48v … led voltage drop

[johnheath]

I am building a G9 p2p and, having mounting everything except the pre circuit, I fired it up today to take the first measurements of the power supply and 12 vdc for heaters and 48volts for phantom power. Since there is a 10k variable resistor to adjust for the 48 volts it is very easy to get it just right.

Now… since I am a half blind man I wanted to add a led to mark that the phantom power is on. Since the draw is 1,2 volts and there are two channels I lose 2,4 volts from the 48.

My question is… Is it ok to set the phantom power to 50,4 volts to be able to operate two channels with the 48 volts each…or should I set the trimmer on 48 volts and accept that the phantom power is 45,6 volts when using both channels?


Cheers

/John

 

[johnheath]

Forgot the schematic

 

[joaquins]

Oh, no, do it in parallel, maybe at the 12V switch, so you power up your LEDs with 12V, you already have the 3 pos switch, one switching 12V and the other 48V, the unused pin of the 12V to both diodes in series with a series resistor to set the current, so  you have your 2.4V drop (I think it will be higher, but if you say 1.2V per LED) so you have 9V let's say, to set it to ~10mA you need 91Ω resistor, use 100Ω, maybe bright will be enough, if not you could use 82Ω or a bit lower without burning the LEDs. Don't put them in series with your 48V, they won't turn up when you don't have enough current on your phantom load, the mics, if using a dynamic mic or you don't have anything connected, even if your phantom is on your led will be off.

JS

 

[johnheath]

Hi JS

Well, I forgot to mention that I am not using a 3-pos switch for the pad and 48v. I use there DPDT-switches since I didm't want the relay at all.

So… the 48 circuit is basically the same but from one of the matching 6k8's I couple another 6k8 that goes to the anode of the led and the cathode is grounded. After the last 6k8 there is roughly 9volts that feeds the leds. Each 48v per channel is parallel to each other.

I think that the 12vdc is more important to keep as it is… I can be wrong here though

 

[joaquins]

A LED will shine fine with 10mA, maybe you want more but let's say 10mA, it's what a mic gets from phantom, usually, so connecting the LED there, is using the current for 2 channels in one. Using the 12V which is for heaters, 10mA is nothing since you are getting ~1A from there to the heaters, Voltage won't change and current will change very little, is more efficient using 12V (only 90% of power loss) against 48V where you will have about 98% of power loss. It really doesn't matter.

  If you can, use the 12V, as it's in parallel it won't affect the other things in your 12V rails. Then, if you can't get the 12V there (because the phantom switch doesn't have spare pins for example) use the 48V, should be fine, you will need 4k7 resistor to be about 10mA.
  As you are using DPDT switch, you only need half, connect the 12V to the LED in the other half with 1k resistor in series, I was wrong with 100Ω, only by an order of magnitude... Then step one value down if you want more bright or now value up if you want less bright.

JS

 

[johnheath]

Thank you Joaquins

It worked just fine and the 1k resistor gave 7,2 volts for the LED so… prefect!

And the 48v remains the same on both channels.

Thanks again… you have to admit that before the internet…this would have been impossible

/John

 

[joaquins]

I don't know if impossible but at least would take month to mail 7 letters from Europe to South America... Times are faster.

You are welcome.

JS

 

[PRR]

LED in series with Phantom will only tell you that something is *sucking* Phantom current.

It will not tell you that Phantom is ON *before* you plug the mike in!

If you plug in something non-Phantom, and it blows-up, there may only be a brief blip and then darkness, no clue what you did.

Normally the LED is wired 48V to Ground, to show the 48V is present.

48V-1.6V at 5mA is a 10K resistor.

 

[joaquins]

LED in series with Phantom will only tell you that something is *sucking* Phantom current.

It will not tell you that Phantom is ON *before* you plug the mike in!

If you plug in something non-Phantom, and it blows-up, there may only be a brief blip and then darkness, no clue what you did.

Normally the LED is wired 48V to Ground, to show the 48V is present.

48V-1.6V at 5mA is a 10K resistor.

I mention led on only with condenser mics connected, also as he said is a half blind man I prescribed 10mA for LEDs...

JS

 

[johnheath]

Well the thing was to create some sort of "marker" that the switch is "on" and 48v is sent to the mike… I was just "blind" to not see the 12vdc as an possibility to feed the leds instead of the 48v. In the G9 schematic it all rely on a 3-pos switch with markings on the chassi… I just wanted a Led instead for easier enlightenment