There are two components in this "transformerless" M300 Gefell mic I'm curious about. What's that dome lookin' thing? In the 2nd and 3rd pic, there is another example from a different Gefell mic body (mv200). And also the rectangular package. I believe it is stamped 03YH017 09.94. My searches came up empty. Thanks!

 

Looks like it could be an oscillator but I cannot really tell.

 

Might also be a small enclosed filter but most likely an enclosed combination amp and impedance converter.

 

Thanks for the replies. So all of those things - oscillator, amp, impedance converter - are all somewhat akin to a transformer. I guess I'll send the mfg a note. Maybe they'll just tell me

 

There are two components in this "transformerless" M300 Gefell mic I'm curious about. What's that dome lookin' thing? In the 2nd and 3rd pic, there is another example from a different Gefell mic body (mv200). And also the rectangular package. I believe it is stamped 03YH017 09.94. My searches came up empty. Thanks!

Did you look up info on the mic?

On the electronics side a very clever technique is used to power the circuitry and bias the capsule. The usual DC-DC converter that scales up the phantom power to the required internal voltages uses an optical coupler which effectively eliminates any phantom supply noise or spurious interference. A relatively high 80V polarising voltage is generated for the capsule, which is the key to the impressive SPL handling. Like most modern mics, the M300's output is transformerless.

One of the two (rectangular & circular) components is probably the optical coupler, the other an amp/impedance converter.

 

Did you look up info on the mic?

That was helpful, thank you!

I own a similar version of that mic, the MV200. It does not have the rectangular device. And I don't think it has the opto-coupler. So I'm guessing that is the OC. I'm curious how the opto-coupled power supply circuit would work.

My mic does have a similar (but different) round device. Maybe that is part of the polarization voltage generator, or maybe something for impedance matching. Though using a 'coil' of any sort for impedance matching the signal does not seem consistent with a transformerless design. I haven't opened my mic up to trace the circuit.

 

I'm curious how the opto-coupled power supply circuit would work.

I hope I'm not wrong and make a fool out of myself here, but...

The quote I posted said "a very clever technique is used to power the circuitry and bias the capsule". I don't know everything I should about microphones, but I take this to mean that the capsule only needs a voltage bias, it doesn't need current. So the purpose of the optocoupler would be to electrically isolate the capsule by passing the signal voltage but not current. The rest of the circuitry would be before the coupler, and thus would be able to receive whatever current is necessary.