Members,

My project is creating a preamplifier connecting an avionics headset (David Clark P/N 12512G-11) microphone to my audio mixing board.

The headset microphone is described as a "noise suppressing, 5 ohm dynamic moving coil part # DC-87".

The link to the headset is:
https://www.davidclarkcompany.com/product/?ItemNumber=12512G-11.

I have worked up preamplifiers for pro-level gear (600 ohm, balanced XLR) and "home" unbalanced gear yet this is presenting a challenge.

From what I have observed, this headset is used in a very noisy environment (both electrically and mechanically) and plugged into a long extension cable, leading me to focus on a balanced input preamp design.

I am looking at the THAT1512 chip. Should I be considering an input impedance-matching transformer?

Thank You

 

Members,

My project is creating a preamplifier connecting an avionics headset (David Clark P/N 12512G-11) microphone to my audio mixing board.

The headset microphone is described as a "noise suppressing, 5 ohm dynamic moving coil part # DC-87".

The link to the headset is:
https://www.davidclarkcompany.com/product/?ItemNumber=12512G-11.

I have worked up preamplifiers for pro-level gear (600 ohm, balanced XLR) and "home" unbalanced gear yet this is presenting a challenge.

From what I have observed, this headset is used in a very noisy environment (both electrically and mechanically) and plugged into a long extension cable, leading me to focus on a balanced input preamp design.

I am looking at the THAT1512 chip. Should I be considering an input impedance-matching transformer?

Thank You

I think the transformer would be advisable. 100uV is a really tiny signal, and to amplify that without adding any noise isn't easy. Designed any good moving coil cartridge pre-amplifiers lately?

 

Not really. Mostly test/repair and refurbish/replace.

Any favorite transformer manufacturers?

Thank you

 

Not really. Mostly test/repair and refurbish/replace.

Any favorite transformer manufacturers?

Thank you

Not really.
A ribbon microphone transformer would have about the right voltage specs, but you don't really need the extended bass response that "audiophile" mics would have.

 

Really, to couple from that 5 ohm dynamic microphone and avoid noise pickup, you can use a small output transformer like would be used for an older small pocket radio. The balanced pair from the DClark mic to the 4 ohm side of the transformer, the secondary to the differential inputs of a quiet op-amp.And tie the transformer frame to the system common. That should be fairly noise resistant. Use a feedback resistor on the op-amp for a gain about 100

 

Really, to couple from that 5 ohm dynamic microphone and avoid noise pickup, you can use a small output transformer like would be used for an older small pocket radio. The balanced pair from the DClark mic to the 4 ohm side of the transformer, the secondary to the differential inputs of a quiet op-amp.And tie the transformer frame to the system common. That should be fairly noise resistant. Use a feedback resistor on the op-amp for a gain about 100

Like the Eagle LT700
https://www.ebay.co.uk/itm/263690340712

 

A caution about my suggestion in post #5 is that the transformer selected should be "small" because energy is required to produce the magnetization that makes a transformer function. So the more iron the more energy required.