48v battery power with 9v batteries?

[djsimmonds]

hi,

this may not be the right place for this, but i think some people will have valuable input. i would like to build a portable battery-powered mixer with 48v phantom power for condenser microphones. i was thinking about using a max1044 chip based on rg keen's article (http://www.geofex.com/circuits/+9_to_33.htm), and then a second max1044 with the +25 and +33 as the ground and +V, respectively, to get +41 and +49 (or would it be +40 and +47, because of the 8v difference between +V and ground?).

1) would this work?

2) what would battery life be like in this arrangement? i would hope for at least 2-3 hours of recording time. is this even feasible? some details i am thinking about:
- i would be using these batteries: http://www.amazon.com/pieces-250mAh-capacity-rechargeable-Battery/dp/B001CON7PS/ref=pd_bxgy_e_text_b - 9v @ 250mA
- the mixer would be a 2-4 input mixer, at 1.5mA per channel (@9v). i'm not sure about the current draw of the mics, but i would assume about 5ma @ 48V (so ~25ma @ 9v). so the total setup would be ~60mA @ 9v, i believe.
- i wouldn't mind mind hooking up several batteries in parallel - 2, 4, heck, even 6 if that's what it took (i can always recharge them...); in fact, if i wound up needing that many batteries, then perhaps it would even be wiser just to hook up 5 in series for the phantom power, and 1 separately for the mixer power.

thanks in advance for the help!

dani

[JKowalski]

You can just add more sections to the end of the capacitor/diode chain in RG's article to get the 48 volts. Every section will add about 8 volts - two more and you have about 49 volts.

I think there's some charge pumps that take in up to a 18V input, so you could series a pair of nine volts and then you'd only need three of those capacitor/diode stages.

A standard 9V can output 600maH, so divide that by your 60mA and you have about 10 hours of use. I would derate that, though, IRL I would expect maybe 6-8 hours. Parallel some and you'll get more lifetime.

[Ripthorn]

Most condenser microphones have a current draw of 2-20ma at 48V.  You should check your battery's mah rating to tell you roughly how long it would last.  Totally possible with a MAX1044 or similar.

[darron]

also note from the datasheet:

200µA Max at 5V


just to keep in mind.

[frequencycentral]

~80 volts is the highest I've gone with MAX1044 - enough to drive the plates for a small tube amp: http://www.diystompboxes.com/smfforum/index.php?topic=73222.180

You might consider LT1054 if you want more ma than the MAX can give.

[djsimmonds]

thanks for all the responses!

[therecordingart]

Bumping an old post, but do your mics need a full 48 volts? I know that traditionally phantom power is described as 48 volts, but there are a lot of condenser mics out there that will run much less. For example, the Shure SM81 will run on anything between 11 and 52 volts. Take a look at the datasheets for the mics you are using because this could be a fairly simple thing to do.

[Processaurus]

I would be curious to know how the little digital pocket recorders that have phantom power for external microphones make their +48 supply from 3v.

[therecordingart]

I would be curious to know how the little digital pocket recorders that have phantom power for external microphones make their +48 supply from 3v.

It's doubtful that they are putting out a true 48 volts. The recorders with a 3.5mm mic input probably only put out a handful of volts for those little electret elements.

[Processaurus]

I would be curious to know how the little digital pocket recorders that have phantom power for external microphones make their +48 supply from 3v.

It's doubtful that they are putting out a true 48 volts. The recorders with a 3.5mm mic input probably only put out a handful of volts for those little electret elements.

No, I meant 48v phantom power like the Zoom H4 puts out to power condenser mics.