Pedal Power from Phantom Power?

M

matmonster58

Active member
My mxr m81 bass preamp is cable of running on 9volt dc/batter/or phantom power. It's one of my favorite features because I can just grab and go, no power chords needed.

I working on my own preamp right now and I would love to add a phantom power feature. Phantom power is 48V and can provide a maximum current of about 10mA. There are pedals that can be optimized to run on such a low current, but I'm going to need some wiggle room.

Since I'm wanting less voltage and more current to run my pedal, I'm thinking some kind a buck-converted is going to be the route to go. Have any of yall made phantom powered pedals or have any insight on how to go about designing the power section?
 
from what i understand, a 48V 10ma supply should give you more than 10ma @ 9V.

my terribly brief understanding of Ohm’s law calculations tells me that 48v @ 10ma is 0.48W

0.48W / 9v = 53ma

could be wrong though 😅
 
Depending on the buck converter, going to lose some as heat
Eering on the side of caution, 20%.
But what happens if you don't have phantom power?
Also, mix cables don't necessarily make great instrument cables.
Crappy mix cables can make terrible instrument cables. Probably not a huge deal if your bass is all bass but if you slap, you'll hear it.
Or are you looking to build a preamp/DI box?
I read it as onboard preamp...
 
jwin615 said:
Depending on the buck converter, going to lose some as heat
Eering on the side of caution, 20%.
But what happens if you don't have phantom power?
Also, mix cables don't necessarily make great instrument cables.
Crappy mix cables can make terrible instrument cables. Probably not a huge deal if your bass is all bass but if you slap, you'll hear it.
Or are you looking to build a preamp/DI box?
I read it as onboard preamp...
Click to expand...
A preamp pedal/di. I should be able to get at least 30mA at 12v I believe
A boss ge-7 is speced to draw 30Ma
I'm using a similar topology so I should be able to get in a similar ballpark

I'm going to have to spend some time tracking down some high quality, low power opamps though. Tl062s should work but I want something quieter
 

LM5168 data sheet, product information and support | TI.com

TI’s LM5168 is a 6-V to 120-V wide VIN, 300-mA DC-DC converter with Fly-Buck™ capability. Find parameters, ordering and quality information
www.ti.com

A TI LM5168 looks like it could work. The spec sheet shows >75% efficiency when converting 48V to 12V, switching at 500kHz. This should give me at least 30mA @ 12V or 25mA @ 16v if i can spare some current for more headroom.

I'm a little worried about switching noise but my schematic as is naturally rolls off above 10kHz so it shouldn't be an issue
 
It's going to have a standard 9vDC power section option, that part is easy. As far as can tell, there is no standard design for phantom power for pedals so I have to figure it out.

My inspiration for this preamp is the mxr m81 and its phantom powered capability sets it apart from any other preamp

90% of the time I grab a bass, the mxr m81, and a 1/4" cable for gigs

I want all the convivence of the m81 with a few tweaks to better suit my needs (high impedance buffer, 4 band eq instead of 3 band w/ parametric mids, mute switch ...)
 
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Since I'm going use this to gig, I don't get a choice what I plug into. The IEC phantom power spec has 6.8k resistors on each power pin. At a maximum, each pin can deliver 7mA for 14mA total. While custom pres or studio equipment can be spec'd to whatever, image any pro audio/live equipment is going to be IEC spec'd.

Out of curiosity I just measured my cheap presonus interface. It delived ~10mA
 
I can see that happening...
"Gee, we're maxed out on the phantom power... sorry, got nothin' left for you"
or at smaller gigs/venues...
"Oh, this mixing desk doesn't have phantom power..."

I dunno fer shr, but I vaguely recall being at gigs where phantom power was absent.


For a low-power op-amp, I'd ask @Passinwind — he'll be sure to have some suggestions in that department.
 
Feral Feline said:
I can see that happening...
"Gee, we're maxed out on the phantom power... sorry, got nothin' left for you"
or at smaller gigs/venues...
"Oh, this mixing desk doesn't have phantom power..."

I dunno fer shr, but I vaguely recall being at gigs where phantom power was absent.


For a low-power op-amp, I'd ask @Passinwind — he'll be sure to have some suggestions in that department.
Click to expand...
How many opamps? FET, bipolar, or both?
 
I'm telling ya, rolling your own with the 4S 18650 battery sleds and the MP1584EN *just works*. Dead silent, massive AH. I have a 16 battery, loaded parallel in the sleds, sleds in series that produces 16v with 8.8AH, two chips do ADJUSTABLE DC to DC at 450mhz with 2A per chip. They smoke at 3A. The replacement chips (I think mp2330en) are capable of 3A continuous, but I can't find anyone actually putting it into a easy to wire layout. Plus the older ones are cheap.
 
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