an open circuit (idealy).
However, in the manual they state that the input impedance is 5 Kohms and the output is 0-5 Kohms. Interpreting this directly I understand that the driving device always sees 5 Kohms at the output, no mater what is after the passive controller and at which volume the controller is set (I don't know how this can be achieved with a passive device), and the device that is driven sees from 0 to 5 Kohms at the input, depending on the volume of the controller (thus meaning that at minimum volume it will short the input of the device that is driven).
Could it however mean that the driving device sees at the output 5 Kohms + the impedance of the driving device, and the device that is driven sees at the input 0-5Kohms + the output impedance of the driving device (thus not shorting the input).

For example:
processor (out Z: 50 ohms) -> passive controller -> power amplifier (in Z: 600 ohms)

A:
- the processor sees 5 Kohms at the output.
- the amplifier sees at the input 0(short) ohms at minimum controller volume and 5 Kohms at max volume

B:
- the processor sees 5.3 Kohms at the output
- the amplifier sees at the input 50 ohms at max volume and 5.05 Kohms at min volume

Which of the two chases is correct, if any?

Thank you.


[1] https://www.jblpro.com/ProductAttach...ual_090215.pdf

Last edited by Zaharescu Mihai; 21st December 2017 at 11:38 AM.
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Old 21st December 2017, 09:36 AM   #2
GeorgK is offline GeorgK  Austria
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Join Date: Jan 2005
Location: Vienna
With Volume full up, the load for the source is the 5k Pot resistance in parallel with the input of the next device, so eg. 5k||600 = 535 Ohms. The receiving input (the amp in your case) is then being driven with the source impedance of the sending device.

Output impedance of the Controller gets higher when turning volume down, just as the load resistance of the driver inreases until the latter reaches 5k when pot is fully down. Cannot draw a schematic from here that makes this clearer, but maybe somebody eles will?
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Old 21st December 2017, 11:27 AM   #3
Zaharescu Mihai is offline Zaharescu Mihai  Romania
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Join Date: Dec 2017
Location: Bucharest
Is this correct (attached image)?

Meaning that:
- when R2=0 : the processor sees 535 Ohms and the amplifier 49.5 Ohms (full volume)
- when R2 = 5K : the processor sees 5K and the amplifier 0 Ohms (mute)

It's a bit unclear about the 0 Ohms impedance, maybe I got something wrong...

[edit] sorry, 600 instead of 300 in the image, but the idea is the same.
Attached Images
File Type: jpg Passive-Monitor-Controller-Impedances.jpg (181.4 KB, 21 views)

Last edited by Zaharescu Mihai; 21st December 2017 at 11:38 AM.
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Old 21st December 2017, 12:35 PM   #4
GeorgK is offline GeorgK  Austria
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Join Date: Jan 2005
Location: Vienna
the schematics are not easy to read because you drew GND on top, but ok, you got it.
That the amp actually sees zero with volume turned down does not mean you have zero source impedance. This is the impedance the amp sees, but the value is useless in your application.
As you go near zero with your volume, the signal hast to pass more and more of the 5k resistor, so lower input impedances produce more loss at a given pot position.
So near zero it has almost grown to 5k. Amongst others, his theoretically may imply more interference, but practically will do no harm as long are cables are kept *short*.
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