Looking for HIGH gain microphone preamp circuit.

[ken3983]

I am building a shotgun microphone and I need a low noise high gain circuit for a microphone preamp.I'm trying to use transistors instead of IC chips.I might go with the LM386 as a power amplifier but I am in desperate need of a really good preamp covering from low to high Hz(50-20k maybe).Anyone have an idea?

-Ken

 

[k7elp60]

Can you give us an idea on how much gain you need. In volts or dB? As I recall the LM386 only needs about 50mV input for full output.

 

[ken3983]

I am looking for dB gain.I need something to increase the sound the microphone is going to pick up and then it being passed on to a power amplifier.I might seem a little vague and I'm truly sorry.I am going to get a pack of transistors and check the hfe on each on of them with a multimeter and separate the ones with the highest hfe gains to use those.That may not make any difference though.I have seen a schematic that said the gain was about 70 dB in the audio range and the gain was based on the sum of the transistors hfe divided the ratio between the input and the load.Make any sense?

-Ken

 

[Nigel Goodwin]

I am looking for dB gain.I need something to increase the sound the microphone is going to pick up and then it being passed on to a power amplifier.I might seem a little vague and I'm truly sorry.I am going to get a pack of transistors and check the hfe on each on of them with a multimeter and separate the ones with the highest hfe gains to use those.That may not make any difference though.I have seen a schematic that said the gain was about 70 dB in the audio range and the gain was based on the sum of the transistors hfe divided the ratio between the input and the load.Make any sense?

There are lots of special low noise opamps available at very reasonable cost, designed for low noise audio preamplifiers - far easier to use one (or more) of those. Try looking at the OPA2134 from Burr Brown.

You might also try looking here **broken link removed**.

 

[chemelec]

I have use this preamp for that application and it works pretty good.
Connect the output to Any small IC Power amp.

**broken link removed**

Gary

 

[k7elp60]

A gain of 70 db relates to an voltage gain of 3,162. If we take the square root of 3,162. Square root = 56.24. I would think a two stage amplifier with transistors is possible. If you use a common emitter circuit and let the unbypassed emitter resistor versis the collector resistor make the gain about 60 for each stage that should work. As the overall gain to A1 X A2. If the transistors have a minimum hfe of 100, it should work fine. Common transistors like 2N3904 may even work.