Design me a phantom powered meter

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TijuanaKez

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Jul 19, 2011
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A wee lil project for someone familiar with the pitfalls of phantom power and what can and can't be done with it.
Was going to tackle this myself as a learning experience, but too many other things going.

Only a wee budget, but I imagine this would be a very quick and easy job for the right person.

Basically, I have a bunch of custom passive DI's I've built for my band etc.

I want them to show when there is signal present via LEDs. Could be a bar graph, or series of small LEDs, whatever really.
But it needs to be powered by phantom, not battery, and it needs to be buffered from the audio signal.

To be clear, I've breadboarded up various designs of meter using comparators etc. I don't really need help with the meter side, there's plenty of info around for meters.
The tricky part would be designing the circuit including ultra low power LEDs, opamps for the driver/buffer, comparators whatever to work with a power reservoir coming entirely from phantom which is sub 10ma.

Instead of asking for tips and help in the other forums, I feel like this is worth something in the order of a nice bottle'o whisky for someone who's done something like this before.

I dont need board design, just a circuit schematic I can mess around with.

PM if you can help me out.
 

ruffrecords

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Nov 10, 2006
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Norfolk - UK
It is always a good idea when asking for help to include your location in your profile. Shipping on a bottle of whisky might be expensive to some parts of the world.

Cheers

Ian
 

chrisregent

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Dec 21, 2013
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31
if you use high efficiency leds so more light for less current (probably only 0.2mA for 12 leds, in a string with constant current source (transistor, two diodes and two resistors), switch them on/off with LM339 or even lower current version TLV1704 or LP399-N comparators
plenty of low current opamps out there to give some gain, differential input and rectification.
if there was some pre planning, you could use a centre tap transformer to get the phantom.
 

abbey road d enfer

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Jan 22, 2008
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13,473
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Marcelland
It is commonly done by inserting an LED in series with the rail. The luminosity of the LED is a pretty good indicator of the operation.
KISS.
 
Last edited:

chrisregent

Active member
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Dec 21, 2013
Messages
31
that's great but he's talking about a signal level meter for the audio signal after a transformer based DI feeding a mic line.
 
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