Topic: AT8533 circuit?

[Chuck]

I'm wondering what the circuit is inside one of these. Is there a transformer in there? Or, is it just a passive voltage divider or an active circuit? I want to build a couple devices that do essentually the same thing, but I don't need the bass roll-off.

[poorlyconditioned]

I'm wondering what the circuit is inside one of these. Is there a transformer in there? Or, is it just a passive voltage divider or an active circuit? I want to build a couple devices that do essentually the same thing, but I don't need the bass roll-off.

There are various versions.  Typically they have some kind of current source to drop a certain voltage (like 4V) to bias the FET.  Then there is a one or two transistor roll-off circuit, followed by a single transistor that drives a transformer primary in emmitter-follower mode.  The secondary of the transformer drives the cable.

These are very convenient if you already have phantom power.  Just plug and go.  And they can drive a cable for a long distance (balanced, low-impedance).

  Richard

[Chuck]

Richard, I figured you would know

Do they do more than convert 48v to 9v DC? I'd guess that the transformers are used to match impedences?

I'm just looking to power some electrets (on cables terminated with mini-XLR connectors) with 48v phantom power from a V3 and/or DMIC-20. I'd like to build it all into an xlr connector. Is a zener diode with a 10k current limiting resistor too primative?

[poorlyconditioned]

Richard, I figured you would know

Do they do more than convert 48v to 9v DC? I'd guess that the transformers are used to match impedences?

I'm just looking to power some electrets (on cables terminated with mini-XLR connectors) with 48v phantom power from a V3 and/or DMIC-20. I'd like to build it all into an xlr connector. Is a zener diode with a 10k current limiting resistor too primative?

A zener diode or similar (transistor with resistor voltage divider) will work just fine.  To power the mics.  The reason for the driver transistor plus transformer is to provide a *low impedance* and *balanced* output.

You can provide a hack solution with all passive components, and that will be fine if you don't drive a cable (just plug right into a DMIC20 or similar).  This is what the Naint or other people were doing with a few passive components and an electret.

I suggest visiting the Yahoo group "micbuilders" if you want to do this.  Lots of electronics hackers over there...

  Richard

[Chuck]

Thanks for the info, and +T