Passive mic preamp ?

[thomasdf]

Hello all ... just a thought ...? Considering some transformers offer "free gain", can we imagine a single transformer, or a serie of transformers acting as a passive microphone preamplifier ? Let's say a dynamic mic on a loud source !

 

[ruffrecords]

In practice you need some power gain. WIth passive parts alone, power put cannot be greater than power in. Add a power supply and you can achieve power gain.

On the other hand, back in the 60s I had a Brenell tape recorder with two line level inputs (about 100mV sensitivity?). I fed each input from a ribbon mic and a Grampian 600:50K input transformer and successfully recorded my mates blues band. I still have the tape.

Cheers

Ian

 

[JohnRoberts]

Transformers don't provide free gain while they can step up voltages as per their turns ratio. As the voltage gets stepped up the drive capability falls. A step up transformer followed by an active buffer is a pretty common topology.

Another mic transformer application is where a step down transformer drops the output of 600 ohm microphones to work well into low Z mic inputs (expecting 150-200 source impedance).

JR

 

[thomasdf]

All right Thank you !