preamp supply w/ 48v power

[impsick]

hi, can someone please check this layout for me? its for a mic pre with 48v phantom power. My transformer is a toroidal 16.5v - 0 - 16.5v ct.
so im a little confused with the ct in regards to ground and stuff.
thanks.



also say i have another tranformer that is dual sec. 8.5v
can i make a supply like the one i made?
what should be done differently?

[AndrewT]

Hi,
the 317
the 317 needs a cap on the adj pin to bring it's performance up to the already poor regulation of the 78xx/79xx regulators.
The 1uF (or is it 100nF?) on the output may be too far away from the reg pins.
The input pins have no small stability cap. Do you take the chance on stability with the remote caps? or put in a pair of pads just in case?
When the 48V+ supply starts up and the output is sitting at 0v what is the input voltage from the smoothed and rectified supply? Does it exceed the maximum for the regulator?
How do you get +48v from a 16.5Vac or 33Vac CT supply when the 0v is already committed to a dual polarity supply?

the 7815/7915
the input and output caps are too far away from the pins.
the input smoothing 0volt connection should not be commoned with the supposedly quiet 0v going to the pre-amp.
It needs a separate connection going to the audio ground @ the amplifier.

Finally, do you want to consider RC snubbers at the output?
Interference suppression at the AC input?
Is 317/7915/7815 performance good enough for a microphone supply?
How did you post that 176kb pic?

[paulb]

You should post a schematic. The +48 supply doesn't look like it will work.

[impsick]

hey thanks for the replies. i've been away.
the schema is from esp i'll get it. i've been working on another one though too. ill post that one also

[impsick]

ok actually im not sure if this was from esp. but is this schematic wrong? did i not fallow to suit with it? besides the caps on the ac lines.


here is another one that im trying to make. is this one correct?


Andrew what do you mean how did i post the pic?

[AndrewT]

Hi,
the 176kb pic is above the 100kb limit.
What did you do to get the pic to show?

[impsick]

i dont know i believe its a .bmp file. i just uploaded it to photobucket. i didnt know there was a limit.

[FastEddy]

Schemo #1: I would put C6, C7 and C11 on the output side (or way downstream on the pre-amp board ...)

A single common ground point on the PS board ... with a single ground connection to the powered boards & devices ... Lookin' good!

Image below = note that the terminal block (center / top) is where all the grounds come together in the multiple PSUs, ampboards and filter caps. Each amp board also has a single ground connection (bottom / foreground) for +/- power in, signal in & speaker output. (Chassis has its own power ground lug [lower right foreground almost hidden] for line cord power in and completely isolated from all other modules.)

[impsick]

thanks eddie! hey i got that pre amp down sized to 3"x4". i'm putting it together now. i'll post a pic on the other thread.

[impsick]

how is this? im not sure if i got the phantom power section right. i think its like a voltage doubler or something. i used the schematic from the Green Pre power supply but used 78,79xx's instead of 317,337.