Help/advice/guidance translating schematics onto a pcb

[ruffrecords]

if you take a look at the schematic I have a 10k resistor before the LED. Does that not solve the problem of 48V being too much for an LED?

However, looking at a Neve 1073 schematic from AML, theyve done what you suggested for the LED. Double pole switch, sending the main +16V power to the LED (with the same 10k resistor before hand. Gonna do some investigating and see what works best. If I can make it work with the 48V that'd be ideal so I dont have to route another big power track across the whole board

Just for completeness, the original 1073 did not have a phantom supply switch.Phantom power was switched globally across an entire mixer.

Cheers

Ian

 

[djmiggymigz]

Interesting thread and a good steer for me about KiCad. I'd always done PCB layouts on grid paper in the past or perhaps tracing paper over a 0.1" grid with red pencil on one layer for east-west, and blue pencil on a second layer for north-south ...

With "more time on my hands these days", I was looking for something to bring my PCB layouts into at least the 20th Century, if not right into the 21st ... anyway, the upshot was I downloaded CircuitMaker but I can't say I love it, so I'll be happy to look at an alternative!

Learning a lot here. Thanks gents!

Super happy to hear others are learning here too! I sometimes feel bad for my almost infinite questions but there is so much that goes into this that at the very least a little guidance in the right direction feels needed and is immensely appreciated. Thanks to all who've lent a hand already!!

I couldn't recommend KiCad enough. I only downloaded it a week ago and it makes a whole lot of sense to me already. The biggest challenge is learning the ins and outs of the actual electrical engineering side of things. Learning how to use the software itself is cake in comparison. PLUS, you can export you .gbr and drill files, drop them right into JLC and have your custom pcb's in hand within 2 weeks. So very cool to me

 

[djmiggymigz]

Just for completeness, the original 1073 did not have a phantom supply switch.Phantom power was switched globally across an entire mixer.

Cheers

Ian

Whoa meaning if phantom was on one channel it was on all the channels??

I've also noticed that the original 312 design doesnt seem to have phantom power either! I suppose maybe that's because dynamic/ribbon mics were still the majority of mic lockers? Thus 48V wasnt standard or needed until later on?

 

[zamproject]

if you take a look at the schematic I have a 10k resistor before the LED. Does that not solve the problem of 48V being too much for an LED?

No, 10k under 48v is 5mA, on the low edge for a LED (depending how bright you want it) 5k may be better

What I mean is that phantom power for one mic is specified around 10mA, let say you have a console with 16 mic input, 48V rail may be scaled to offer around 160+ mA (in fact it is often less as manufacturer cut corners and suppose you won't plug 16 phantom powered mic at once...).
If you add a LED signalling status on each input on the same rail you will overload it as you need 160mA too (@10mA each) to light the LEDs.

Also you better isolate/separate audio supply from signalling supply, usually a 5V rail (modern LED) or 12 to 24V (bulb) is used for all light visual feedback and relay.

I've also noticed that the original 312 design doesnt seem to have phantom power either!

API 312 is a part (preamp) of modular console, I never look at API console block diagram, but the P48 is probably handled outside the input module with dedicated supply bus/rail directly wired to previous routing module or mic input connectors.

meaning if phantom was on one channel it was on all the channels

yes, usual practice back then...

 

[ruffrecords]

Whoa meaning if phantom was on one channel it was on all the channels??

I've also noticed that the original 312 design doesnt seem to have phantom power either! I suppose maybe that's because dynamic/ribbon mics were still the majority of mic lockers? Thus 48V wasnt standard or needed until later on?

It is because in those days, phantom power was not often required. Most studios were still using tube based condenser mics which came with their own power supply.

Cheers

Ian

 

[djmiggymigz]

No, 10k under 48v is 5mA, on the low edge for a LED (depending how bright you want it) 5k may be better

What I mean is that phantom power for one mic is specified around 10mA, let say you have a console with 16 mic input, 48V rail may be scaled to offer around 160+ mA (in fact it is often less as manufacturer cut corners and suppose you won't plug 16 phantom powered mic at once...).
If you add a LED signalling status on each input on the same rail you will overload it as you need 160mA too (@10mA each) to light the LEDs.

Also you better isolate/separate audio supply from signalling supply, usually a 5V rail (modern LED) or 12 to 24V (bulb) is used for all light visual feedback and relay.


API 312 is a part (preamp) of modular console, I never look at API console block diagram, but the P48 is probably handled outside the input module with dedicated supply bus/rail directly wired to previous routing module or mic input connectors.


yes, usual practice back then...

okay I totally misunderstood,, 48V is "too low current" for an LED! In that case I'll look into it! I suppose configuring a double pole switch wouldnt be much different than where my layout is right now. However, I dont at all understand how +48v wouldnt provide enough current for an LED but if I use the +16v rail that would?? Don't feel compelled to answer that (unless you want to!!) as I know that's a relatively speaking basic electronics question!

 

[zamproject]

I dont at all understand how +48v wouldnt provide enough current for an LED but if I use the +16v rail that would??

maybe because V=R*I....
Now if you want to use a 30mA P48 for a single preamp it's up to you !

 

[MidnightArrakis]

okay I totally misunderstood,, 48V is "too low current" for an LED! In that case I'll look into it! I suppose configuring a double pole switch wouldnt be much different than where my layout is right now. However, I dont at all understand how +48v wouldnt provide enough current for an LED but if I use the +16v rail that would?? Don't feel compelled to answer that (unless you want to!!) as I know that's a relatively speaking basic electronics question!

[48V is "too low current" for an LED] -- NO!!!.....48V is -- NOT -- "too low of a current" for an LED!!! It's how the 48VDC power-supply was designed to supply a certain amount of current to its load. BIG DIFFERENCE!!! As an example, condenser microphones typically only draw around 5mA or so. Therefore, the console manufacturers design their phantom power-supply to deliver enough current to supply maybe 10mA to each channel, allowing for enough current to power a microphone that may use around 7mA.

So, let's say you have a 24-channel mixer. Then, the phantom power-supply may be designed to deliver 48VDC @ around 300mA, just for good measure. This works out to be: 24-Channels X 10mA each = 240mA (~1/4-Amp). NOTE: Ian (RuffRecords) could provide you with a much better explanation about this as he once worked at NEVE.

Since you typically don't want to load your power-supply right up to its maximum output capability, you allow for some "headroom" and in my example, I have only allowed for an extra 60mA.

Now, depending upon your LED series resistor and how bright you would like your LED to be, a somewhat typical LED current draw is around 10mA to 20mA or so. And, that's just for a -- RED -- LED. Other colors may draw more current for the same brightness due to how the eye perceives the brightness of different colors.

So, now.....you go tacking on the current load of IC chips for mic-preamps and LED's to show that the circuitry is "ON" and.....you end up exceeding the allowed phantom-power current load of the microphone channel!!! So.....how could you fix this problem???

EASY!!! ..... You just design your phantom power-supply to be able to deliver 1-Amp to each mic-channel!!! Then, your phantom power-supply becomes a 48VDC @ 25-Amp (allowing for a smidgen of "headroom") power-supply that's the size of a brick!!!

Now.....you can add-on all of the LED's and peripheral circuitry to your hearts content and probably -- STILL -- have enough current left-over to light-up an LED Christmas Tree for holiday events!!! Do you see how things go here???

[I dont at all understand how +48v wouldnt provide enough current for an LED] -- It's all in the power-supply design.

[the +16v rail that would??] -- It's all in the power-supply design.

As I pointed out above, the console manufacturers -- COULD -- design their phantom power-supplies to provide 25-Amps if they wanted to!!! But, why would they??? Their -- intended -- total current load is anticipated/expected to be: 24 X 10mA. The console companies aren't allowing, nor are they expecting, for you to increase the current-load demand by adding-on additional circuitry. They (apparently "foolishly") designed their phantom power-supplies to -- ONLY -- provide enough current to power a microphone. The console manufacturers should have anticipated that you would want to plug a toaster-oven into an XLR!!! Right???

In any case.....here's a handy little calculator that will assist you in calculating what value an LED series resistor needs to be:

https://www.digikey.com/en/resource...ors/conversion-calculator-led-series-resistor

[maybe because V=R*I] -- More below:



Hope this helps!!!

/