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Looking for a good howto/schematic for an FM Radio

post #1 of 15
11/1/10 at 6:10pm
Thread Starter 

Well I have my collection of assorted audio goodies, but it seems I am forgetting about the good old reliable radio. FM that is. I know how to make an AM radio. I learned that in about the 3rd grade, however, I've never tried with FM.

 

I wanted to try to make a really simple and cheap FM Radio and then hook it up to a cheap LM386 amp and a cheap speaker. Total project cost: $10?

 

So, I've found one how to, but maybe other people have other experiences? (IE better sound quality, or optimization to the project in the link)

 

I don't quite get the variable capacitor thing...What value

 

http://www.somerset.net/arm/fm_only_one_transistor_radio.html

 

Thanks. 


Edited by TheLaw - 11/1/10 at 6:25pm
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post #2 of 15
11/4/10 at 11:17am

Why not just grab a older Sony clock radio from Goodwill or such?  Just recase it. 

 

The other option is to find an old mono tube FM radio on eBay, I have a Hallicrafters unit I'm using as a chassis for a special headphone amp.  The tuner uses about 5 tubes, but I have a boat load of them from old consoles.  A mono FM radio is far easier to do than a stereo radio too. 

 

 

The cap is variable, the RS one was 15-250pF and salvaged, but you would need to order the part number the other design provided for that design you linked to. 


Edited by BoilermakerFan - 11/4/10 at 11:23am
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post #3 of 15
11/4/10 at 11:57am
I'd also recommend picking up an old tubed FM radio and restoring it. The old radios are a lot of fun and you'll get great sound.
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post #4 of 15
11/4/10 at 4:39pm
Thread Starter 

Well I see where both of you are coming from but I am kind of interested in making my own, hence being in the DIY section. Well I'll still have to see. Thanks.

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post #5 of 15
11/4/10 at 4:47pm

Then find the schematic from a later model tube tuner and recreate it. Something like a Conrad-Johnson, Marantz, etc.  If you really want SS, then I love the tuner section in my '70s Yamaha CR-620 receiver.  You could have a sweet dial made at FPE...  Or make your own from a transparency and color laser printer. 

 

Salvage the variable tuning capacitor from a similar radio so that it will be easier to setup. 


Edited by BoilermakerFan - 11/4/10 at 4:49pm
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post #6 of 15
11/4/10 at 6:43pm

If you want schematics, you can order Sam's Photofacts for hundreds, if not thousands, of FM tuners.

 

Keep in mind that you'll probably spend a bit of time hunting down the correct tuning and variable air capacitors.

 

FM sets are also kinda picky about component placement.  Any time you do surgery on the old tube tuners, you have to spend a bit of time aligning them.  It's a little trickier than the AM units, as well.

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post #7 of 15
11/4/10 at 7:00pm
Thread Starter 

Yikes. It does sound tricky, but I don't mind a bit of a challenge. The variable cap is still something I am uncertain of so a bit of research I guess. Thanks to all.

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post #8 of 15
11/4/10 at 7:03pm

You can find some variable caps over at Nebraska Surplus.  If you have any Hamfests in the area (check www.arrl.org) you'll probably find some there, too.

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post #9 of 15
11/4/10 at 7:04pm
Thread Starter 

But in regards to the schematics. I am looking for something super simple. I don't care how it sounds. It'll be joined with an LM386 so we aren't going audiophile here.

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post #10 of 15
11/5/10 at 10:36am

I found several here, under the images tab

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post #11 of 15
11/5/10 at 10:57am

Ari, you crack me up man, good deed!

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post #12 of 15
11/5/10 at 12:03pm
Thread Starter 

Okay that's a bit more complex than I had hoped it would have been. Maybe some other time. But I am still surprised of the lack of results. Sure there are a lot of schematics but not a whole lot of people discussing how to make the,.

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post #13 of 15
11/5/10 at 12:05pm
Thread Starter 

Most of them want to use a TDA7000 which was around during the time of the dinosaurs. That doesn't really matter to me except the fact that TDA7000 availability is very limited. What other chip? Hmm...

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post #14 of 15
11/5/10 at 12:29pm

Because it's an old, established technology that doesn't really fail and the sound quality of most radio tuners and the corresponding stations today is mildly better than a 128kbs MP3 file.  The new technology is Hybrid Digital and those chips are patented and probably don't have single piece pricing yet. Careful shopping at a thrift store will yield all the parts you need to roll your own tuner. 

 

But my main point was to pick a schematic you like, or better yet, grab the old radio for the parts and make your own board, upgrade as you wish, and go from there, but a tube FM tuner is something else, and no SS setup will sound anywhere close.  The tubes are all over the place, I have hundreds of them.  Heck, if you want, I pulled the amp from my old Silvertone console.  I was going to redo the FM tuner and integrate it into a table radio alarm clock, but I now have a better FM tuner so it's just sitting on the shelf.  It uses 25xxx Spud tubes for the outputs through little OPTs that I plan to keep, but I'd be willing to part with the rest of the console sub-chassis.  It has a phono section and AM/FM radio.  You can take all the parts, pull them and recase them any way you wish.  That is DIY and reusing old bits. 

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post #15 of 15
11/5/10 at 12:38pm

Sent you a  PM...

 

What about buying a great tuner component, then spend the effort on a DIY antenna?  The best part about is that if you have favorite local stations, you can actually tune your antenna to boost those target frequencies for even better reception.   

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