trouble finding/designing electret amp circuit with AGC, wihtout fets

[fezder]

I can find simple 100x amplifier circuits for electret mikrophone, but can't find/design any amplifier circuit that would have AGC (low noises are amplfied much, but high-volume noises are compressed so output doesn't clip if there is too loud sound)
Adafruit sells breakout board that has AGC, but i see it quite expensive as there is shipping costs too.
so, this is basic electret amp i use currently
https://www.sparkfun.com/datasheets/BreakoutBoards/Amplified-Mic-Electret-v14.pdf
Why i'd like to have AGC is jut for in case and learning on the way
and i don't have any suitable fets, only irf 540's so that's why i'm looking for one that uses transistors instead.
I do know that AGC does something in opamps feedback, probadly in negative input of opamp
Thanks!

 

[Tony Stewart]

The MAX9814 chip used in Adafruit's board is perhaps the best low cost choice with full featured AGC chip. But crude AGC can be done with diodes low noise Op Amps or OTA's. https://www.maximintegrated.com/en/products/analog/audio/MAX9814.html

 

[fezder]

Too bad that MAX9814 doesn't excist as DIP or SOIC package, then again, considering how ''often'' i need microphone amplifier, might be worth that price. Of course i'll buy much more than just one breakout board there....What is OTA?

 

[Tony Stewart]

Learning to make small PCA's will be very good to you.

These chips can be soldered with solder paste using a syringe and a hotplate/or toaster oven with DIY help guides.

 

[fezder]

Learning to make small PCA's will be very good to you.

i agree, more and more stuff come in small packages, it's like putting money to bank to learn solder tiny packages.
Currently i have only 0.3mm iron and hot-air station, haven't bought/made pots yet

 

[Tony Stewart]

With the right solder-flux a preheated toaster oven can be used, or a hotplate and hot air nozzle with a syringe bead of solder along the pads and a good soldermask.

 

[audioguru]

Years ago, Philips made "compandor" ICs that compressed or expanded audio.

 

[KeepItSimpleStupid]

proto-advantage is now making some power pad adapters. See https://www.proto-advantage.com/store/product_info.php?products_id=3100193

They usually have stencils and full kits available too. If there's a Digi-Key p/n for the part you want, you can get them already soldered.

Finding one means to carefully look at the dimensions.

==

OTA = Operational Transconductance Amplifer. See LM3900 or Norton Amplifier.

 

[fezder]

Hmm, yeah i've ordered once from proto, suppose i could use their services again. Bought some FPC adapter, which is still unused...

 

[Les Jones]

I have seen design for agc circuits using an LED and LDR as the gain control part. I have not tried this myself. I Googled "audio agc using ldr" and found this design https://www.electro-tech-online.com/threads/automatic-television-volume-limiter.96341/
You probably have components in stock to try this method.

Les.

 

[fezder]

Hmm, might be worth shot, i do have LDR's and normal leds, didn't knew that ldr work with led's,. Argh, that circuit needs dual-supply it seems, then again there is split supply circuit too in there

 

[ronsimpson]

Look at the SSM2167. It includes everything for $1.34 at DigiKey.com

 

[fezder]

thanks ron! although it's SMD package, that one can be hand-soldered
I suppose with that ic, input is where of course mic is connected, but all needed in input is bias-resistor, like in normal mic-amp circuits?

 

[Nigel Goodwin]

Why are you actually wanting AGC?, in the VAST majority of mike applications it's not wanted, and is positively a very poor idea.

 

[fezder]

Well, i figured that if i someday need that, i'd know what possibilities there are. currently i don't have application needing AGC, but this was merely to know-how. Of course, when that need rises, technology can be much farther than nowadays and need to look other alternatives...

 

[Nigel Goodwin]

Well, i figured that if i someday need that, i'd know what possibilities there are. currently i don't have application needing AGC, but this was merely to know-how. Of course, when that need rises, technology can be much farther than nowadays and need to look other alternatives...

Just wasting your time then?

By the time, if ever, that you want AGC, any current solutions are likely to be LONG obsolete

 

[fezder]

well, in fact i do have project perhaps involving AGC, that led-cube i'm working on, i'm planning it to react surrounding noises and that might need AGC, not sure. Should compare behaviour with and without AGC to see which behaves better

 

[audioguru]

Some people like hearing the slow attack of the compressor on radio and TV stations. BLAST then the sound drops to normal level. Or the background music level pumping up and down with the beat of the music.

 

[Nigel Goodwin]

well, in fact i do have project perhaps involving AGC, that led-cube i'm working on, i'm planning it to react surrounding noises and that might need AGC, not sure. Should compare behaviour with and without AGC to see which behaves better

Here's a simple (and pretty common) circuit to play with.

**broken link removed**

 

[fezder]

Thanks nigel, gotta test that circuit, seems easy. AG, good point, i'll test with and without to see. I just recalled that your circuit which had AGC.