Please read the description first. Two circuits (easy to make) are showed as microphone amplifiers for an electret microphone capsule, working on 3 Volt nominal (minimum 2,2 Volt).
In both cases made with 3 x a BC 547 b transistor (Hfe 350, NPN-Si).
Next video (16 July 2024) is here [ Ссылка ]
I tested the EMY 63 M/P capsule (somewhat noisy) and another electret capsule, salvaged out of (I think) an old casette player. The latter had a substantially lower noise. I cannot give a type number, because it was not printed on it.
More important is that, in fact, any standard electret microphone capsule can be used in this case, in both circuits.
Everything important is told in the video, about both the schematics, so I don’t have to reiterate that.
Schematic 1 (with the volume control) is somewhat noisy, but it is very suitable to pick up faint sounds in a room. With, of course, a certain amount of background noise. The articulation of voices is very sharp, thus good understandable. It can start clipping when the volume control is set to its maximum.
Schematic 2 (the one demonstrated) has less noise and a somewhat better “stark signal” behaviour of the microphone, thus it is difficult to get this pre-amp “clipping”. Good suitable to drive an audio amplifier in a big room (restaurant or so), a radio transmitter etc.
Because of that behaviour there are 2 points: it is very simple & works good without AVC (automatic volume control), together with that EMY 63 M/P capsule. I am sure it will also work good in this regard with other electret capsules.
Please note: these circuits are well thought-out and developed, but they are simple. Thus no high tech (with say AVC, with a adjustable time delay, etc, etc), but they are simply “good” for their purpose.
The used electrolytics can work a little bit to mitigate stark audio signals and thus prevent clipping and distortion of the pre-amp.
About Schematic 2: when you replace the headphone (15-32 Ohm) with a 32 Ohm resistor, you can take out the amplified microphone signal (opposite to minus/earth/ground) via a capacitor of 2.2 uF (preferred non-polar). Do that out of the emitter of the end-transistor. I did not test that, by the way. The same applies to circuit 1.
Test, try, experiment. Key is here: adaptation from the output of the pre-amp to the input voltage that the end-amplifier needs. In consumer electronics that is often 0,8 Volt AC (standard maximum line level).
Things in general when making sensitive audio pre amplifiers of any kind: shielding and a supply voltage that is absolute free of hum are essential. Thus for portable applications: supply them via Ni-Cad or Ni-Mh or Carbon Zinc or Alkaline batteries. And shield the circuit with (ideally) tin plate.
For workbench-work with Pre-amp 2: make a mains power supply (50 Hz-60 Hz) that is absolutely free of hum. Some circuits of that ( made with 1 or 2 Transistors, Miller effect) are on my YT Channel.
My You Tube channel trailer is here: [ Ссылка ]_
Type there the keywords that you like (e.g. radio/audio/amplifiers/test/filter/) in the “looking glass” = search function” and give “enter”. Via that you can find specific video’s (under the say 1500 published).
When you search, search always “NEWEST FIRST” to get the right overview.
You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in.
My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there. [ Ссылка ]...
I keep all my YT videos constant actual, so the original video’s with the most recent information are always on YouTube. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. Upload 14 July 2024.
