Phantom and 24 for various oldies.... 2448 Power supply PCB!

[dmp]

I want to power some power hungry preamps with this - ez1290s. How much current can the 24v rail supply?
The LM317 can supply 1.5A with proper heatsinking, while switching to a LM350 could potentially allow 3A.

 

[r2d2]

...A condenser mic like u87 require 0,8mA at 48 phantom
the c414 take 4,5mA
if you have 2 preamps n-e-v-e style , with or without eq or filters
a stereo overhead set with 2x u87  ,
then 0,8mA  X 2

need to check if 48V have enough power also for some led

in case some led light as well is added

and about 1A can be not enough ,

or i'm wrong?

peace

 

[dmp]

Well, even if you allow 10mA currrent per channel for phantom mics, you can power ten and still be at 0.1 Amp...

 

[r2d2]

to "dmp"
unfortunately
in the "specifications" post (at the start of this discussion)

it's not indicate how many "ampere" the 48V "rail " supply
also if it can supply some 5V or 2V led light as well
(light status indicator is ever good thing)

hope the "manufacturer" (IJ) add this detail soon
(obviously for who are not electronic "engineer"..)

peace

Well, even if you allow 10mA currrent per channel for phantom mics, you can power ten and still be at 0.1 Amp...

 

[r2d2]

??? i'm a bit " amazed "....

found on the web a post where a guy talked with di-g-i-k-ey support
that say the 48V scheme  it's "wrong" and not work...
???
here about the "support" talk...
***** : "user" i suppose
xxxxxxx: "support" , i suppose

*****: hello, checking for part i need to get 48v from toroidal psu regulated with tl783
xxxxxxx: What is you input voltage?
*****: +24V toroidal secondary
xxxxxxxx: This is not an amplifier.  Input voltage has to be greater than the output voltage.
xxxxxxx: If you want 48v output you will need more than 48v on the input.
xxxxxxx: What ouput voltage do you want?
*****: +48V
xxxxxxx: OK, what is your input voltage?
*****: +24v  from a toroidal
xxxxxxx: OK, then that will not work.
xxxxxxx: This is a regulator not an amplifier.
xxxxxxx: Input voltage has to be greater than the output voltage.
*****: are you shure ? , it's cannot be a "doubler
xxxxxxx: That will not work.
*****: can you tell me why?
xxxxxxx: The regulator has a 1.27v drop, so the minimum input voltage must be 49.27v.
xxxxxxx: Also, those diodes will have a voltage drop.
xxxxxxx: That's because that is what Comes from your transformers after the bridge rectifier.
xxxxxxx: But, you need more input voltage to get 48v output on the regulator.
xxxxxxx: The regulator has a 1.27v drop, so the minimum input voltage must be 49.27v.
xxxxxxx: That minimum is after the bridge rectifier.
xxxxxxx: Common diodes have a .6v or .7v drop, so that is 1.2v to 1.4v drop added on.
xxxxxxx: There is no amplifier.
xxxxxxx: The bridge rectifier convertes the AC to DC.
*****: sorry but the info i'm reading say 2x25 toroidal?
xxxxxxx: get a different transformer would be the easiest?
xxxxxxx: it would give you 56V, which should be enough to regulate that.
xxxxxxx: 200mA Is that enough current?
*****: hmmm a bit little , have to connect 6 or 8 devices that require 10 or 15mA each and 2 or 3 led lights for each device
xxxxxxx: The max output current of the regulator is 700mA
xxxxxxx: Also are you putting the LEDs in series or parallel?
*****: parallel
xxxxxxx: OK You can use ......

??? ??? ???

peace!

 

[Harpo]

??? i'm a bit " amazed "....

found on the web a post where a guy talked with di-g-i-k-ey support
that say the 48V scheme  it's "wrong" and not work...
???
here about the "support" talk...
***** : "user" i suppose
xxxxxxx: "support" , i suppose

*****: hello, checking for part i need to get 48v from toroidal psu regulated with tl783
xxxxxxx: What is you input voltage?
*****: +24V toroidal secondary

24V AC toroidal secondary (no + or - in AC), followed by a voltage doubler circuit.

xxxxxxxx: This is not an amplifier.  Input voltage has to be greater than the output voltage.
xxxxxxx: If you want 48v output you will need more than 48v on the input.
xxxxxxx: What ouput voltage do you want?
*****: +48V
xxxxxxx: OK, what is your input voltage?
*****: +24v  from a toroidal

about 66.7V raw DC in front of the regulator.

xxxxxxx: OK, then that will not work.
xxxxxxx: This is a regulator not an amplifier.
xxxxxxx: Input voltage has to be greater than the output voltage.
*****: are you shure ? , it's cannot be a "doubler
xxxxxxx: That will not work.
*****: can you tell me why?
xxxxxxx: The regulator has a 1.27v drop, so the minimum input voltage must be 49.27v.

This TL783 has a typical reference voltage of 1.27V for a range in between 1.2V .. 1.3V.
Dropout voltage is at about 10% for a TL783, so for +48VDC out you'd need at least about 53V raw DC in front of your regulator to maintain regulation.

xxxxxxx: Also, those diodes will have a voltage drop.
xxxxxxx: That's because that is what Comes from your transformers after the bridge rectifier.
xxxxxxx: But, you need more input voltage to get 48v output on the regulator.
xxxxxxx: The regulator has a 1.27v drop, so the minimum input voltage must be 49.27v.
xxxxxxx: That minimum is after the bridge rectifier.

see previous reply for dropout voltage.
That minimum voltage is in front of the regulator. (pin 3 for the TL783). This part of circuit doesn't use a bridge rectifier.

xxxxxxx: Common diodes have a .6v or .7v drop, so that is 1.2v to 1.4v drop added on.
xxxxxxx: There is no amplifier.

This circuit uses a voltage doubler pre rectifier.
You loose current for more voltage (K-factor 4 for villard doubler), usually no big deal for +48V phantom.

xxxxxxx: The bridge rectifier convertes the AC to DC.
*****: sorry but the info i'm reading say 2x25 toroidal?

xxxxxxx: get a different transformer would be the easiest?
xxxxxxx: it would give you 56V, which should be enough to regulate that.

2*25V toroidal seems to relate to a different circuit.
2*25V AC wired in series would be 50VAC, (50VAC - 2*0.6V diode drop)*SQR(2) is 69V raw DC.
No idea, how he's getting 56V.
This circuit uses 2 separate 24VAC transformer secondary windings for the 24VDC part and the 48VDC part.

xxxxxxx: 200mA Is that enough current?
*****: hmmm a bit little , have to connect 6 or 8 devices that require 10 or 15mA each and 2 or 3 led lights for each device

One worst case dead shorted mic cable will draw 48V/(6K8||6K8)=14mA, leaving nothing for your mic. 8 of those (shorted multicore) will draw 113mA. For usual expect 8 phantom powered mics to draw about 40mA, so a (40mA*K-factor 4) 200mA rated transformer secondary should be sufficient.
No idea why you think you'd need 2 or 3 LEDs for each device. (On - really On - yeah, for sure)
Better use a DPDT switch and a lower voltage rail for LED supply to get rid of generated heat in your current limiting resistors for the LEDs.

For the circuit in question I'd remove D10 (for protecting the regulator from C13 in a shorted output condition this diode would better be placed across R5, same for the 24V part) and remove C13 as well.

 

[Stagefright13]

Why would ya ever tap the 48 volts for a 2 volt led? Just tap it from the lowest voltage available. The switch will light the LED regardless of where the voltage comes from.

John

 

[r2d2]

when you give 48V to a mic
better have a light that say : "you have a 48V on a mike" .....   
( ....i want ever have a light that talk about)
for be shure the 48V is really present
the led light have to take 48V from switch (at outoput pin)
then 2 cables at the switch output pin
1 go the xlr pin 2 and 3 (with 6k8)
the other go to the anode led light pin

the led light cathode pin go to 0V source or to ground
(i said something wrong?)

peace
 

Why would ya ever tap the 48 volts for a 2 volt led? Just tap it from the lowest voltage available. The switch will light the LED regardless of where the voltage comes from.

John

 

[ruffrecords]

The IEC spec for phantom power states that it must be capable of supplying up to 10mA to each mic.

Cheers

Ian

 

[Harpo]

when you give 48V to a mic
better have a light that say : "you have a 48V on a mike" .....   
(i want ever have a light that talk about)

Quite usual to have a status LED for activated phantom voltage per channel, but not 2 or 3 LEDs.

the led light have to take 48V from switch (at output pin)

Why, if you can easily avoid it?

then 2 cables at the switch output pin
1 go the xlr pin 2 and 3 (with 6k8)
the other go to the anode led light pin

This would be the minimal version.
For usual you have phantom voltage connected to a throw position of a DPDT switch. Switch pole connects to another maybe 220R series resistor. Resistor other side splits  to your 2*6K81 resistors and to a maybe 47uF/63V electrolytic cap. Caps negative side connects to phantom reference voltage (0V) and to opposite throw position of this switch. This R/C forms a 15Hz lowpass filter to reduce remaining ripple if any by -16dB and discharges a loaded cap thru this bleeder resistor when the switch gets disengaged.
The LED is supplied from the other pole/throw of the DPDT switch.

the led light cathode pin go to 0V source or to ground

Without a current limiting resistor in between (your description is +48V -> switch -> LED -> 0V), better stand back when the LED takes off to fly thru your room.
Supplying LED from 48V (better don't), this required current limiting resistor is (rail voltage - typical LED forward voltage) / wanted (=< max.allowed) LED current, giving (48V - maybe 2V) / maybe 0.01A = 4600 ohms for these example values. You'd probably use a standard 4K7 resistor. This has to stand (48V - 2V) * 0.01A = 0.46W, so better use a 1W rated part. Supplying the LED from a 24V rail instead, a 2K2 1/3W part would be sufficient for these example values. Just look up the datasheet for your type/colour/efficiency LED to not exceed parts limits.

[quote author=ruffrecords]
The IEC spec for phantom power states that it must be capable of supplying up to 10mA to each mic.[/quote]
Ian is spot on.
Your 30VA (=2*15VA) 2*24V transformer will supply your 2 channels phantom voltage easily from one of these 15VA secondary windings.

For your probably wanted 2 channel neve-alike preamp, the other 15VA rated 24V transformer secondary winding might be just sufficient.
(15VA/24V) / formfactor_K 1.8 for fullwave bridge = 0.34A. A little less (~300mA) in a 10% low mains scenario. A single 1290 without bells and whistles will draw about 120mA. Add your status LED currents and voltage setting network at LM317, this 30VA might get tight.

Harpo

 

[r2d2]

hey "harpo"
nice post
please there is a scheme about follow "setup" ?

This would be the minimal version.
For usual you have phantom voltage connected to a throw position of a DPDT switch. Switch pole connects to another maybe 220R series resistor. Resistor other side splits  to your 2*6K81 resistors and to a maybe 47uF/63V electrolytic cap. Caps negative side connects to phantom reference voltage (0V) and to opposite throw position of this switch. This R/C forms a 15Hz lowpass filter to reduce remaining ripple if any by -16dB and discharges a loaded cap thru this bleeder resistor when the switch gets disengaged.
The LED is supplied from the other pole/throw of the DPDT switch.
Harpo

regarding the led resistors ,
for a 2V 20mA led , a 2k3 resistor can be enough

peace

 

[Harpo]

please there is a scheme about follow "setup" ?

something like this.

regarding the led resistors ,
for a 2V 20mA led , a 2k3 resistor can be enough

What is the supply voltage for the LEDs ?
You already looked up the LEDs typical forward voltage for wanted LED colour ? (red/green/yellow/amber/blue/white differ)
20mA would be the max.current, this type of LED can stand. For less blinding brightness you probably only allow for maybe 10mA.
For formula to calculate the min.resistor value and min.required rating, see previous post.

 

[r2d2]

hey "Harpo"
thanks for post the info and scheme
a 20mA led can be this this O
peace

please there is a scheme about follow "setup" ?

something like this.

regarding the led resistors ,
for a 2V 20mA led , a 2k3 resistor can be enough

What is the supply voltage for the LEDs ?
You already looked up the LEDs typical forward voltage for wanted LED colour ? (red/green/yellow/amber/blue/white differ)
20mA would be the max.current, this type of LED can stand. For less blinding brightness you probably only allow for maybe 10mA.
For formula to calculate the min.resistor value and min.required rating, see previous post.

 

[r2d2]

.....about pin 1 and 48V wire scheme (posted)
the cable shield (xlr pin 1)
can be connected only to the chassis ground including the 47uF cap (as in the scheme)
and then avoid connection to the pcb ground ?
(pcb just have ground connection)
peace

something like this.

 

[Harpo]

.....about pin 1 and 48V wire scheme (posted)
the cable shield (xlr pin 1)
can be connected only to the chassis ground including the 47uF cap (as in the scheme)

Yes. Mic phantom voltage is 48V above mic shield voltage potential. The connection from 48V reference voltage (G48 from Igors schematic) to XLR-pin1 for the current return path is missing in your description.

and then avoid connection to the pcb ground ?
(pcb just have ground connection)

No need to connect your +24V reference voltage (G24 from Igors schematic) to your chassis ground.
The only other connection to your chassis, except phantom reference voltage, is the always connected safety ground from your IEC inlet.
Your input transformers exclusively reflect the differential signal between XLR-pins2/3 to your neve-style preamps.
This '2448 Power supply PCB' is a 24V and a 48V psu (two completely separated power supply units, no common reference voltage) on a single pcb, fed from a mains transformer with dual secondary windings. Using two separate mains transformers instead would make it even more obvious.

BTW. Try to be a little more correct with your numbers. For your previous LED question, a 2K3 resistor for limiting the LED current is no common avail.standard resistor value, so either wrong or typo and without a related voltage, this resistor connects to in series with your LED, this question doesn't make much sense anyway. Following the link from the other forums thread, your 30VA transformer only seems to be a 25VA transformer (=12.5VA AC per secondary winding) for the 24VDC and 48VDC supplies, probably not enough for the 24V part of two neve-style preamps.

 

[r2d2]

Hey "Harpo"
thanks for post

you think might be like
in the attahced image ?

peace

.....about pin 1 and 48V wire scheme (posted)
the cable shield (xlr pin 1)
can be connected only to the chassis ground including the 47uF cap (as in the scheme)

Yes. Mic phantom voltage is 48V above mic shield voltage potential. The connection from 48V reference voltage (G48 from Igors schematic) to XLR-pin1 for the current return path is missing in your description.

and then avoid connection to the pcb ground ?
(pcb just have ground connection)

No need to connect your +24V reference voltage (G24 from Igors schematic) to your chassis ground.
The only other connection to your chassis, except phantom reference voltage, is the always connected safety ground from your IEC inlet.
Your input transformers exclusively reflect the differential signal between XLR-pins2/3 to your neve-style preamps.
This '2448 Power supply PCB' is a 24V and a 48V psu (two completely separated power supply units, no common reference voltage) on a single pcb, fed from a mains transformer with dual secondary windings. Using two separate mains transformers instead would make it even more obvious.

BTW. Try to be a little more correct with your numbers. For your previous LED question, a 2K3 resistor for limiting the LED current is no common avail.standard resistor value, so either wrong or typo and without a related voltage, this resistor connects to in series with your LED, this question doesn't make much sense anyway. Following the link from the other forums thread, your 30VA transformer only seems to be a 25VA transformer (=12.5VA AC per secondary winding) for the 24VDC and 48VDC supplies, probably not enough for the 24V part of two neve-style preamps.

 

[Harpo]

Hey "Harpo"
thanks for post

you think might be like
in the attahced image ?

??? No. (and the cap will explode,...)

 

[r2d2]

Hey "harpo" , thanks for post
you are right !
sorry bad cap "sense" ....
reworked scheme

new one attached ,

sorry for question
the connector pin "29" have to be connected to "star" ground ?

peace!
(all over)

Hey "Harpo"
thanks for post

you think might be like
in the attahced image ?

??? No. (and the cap will explode,...)

 

[Harpo]

the connector pin "29" have to be connected to "star" ground ?

: We are getting better and better every day in mindreading....
Why don't you just say what you want to build. Neve (if it is ment for a Neve at all) built more than one type of preamp. What's yours?
These questions seem a little misplaced in Igors psu thread.

 

[r2d2]

hey "Harpo" thanks for post !!!
you are right ,

for "vari" reasons the "argumentation"
started from "a psu for oldies" ,
and for the fact that it's for different types of "oldies"
the "argumentation" began to expand about the various aspects and details
that can change depending on the type of "oldie" this "psu"
have to "give" power / life ,

many other details are a "bit / much " important
about how to fit properly this power supply " for various oldies.... "
(ground , star ground , humm ... , xlr pin 1, etc...)

and talk about it in the same place
could only amplify the power and versatility of this psu may have , (" for various oldies.... ")


I read several hundred pages of this forum
and many members are very experienced engineers
(like : you! , many others , ....and "of course " the "manufaturers",igor ,jakob,volker , jeff, mnats , etc...)
Most of the other much less ,
someone also true electronics beginners  ,

"Diy" is a great thing ,

and frequently requires very long time to find all the information necessary ,
also from different threads and forums ,
(i checked meta , unfortunately no threads about how fit properly the psu for "oldies" ,
even about "racking" "oldies"  properly , i mean no metal work , but electronics and electrics)

why not "Clustering" the related information in a thread that " supply / proposes " a psu for "oldies" ,
" amplifying " the potential use of the same , adding to the thread : schemes, tricks, tips , etc...

this is my "humble" opinion , 

peace
(anytime and anywhere)

the connector pin "29" have to be connected to "star" ground ?

: We are getting better and better every day in mindreading....
Why don't you just say what you want to build. Neve (if it is ment for a Neve at all) built more than one type of preamp. What's yours?
These questions seem a little misplaced in Igors psu thread.