Amplify Unpowered Mic

[amanisdude]

Hi all!

In keeping with my newbie status, I'm trying to do something somewhat dumb, but necessary. I need to broadcast a feed from an unpowered, unbalanced microphone via an FM transmitter (one of those devices that you plug into your MP3 player in the car to hear your music over the stereo).

Essentially, I need to cheaply and reliably broadcast whatever is being picked up by the microphone. I tried to hook the mic up to the transmitter directly using a coupler, and that obviously didn't work. Any ideas on how to do this without adding too much cost to the equation?


‒amanisdude
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EDIT: I should note that, if no cheap off-the-shelf options exist for this, I have no problem opening up and modifying devices that are not inherently designed for what I am doing. I've been gaining some good practice with a soldering iron recently.

 

[PRHunt]

Well, you are going to need amplification for the mic. Which mic will you use?

Very likely doable. Cheap? Maybe not so much.

What would be the budget?

Paul

 

[amanisdude]

Hey again, Paul.

I'll be using a 3.5mm Hands Free Computer Clip on Mini Lapel Microphone by Neewar. I suppose I can go as high as an extremely exuberant $10, but any higher may not be worth it. (Up to $20 might be okay, but that's the max.) If it is cheaper to actually build an amp or hack something from the dollar store, I'm open to that as well. Basically, as long as a good signal gets to the FM transmitter, I'm happy. Thanks for your help again!


‒amanisdude
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[Bobbsy]

You need what is known as a mic pre amp and I doubt you're ever going to find one for your budget. Maybe you should look through your junk cupboard and see if you can find something like an old cassette recorder or dictaphone that will let you plug in your mic then listen to the output on the line out.

I'm curious what you're trying to achieve though...those things that broadcast your MP3 player to a car radio typically only have a range of a few feet so it's unlikely the FM broadcast will go any farther than you could yell anyway.

 

[PRHunt]

I'm racking my brain. The mic in question will probably be an electret and would require a smallish DC bias voltage, but not phantom.

I wonder how much gain would be needed?

There's a little Velleman kit I found for about $10 which would provide 40dB gain. The kit needs power - 10V to 30V DC, 10ma. A regulated 12V or 15V DC wall wart should work. You'll need suitable connectors, and you could improvise a little box to enclose the board

The other issue will be powering the mic - information in that regard can be found here and here

You could tap off some voltage from the power supply for the mic bias.

Bottom line is: I can't say if this will work, and I'm not volunteering to experiment

Certainly there are better mic preamp kits - like this one - but price and complexity increase, as does the need for superior regulated split power supplies.

Paul

 

[amanisdude]

Haha, thanks Paul and Bobbsy.

Yeah, that final link by Paul is a bit out of my price range. ^_^" But I took a look at the Velleman kit, and it does look promising. I assume, though, that it needs some kind of external system in order to control the output gain (not to mention to plug in the mic), which may or may not be a problem if I can find or build such a system in an inexpensive manner. If that's within the realm of possibility on my budget, it might just work for my application (if I can find a seller with low shipping charges, that is ).

In terms of what I am actually doing, long story short, I'm trying to help webcast a wedding, and I need a "wireless" boom mic setup that will transmit the audio to a nearby camera rig (no more than 6‒8 feet away), which will pick up the signal, record it to tape, and re-transmit the audio (along with video from the camera) via a 900MHz transmitter to a base station, which will broadcast feed over the Internet. ^_^""

As far as the power supplies go, that should be no problem since the kit has to be mobile anyway, meaning the whole thing will be powered by battery. (8 D-size batteries is what I'm thinking, since the FM transmitter will be powered through a car's cigarette lighter DC plug wired to the battery with alligator clips. )

Anyway, the lowest price I've found for the Velleman has been Jameco, whose base price is $9.95 before shipping and tax. I'll look around some more and read up on the kit, but if it works, I'm all for it! Have you ever built/used one yourself, Paul? If so, was it sufficient for your application?


‒amanisdude

P.S. ‒ I did find a portable tape recorder, but it needs to have a cassette inserted and recording in order to test the audio (which probably won't be a problem since I need to record the audio anyway). But I haven't been able to test it out yet, and I'm not sure if it'll pass the mic signal to the headphones while recording. I'll give it a try and let you know. (Part of me is still leaning toward the Velleman, though, just because it's assembly required. )
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EDIT: Nevermind about the external system for the Velleman! I just noticed trimmer component RV1! Guess I wouldn't need any additional components except for a 3.5mm jack and some power leads.

 

[Bobbsy]

Thinking laterally, if you have a local audio hire company they'll probably rent you a "proper" radio mic (with a much more reliable range and better quality) for around $20 a day or so. It might save you a lot of bodging and headaches. Some would need mains power at the receiver but ones designed for TV use have battery receivers as well as transmitters.

Worth a look.

 

[PRHunt]

In terms of what I am actually doing, long story short, I'm trying to help webcast a wedding, and I need a "wireless" boom mic setup that will transmit the audio to a nearby camera rig (no more than 6‒8 feet away), which will pick up the signal, record it to tape, and re-transmit the audio (along with video from the camera) via a 900MHz transmitter to a base station, which will broadcast feed over the Internet. ^_^""

Ok.

As far as the power supplies go, that should be no problem since the kit has to be mobile anyway, meaning the whole thing will be powered by battery. (8 D-size batteries is what I'm thinking, since the FM transmitter will be powered through a car's cigarette lighter DC plug wired to the battery with alligator clips. )

Battery power should be fine.

Have you ever built/used one yourself, Paul? If so, was it sufficient for your application?

No I have not built this kit. I just did a quick search of kits, having a basic idea of what you wanted to do.

I have one of these ready to build. I'm guessing that might be a little outside your price range

The only other suggestion I can think of is hiring something. Are you doing this as a favour for someone - maybe they could just pay to hire a wireless mic set-up for the event? Anyway, you know your own circumstances. I do admire your ingenuity!

Paul

 

[Bobbsy]

Ok.
Anyway, you know your own circumstances. I do admire your ingenuity!

Paul

Yeah....it sound exactly the sort of thing I'd try to do myself...then get paranoid about spoiling the wedding and scramble to rent a radio mic at the last minute!

 

[amanisdude]

I have one of these ready to build. I'm guessing that might be a little outside your price range

Ha! That's definitely outside my range. Maybe after 5 years of saving, I might be a customer.

Yeah....it sound exactly the sort of thing I'd try to do myself...then get paranoid about spoiling the wedding and scramble to rent a radio mic at the last minute!

LOL. I'm actually feeling pretty good about this. I've done several tests, and there are only a few more "obstacles" to work out. Nevertheless, I'd learn far more from doing it myself then renting some equipment. If all goes well, who knows. I might even start an even webcasting company.

...But, ...just in case in case I'm wrong, at what kind of place would you rent that sort of equipment for only $20? I'm not sure how different things are in Australia (I'm in the States, San Francisco area), but I've never seen anyone rent anything for $20 around these parts, currency conversion or not. Nevertheless, I'll search around. Thanks for the suggestion.


‒amanisdude
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EDIT: I was wrong! I found this place in San Francisco that seems to rent out some top-notch audio gear. Looks like I found my Plan B (which might just transform into Plan A ). Thanks Bobbsy!

 

[Bobbsy]

Well, I was basing my price on what I used to spend in the UK where I could get a good wireless mic for £40 (about $60) for a week.

Funnily enough, I was just about to post a link to exactly that place in SF which was the first result on a Google search. That Sennheiser G2 lapel mic would likely be ideal for you...and I've used them hundreds of times and can vouch for the quality and reliability.

(Last stage musical I mixed in the UK I had to frequency coordinate and licence 22 of them at once!)

 

[PRHunt]

I've always thought this was a place full of solutions just waiting for the right problem to come along

 

[amanisdude]

Welp, I couldn't resist. The more I looked into that tiny Velleman module, the more it seemed perfect for my application, and since it was in my price range, I went ahead and ordered it!

Besides, even if I don't use it for this particular project, knowing me, I know it will come in handy down the road. Nice find, Paul!

Well, I was basing my price on what I used to spend in the UK where I could get a good wireless mic for £40 (about $60) for a week.

Funnily enough, I was just about to post a link to exactly that place in SF which was the first result on a Google search. That Sennheiser G2 lapel mic would likely be ideal for you...and I've used them hundreds of times and can vouch for the quality and reliability.

(Last stage musical I mixed in the UK I had to frequency coordinate and licence 22 of them at once!)

What can I say. I pre-googled you. The Sennheiser G2 is definitely a step up, but it's getting up there in cost. (Might I remind the class that I'm essentially broke?) At any rate, for the application, the Sennheiser ME 66 and boom would probably be more ideal, but it still doesn't resolve the wireless transmission problem.

Plus my brother just walked in with a karaoke machine, and my mind immediately went, "Ooh! Free mics!" so I'll be giving them a whirl, too.

And, good God! 22 wireless mics! I didn't even know that many channels existed on that band!

I've always thought this was a place full of solutions just waiting for the right problem to come along

Indeed it is! I don't know where I'd be without you guys! You certainly saved me a lot of hippocampal neurons.


‒amanisdude
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[PRHunt]

Indeed it is! I don't know where I'd be without you guys! You certainly saved me a lot of hippocampal neurons.

Good on ya! Onward and upward! You can't be too careful with your hippocampal neurons, cerebellar neurons or corpus callosum... gad, there's a whole CNS full of precious stuff!

Anyway, go and get all your bits together, and feed back some progress updates.

Paul

 

[Bobbsy]

If my hippocampal neurons can survive a bottle of Bundy a bit of FM theory ain't gonna hurt them!

 

[amanisdude]

Good on ya! Onward and upward! You can't be too careful with your hippocampal neurons, cerebellar neurons or corpus callosum... gad, there's a whole CNS full of precious stuff!

Can't argue with that! I'm sure I've had my share of damage to that system already.

Anyway, go and get all your bits together, and feed back some progress updates.

Paul

Will definitely do! Right now I'm just waiting for my order to ship and arrive. I'll let you guys know if it actually works.

If my hippocampal neurons can survive a bottle of Bundy a bit of FM theory ain't gonna hurt them!

Haha, very true! But I'm sure as the wedding day approaches, my brain will be awash in neurotoxic hydrocortisone. Your guys' continued help has staved off this process for several weeks, I'm sure.


‒amanisdude
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