How come my computer isn't supplying enough power for +48V?

Holla homies!

I sort of had an epiphany today!

Two years ago I decided to get more serious with home recording and bought a Line6 TonePort UX2 (USB interface) to replace my SoundBlaster Audigy. I had bought SONAR 2 three years earlier and until then used my Yammy MG10/2 mixer to suply I/O for my card and for powering my Shure PG81 SDC.

Half the reason why I bought the TonePort was to have integral mic pres to use with my new sE Electronics SE2200a LDC. But when engaging phantom power I had to turn the inputs to max to get a reasonable signal level and then the noise was overpowering (also tried connecting the interface to my laptop and it was the same)! I wrote off the TonePort's pres as crap and continued to use my mixer for mic pres, cause using that I had no problems achiving healthy signal levels with only very little gain (I later upgraded to an M-Audio DMP-3 preamp which had a huge gain surplus).

I bought a new PC last January (same time I upgraded to SONAR 6PE), and gave the TonePort another spin, but the issue remained.

So today I got my Focusrite Saffire Pro 10 I/O (FireWire interface) in the mail and I was dying to take its acclaimed preamps for a ride. I plugged in my mics and my heart sank as THE SYMTPOMS WERE IDENTICAL (same results with both SE2200A and Røde NT2A)!

I was saved by engaging the included PSU which boosted signal levels like 20 dB, and I'm a pretty happy camper now!

So it's clear now that my computer does not supply sufficient juice to the units for phantom power operation! Why is this (recall that I've tried three different PC's), and can the problem be remedied?

Sven


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Edited for clarity

Sven, I'm not sure what the problem is but it sounds gain-related, and not something with your phantom power.

Thanks for your replies!

Miket5: Custom built computers (except for my HP Laptop). My first DAW PC had a 450W PSU and my current one has 550W. That should suffice, shouldn't it?

J Boy: I forgot to mention that dynamic mic work fine with both units, so I'm pretty sure it has something to do with phantom power (normally my condensers require far less gain than my dynamics).

Tonmann: The Focusrite is a FireWire unit and the problem is the same!

Sven

So it's clear now that my computer does not supply sufficient juice to the units for phantom power operation! Why is this (recall that I've tried three different PC's), and can the problem be remedied?

As far as I know the Firewire Protocol states that it should handle 500ma of current draw through the Firewire DC Voltage supply and your 48v Phantom power draws a miniscule amount, but in real life a lot of Laptops and some desktops can't supply close to that with marginal 250w-300w power supplies it can't happen.

I advise my clients to use the supplied wall warts anyway just to be certain that you are getting sufficient juice to the device if your PC or Laptop isn't giving an abundance of Aux power to the FW port

I don't think this is related to your computer power supply. Phantom power for the mic comes from the device it's pluged into NOT the computer connection to the device. The interfaces may be designed to run lower voltage phantom power when operateing on bus (USB or Firewire) power but that is no fault of your computer that would happen on ANY computer.

Sven, Mine is 600 W Power Supply.
Like I said I had issues with the laptops but not the desktop.

There is more to this than meets the eye. There are actually 2 voltages that a USB port can "legally" output, either 5V or 3.3V. However I have not yet seen a PC that uses the 3.3 V standard but it is possible and worth checking. As the soundcard must use some form of inverter to boost the voltage to 48V (but see later comments on Phantom Power) then a 3.3 V USB port will also reduce the phantom power probably by a similar percentage.

Secondly with regard to phantom power. Does the toneport specify it provides 48V phantom power or just Phantom power? The reason is that many units providing phantom power provide much less than 48V. Some are as low as 12V!
This is usually fine if you are using an electret type mic as many do not require the higher polarising voltage and will work fine at 12V. The Rode is NOT electret so any reduction in the polarising voltage to the actual mic (not internal pre-amp) will result in both reduced output AND increased noise at the same time.

If you want more info here is a thread on the recording forum where there is a lot more info (and also some BS but not from me ;<) ) Discussion of Phantom power.

Phantom power supplies in pro sumer gear are notoriously suck ass. Further more the current requirements of *transformerless* microphones is often times 4x the requirement of a transformer design.

What do the manufacturers say the current draw on each of your mics is?

What do the manufacturers say the current capacity (before voltage drop) of each preamp is?

How about total phantom power current capacity for all the inputs combined? Hint: it's almost never the sum of the each capacity.


When you've answered all these questions you'll understand that the very idea of powering your transformerless condensor mic with bus power is a very bad idea. At least use the dedicated power and don't overload it for best sound.

best regards,
mike

Hmmm, my old usb mbox 1 (with is, ooh, so cool Focusrite pres, lol), drives mics just fine. Admittedly, they're garden variety crapolas a smattering of Studio Projects, rode, oktava, mxl, and a lone 414 but there you are.

Who said 50mA?

bvideo in post number 14 which is the post I was replying to!

(in reply to bvideo)

I agree with what you said with checking the spec's, which is exactly why I said the same thing.

While the specs. you quoted for the MOTU 896 HD does appear to be a bit mean it is also worth noting that every mA of current drawn by a mic will cause at least 2.35V drop of that particular phantom output. This is the MINIMUM drop I would expect as 2.35k is the minimum phantom impedance I have ever seen although some are higher. Several boards I have used have 6.8k resistors which in parallel will give 3.4V/mA drop so even a fraction more than 1mA will cause the output to fall below the 48V - 10% spec anyway.

There are many "prosumer" units with inadequate phantom voltage to start off with. See the other thread I linked to - some units even give an EMF (unloaded voltage) of only 12V although this seems rare but the are apparently several that only provide 24V. Likewise there are many mic's nowadays that draw more current than they really should and the problem compounds. The biggest culprits in this sense seem to be Electret mic's which are often the lower end offerings for both LDC and SDC mic's.

Of course MOTU could argue that they would only expect the best Mic's to be used and would happily power 8 Neumann U87's! :<) (but I still think that spec you gave is a little mean!).

ORIGINAL: Mr. Ease

ORIGINAL: bvideo

Hard to see how the USB spec would allow enough power to a device for a 48V phantom power. It is not a problem with your PC or your interfaces. A USB device must not draw more than 500mA. A perfect voltage pump, and there is no such thing, would give around 50mA at 48V. But the interface itself needs power too, so the available current for the Phantom power would be quite small, possibly inadequate for some mics that require 4mA to 10mA. Quite possibly the interface simply doesn't even try to supply phantom power without an adapter.
Bill B.

It is not normal for a condensor mic to need this amount of current. The 48 V is only required as a polarising voltage hence the steady state current (once the mic is charged) tend to zero as only fA or at most nA are required for the input in the presence of a signal to maintain the charge. The pre-amps rarely take (nor need to) more than a few mA. This is no where near the 50mA you quoted at 48V. IIRC the Rode needs less than 5 mA. It is almost trivial to design such an inverter with 90% + efficiency so the overall requirement should be no more than 55 mA at 5 V. Note that this includes powering the pre-amp/buffer stage.

Whilst this is all possible and certainly not difficult to achieve, I have no idea whether the toneport achieves this. That is why it is crucial to check the spec's of both the Toneport and Mic to ensure they can work together as specified.

Again I suggest anyone interested reads the link I gave in my last post as I really don't want to repeat all the effort when it's already available.

BTW Phantom power will ALWAYS show voltage drop when loaded as they must by their very nature have a high source impedance - otherwise we would never see any signal at the input of our pre's! Most have output impedance of around 2.35k (4.7k on each line) so even when completely short circuited even a "perfect" phantom power source would only provide around 20 mA. Another reason why claims of a 50 mA requirement are way off the mark.

I should clear up this misinterpretation of my post. I didn't say 50 mA was a requirement. I said possibly 4 mA to 10 mA might be a requirement for mics. I didn't know how many mics the OP was using, but a pair of real-world mics might be in that range.

I said a USB device could give 50 mA at 48V only if there were no other circuitry. Of course the interface DOES have other circuitry, not just pres, but the USB interface chip most likely w/ embedded CPU & fifos, A/D/A, meters, phone and line outputs, and SPDIF interface and chipset, and miscellaneous circuit glue all snacking on the 5V/500mA maximum that is available by spec to a USB device.

It's quite clear as you said checking specs is crucial. I didn't find any power spec on the UX2, nor do I know what components are in the box or what their power reqts are, so maybe I shouldn't have said anything. The UX2 specs do say, however, don't run it on an unpowered hub or on a hub with other non-self-powered devices connected. That seems to hint at high draw. Since the 48V power didn't meet Sven's mic requirements on USB power, and given the USB power limit (sometimes by spec more than practice) I still think it's worth saying it's not likely the PC's fault.

Bill B.

Hi, Sven,

This may be dumb question on my part, but I’m just trying to be helpful. While trying your condenser mic through the TonePort UX2, do you have the Gearbox software open with the Gearbox Input Select Dropdown set to either Mic 1, Mic 2, Mic 1 & 2, Mic Stereo or Instrument and Mic? Also you have to be sure to have one of the Gearbox vocal preamps open or you’ll be hearing the mic through whichever guitar preset that you used last, which would surely cause a volume and noise problem.

For what it’s worth, I’ve used the UX2 on 3 different laptops and 2 desktop PCs and never had a problem powering my condenser mics using the TonePort’s phantom power. I usually have the Mic gain knob on the UX2 box set between 5 and 7 and get a decent volume level with zero noise.

Have you tried the mic through a “non computer based” phantom powered mixer or preamp to be sure that the mic is functioning properly?

Hopefully, you’ll find a solution soon!
Best wishes,
Bob

500 watts through such a small connector?! Never! It would blow up into smoke!
Maybe you mixed 500W with 500mA?

Ooops , Sorry you are right, got my milliamps and watts confused

What does any mean? What mics have you tried?

ORIGINAL: MQ

SvenArne,

If you have a simple multimeter you could check that you have 48V in one of the two mic-inputs on the UX2.
Just put one probe in the left "eye" and the other probe in the right "eye" of the contact. Now you could see if you have 48V between the to terminals. Dont forget to actually press the +48V button first on the UX2.

We have no problems with ANY mic using the UX2 and I guees your problem is somewhere else. (Corrupt Mic-cable, corrupt microphone, Gearbox-setup mistake...) have you checked that the microphone works in any other mixerinput (48V)?

MQ

Good Idea, I should borrow a multimeter and test the contacts!

Regarding your second paragraph, I've already eliminated all such error sources (three different condensers, a ton of different XLR cables, every concievable combination of GearBox parameter settings). Recall that I have exactly the same problem with my Focusrite Saffire Pro interface when bus-powered, but not when PSU-powered.

Sven