Low Noise Balanced Microphone Preamp (PCB also). - diyAudio
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Old 19th April 2007, 01:18 PM   #1
Ayne is offline Ayne  Pakistan
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Default Low Noise Balanced Microphone Preamp (PCB also).

Click the image to open in full size.
Circuit Diagram.

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Click the image to open in full size.
PCBs.

Ur comments.

I am discussing this circuit on:
This

Thanks.
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Old 19th April 2007, 06:30 PM   #2
Minion is offline Minion  Canada
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This is pretty much the exact same curcuit as found here:

http://sound.westhost.com/project66.htm


Your PCB looks good accept that for Home etching it would Not be Ideal as there is very little space between the Traces which would make it very hard to etch.....

If you wanted to add Phantom power to the Preamp you could simple add 2 6k8 resistors to Pin 2 and 3 with that connecting to your 48v Phantom supply and then Putt a couple 47uF-100uF DC Blocking caps after the 6k8 resistors at the input and you can then supply Phantom power to your Mics.....

You can also use a simple Voltage tripler config to your PSU and a 317 regulator to get your 48v Phantom Voltage......

Cheers


PS: the 47uF caps before the TL071 are actually 4.7uF.....
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Old 19th April 2007, 07:45 PM   #3
Ayne is offline Ayne  Pakistan
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Yes it is not my circuit.

I copy the circuit from there, i only make the PCB for us.

What is Phantom power ????
Plz explain.
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Old 19th April 2007, 08:43 PM   #4
Minion is offline Minion  Canada
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Phantom power is what you need to use Condencer Mics...

Most Mixers and preamps have this feature as Most Studios use Condenser mics.....

I have a PSU design and PCB for a PSU that Provides Regulated +/-15v and +48v phantom power for use with Mic preamps and uses the LM317/337 Regulators....

If you want it let me know and if you want a detailed description on how to implement Phantom power Let me know...

Cheers
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Old 19th April 2007, 09:04 PM   #5
Steven is offline Steven  Netherlands
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Default Noise

Noise behavior of the BC559 is not optimised for the typical source resistance of dynamic microphones; its base spreading resistance Rbb' is too high. Look for the type of transistors that are used in MC head amps, typically types with a larger geometry, such as medium power transistors. The 2N4403, mentioned in the original circuit description, is not even so bad. Or use some 2x10 pieces BC559 in parallel to lower the voltage noise.
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 19th April 2007, 11:43 PM   #6
Minion is offline Minion  Canada
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You could also make a Ballanced output with this preamp by adding as little as a Resistor and a Capacitor or for better ballanceing a Dual opamp in a Ballanced Line driver configuration or a Line driver chip like the DRV134.....

Cheers
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Old 20th April 2007, 06:33 AM   #7
Ayne is offline Ayne  Pakistan
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Quote:
Phantom power is what you need to use Condencer Mics...

Most Mixers and preamps have this feature as Most Studios use Condenser mics.....

I have a PSU design and PCB for a PSU that Provides Regulated +/-15v and +48v phantom power for use with Mic preamps and uses the LM317/337 Regulators....

If you want it let me know and if you want a detailed description on how to implement Phantom power Let me know...

Cheers
Yes plz in detial. and PCB also if possiable.
Thank u very much.

Quote:
Noise behavior of the BC559 is not optimised for the typical source resistance of dynamic microphones; its base spreading resistance Rbb' is too high. Look for the type of transistors that are used in MC head amps, typically types with a larger geometry, such as medium power transistors. The 2N4403, mentioned in the original circuit description, is not even so bad. Or use some 2x10 pieces BC559 in parallel to lower the voltage noise.
Editor's Comment on that web.(therefore i chose BC559).
As with all circuits presented on these pages, feel free to experiment. The 2N4403 transistors may prove difficult for some readers to obtain, and BC559s can be substituted with some possible increase in noise. I would expect that any increase will be acceptable for most applications. Performance should otherwise be much the same as described.
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Old 20th April 2007, 05:40 PM   #8
Minion is offline Minion  Canada
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Hi, here is a Basic Picture of how to implement phantom power to your Mic Preamp curcuit....

This curcuit goes at the input of your Preamp with a switch between the Power supply and the preamp PCB so you can turn the Phantom power on and Off......

Below it is the PCB and Stuffing guide for a PSU used for Mic preamps....It is the one that is used for the "Green Preamp" and is a very good PSU Design.....

Have any questions?? Jusr ask....


Cheers
Attached Images
File Type: gif phantom and psu.gif (58.2 KB, 683 views)
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Old 22nd April 2007, 09:41 AM   #9
Ayne is offline Ayne  Pakistan
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Just compare.

Which circuit will be the best for MIC PreAmp and why??

Circuit A
Click the image to open in full size.

OR

Circuit B
Click the image to open in full size.

Thanks.
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Old 22nd April 2007, 01:43 PM   #10
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IMO, neither one. A is not really balanced. You should use either a 3-amp instrumentation configuration, or a commercial instrumentation amp. There's a popular design on-line using an IN-something instrumentation amp that looks decent- probably easier and better than the discrete design. Also, the op-amp choice on both circuits is pretty low-fi. A dynamic mic is fairly low impedance, so you can do better noise-wise with better amps. Finally, I'd never build a mic preamp without the provision for phantom power, because once you try a large diaphragm condenser mic, you'll be addicted and want to use it for many situations.
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