Continuing the talk of +48V Phantom Power

[electronaut]

A friend and I are trying to figure out how to design the ideal phantom power supply, and we were wondering what might be the biggest advantages.

Specifically:

1) Should a Phantom power circuit be capable of delivering +48V under all loads? (The traditional 6.8K resistors which supply the phantom voltage to the microphone reduce the voltage available to the microphone according to its current requirements. Would it be better to supply a solid 48V, regardless of current draw, to the microphone?)

--or--

2) Are microphones designed specifically to operate at the reduced voltage after their current passes through the traditional 6.8K resistors?

3) What is the highest +48V current draw you've ever seen on a microphone?

4) What other specifications would be part of an ideal phantom power design?


Thanks in advance to anyone who contributes!

E.

 

[Samuel Groner]

Would it be better to supply a solid 48V, regardless of current draw, to the microphone?

No.

Are microphones designed specifically to operate at the reduced voltage after their current passes through the traditional 6.8K resistors?

Yes.

What is the highest +48V current draw you've ever seen on a microphone?

Earthwork mics need 10 mA, the highest reading I'm aware.

What other specifications would be part of an ideal phantom power design?

* zero noise (no AC current)
* slow switch on/off to avoid clicks & pops (there's a thread about this)
* perfect matching of the 6k8 resistors
* ideally, the 6k8 resistors would be bootstrapped for common-mode signals to avoid CMRR-degradation due to source impedance imbalances (check this http://www.jensen-transformers.com/an/ingenaes.pdf for detail) - but this gets very fancy...

Samuel

 

[Marik]

[quote author="Samuel Groner"]

Earthwork mics need 10 mA, the highest reading I'm aware.

Samuel[/quote]

No wonder they sound good :razz:
Being electrets, they don't need high polarization voltage, so significant voltage drop is not that much of an issue.

 

[Guest]

some of my dual answers {solve it with dual circuits}:
[quote author="Samuel Groner"]Would it be better to supply a solid 48V, regardless of current draw, to the microphone?

No.
[/quote]
Yes, but preamp must be current input. And only for active mics.

Are microphones designed specifically to operate at the reduced voltage after their current passes through the traditional 6.8K resistors?

Yes.

No, in the DIN blablabla norm is diferent resistors values for diferent
phantom voltages.

Samuel

xvlk

 

[Samuel Groner]

Yes, but preamp must be current input. And only for active mics.

:? Explain!

No, in the DIN blablabla norm is diferent resistors values for diferent
phantom voltages.

True, but the question was about 48 V.

Samuel

 

[rafafredd]

I think the perfect phantom power is a perfectly ramped one.

 

[Greg]

[quote author="rafafredd"]I think the perfect phantom power is a perfectly ramped one.[/quote]

I bought an FMR Audio RNP a while back and it has a ramped phatom power.