Diy Mic preamp with 48v phantom power - diyAudio
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Old 12th November 2008, 04:16 PM   #1
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Default Diy Mic preamp with 48v phantom power

I am thinking about building a mic preamp for my CAD E-100 and was looking for some advice. First, I'd like to use mostly spare parts which I have an abundance. I already have power supply considerations taken care of. Right now I'm trying to decide between using tl074s or 4558s which I have an abundance of. I also have TA75064s and 1458s which neither seem to be up to the task. I would like to use op amps to simplify my design. I am a novice in analog design so any help would be great.
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Old 12th November 2008, 04:34 PM   #2
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Most mics are designed to handle a lot of SPL so the optimum noise level for a general purpose preamp is pretty low to be useful. The TL074's might not be up to the job.
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Old 12th November 2008, 11:55 PM   #3
Minion is offline Minion  Canada
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Look into getting a few INA217 or That 1512 IC"s....

They are Mic preamp Ic"s that sound very good and are super easy to build with, you can probably get them for $3-$5 a piece....

You can make a ballanced Input preamp with One DIP8 chip and about a dozzen extra parts (Minus PSU) on a PCB a couple inches square.....

I have built several and I use them all the time in my studio....

Cheers
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Old 14th November 2008, 02:41 AM   #4
dmills is offline dmills  United Kingdom
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Seconded.

The fet input opamps like the 074 are poorly suited to being driven from low impedance sources (far too much voltage noise), and while you could do something involving external transistors, a chip designed as a mic preamp is a better bet.

You will want to pay attention to the datasheet circuit for protecting the inputs from phantom power accidents as a hundred uf or so of cap at 48V suddenly being discharged into an IC input can degrade it.

Have fun.

Regards, Dan.
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Old 14th November 2008, 02:46 AM   #5
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Seventh Circle Audio offers a bag of parts and board based on the THAT chip for pretty short money. You still need to supply power.
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Old 22nd December 2008, 02:37 PM   #6
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Minion:

I've noticed your posts here and at Home Recording on the mic preamps that you've built. I'm looking to build something cheap for starters. Is it possible to get a copy of the schematics that you settled on for the preamp and power supply? PCB designs would be nice but not necessary - I could go from the schematics.

I'm not that great with electronics but can read schematics. I'm aware of the mic preamp schematic for the IAN217 that TI publishes, but have read at various sites on the internet of various modifications that folks have suggested, and either get lost with some of them, or they're just suggestions and not necessarily tested.

It sounds like you've arrived at a design through effort on several preamps.

Any help would be greatly appreciated.
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Old 22nd December 2008, 05:03 PM   #7
Minion is offline Minion  Canada
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The actual Power supply I use is the same one used in the "Green Pre" which is also simular to the "Five fish" power suply and many others...It uses the Basic Datasheed implementation of the LM317/337 regulators and use a voltage tripler and a lm317 for the Phantom power....

For the Life Of me I can not find a schematic or PCB design for the PSU but I"m sure there is a schematic for the five fish PSU at there web site.....

as for the INA217 I have setteled on a pretty basic implementation , no Ballanced outs, No DC servo...Just go by the datasheet schematic and implement the features you want and omit the ones you don"t....Remember to use a good quality output cap (about 470uF) if not useing the DC Servo....

Without the DC servo and Ballanced outs you can make a PCB that is extremely small.....

Cheers

PS: this PSU schematic is very close to the one I use accept I use the LM317/337 regs and not the LM7XXX series regs...
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Old 25th June 2009, 08:35 PM   #8
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Hi Minion,

this Puwer Supply Schematic is pretty exactly what I'm looking for, only that I need +/-15V instead of +/-18V.

So I'm wondering if I could use a Transformer with 18V secondary output(and adjust the voltage regulators) instead of 20 in the schematic and still be able to get the 48V... Or would I have to change other Parts/values as well?
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Old 25th June 2009, 09:02 PM   #9
Nisbeth is offline Nisbeth  Denmark
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You can pretty much leave it as is I think. If you are having problems keeping the LM317 stable with the at 36VAC input (not likely with the low current draw, but possible) you can substitute an LM1086 which is the low-drop version.


/U.
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Old 25th June 2009, 11:05 PM   #10
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Cool, thanks a lot.

I'll try the LM317. If that doesn't work, I'll see where I can get a LM1086.
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