Amplifier for very low voltage signal? - Page 1
Forum section: electronics / beginners

author: Psburg
author_rank: Newbie
timestamp: September 16, 2020, 06:28:06 pm
content: I am trying to build this tunnel diode noise generator, and wondering what to use as an amplifier?Running the circuit just with a 1.5v AA and a 10k pot I had (the noise is generated by running the diode under it's peak Vp Ip, in this case 0.18v)

author: ledtester
author_rank: Super Contributor
timestamp: September 16, 2020, 06:39:11 pm
content: This video series has some good info:https://youtu.be/Xn9LNgVKdqI

author: madires
author_rank: Super Contributor
timestamp: September 16, 2020, 06:52:11 pm
content: Multiple OPamp stages with low gain for maximum bandwidth, for example.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 16, 2020, 06:56:46 pm
content: Quote from: ledtester on September 16, 2020, 06:39:11 pmnot much you can do with just 1.5V AA running opamps... for that purpose he probably need an RF MMIC (not aware anything that can be run from 1.5V) or if the frequency is low, he maybe can just build from 2 jellybeans transistors similar to MMIC or simply common emiter NPN if he aimed for maximum swing discounting distortion.

author: ledtester
author_rank: Super Contributor
timestamp: September 16, 2020, 07:00:36 pm
content: Yeah - the videos are more about measuring the signal. Probably need to know more about the intended application and what kind of amplification is needed.

author: Psburg
author_rank: Newbie
timestamp: September 16, 2020, 09:24:22 pm
content: Thank you for the replies, not looking for much amplification, at least enough to hear it on a piezo earpiece or 8ohm speaker.

author: magic
author_rank: Super Contributor
timestamp: September 17, 2020, 06:17:53 am
content: Driving 8Ω speakers from a single AA battery may prove difficult.For crystal earpieces, maybe something like that? They say it workshttp://www.techlib.com/electronics/crystal.html#onetransistorYou are interested in the part between the 1µF capacitors. Maybe even 100nF would suffice (it's mainly about bass response).For 1V operation, reduce 100k to 10k and 10Meg to 100k.I would use even smaller transistors like 2N3904 or BC547 or similar 2SC stuff. It helps to have high beta at low collector current.One such stage will have some20~30x gain, depending mainly on battery voltage. Two or more may be needed.Nope, a bit under 10x gain. Oh well, add more stages. Or increase the base resistor to 220k or 330k. It will never have more than 30x gain, though.No idea how much noise your diode generates and the amp may prove to make more by itself. Maybe you don't even need the diode

author: David Hess
author_rank: Super Contributor
timestamp: September 18, 2020, 05:47:21 am
content: Up to 5 MHz or even higher, current feedback operational amplifiers with a gain of 100 per stage, 20 dB, are feasible. For RF applications, shunt feedback transistor stages, like RF MMIC amplifiers, would be suitable.That schematic is probably intended for an RF application because that many stages would oscillate due to feedback from the output to input and through the power supply if the gain per stage was very high.