Battery powered mic pre with phantom

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JN

Member
Joined
Mar 4, 2013
Messages
7
Location
EU
Hi guys,

A long time reader on this forum, just registered now.
I am in need of a portable microphone preamp powered by batteries only, for location dialogue recording, ambience, wildlife, outdoor recording for sound design etc.

I'm on a budget, so anything like a recorder from Sound Devices or similar is way out of my league. Out in the open a laptop with a USB-powered audio interface is way too awkward to handle. Instead, I have a Zoom H2n recorder which features a 2 channels external microphone input. I'm planning on using the Zoom as an AD-converter/recorder.

What I need is a low cost microphone preamp with a phantom power option as well. Everything should be powered by batteries only, so low power consumption is essential. I think the Green Pre would be suitable for this but for simplicity and lower cost, I'm going for the Project 66 preamp by Rod Elliott. I don't know the sound quality of this preamp but I think it is worth a try. Besides, as far as I can tell, all components is pretty standard and easily accessible.

1) Off the top of my head, a bipolar power supply from batteries could be done like in the attached schematic. Is this the right way?

2) Am I over-complicating the phantom part?

3) The "Project 66"-preamp runs on +/- 15V. I assume there will be no problem running this on +/- 9V (maybe compromising sound quality or maximum gain), but would it be fine with +/- 18V?

Hope you can help me out.
Thanks!
 

Attachments

  • Battery Powered Mic Pre Schematic #1.pdf
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Consider INA217AIP (P means it has legs). It is a hair better preamp, and lots less parts for you to fiddle. Farnell, DigiKey, and Mouser have ample stock. Yes, it is $7 apiece instead of 7 cents like Rod's plan, though by the time you buy jacks box and batteries the difference in total outlay may be small. (And TI has 'free sample' but I don't see how to ask for two.)

Since you can't possibly need a whole Volt to smack the Zoom H2n it does seem a waste to run 30V even 18V to get there; however I don't have a sharp low-volt plan laying around. A 1:7 mike transformer (often readily available in guitar/PA shops as an inline adaptor) into a TL072 at single 9V would be one path.
 
Thanks guys, really appreciate the suggestions.  :D

PRR said:
Consider INA217AIP (P means it has legs).
Definitely looks interesting! The simple outlined microphone preamp design in the data document exactly looks like what was on my mind. A better sounding preamp with less components  :)

I've realized the need for limiting the amount of batteries in the construction. Even though it is DIY, I still need to have useable box with no batteries flying around. Thus, 18V phantom power should be ok for most shotgun mics, right?

PRR said:
Since you can't possibly need a whole Volt to smack the Zoom H2n it does seem a waste to run 30V even 18V to get there
You're probably right about the Zoom, would a simple +/-9V supply be inadequate for the INA217? I know, the specs go as low as +/-4.5 (and even lower for the OPA137) but I'll guess that would be too small a supply for the purpose of a microphone preamp.

mylesgm said:
JLM audio has a kit which gets a pretty good rap, it's rechargeable battery powered in a rugged case and gets very good audio reviews.  jlmaudio.com
Interesting as well. I can't seem to locate the item though. Do you know the name of the kit?
 
JN said:
I know, the specs go as low as +/-4.5 (and even lower for the OPA137) but I'll guess that would be too small a supply for the purpose of a microphone preamp.

Uh, "too small a supply for the purpose of a mic preamp?"

I don't think so. Supply rails basically set the maximum output voltage. They don't have anything to do with the gain. If the device to which the preamp connects has +/-5V rails, a preamp with a +/- 18V supply can easily clip it. A preamp with +/- 5V rails is likely a good fit.

-a
 
INA217 datasheet says max output swing is typically 1.8V-2V below/above V+/V-. So if you can swing up to 7VP-P on a +/-9V supply, that's a max output of +10dBu. Should be plenty to work with for your purposes.
 
JN said:
Thus, 18V phantom power should be ok for most shotgun mics, right?
Suggest you check the specs for the shotguns you want to use.

If you need P48V phantom, a stack of 5x9V PP3s works well.
 
now if you want a slick unit 

(ha ha...hey Beavis  ha ha, ha,... he said.... slick unit...  ha ha)

then add a vu meter with a switch that also reads battery voltage,

yes, DC will go thru the VU bridge rectumfriar.

(hey Beavis  ha ha ha...)  :D
 
if you're doing mobile recording, and by chance using a laptop, there are a lot of interfaces that are bus powered.  MOTU Traveler/Ultralite for sure, a whole bunch of others as well...
 
@ Andy Peters & gemnini86
- Thank you very much for the explanations. This definitely cleared some things for me. I'll guess PRR tried to tell me this in his first post. I'll have worries about running the preamp on 9V then!

@ CJ
- Sure, of course I want a slick unit, haha 8) Seriously, a battery checker would indeed be not just a cool feature but also a need-to-have feature for a mobile recording setup. The only thing I'm a bit concerned about is the additional costs as well as how fragile it would be. But if I can find something cheap and small ...
Regarding monitoring, for now my plan is use a pair of headphones plugged straight into the Zoom (got a pair of UE-18 IEMs from when I was gigging a lot with bands). But thanks for the suggestion though.

@ ricardo
- You're absolutely right. Need to check the mic specs! ;D

@ mulletchuck
- Thanks for the suggestion. Unfortunately, I think a laptop-interface solution would be too fragile and bulky for my situation. I have to be able to move around quickly in all kinds of outdoor locations (urban, forests, beaches, fields etc). So, I need a simple solution that can be carried around and most importantly is quick to setup.
 
I like the idea of a separate power supply for the pre-amp/mic for optimum recording time. But you need more/different batteries, and a bulkier rig. Last year I looked on-line at a bunch of field recording devices. You already have a recorder, so this may not be an economical option, but there are a few devices that have powered inputs.
Tascam DR-07mkII is the cheapest, you would need input adaptors, other models: Zoom H4, Tascam GT-R1, Tascam DR-100mkII, Marantz PMD620. I made a spreadsheet last year to compare the features of what was available then, there may be different options now. I ended up using a Playskool toy cassette recorder that I got for free.
 
Tascam DR-07mkII is very good!  the built in mics are incredible for their size,

a little shy of storage space when using the hi quality avi format,

i believe it has a 24 bit A to D, MP3 files not that great but take much less space,

you might be able to get a bigger storage thingy to put in there,

 

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