About mic-preamp specs

[JAY X]

Hi!

I have a bit of trouble in my head about this...

When a mic is specified to be 150ohm into 1K or 1200R bridged impedance, as today most or all mics have a balanced output, It would be more correct to say : 300R into 2K or 2400R ¿Right?

For example, Neumann specifies his microphones as 150R, 75R, or 50R output impedance into 1K load. Double those values to have the truth...

Jay x

 

[DarkSky]

Double those values to have the truth...

I don't believe so.

The impedance of a balanced input is the measure across the +ve and -ve input connections. For an unbalanced input, it's between the signal and ground. Either way it's the same (in a feed to an unbalanced circuit the cold [-ve] goes to ground but the impedance across the input doesn't change).

 

[JohnRoberts]

The "150 Ohm" is referring to the mic's output impedance, the load or recommended termination does not change that.

JR

 

[ccaudle]

When a mic is specified to be 150ohm into 1K or 1200R bridged impedance, as today most or all mics have a balanced output,

The output of a microphone is between pins 2 and 3, so if the spec says 150 Ohms that means the impedance driving pins 2 and 3. Typically balanced, so you can think of that as 75 Ohms source impedance of pin 2 and 75 Ohms source impedance of pin 3. The source may not literally be in two components, e.g. a transformer output has a single component (to a first order, neglecting parasitic behavior for the moment) which defines impedance. A solid state output device will typically have two physically separate components connected to pins 2 and 3 which define the source impedance.

Similarly the load impedance of e.g. 1200 Ohms is the impedance from pin 2 to pin 3. That may be a single component, e.g. a transformer primary winding, or may be two physically separate components each of half the value, which is typical on a solid state input.

 

[JAY X]

Hi All!

Merry Christmas!!.
Ok, now I understand better. Thanks by unravel my head!!

Jay x