Hi All.I'm looking for a very low noise amp chip, about 1 watt is all I need. I have used the LM386 (crap) and the TDA2822, more satisfactory, but I need to get rid of more of the white noise/hiss. Any ideas on a more suitable chip, or components to help aleviate the problem. Many thanks, Rob Melbourne, Australia.
The input is from an electret microphone. I used a circuit which used the LM386 chip, which had a settable gain of 20 or 200, using a resister or trimpot across pins 1 and 8 or 1 and 4 (can't remember exactly). The amplification was great, but the noise level is too high for my purpose.
Voltage is from a 9V battery into a 408Mhz radio transmitter. then another unit from a 408Mhz receiver to another amp. I used an LM386 circuit for both amps, but the noise level was too high. The TDA 2822 improved things a bit, but still not ideal.
You need a proper pre-amp stage bewtween the mic and the power amp.
There are a few op-amps designed for lowish noise audio work that would be perfectly fine for such a stage and inexpensive too. I won't suggest any particular one since the best tend not to be happy with low voltage supply rails and you haven't given that nugget of info away yet.
Can you work out a decent pre-amp stage for yourself btw ? Things like avoiding using inverting configuration and using large value resistors.
Are you sure you need the high current output capability of the LM386 to drive these loads? An ordinary, but much lower noise opamp may do just fine, with less supply current and just a couple extra parts.
Hi to Pooh Bear and John P Thanks for your ping pong replies to the group. I am finding them very entertaining. As for the infor I'm looking for, maybe I should give you a brief insite into what I know about electronics design: Not much - That's about it. I used to make kits as a kid and watched my dad in the workshop (He was an electronics technician).
Here is what I needed. I had an idea for a university project which required me to amplify minute sounds and transmit them wirelessly. This is to be a wireless stethoscope. I needed to provide some gain prior to inputting into an analogue radio transmitter. Using the LM386 was the only way I knew how and had the simplest circuitry. (John, I think you nailed it in your comment:
Quote: "You should ask him. ;-) My guess is that it was the only way he knew to make a times 200 gain block. If so, he has a pleasant surprise in store."
I have since designed but not yet implemented a 2N3904 with a couple of resisters and caps, which may improve things as suggested by Pooh Bear. The other thing was whether I needed a power amp at all, also suggested by Pooh Bear. But at that stage you didn't know what the exact aplication was. The above information may now shed some light.
So, that's where I'm at. This project is proof of concept only for me, and thus far I'm proud of myself for getting it to work, even at this stage. (Even tough you may think I'm an uneducated electronics idiot. And you may be right). All my recent electronics education has been don'e with library books and the internet.
I do however thank you both for your replied and will watch for any other posts.
Many Thanks in advance, Rob (Fonz) Melbourne, Australia.
PS: The Fonz is a shorteneing of my actual surname, and not because I think of myself as anything similar to the Happy Days Icon.
I think it is time for you to go over the basics of opamps as a universal gain block. After you understand how to use a few resistors to program any opamp for any gain and input impedance, we can help you pick a particular one that suits your supply voltage, output current requirement, frequency range, noise, etc.