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?
so im a little confused with the ct in regards to ground and stuff.
thanks.
An externally hosted image should be here but it was not working when we last tested it.
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?
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?
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?
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.)
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.)
Attachments
Re: 48 volt sources. The important thing is not to exceed ~ 50 volts as this may pop parts up stream = 
... sometimes the mic makers will use tiny little caps in the mic built-in amp boards that have tight upper limits on that 48 volt line ... like they might use 50 volt caps wich degrade quickly above 50 volts. 43 volts is OK, but you might try to get it above 45 volts. This could be done with a trimming resistor (pot) to "tweak" the output ... you might consider adding the solder pads for this just in case the end user / builder wants to get a little closer to the target ... (Actually many phantom power devices will work as low as 30 volts, but it is good to try to stay close to expected performance ... when a mic is out there on a very long cable, phantom power voltage can drop off pretty quickly with cheap cables.)
RE: PSU board ... looks just fine. ... C12, C13 = plastic 0.1 uF snubbing caps?
... you might want to add another one parallel to C9 to quiet down that phantom power line ... or not.
... sometimes the mic makers will use tiny little caps in the mic built-in amp boards that have tight upper limits on that 48 volt line ... like they might use 50 volt caps wich degrade quickly above 50 volts. 43 volts is OK, but you might try to get it above 45 volts. This could be done with a trimming resistor (pot) to "tweak" the output ... you might consider adding the solder pads for this just in case the end user / builder wants to get a little closer to the target ... (Actually many phantom power devices will work as low as 30 volts, but it is good to try to stay close to expected performance ... when a mic is out there on a very long cable, phantom power voltage can drop off pretty quickly with cheap cables.)RE: PSU board ... looks just fine. ... C12, C13 = plastic 0.1 uF snubbing caps?
... you might want to add another one parallel to C9 to quiet down that phantom power line ... or not.
Some Questions
What supply voltages u gave to ur circuit i mean what is the output of ur Transformer secondary???
I am asking because i make this (Circuit attached) in simulation and it is only giving 38.40Volts Approx...
One thing more,
I read the datasheet of LM317... and it's maximum input supply voltages is equal to 40 Volts.... Is ur LM317 is working right on above (as u said "43.8v to my surprise") of it's supply voltages??? Or it is getting hot??
Thanks
What supply voltages u gave to ur circuit i mean what is the output of ur Transformer secondary???
I am asking because i make this (Circuit attached) in simulation and it is only giving 38.40Volts Approx...
One thing more,
I read the datasheet of LM317... and it's maximum input supply voltages is equal to 40 Volts.... Is ur LM317 is working right on above (as u said "43.8v to my surprise") of it's supply voltages??? Or it is getting hot??
Thanks
Attachments
16.5v - 0 - 16.5v
im getting 15v+/-
and 43v+ relative to zero.
im pretty sure its working fine. right now hooked up to my pre with a condensor mic there is no audible hiss till gain is up to max.
the supply circuit was taken from the green pre, a well known diy pre.
but i know what your saying i was confused myself. i thought for some reason the 317 regulates up to 37v. i dont knonw why that was in my head but it works (for now).
it gets a little warm w/ a small heat sink on it but not bad at all
im getting 15v+/-
and 43v+ relative to zero.
im pretty sure its working fine. right now hooked up to my pre with a condensor mic there is no audible hiss till gain is up to max.
the supply circuit was taken from the green pre, a well known diy pre.
but i know what your saying i was confused myself. i thought for some reason the 317 regulates up to 37v. i dont knonw why that was in my head but it works (for now).
it gets a little warm w/ a small heat sink on it but not bad at all
Warm is noticably warm above local ambient temp = warm to the touch after about three minutes or more. Hot is noticable without burning or blistering fingers = might need attention if you can't touch it for more than three minutes duration. Too hot is burny, blistering fingers after ten seconds or less = bad. Really too hot is smokin' hot = stinking. 
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