Preamp or DI box?

[MT]

Hi there, new to the forum and the MBR. Been reading all the posts I can about using an external mic, but I have a question.

I want to mic my amp cab with a sure sm57. I've read to use the GTR IN jack and that it helps to have a mic preamp to bring the impedence up. But I don't have a mic preamp. I do have an old DOD ac265 DI box, and was wondering if I could use that somehow.

Would it be possible to connect the mic to the xlr side of the box and run a 1/4" cable from the output/thru-put jack on the other side of the box and then into the GTR IN on the BR? Or is the DI only for connecting a 1/4" unbalanced signal to an XLR balanced signal? 

[64Guitars]

I want to mic my amp cab with a sure sm57. I've read to use the GTR IN jack

No. The GUITAR IN is for guitar and the MIC input is for a microphone. Whoever suggested that you plug your microphone into the guitar input was probably under the mistaken impression that you have to use the guitar input if you want to use the insert effects from the GTR bank. That's not true. You can use any effects bank with any of the inputs. They merely default to the most likely choice, but you're free to change it.

So plug your SM57 into the MIC input using a suitable adapter (the MIC input is stereo). But be sure to switch the PlugInPower OFF (see page 114 of the Micro BR manual, 3rd edition) before you connect your microphone. Otherwise, you might damage the mic.

[64Guitars]

Sorry. I just noticed that the Shure SM57 cable has a male XLR connector on the end, rather than a 1/4" phone plug. So you'll need a XLR Female to 1/4" Male Mono adapter to go with the Stereo 1/8" Male to Dual Mono 1/4" Female adapter I mentioned earlier.

 

Unless, of course, you can find a Y adapter with a 1/8" stereo plug on one end splitting to two XLR mono connectors.

[MT]

Thanks for replying. I see what you're saying. So I need to use the LINE IN/MIC jack with the right adapters.

However, the sm57 I believe is a dynamic mic, and...

If it is a dynamic microphone be aware that the Line IN is not designed to have dynamic microphones plugged directly. The mics must be amplified and have the same inpedance as the Line In first. This can be done using a Microphone Pre-amp

I'm wondering if I can use a passive DI box instead of a mic pre-amp, just to match the impedence levels?

[64Guitars]

OK. Well Pedro (admin) actually owns a Micro BR and I don't, so he's probably right. Although, the manual does mention dynamic mics connected to the external mic input several times. Still, a condenser mic is probably a better match for the Micro BR's external mic input. Not because of impedance but because of gain. Condenser mics generally have much higher output than dynamic mics, and the Micro BR's external mic input doesn't quite have enough gain to adequately boost the low level produced by a dynamic mic like the Shure SM57. A mic preamp is one way to solve this problem. Another option is to use a mixer connected to the BR's Line In jack. As well as serving as a mic preamp, the mixer could come in handy in other ways, so it's the most versatile option. But some people prefer the warmth of a tube mic preamp. Shure recommends their A85F Line Matching Transformer which provides a 24dB signal boost.

The DOD AC265 is a passive direct box, which means it doesn't provide any gain. It will match low impedance devices to high impedance inputs, but its impedance (50K ohms) is actually too high for the Micro BR (18k ohms). This will make the mic's signal even lower. So, you should consider a mic preamp, mixer, or line matching transformer instead. Actually, I have a couple of concerns about the line matching transformer. 1) I suspect that, like the DOD AC265, the A85F's impedance may be too high for the Micro BR and that will reduce its gain. 2) It's not clear to me how the A85F achieves its gain. Does it contain a small inline preamp? If so, what powers the preamp? A battery? I'd want to learn more about the A85F before deciding to go that route. I like the versatility of a mixer, and I'm sure its headphone output would sound much better than the BR's. On the other hand, Musician's Friend's price for the ART Tube MP Studio preamp is quite attractive, and it has that cool VU meter. 

[hewhoiscalledj]

A condensor mic will require phantom power (48V) which the MBR is unable to provide. It only gives like 4V of power whihc is suitable for little mics like the Sony ECM-DS70P Electret Condenser Stereo Microphone

The dynamic SM57/58 should work fine through the EXT input but a pre-amp would do wonders for the sound.

Not sure about the DI box. Do those things provide phantom power for condensors? I dont think so but i could be wrong.

[AlchemyMN]

Options:
1. Battery powered condenser.
2. Pre-amp with any kind of mic
3. DI/dynamic mic if you can't do 1 or 2 - I've had better luck with the internal mic than dynamic mics.