+150V DC @ 1A Phantom Power For Tube Mics?

[northsiderap]

Has anyone done a +150V @ 1A phantom power for a tube mic?

I know it is probably cost prohibitive, but you could run all power through a standard XLR cable and use a voltage divider for your heaters. Well heck, maybe a discrete regulator.

I'm new at the whole DC power thing, so I'm sure there's plenty of bad angles on this that I just can't see.

Would one have to take special care in the PSU side to protect the mic transformer from transients?

 

[PRR]

> +150V @ 1A phantom power....and use a voltage divider for your heaters.

Offhand, I can't think of a mike-tube that needs 1 Amp. Pencil 0.3 Amps.

OK, say we bring the full 150V into the mike to feed the plate, and drop some of it to the heater. 150V-6.3V= 144V. This is at 0.3 Amps. 144V*0.3A= 43 Watts of utterly wasted heat inside the microphone. (150 Watts of mostly wasted heat if you insist on 150V 1A.)

Put a 40W lamp inside an MXL990, it will almost fit. Power-up and hold it through an entire song. Ouch! Put it in the rubber-band mount. Ooops!

Even aside from the enormous power (heat) you plan to supply to a delicate mike: A very common fault in mike lines is a broken shield connection. When that happens the mike case can rise to the phantom voltage. You wonder why the mike aint working, wander over to the (grounded) patchbay or console.... 150V shock.

48V was picked specifically because (at that time and place) 48V was commonly accepted as safe. Current EU thinking leans toward 24V as the maximum around untrained people; the 48V Phantom will persist only through inertia.

While XLR are rated over 1A, it's not a great idea if you hot-plug often.

Phantom power IS power and many electric codes can claim jurisdiction. In the US there are "Classes" of power-limited circuits, intended for doorbells and other small loads. One goal is to limit the energy so a fault can't start a fire. This smells like the very upper limit of "power limited circuits", where you have to wire like "real" power wiring.

Also: sooner or later you will plug a transistor Phantom mike into this line. The 60V transistor inside will break-down. It isn't unusual for Phantom supplies to fail and put out 70V or 90V.... but they don't have 1 AMP of current behind them. (Or even 0.3A.) The mike will explode. And Murphy's Law assures this won't be your $60 MXL990, it will be the Artist's personally owned favorite Big German Brand mike.

> if this is a really bad idea.

I don't see a good idea here.

 

[northsiderap]

[quote author="PRR"] > +150V @ 1A phantom power....and use a voltage divider for your heaters.

Offhand, I can't think of a mike-tube that needs 1 Amp. Pencil 0.3 Amps.

OK, say we bring the full 150V into the mike to feed the plate, and drop some of it to the heater. 150V-6.3V= 144V. This is at 0.3 Amps. 144V*0.3A= 43 Watts of utterly wasted heat inside the microphone. (150 Watts of mostly wasted heat if you insist on 150V 1A.)

Put a 40W lamp inside an MXL990, it will almost fit. Power-up and hold it through an entire song. Ouch! Put it in the rubber-band mount. Ooops!

[/quote]

The wattage wasted through a voltage divider could be more like 10W with a sub-miniature running at <150mV A+ and 100V B+. Still probably not friendly.

[quote author="PRR"]
Even aside from the enormous power (heat) you plan to supply to a delicate mike: A very common fault in mike lines is a broken shield connection. When that happens the mike case can rise to the phantom voltage. You wonder why the mike aint working, wander over to the (grounded) patchbay or console.... 150V shock.

48V was picked specifically because (at that time and place) 48V was commonly accepted as safe. Current EU thinking leans toward 24V as the maximum around untrained people; the 48V Phantom will persist only through inertia.

While XLR are rated over 1A, it's not a great idea if you hot-plug often.
[/quote]

This one was a little bit more for personal use - a vocal condenser with sharp sticks around it so it pokes you in the eye if you go near it. :shock: Also, a separate PSU box.

[quote author="PRR"]
Phantom power IS power and many electric codes can claim jurisdiction. In the US there are "Classes" of power-limited circuits, intended for doorbells and other small loads. One goal is to limit the energy so a fault can't start a fire. This smells like the very upper limit of "power limited circuits", where you have to wire like "real" power wiring.
[/quote]

I didn't think about fault heating. I guess that's a topic that could be addressed by using a conventionally fused power supply box with a separate cable running out to the mic., which is more like what I had in mind.

[quote author="PRR"]

Also: sooner or later you will plug a transistor Phantom mike into this line. The 60V transistor inside will break-down. It isn't unusual for Phantom supplies to fail and put out 70V or 90V.... but they don't have 1 AMP of current behind them. (Or even 0.3A.) The mike will explode. And Murphy's Law assures this won't be your $60 MXL990, it will be the Artist's personally owned favorite Big German Brand mike.

[/quote]

I should have clarified a bit on what the mic's purpose was and what the layout would be. I surely would plan on using a separate PSU box, and NOT try to phantom one of my preamps with 150V.

 

[bcarso]

So---a separate PS box? Is this all an exercise to get away with a 3 pin XLR? Or do you envision the power coming from the phantom connection still somehow?

I'd use a 5 pin XLR or some other nice multipin conn. on the custom mic and manage the B+ and quiet filament power on the other pins. For that short a distance you could run unbalanced to the PS box and convert to balanced inside before running back to the console.

 

[northsiderap]

Yeah I was trying to get away with using regular connectors. The PSU could sit on the ground with six-foot cable if I really needed to run unbalanced.

No use of the standard 48V phantom, not enough juice for the heaters. I simply meant a PSU box that sends the voltage balanced through two pins and is taken at the microphone from the transformer center tap.

How about 6V @ 250 ma for sub-miniature tube heaters & a 6VDC - 100VDC converter inside the mic for the plate?

 

[PRR]

My opinion is that the complications of deriving two quite different proportions of significant power exceed the cost of just buying a few 5-pin connectors. And reduce risk to other XLR gear in the room.

But it's your mike, your studio. I don't see a reason it can't work.

 

[Larrchild]

My first sound gig was a 2000 seat theater. I used XLR's on the stage monitor cables. One day, as portrayed here, I plugged a monitor cable into a mic line on stage.

After everyone in the theatre got up off the floor, we saw cone material wafting down from the overhead cluster.

Use a 5-pin for god's sake.

 

[Guest]

Isn't 130v the DPA/Schoeps standard?
Anybody any idea why?

 

[Emperor-TK]

[quote author="Larrchild"]My first sound gig was a 2000 seat theater. I used XLR's on the stage monitor cables. One day, as portrayed here, I plugged a monitor cable into a mic line on stage.

After everyone in the theatre got up off the floor, we saw cone material wafting down from the overhead cluster.

Use a 5-pin for god's sake.[/quote]

That is a funny and scary image there. :grin: :shock:

My NHT studio monitors (A-10's) use XLR's for the speaker level signal. I'm not too crazy about that idea either. At least they supplied bright orange XLR cables for the speaker lines, and it's pretty much a fixed install.

 

[Crusty2]

[quote author="uk03878"]Isn't 130v the DPA/Schoeps standard?
Anybody any idea why?[/quote]

From B&K. It's to polarize the capsules. IIRC, it's a 4-pin XLR connector standard.

 

[adrianh]

Northside;

Good idea I really like it. But...........

Do not do it with 3 pin XLR's too many chances to cook someone.
You hurt a client, they amd their lawyer will own a studio, and you will
be hungry.

I my studio I run +150V and +17V to the tracking room.
150 is for mics and mic pre's. The 17 is to feed filament regulators.
I have not implemented this yet I want to use SAFE legal connectors.
And I need a way to ramp up the voltage for the 150.
Hot plugging 150VDC will wear a connector contacts very fast.
If you think about it and implement it correctly go ahead but
use a special type of connector.

It can be done but not with a 3 pin XLR.