Does an audio interface's type of power supply affect it's phantom power output

spantini

COO of me, inc.
While looking around at available audio interfaces, I've run accross articles and forums discussing USB interfaces utilizing one of several power supply options: USB; Wall wart (various supply voltages); AC (internal supply) from 100-240V wall outlet.

One topic of discussion fell on how the type of power supply affects the performance of condenser mics using 48v Phantom power. Basically saying that USB and Wall Wart sources will not supply enough voltage to supply the full 48v to a condenser mic - thus diminishing the mic's performance.

Several commented on how an AC source to an interface's internal power supply will deliver the full 48v to Phantom Power - thus allowing a condenser mic to achieve it's full potential.

I have no idea either way on this, that's why I was browsing about, looking for some answers.

I'm using a 2-In interface, USB powered from my desktop PC. My AT2020 XLR mic "seems" to be getting the job done as far as my current needs go - light vocal and acoustic guitar. This combination produces plenty of gain from the mic. Now I'm wondering if moving up to an interface with an internal AC power supply might not increase this performance. Could there be mic characteristics I'm not currently realizing due to possible lower voltage from the Phantom Supply? I dunno..

Working my way through most of the USB interfaces listed on Sweetwater's site, a rough guestimate would be that USB interfaces are 99% powered by USB or Wall Wart. The remaining 1% are powered by their internal 100-240V internal AC supply.

So.. this would seem to indicate (possibly) that lower supply voltages are getting the job done. Even interfaces priced in the $2500-$4000 range are nearly all Wall Wart powered with voltages of 12-24V (as shown on their rear panel power connection port).

____________________

I'm just throwin' that out here welcoming any and all comments.
 
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TalismanRich

Well-known member
The power supply for my Tascam is rated 12v and I think 1.8A. Since phantom power generally maxes out at 7mA. There's no way that it won't be able to supply sufficient current and voltage for even 8 channels of phantom power.
 

keith.rogers

Bobby'); DROP TABLE USER
Very few have 120VAC going directly in if I had to guess.

USB (buss) power might be a limitation, depending on the design, how close to spec your computer really is, especially a laptop in battery power, and maybe the devices you’re trying to power.

You should assume that if it has 4 mic pres, it’s likely to have a “wall wart” that has been specifically designed to meet the power requirements of supplying phantom power (for microphones) to all channels. If you grab any old USB adapter and not the one it came with, all bets are off, of course.

Some USB 3 capable interfaces can run off a high power bus if your computer has one. (My Steinberg UR44C can run off the buss power, but I use the external supply.)
 

TalismanRich

Well-known member
Keith is right in that the majority of gear like this, even if it has a mains plug, is probably using a switching power supply inside the box. For something like an interface, it would probaby be a 1 or 2 amp supply. Save power amplifiers, you just don't see the types of linear power like in the olden days. Between the relatively large (and costly) transformers, and the inefficiency of a linear supply, there's little incentive to go that route.

I'm wary of USB buss supplied power, especially in laptops. When you have to run a processor that is pulling 18-20 watts at max, a display, drives and other chips, you could really tax the supply if it's not chosen properly. With a desktop and a 250-500 watt supply, it's not as much of an issue, especially if you matched the supply to easily cover your processor and video card.

BTW, you don't have to worry about having enough polarization voltage on the 2020. It's actually an electret condenser capsule.
ELEMENT -Fixed-charge back plate permanently polarized condenser

Power requirement is 48v 2mA to run the circuit.
 
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spantini

COO of me, inc.
Thanks, guys :-) With a little more digging, I found some good info relating to this over at Audio-Technica's Support page. It does mention that the AT2020 is very particular about receiving the full +48V for proper operation. Good news is.. the symptoms I might expect to see at lower Phantom power levels are not present on my end.

I've added a digital multimeter to my next shopping list I may just have to break down and buy an inexpensive voltmeter to test my interface and cables. Everything is working fine, this would just be confirmation.
 
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rob aylestone

Well-known member
The thing with power supplies is that they are supposed to be DC. Poor switch mode designs have very high ripple from the high-frequency switching and dodgy smoothing, so lots of harmonics, BUT, the voltage is what the design needs, as it current supply. It’s not hard to find 48V phantom from 9volt batteries, with the required current, but so many mics might say phantom power 5V - 48V that operation on say 22V works, but not on every mic. Voltage multipliers can produce many thousands of Volts if you have a taser, for example.
 

TalismanRich

Well-known member
My old EV Electret condenser mic runs off of a single AA 1.3v battery. It will run for a long time on that single battery.
 

spantini

COO of me, inc.
@CoolCat mentioned the Shure SM81 in another thread hereabouts. The specs on that show Phantom Power operation at 12-48 Vdc.

So what's it gonna sound like when fed a minimum 12 Vdc.. or any amount up to the 48Vdc?

Is there some simple consumer device which can be used to dial my interface's Phantom power up and down from 12-48 Vdc - - like a rheostat of sorts?

Or is this voltage irrelevant as long as the SDC gets enough amperage? Hmmm.. :unsure:
 

ecc83

Well-known member
Phantom power in USB 'bus' powered interfaces is a sore point for me. I have had my otherwise excellent Native Instruments KA6 for some years now and its one failing is feeble phantom current delivery. The AI has a lot of features, two mic/iine/instru inputs, two more balanced line inputs, four balanced line outputs, MIDI I/O, S/PDIF I/O and headphone OP. The XLRs power my Sontronics STC-2 LDC perfectly well and a pair of AKG P150s but WON'T power a FetHead and is low voltage on a pair of Behringer C2s.*

Let me state STRAIGHT AWAY. This problem HAS been fixed on the KA6 Mkll!

The problem is all the more frustrating because reviewers rarely test for spook juice delivery and mic mnfctrs often do not give the current demand of their mics (Berry do in fact, a piddling 3mA).

There should be no problem getting enough current from AIs fed from a wall rat. A good quality (i.e. low noise) 12V 2A SMPS rat could power 200 mic channels at the max 10mA so even a 16 mic input AI would be beer into water!

A test plug can be made with a pair of 6k8 resistors when the voltages at pins 2&3 should be 24V indicating a total current capability of over 7mA which should be enough for most phantom devices.

If there is interest I could give more details in a waffle in the 'DIY' section?

Dave.
 
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