A few beginner questions about mic preamp

Thread Starter

allisonr

Joined Aug 16, 2016
27
Hi,

I've got a few beginner questions about what I should consider when building this mic preamp (this article gave me the idea to tackle this IC due to its great performance in low noise applications http://www.audiomasterclass.com/the-famous-5-preamp-everything-you-need-to-know).

I know how to solder and follow drawings but little else about how a circuit works, hence my probably dumb questions.
This preamp should possibly include a peak limiter (most sound sources would be very quiet but there could be some occasional sudden spikes):





The drawings are not mine, they come from a TI datasheet and from http://sound.whsites.net/project67.htm, I'd like to know:

1. Can I omit the 48V phantom power (since my input wouldn't probably need it)
2. Should I balance the output or only the input?
3. If my input mic is actually a piezo transducer which may be accidentally hit from time to time due to handling and movement, will the IN4148 diodes suffice to block harmful voltage spikes on both IC and output?
4. Since my output will be a portable recorder (or possibly more than one kind of portable recorder) and they have 2 kohm (one type) and 1.6 kohm (other type) impedance, could I get a proper impedance with just one circuit I would I have to build one for each, or preferably have to match impedance (datasheet states best results are at 200 ohm input impedance)?
5. How should I merge both so that I can just set the input, preamp and recorder and leave it recording without worrying about clipping?
6. Should I have to adjust the preamp output so that it doesn't yield too much voltage to such portable recorders?
7. Since the preamp IC supply range is 4.5/18 V, can I power it with 4 Li-ion batteries (3.7 V each, yielding 14.8 V) with the same parts shown in TI's drawing, or should I have to recalculate resistors and capacitors value due to the different voltage?
8. Am I missing something else obvious that my clear lack of know-how makes me easily miss?

Thank you

Allison
 

MrChips

Joined Oct 2, 2009
21,826
1) You can omit R1 and R2 if it is not a powered mic, i.e. no phantom power needed.
2) Balanced input is required when using a mic that has balance signals. Does your piezo mic supply a balanced output?
3-8) The output level of a piezo mic should be high enough that you can plug it into a portable recorder. There should be no need for amplification.

What is the brand and model of your portable recorder?
Most portable recorders have automatic gain control (AGC). It automatically adjusts the gain to amplify weak sounds and to suppress loud sounds to avoid clipping.
In most cases you cannot disable the AGC.
 

Thread Starter

allisonr

Joined Aug 16, 2016
27
1) You can omit R1 and R2 if it is not a powered mic, i.e. no phantom power needed.
2) Balanced input is required when using a mic that has balance signals. Does your piezo mic supply a balanced output?
3-8) The output level of a piezo mic should be high enough that you can plug it into a portable recorder. There should be no need for amplification.

What is the brand and model of your portable recorder?
Most portable recorders have automatic gain control (AGC). It automatically adjusts the gain to amplify weak sounds and to suppress loud sounds to avoid clipping.
In most cases you cannot disable the AGC.
Thanks for your prompt replies.

I don't know if my piezo mic can produce balanced signal, basically it's just a piezo disc with an electrode soldered on a side and the one on the opposite side. Maybe if I solder one more electrode from each side I can make a balanced input?

Unfortunately due to my intended use, the output level wouldn't be high straight out from the piezo, hence my idea to use a constantly as high of a gain as possible (with an auto peak limiter to automatically turn down gain when clipping could/would otherwise occur) with a low as possible distortion, as I believe that IC could give.

My recorder is an Olympus LS-12, the other one (not necessarily used at the same time, but maybe from time to time) is a mobile phone which would also work as a portable spectroscope.
They both can have gain disabled or set at minimum, which is something I'd prefer since their amp is obviously more noisy than what this IC should be able to do.

Thank you
 
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