microphone pre amp circuit - Page 1
Forum section: electronics / beginners

author: Flump
author_rank: Frequent Contributor
timestamp: September 12, 2013, 09:22:03 am
content: Hi AllI need to make a mic preamplifier to go between a ham radio and a dynamic (not condensor or electret) unamplified mic.I found this diagram on the web and also found it on a youtube video by hackaweek and he says on there you canremove R1 if not using an electret mic but wouldnt that feed the supply voltage directly into the mic element ?Also i would like to add a gain control, where would the best place for it be and would it be in seriesor taking the signal down to ground ?And lastly would i be better off using an op am than a transistor amp ?here is the diagramhttp://192.254.181.54/audio?page=50

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 12, 2013, 09:35:53 am
content: Hi , I'm also a Ham Radio operator , it would hurt you to look at this by Alan W2AEW, who is also on here, I use this circuit with my Kenwood TS820, and always get good audio reports

author: Flump
author_rank: Frequent Contributor
timestamp: September 12, 2013, 09:45:21 am
content: That's way too complicated for what I need at the moment, a project for later I thinkRight now i just need to increase the gain of he mic as you have to be right up close to itand its a desk mic.

author: ConKbot
author_rank: Super Contributor
timestamp: September 12, 2013, 04:30:50 pm
content: Quote from: Flump on September 12, 2013, 09:22:03 amRemove R1, not replace it with a shortQuote from: Flump on September 12, 2013, 09:22:03 amDo it after your amplifier, with a log-taper pot, rather than varying the gain.Quote from: Flump on September 12, 2013, 09:22:03 amDefine better. Find an opamp with a 300 MHz GBW product for $0.15Though you only need about 20MHz of that to get from 1.5mV, to 1.5v at 20khz bandwidth. (though I suspect you wont need that much for your radio)Either way I suspect the simple class A amp will suffice as long as your mic isnt too far away from the preamp. (with the circuit ground referenced the way it is the common-mode rejection of the mic wont be great)

author: Flump
author_rank: Frequent Contributor
timestamp: September 13, 2013, 03:00:44 am
content: Thanks very much ConKbot O0Never heard of log-taper pots before so will do some research on themill try in series and taking it down to ground to see which works best.I wondered weather an opamp might be more suitable in regards togain and frequency response.This is all new to me some I am learning as I go along.

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2013, 04:55:30 am
content: Log taper pots are generally marked as a B taper, they generally are used as volume controls. The linear ones are either marked A, L or no marking.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 13, 2013, 07:42:11 am
content: Quote from: SeanB on September 13, 2013, 04:55:30 amBack in the day,log pots in Australia were labelled "C" curve.I'm not sure if this was just an Oz thing,or not.The first one marked "B" that I saw were Japanese,so maybe they chose "B" & other countries changed to avoid confusion.

author: Zero999
author_rank: Super Contributor
timestamp: September 13, 2013, 01:20:56 pm
content: How about the LM386? I know it's more of a power amplifier but it might do what you want.

author: Flump
author_rank: Frequent Contributor
timestamp: September 30, 2013, 11:06:34 am
content: Update on thisI built the above circuit and it works very very well as a pre ampfor a ham radio, there was some issues with rf getting in to the ampbut a small ceramic across the output and Gnd cured that so im well happy.Next stageI want to add treble and bass controls to the amp and i found a passive circuit to do thatbut dont know which order to have them amp into tone OR tone into amp ?which would be best and why ?amphttp://www.electroniq.net/audio?page=50tonehttp://www.electronicecircuits.com/electronic-circuits/bass-treble-tone-control-circuitthanks in advance i love learning about electronics O0

author: w2aew
author_rank: Super Contributor
timestamp: September 30, 2013, 01:32:49 pm
content: The tone control circuit is basically the same one that I used in the D-104 preamp that I did. The video is shown above.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: September 30, 2013, 05:15:52 pm
content: Something else to look at.Dynamic microphone preamp circuit diagramhttp://www.electroschematics.com/506/dynamic-mic-preamplifier/

author: Flump
author_rank: Frequent Contributor
timestamp: October 01, 2013, 09:51:36 am
content: Thanks for the link Crazy ApeThats a cool websitelots of interesting stuff on it