microphone pre amp circuit

[Flump]

Hi All

I 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 can
remove 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 series
or taking the signal down to ground ?

And lastly would i be better off using an op am than a transistor amp ?


here is the diagram
http://192.254.181.54/audio?page=50

[M0BSW]

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    

[Flump]

That's way too complicated for what I need at the moment, a project for later I think


Right now i just need to increase the gain of he mic as you have to be right up close to it
and its a desk mic.

[ConKbot]

you can remove R1 if not using an electret mic but wouldnt that feed the supply voltage directly into the mic element ?

Remove R1, not replace it with a short

Also i would like to add a gain control, where would the best place for it be and would it be in series
or taking the signal down to ground ?

Do it after your amplifier, with a log-taper pot, rather than varying the gain.

And lastly would i be better off using an op am than a transistor amp ?

Define better. Find an opamp with a 300 MHz GBW product for $0.15    Though 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)

[Flump]

Thanks very much ConKbot    O0

Never heard of log-taper pots before so will do some research on them
ill 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 to
gain and frequency response.

This is all new to me some I am learning as I go along.

[SeanB]

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.

[vk6zgo]

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.

Back 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.

[Zero999]

How about the LM386? I know it's more of a power amplifier but it might do what you want.

[Flump]

Update on this

I built the above circuit and it works very very well as a pre amp
for a ham radio, there was some issues with rf getting in to the amp
but a small ceramic across the output and Gnd cured that so im well happy.

Next stage

I want to add treble and bass controls to the amp and i found a passive circuit to do that
but dont know which order to have them amp into tone OR tone into amp ?

which would be best and why ?

amp
http://www.electroniq.net/audio?page=50

tone
http://www.electronicecircuits.com/electronic-circuits/bass-treble-tone-control-circuit


thanks in advance i love learning about electronics  O0

[w2aew]

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. 

[Crazy Ape]

Something else to look at.
Dynamic microphone preamp circuit diagram
http://www.electroschematics.com/506/dynamic-mic-preamplifier/

[Flump]

Thanks for the link Crazy Ape

Thats a cool website
lots of interesting stuff on it