matching mic and transformer mic impédance

[Kamel]

most of mic transformer have a 150-200 input impédance, but when i read mic specification, eg C414, but it is not the lone, the load is given higher than 150 or 200, a lot of time beetween 500 to 2100 ohm, so does the transformer input mic will overload the mic? does i have to calculate a pad to adapt them?

 

[clintrubber]

It's not rare to see confusing descriptions: it looks like the load on the mic is around 200, but they meant that the input is intended for 200 Ohms source. This is not always true though, loads that low do exist.

Please rate how helpful this reaction was :wink:

 

[Kamel]

i made a test with C414, where the given load by the manufacturer is 2100 ohm, i try with a cinemag CMMI8, directly load, and with 2 1k serial resistor to simulate the load given by AKG, and the sound of the mic is not the same, specially at low frequency, of course the pre need more gain but it is a not too low level mic

 

[RodC]

Check this out:

http://tinyurl.com/el9bh

 

[JohnRoberts]

Transformer should be sized to handle peak signal levels and not introduce noise due to it's winding impedance, but mic termination is established by turns ratio, and a resistive termination across secondary.

JR

 

[rodabod]

[quote author="Kamel"]i made a test with C414, where the given load by the manufacturer is 2100 ohm, i try with a cinemag CMMI8, directly load, and with 2 1k serial resistor to simulate the load given by AKG[/quote]

Can you explain a little more clearly? What was attached to the secondary of the transformer?

most of mic transformer have a 150-200 input impédance

As Peter says, this is often a misunderstanding as turns ratios are sometimes described as impedances. The actual input impedance depends on the ratio, and what is loading the secondary - eg. a 1:2 trafo with 4K on the secondary will look like 1K on the primary. Similarly, the 200 ohms of the mic will look like 800 Ohms on the secondary if you see what I mean.

 

[Kamel]

a tube stage ala NYDave, wich have a high impedance input, the transformer operate a stepup gain voltage and the impedance seen on the secondary is reflected on the primary, if i understand, when Akg give a nominal load of 2100 with a step up of 8 (impedance ration is 64) i have to load the secondary with a 120k to reflect the 2100 needed isn't it?

so why call it 200 ohm input transformer?

thanks for all to unconfuse my mind

 

[rodabod]

[quote author="Kamel"]
so why call it 200 ohm input transformer?[/quote]

Because it's designed for use with nominal microphone impedances on the primary; 200 Ohms.

It's useful to describe a transformer as a 200: ***K transformer when you are interested in the impedance at the secondary (say you want to optimise noise performance by choosing a particular impedance).