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Microphone preamp questions

O

Orbison

Well-Known Member
I'm shopping for a replacement for my Mobile Pre so I can run REW to test my system.

My understanding is that a condenser mic needs phantom power to work. In a music forum I read that a USB connection alone cannot provide enough power for this to work. Yet the portable preamps I've been looking at claim to provide 48v phantom power without a "wall wart" power supply. What's the deal?

I'd also appreciate opinions on the Focusrite Scarlett 2i2 preamp if any of you have any experience or knowledge related to it.

Thanks -
 
Well the mobile pre (which I also use) runs off of usb alone and provides phantom power, so clearly it's possible... Maybe some older usb ports on laptops or something can't manage it, or if you're on a hub, I don't know. Why do you need something other than the mobile pre?
 
A simple USB audio device, which is very common, isn't designed to provide phantom power. Chances are that's what the guys on the other forum we're talking about. Any semi-pro USB recording interface will likely provide phantom power on one or all of its XLR inputs for powering condenser microphones.

A USB port alone, without anything between it and the standard mic, cannot power correctly - especially 48V.

You need a device with built in electronics to take the power provided by the USB port and convert it into the proper low current 48V needed for a condenser microphone.

Just check the specs of whatever device you are thinking about buying. If the manufacturer claims it can provide phantom power it the XLR input, you are covered.


Advice: Don't over-think this. The phantom powered mic interface for USB connectivity market has been commoditized and there are literally thousands of excellent options to choose from. They all outperform your requirements and all I'd be concerned with is having the right features at the right price from a reputable brand I can get support & drivers from in the future.

I like Tascam, M-Audio, Presonus, Edirol, Alesis, and others right now. With so many excellent choices, this choice does not require a huge amount of research.
 
PaulyT said:
Why do you need something other than the mobile pre?
Click to expand...

I no longer have the Mobile Pre. I got rid of it a year or two ago after I had a lot of problems with the True RTA software not working properly. Yeah, I probably should have kept it, but now I want to try again with the REW program so I wanted to try a different preamp. 20-20 hindsight being what it is, I should have tried it with the REW program back then. Go figure. :doh:
 
Orbison said:
I had a lot of problems with the True RTA software not working properly.
Click to expand...
What kind of problem? Did you do the latest update through their website?
 
Flint said:
A simple USB audio device, which is very common, isn't designed to provide phantom power. Chances are that's what the guys on the other forum we're talking about. Any semi-pro USB recording interface will likely provide phantom power on one or all of its XLR inputs for powering condenser microphones.

A USB port alone, without anything between it and the standard mic, cannot power correctly - especially 48V.

You need a device with built in electronics to take the power provided by the USB port and convert it into the proper low current 48V needed for a condenser microphone.

Just check the specs of whatever device you are thinking about buying. If the manufacturer claims it can provide phantom power it the XLR input, you are covered.
.
Click to expand...

I understand all of that, I was just curious & wanted a little clarification. Thanks!
 
DIYer said:
Orbison said:
I had a lot of problems with the True RTA software not working properly.
Click to expand...
What kind of problem? Did you do the latest update through their website?
Click to expand...

Yes I did the updates and followed the procedures carefully - from both True RTA & forum members here that were using the same setup. However, no matter how many times I ran it, there was no consistency in the results, so for me it was totally unreliable. I could do multiple sweeps from the same position without changing anything and get wildly different results, none of which agreed with my spectrum analyzer or what I was hearing. I also tried it on my secondary HT setup in another room with the same results. There were some members here (or at the S&V forum) who also had problems and the general opinion was that the software was" buggy".
 
Orbison said:
I read that a USB connection alone cannot provide enough power for this to work. Yet the portable preamps I've been looking at claim to provide 48v phantom power without a "wall wart" power supply. What's the deal?
Click to expand...

The deal is that a USB powered audio interface has dozens of different small DC-to-DC power converters which can take the 12V DC power from the USB connection and convert it to whatever is needed for the devices components. In some cases components require 1.5V, 5V, 12V, and in the case of Phantom Power, 48V. As long as the total consumed power is lower than the limits of the USB hub the device is plugged into, you can get pretty much any voltage you need.

Phantom power for condenser mics is used for two purposes, one is to charge the mic element where a membrane is suspended between two electrical grids, much like a capacitor. This is similar in concept to electrostatic speakers, but operating to turn acoustic energy into voltage - as a microphone. Some mics also add electronics as preamps, EQ, loading, even powered polarity and EQ filter settings.

Orbison said:
I'd also appreciate opinions on the Focusrite Scarlett 2i2 preamp if any of you have any experience or knowledge related to it.
Click to expand...

That is a great unit. The only gap I can see is the lack of pads for the mic inputs which come in quite handy when measuring things close-in - e.g. woofer performance below 200Hz indoors can be measured relatively accurately by placing the mic mere centimeters from the cone to get decent isolation from the room (same for enclosure ports).
 
CMonster said:
Orbison said:
I'm shopping for a replacement for my Mobile Pre so I can run REW to test my system. Thanks -
Click to expand...

Why not just get the USB microphone that most people use with REW?
Click to expand...

I thought about that because I read on a music forum that it didn't need a phantom power supply. However I'd still be stuck with the crappy sound card in my laptop. If I had a desktop, I'd put in a good sound card & be all set.

Thank you guys. I appreciate your help.
 
I have a general question about liability and lawsuits:

What is negligence?
1) One could argue that no matter what the cause, no plant should ever explode. So, by the very fact it exploded the owner was negligent.
2) It is crazy to assume that anyone anywhere can be 100% assured that their stuff will never, ever fail and an accident is impossible. So a plant owner making all "reasonable" efforts to prevent an explosion is doing all that can be expected while still trying to run a business which employs hundreds of people in a community. Running a business requires that business remain profitable and competitive, and doing everything possible in ever way to prevent an explosion might be prohibitive to its profit and competitiveness.

What is it? What is reasonable?

I know many industries have tried to develop standards for what is reasonable in order to put all the competitors on a level playing field in terms of the costs of doing business, but then you run into non-US companies being cheaper with the same products since they don't define reasonable safety the same way.

So, the federal government can add tariffs to goods where this is a clear difference between US safety concerns and foreign safety concerns.

What a mess.

This is why our regulations and laws are so friggin' complex. Every single thing we do to be safer, more competitive, or more advanced leads to dozens or even hundreds of regulations, taxes, fees, and complexities to the nature of doing business.
 
Some pre-amps are known/prized for how they change the sound ("tube warmth", etc) and for your purposes you'll want one that advertises "accuracy". I can't make any specific recommendations, and the three I own are all tube pre's (I wanted the warming).
 
Orbison,

Any updates on this??

I am currently looking into this also.

One of my questions would be with these portable usb interface is how to connect the output to the AVR, it appears most of them just have RCA Analog outputs, is this correct?

I was looking at the Focusrite Scarlett 2i2 with a DBX RTA-M MIC. This will run about $275 with the mic cable. Is this overkill?? Or is it the right set-up to evaluate my room/system with REW.

heeman
 
Yes, I got the Focusrite Scarlett 2i2 preamp and the Dayton EMM-6 mic. The setup works very well with the REW program. My computer is a Lenovo Thinkpad W520 w/Windows 7 64bit. The learning curve wasn't bad either. The REW forum can answer any questions that come up but the program is amazing and easy to use. Highly recommended. Especially the 'waterfall" graphs - essential for comparing the effect of different locations when placing bass traps & subs.

The preamp has 1/4" output jacks so I just got an adapter for an RCA cable - the other end of the cable plugs into an aux RCA jack on the front of my receiver. I paid $110 for the preamp (Ebay) and about $50 for the mic (on sale at Parts Express). $9 for a used tripod on Ebay. REW is free download.

I'm not familiar with the mic you mentioned, but PE supplies a calibration file for the EMM-6.

This type of setup will help you get the most out of that new HT room and new sub! Go for it!
 
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