Ok, got rid of the breadboard and built on a piece of cardboard instead using the original circuit diagram from the original post except that I replaced the R3 1K resistor with a 180Ω since I do not have a high impedance earphone (text on the root page said to do this for regular headphones or a small speaker).

The result is, I can hear stuff! A good start. I have 2 problems though. First is that it sounds like I can only get 1 station with any kind of clarity enough to actually tell I'm hearing something. The second problem is that the darn thing just isn't loud enough. I mean, it's just a test circuit so I'm not expecting to fill the room with sound, but I have to put the speaker against my ear to hear it, and even still it's very hard to make it out. That in turn makes it difficult to tell what kind of station I'm getting and if I'm getting more than one.

I have a couple NTE48 general purpose amp NPN Darlington transistors that I picked up for that "totally bogus" 1W audio amplifier circuit. I wonder if someone can help me use one of those to boost the audio a bit so I don't have to make a trip to the parts store? The NTE48 Datasheet doesn't provide any example circuits like some do so I'm really not sure how to use it.

I thank all of you who have helped me to this point. It's clear the breadboard was the problem up to this point, now that I'm not using it, I can see progress and that's exciting so thanks again. Here are pics of the new build on the cardboard.

 

Do you have any op amps? You can use them with the transistor for something with a bit more juice. A 741 won't work, but older op amps might work, thought the sound would suck.

If you have two transistors of opposite polarities even better. Complementary transistors are even better still, but not absolutely necessary.

I see a 9V battery clip, so that is what I assume you are using.

Or we could go with simple transistors all the way, but the resistor count goes way up.

This is purely preliminary, and it isn't the best. There will be crossover distortion since I am using minimum parts. R3 is to set maximum gain, it could be eliminated if you want but you have to not use the entire range.

There are many other better designs out there. Let me know what parts you have.

 

I have 2 of the NTE48 transistors, and a handful of the more common NPN type 49XX can't remember the other numbers off the top of my head. I am using 9V battery right now, but I can easily use the 12V power supply (actually 13.6V) with a 9V voltage regulator (got plenty of those). No problem there. OP-AMPS I don't have.

 

The design you showed earlier could be modified a bit. Most decent transistor amps use at least 3 transistors. This won't be that good.

I need to look up the other numbers. Have you done a search for any other designs. What are your 3 most common resistors?

 

One last thought before I go to bed for a nap. You could try your design to see how well (or badly) it works.

 

An explanation about why your "radio" works poorly are described with two words in the article:
Low-tech and Simple.
The extremely simple circuit is nothing like a real radio that is usually a super-heterodyne with many stages for good sensitivity and good selectivity.

 

What are your 3 most common resistors?

In my parts box or on the radio? If you're asking about the parts box, I pretty much have the spectrum covered from 0 up to 1MΩ. I have resistors coming out my ears, nose, and mouth.

Here's what I've got in the transistor box:

11x 2N3904 NPN transistors
4x FQP13N10L N-Channel Logic Level MOSFETs
1 NTE2987 N-Channel Logic Level MOSFET
2x 2N5190 NPN Power Transistors
10x TIP50 NPN Switching Transistors

That's what I've got on hand, in addition to the 2 NTE48 General Purpose Amp transistors I mentioned earlier. I picked up a lot of those parts for switching applications as you can see, most of them are meant for that. I suppose if none of those would really work, I could make a trip to Tanner's to pick up a couple parts on my way to work one of these days next week.

The extremely simple circuit is nothing like a real radio that is usually a super-heterodyne with many stages for good sensitivity and good selectivity.

This I understand. This is just a first "experiment" with RF circuits. I'm already learning quite a bit, and it's kind of neat to see what happens to the signal when I get my hand around the L1 RF coil while the radio is on. I did a search for a Superhet radio on google and came across THIS. This looks neat! Click on the link that says "if you want to see how well it works here". It's a WMV video of the radio, pretty impressive for home built, and even on a breadboard it looks. Wouldn't mind trying that one too! What do you think of the schematic?

 

The Super-Het FM radio is a typical "simple" design. Its input is not tuned and does not have AGC so its input transistor will be severely overloaded by strong local stations.

My cheap Sony Walkman radio has a similar circuit and the severe overloading problem (one strong station is all across the dial) so it has a local-distance switch that attenuates signals so that strong local stations do not cause overloading (but then it does not pickup distant stations).
My home stereo and car radio have tuned inputs and AGC so that they pickup distant stations even with many strong local stations nearby.

Modern FM radios (for the last 30 years) use very high quality and inexpensive crystal filters to replace old IF transformers. They use a quadrature detector instead of a ratio-detector or instead of a Foster-Seeley discriminator detector.

 

Now AG, we can't all use tubes like you did when we started.

It is also how a lot of people started. Look at his parts count, our OP has a very simple circuit that works using 2 transistors. I suspect you would want everyone to start with superheterodyne, face it, it is not a beginners circuit. This is, just like a crystal radio (which I started with when I was new). I also build a circuit a lot like his while I was in college.

The the OP, have you tried it with a commercial FM radio next to it yet?

I looked up a simple transistor audio that looks promising...

http://www.colorado.edu/physics/phys3330/PDF/Experiment7.pdf

Again, I'm sure there is better, but this will will work using a protoboard.

How about it AudioGuru? You are bound to have better in your library.

 

Here is another one...

http://www.circuit-finder.com/categ...ifier/588/3-transistor-audio-amp-50-milliwatt

This actually came from Bill Bowden's site, one of my favorites, but it is also in a collection.

http://www.circuit-finder.com/

http://www.bowdenshobbycircuits.info/

 

Good finds Bill, considering how low his output is I was thinking the 2N3904 might be a good start and it certainly doesn't need to be as complicated as that to work. His output is referenced to ground, has no DC on it and exhibits around a 1K output impedance.

As simple as he's wanting at the moment (just to up the volume a little) how about using a 3904 in a common emitter class A config and driving an 8 ohm speaker through a resistor to limit the current from the 9V source?

 

Super-regen and crystal "radios" were used 100 years ago when there were only 2 radio stations in town. Now there are hundreds of radio stations so the radios today must have fgood sensitivity and good selectivity.

A single transistor with its gain at max with no negative feedback has severe distortion when the output level is fairly high. The emitter-follower output transistor has nothing to do with it. The transconductance of a transistor is simply very nonlinear.
An opamp would have distortion so low that you would have trouble measuring any.

Here is your transistor circuit with an input that is 30mV peak and its gain control at max. Its output is so distorted (40% distortion?) that the gain is impossible to measure. The voltage gain is about 180 when measured with a lower input level. Note that there is no load.

This horrible amplifier cannot drive a speaker and cannot drive most headphones.

 

You seem to miss the point of projects for beginners. Small parts counts count, as does simplicity. Maybe you were a uber genius with electronics as a kid, but most of us build from the ground up.

Thanks for the analysis, do you have anything comparable in simplicity that will do better? Serious question, after radios amps are the next most sought after schematic for beginners.

 

Good finds Bill, considering how low his output is I was thinking the 2N3904 might be a good start and it certainly doesn't need to be as complicated as that to work. His output is referenced to ground, has no DC on it and exhibits around a 1K output impedance.

As simple as he's wanting at the moment (just to up the volume a little) how about using a 3904 in a common emitter class A config and driving an 8 ohm speaker through a resistor to limit the current from the 9V source?

Are you wanting to add another transistor amplifier to the circuit in Post #20?

I liked the design because of the push pull configuration, which all other designs lacked.

the one shown on post #1 is pretty bad, it has a lot of gain but the distortion will be atrocious, and with a 50Ω resistor in series with the speaker there is no way it is a 1W amp (unless you count the power consumed).

 

You seem to miss the point of projects for beginners. Small parts counts count, as does simplicity. Maybe you were a uber genius with electronics as a kid, but most of us build from the ground up.

I liked FM radio sound when I was 17. I didn't want cheap crap that barely works.
So I built an Eico FM tuner kit. It used vacuum tubes and worked perfectly. When FM stereo was invented I built a kit vacuum tube stereo multiplex adapter for it. Then I built a Heathkit vacuum tube amplifier for it. My very old oscilloscope is a Heathkit and still works perfectly today.
What happened to good kits?

The very old super-regen FM "radio" project has the "super" oscillation (30kHz) smack in the middle of the stereo sidebands frequencies so the interference whistles must be horrible. Unless you live in the olden days before FM stereo. But hey, it is very simple.

 

Which is exactly the point. Heathkit isn't very available nowdays, we have to use web schematics, which aren't very reliable either. Personally I liked Heathkit, but I didn't buy too much from them. I just sat and looked at their catalogs for hours.

I understand the core company still exists, but they are out of the kit business. Nowdays it is Ramsey who sells kits, a poor second to Heathkit any day.

 

Just a simple one transistor amp that will boost the output so he can hear what's being received, at the present he may not even be sure if it's the commercial FM band. If you note from his list he has little to work with.

 

Bill, I like the schematic in your post# 30 reply, looks simple. I think I might have all the parts I need for the one that uses the 2N3904, but it shows an input of 15V. I don't really have anything to produce 15V, can I use 12? As suspected, it's sole purpose is to hear what I'm getting on this little receiver. I'm not intending on hooking this thing up in my house for a central entertainment center, IT'S SIMPLY EDUCATIONAL! I'll go to something more complicated when I've had my fill of this one, it's just step 1.
I'll need to stop and grab a part or two next time I'm near the parts store, but that's ok... I probably need more stuff anyways (always do).

What happened to good kits?

The market for them died when kids stopped giving a crap. They have computers and video games now, who needs to tinker with electronics? It's sad but it's true. That's why kids don't play outside anymore. Yes, Ramsey has radio kits but they're already designed and tested and don't offer nearly the educational value that starting at the bottom and building your way up does. Especially when you think about how much easier it is to strip out a few parts to add new ones or build up a simple design on something like cardboard or protoboard as opposed to a PCB that you'd get in a Ramsey kit.

 

can I use 12?

Probably so, but you might want to reduce the 2.74K down to 2.2K and the 820 ohm down to around 620. Just rough guesses though.

 

#30 is the 9V version, so I suspect you are talking post #29. Distortion goes down as number of transistors goes up, and if you look close at #30 there is a feedback loop incorporated.

However, I do understand what you are after. Let us know how it works.

You would do yourself a favor getting a small number of parts, such as a TL072, a JR6545, and a LM386 (total cost of all less than $2) next time you visit Tanner's. Op amps are an experimenters godsend, making everything from active filters to audio amps to super simple voltage regulators, both digital and analog. You could add a LM393 and a LM339 for another $1. Any one of the first three parts would have made are really good audio amp with relatively low distortion, for example.

We really are lucky having a stores like Tanner's, AllTex, and BG Micro within easy driving distance.

BG Micro is selling 1000 PN2222A transistors for $12.95, P/N TRN1001. This works out to 1.3¢/transistor. I like 2N2222s, this is their plastic version.

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OMG! I can't believe I left out 555s!