Milkmansound
Well-known member
does anyone have a quick schematic for adding LED's into a phantom circuit? I want to have an LED light up when phantom is on in a PM1000 project that I am working on.
Phantom LED indicator
- Thread starter Milkmansound
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NewYorkDave
Well-known member
Probably the best indicator is one that won't light unless the +48V is definitely present. There's a number of ways you could go about it... The simplest of all, if you can spare about 2mA off the +48V supply, is a low-current LED with a suitably large series resistor between +48 and common. Assuming an LED voltage of about 2V:
R = E/I = 46V/.002A = 23K ohms.
Another method is to use the +48 (divided down as needed) to the base of an NPN transistor, with the LED and current-limiting resistor in series between a suitable V+ and the collector. Emitter to common. The positive base voltage turns the transistor on and lights the LED.
R = E/I = 46V/.002A = 23K ohms.
Another method is to use the +48 (divided down as needed) to the base of an NPN transistor, with the LED and current-limiting resistor in series between a suitable V+ and the collector. Emitter to common. The positive base voltage turns the transistor on and lights the LED.
jdbakker
Well-known member
[Edit: After posting this I saw NYD just beat me to the punch. You snooze...]
If you can spare a mA or two on the phantom supply, I prefer to just hook a hi-efficiency LED + resistor between the mic-side of the phantom switch and ground. That way you have an indication that the phantom supply actually works, and you can see if any decoupling capacitors on the mic side have discharged enough to start (un)plugging cables.
JDB
[but that's just me]
If you can spare a mA or two on the phantom supply, I prefer to just hook a hi-efficiency LED + resistor between the mic-side of the phantom switch and ground. That way you have an indication that the phantom supply actually works, and you can see if any decoupling capacitors on the mic side have discharged enough to start (un)plugging cables.
JDB
[but that's just me]
Milkmansound
Well-known member
this is what I usually do - just put in the LED with a ginormous resistor value to get it down to about 3V with alligator clips.
I like the idea of putting it in to see the caps discharge - nice one!
I guess I needed some reassurance is all - looks like I was not to far off the path.
I like the idea of putting it in to see the caps discharge - nice one!
I guess I needed some reassurance is all - looks like I was not to far off the path.
AnalogPackrat
Well-known member
Hmmm. I have the phantom indicator LEDs on my 312ish pres wired via an approximately 5k current limiter connected to the PP reservoir cap (100uF?). I just sketched this out on a scrap of paper to think about it. As far as AC signals are concerned, the limiting resistor and LED are in parallel with the PP cap, so at the PP feed node any AC sees a low impedance path to ground via the cap or 5k (or more using NYDave's suggested value) and the LED. Downstream toward the mic we have the two 6k81 Rs feeding pin 2 and 3. Seems like any effect the LED would have on our AC mic signal is quite small due to the impedances involved. Or did I miss something obvious?
Does your pre have a local PP reservoir cap between the switch and the feeds to the mic?
A P
Does your pre have a local PP reservoir cap between the switch and the feeds to the mic?
A P
AnalogPackrat
Well-known member
Aaaahhhaaa! That JLM arrangement makes a lot of sense. Looks like I need to revisit my 312ish phantom power switch/indicator wiring. Thanks for pointing that out.
A P
A P
< like the idea of putting it in to see the caps discharge>
and the corolarry, whatever that is, the led can show a slow start also.
and the corolarry, whatever that is, the led can show a slow start also.
khstudio
Well-known member
[quote author="alk509"]I honestly haven't tried feeding an LED off a phantom supply, but I've read in these fora that you can actually hear the LED distorting the mic signal when you do that. Maybe bullshit, maybe not...
Peace,
Al.[/quote]
:shock: wow... that would suck.
I used that method on my 8 channel pre.
Question - What's the easiest way to slow down the turn on when pulling directly off the 48v?
Kevin
Peace,
Al.[/quote]
:shock: wow... that would suck.
I used that method on my 8 channel pre.
Question - What's the easiest way to slow down the turn on when pulling directly off the 48v?
Kevin
there has been a lot of talk on the ramp thing.
depends on how extravegant you want to get.
depends on how extravegant you want to get.
khstudio
Well-known member
[quote author="CJ"]there has been a lot of talk on the ramp thing.
depends on how extravegant you want to get.[/quote]
I think ANYTHING would be better than the "speed of light" turn on I have now :idea:
Kevin
depends on how extravegant you want to get.[/quote]
I think ANYTHING would be better than the "speed of light" turn on I have now :idea:
Kevin
Milkmansound
Well-known member
who has time for any other way?
oh wait, you must bill by the hour :razz:
oh wait, you must bill by the hour :razz:
G
Guest
Guest
Thsi is how John Hardy does it
http://www.groupdiy.com/index.php?topic=3331&highlight=john+hardy
For all his switches - separate 5v line
http://www.groupdiy.com/index.php?topic=3331&highlight=john+hardy
For all his switches - separate 5v line
even a stock 48 will have a ramp due to caps and resistors in the filter sirkut.
i mean you won't have a leading edge that you could use to test slew rate of IPA001 for instance.
i mean you won't have a leading edge that you could use to test slew rate of IPA001 for instance.
jdbakker
Well-known member
[quote author="alk509"]I honestly haven't tried feeding an LED off a phantom supply, but I've read in these fora that you can actually hear the LED distorting the mic signal when you do that. Maybe bullshit, maybe not...[/quote]
Do you happen to have a link to the relevant thread(s) ? I've searched, but none of my keywords have produced anything useful.
There might be a slight amount of AM-detection of CM input signals when phantom is off... but you'd need to have a very hot CM signal plus a mic pre with lousy CMRR to 'hear' any of that (like when your next door neighbour is KRAP-AM). But I might be completely off-base, so I'd like to see arguments/experiences to the contrary.
FWIW, this is what I usually use for phantom switching:
The +48V line has a current limited series transistor regulator per channel. I have never heard birdies with the phantom on or off, but maybe I just haven't found the right high-EMI environment yet.
JDB
[then again, I do most of my recording within less than 7 kilometers of Schiphol Amsterdam Airport, right under one of their busiest flight paths. On the RF stuff I design for work I regularly see nice noise peaks from ATC radar]
Do you happen to have a link to the relevant thread(s) ? I've searched, but none of my keywords have produced anything useful.
There might be a slight amount of AM-detection of CM input signals when phantom is off... but you'd need to have a very hot CM signal plus a mic pre with lousy CMRR to 'hear' any of that (like when your next door neighbour is KRAP-AM). But I might be completely off-base, so I'd like to see arguments/experiences to the contrary.
FWIW, this is what I usually use for phantom switching:
The +48V line has a current limited series transistor regulator per channel. I have never heard birdies with the phantom on or off, but maybe I just haven't found the right high-EMI environment yet.
JDB
[then again, I do most of my recording within less than 7 kilometers of Schiphol Amsterdam Airport, right under one of their busiest flight paths. On the RF stuff I design for work I regularly see nice noise peaks from ATC radar]
[quote author="jdbakker"]Do you happen to have a link to the relevant thread(s) ?[/quote]
I don't, sorry. It has nothing to do with AM detection, though - people have talked about the LED distorting the mic signal.
Peace,
Al.
I don't, sorry. It has nothing to do with AM detection, though - people have talked about the LED distorting the mic signal.
Peace,
Al.
jdbakker
Well-known member
[quote author="alk509"][quote author="jdbakker"]Do you happen to have a link to the relevant thread(s) ?[/quote]
I don't, sorry. It has nothing to do with AM detection, though - people have talked about the LED distorting the mic signal.[/quote]
Very odd. I've just gone over all 106 search results for "phantom LED". Found a lot of interesting stuff (as always), but other than this and some folks suggesting putting the LED in series with the phantom supply (which I could see causing non-linearities), no mention of LEDs causing distortion. And I can't imagine any way in which the LED in the circuit I posted would cause noticeable distortion with only a differential signal, even assuming non-ideal matching of the 6.81k resistors.
Confused,
JDB.
I don't, sorry. It has nothing to do with AM detection, though - people have talked about the LED distorting the mic signal.[/quote]
Very odd. I've just gone over all 106 search results for "phantom LED". Found a lot of interesting stuff (as always), but other than this and some folks suggesting putting the LED in series with the phantom supply (which I could see causing non-linearities), no mention of LEDs causing distortion. And I can't imagine any way in which the LED in the circuit I posted would cause noticeable distortion with only a differential signal, even assuming non-ideal matching of the 6.81k resistors.
Confused,
JDB.
