DIY Mic Building... Transfomers?

[Spooky777]

Hey all, I know this is a strange place to start, but I'm sure most of you have better knowledge than me when it comes to working with electronics.

Anyway, I am making a microphone from an oddball dynamic mic cartridge I found. It's impeadance is 600 ohms. I want to make it balanced for audio recording and as I understand it, it should have a proper output transformer. Can anyone recommend an affordable transformer for this project and the proper way to wire to an XLR jack?

Thank you!

[Steerpike]

A moving coil capsule is inherently balanced; you don't need a transformer, which unless it is a costly, professional type will only do harm to the audio.

You need a twin-core screened cable (two signal conductors and a common screen). Pin 1 of the XLR should be connected to the outer screen of the cable. Connect your mic capsule's two coil leads to pin 3 and pin 2 of the XLR, by means of the two inner cable conductors. The screen is not connected to the mic capsule at all.

[Spooky777]

Any reason why the most popular dynamic mic in the world, the SM58 has one then? Is it to better match the impedance?

Shure 51A303 Transformer for SM58 & SM57 Microphone Capsule: SHUR-51A303 Dale Pro Audio
Shure - Professional Audio - Products

Thank you,

Mark

[Steerpike]

THAT one does, but not all moving-coil microphones have transformers.

Impedance matching is one reason, if the capsule's other design requirements don't give an optimal impedance.
It's also an easy way to give switched impedance options.

Another reason: many setups use phantom powering of the condenser mics. Its possible that a mixed mic setup may put phantom power (48V) on the dynamic mics as well, either accidentally, or because the mixer doesn't allow for individual phantom switching. The transformer is then an added barrier against damage to the capsule and a mild shock hazard for the vocalist.

[Spooky777]

So assume I want to have a transformer in the mic to achieve matched impedance with my mixing console. What sort of transformer would I get? Also, what if I wanted to gain up the output a bit too? I heard something about step up transformers.

Thanks.

[Steerpike]

Modern transistor-input mixing desks don't really care much about mic impedances. As long as it is in the category of "low" - which ALL moving coil mic capsules are.

Some very expensive modern desks, and most vintage desks have transformer input mic sockets where impedance matching becomes important.

But you say your mic is 600R, which is a great match for pretty much all mixing desks - modern and old.

A transformer transforms voltage level AND impedance; you can't have one without the other. If you choose a tranny to up the voltage, you may mess up the impedance matching - but as I mentioned, modern mixers don't much care. But a severe impedance mismatch will upset the extremes of the frequency response - too bright, or no top, depending on the nature of the imbalance.

This is the sort of thing you could use, if you are convinced you need one
Oxford Electrical Products | Transformers | Transformers | Audio Transformer | PCB and Chassis Mounting |Z21805C
or
Oxford Electrical Products | Transformers | Transformers | Audio Transformer | PCB and Chassis Mounting |Z21805E

but I don't think it's going to do much, and they aren't cheap.

Try without a transformer , see what sort of performance you get.

[BudP]

I make extremely high quality mic input transformers and I agree with Steerpike, if you don't have to have it, don't.

Bud

[Spooky777]

Originally Posted by Steerpike

A moving coil capsule is inherently balanced; you don't need a transformer, which unless it is a costly, professional type will only do harm to the audio.

You need a twin-core screened cable (two signal conductors and a common screen). Pin 1 of the XLR should be connected to the outer screen of the cable. Connect your mic capsule's two coil leads to pin 3 and pin 2 of the XLR, by means of the two inner cable conductors. The screen is not connected to the mic capsule at all.

Why is a moving coil capsule inherently balanced? Also, why do you not connect pin 1 (ground) to the chassis of the mic?

[Spooky777]

Originally Posted by Steerpike

A moving coil capsule is inherently balanced; you don't need a transformer, which unless it is a costly, professional type will only do harm to the audio.

You need a twin-core screened cable (two signal conductors and a common screen). Pin 1 of the XLR should be connected to the outer screen of the cable. Connect your mic capsule's two coil leads to pin 3 and pin 2 of the XLR, by means of the two inner cable conductors. The screen is not connected to the mic capsule at all.

Can you please explain why a moving coil capsule is inherently balanced? And why do you not connect the screen/shield/ground wire to the mic chassis?