help need on voltage problem

[bent]

here's the set up:

i use a 120vac in , 24vac out power supply.
this is powering 3 thing:
- a 24vac to 234vac transfo, the out (234) goes to a diode bridge with cap/resist to get 300v dc (tube circuit supply)
-a diode bridge to get +/- 26v dc, then past in a mini board to get +12/-12vdc (futurlec) to powering the microchip board and another miniboard +12/-12vdc for the heater
-and this http://www.extremecircuits.net/2010/05/48v-phantom-microphone-power-supply.html to get 48vdc, but since i didnt have the tl783kc, from the point where is supposed to have the tl783kc  i drop voltage with resistor (5m4) to get to 48 vdc....for powering the phantom power...

i got the phantom 48vdc,
i got the 300vdc,
but the supposed 26vdc, is 46vdc...(so 2 dead miniboard  )

When the power supply (24vac) is connected with a diode bridge only i get 26vdc, but when i apply the circuit (48v phantom) with the other diode bridge on the power supply, then  it rise from 26vdc to 46vdc.....
So i supposed i can't connect more than 1 voltage modification (diode bridge) on a circuit ? can we put 2 different diode bridge to make 2 kind of power ?
what should i do ?  use the phantom circuit only and find a transfo 48vdc to 24vdc to power my miniboard ?

I'm a little lost !   
Help !
bent

[PRR]

> i can't connect more than 1 voltage modification (diode bridge) on a circuit ?

That usually makes sneak-connections which either short-out the AC or change the operating mode to some form of voltage-multiplier.

Getting +/-12V AND +48V from one winding is hard, and will be wasteful.

This will get you there, but the waste in the 12V regulators is twice as much as the useful output.



> since i didnt have the tl783kc, from the point where is supposed to have the tl783kc  i drop voltage with resistor (5m4) to get to 48 vdc....for powering the phantom power...

NO!! You can NOT resistor-drop Phantom power. It MUST be +44V to +52V, unloaded or loaded with 10mA. Some mikes use very little current, some use a lot, and many of them use the 48V as reference (even as capsule bias). Get the regulator.

[bent]

thank's PRR, nice draw...very clear ! 

i was thinking this night about all this, and i was coming with:
- use a 110vac input,
- past into a 110vac to 24vac transfo , or use directly my 24vac wall power supply...
- take the 24vac and past it into a 234v - 24v transfo in reverse, with the bridge-filtering to get the 300vdc
- and also take the 24vac past into the 48vdc phantom circuit with the tl783,
- from the 48vdc tap, make it past into a lm350 regulator to drop to 24vdc to feed my mini board +/-12vdc...

a like those mini board, already assembly, good filtering...

I'll keep posting ....
Bent

[bent]

First modification:
-can't use the tl783 in the first regulation circuit , cause i will drive about 1 a in the 12vdc, and the tl783 is max 700ma....
- so i change the first regulator circuit to use the lm350(3A) to go from 70vdc to 48vdc...phantom power...
- after i use another regulator circuit to go from 48vdc to 24vdc to supply my mini board...

building today....posting to come...

bent

[bent]

OK !
Juste realized that the output of the lm350 is between 0 to 30v, and not dropping the voltage from 0 to 30v ( exemple: 70v to 40v)...
so i rebuild the lm350 circuit and mod it to the tl783 circuit, and tap my other circuit to the 70v

so now i have 48vdc 700mA, tl783 circuit,
and i have a 24vdc 3A, from the lm350 circuit,
and my 300vdc for the tube....


bent

[bent]

well....

the miniboard dont like to be supply by the lm350 circuit !

think ill drop the mini board and do another lm350 circuit to get 12vdc...

bent

[bent]

well...

the 24vac is creating 70vdc with the tl783, and the out of the circuit is 48.7vdc ( phantom )
from the 70vdc, i send it to the other's lm350 circuit that is converting to 24vdc and 12vdc
all voltage is good...

when i put a load on the 12.6vdc , the lm350 is turning off by the heat ( even with a heatsink)...i found that the drop voltage is a step to high ( 70vdc to 12.6vdc)

remove the 70vdc on the input of the lm350, and use the 24vac with a bridge, then i have more than 50vdc, look's like the rectifier circuit of the lm783 is affecting my other rectifier circuit...they share the same ground....

what to do.....
i have 110vac that goes throught a 229d24 to get 24vac
from the 24vac i go to another 229d24 in reverse with rectifier and cap+res to get 307vdc
from the same 24vac i go to the rectifier circuit of the tl783 of extremescircuit.net (phantom power)

I read again the reply by PRR,
and i was wandering if i can remove the -12vdc side and just keep the +12vdc side exactly like the picture...
And i have a question.....on the tl783 circuit there's a 4700uF between the ground and one side of the 24vac, and PRR draw is connecting directly one side of 24vac on the ground ?

bent

[bent]

i'm closing this topic and transfer to
http://www.diystompboxes.com/smfforum/index.php?topic=89637.0
thank's