Shoe Box Radio Upgrade, cool ideas wanted

[audioguru]

Don't forget watts. Big speakers pull more watts.

No.
Big speakers can survive more Watts.

An 8 ohm tiny speaker and an 8 ohm huge speaker both use exactly the same amount of power from an amplifier. The amplifier provides a voltage signal. The amount of power "pulled" is the voltage squared divided by the speaker impedance. Speaker size is not in the equation.

The huge speaker will probably produce more sound level from the same amount of amplifier power that feeds the tiny speaker because a big speaker is more sensitive due to its big cone moving more air than the tiny speaker.

 

[Dragon Tamer]

For the amplifier in the buffer amplifier I was going to use an LM386. The amplifier on the board already is the Sanyo amplifier.
I thought that the inputs may be wrong on the VU meter, thanks for clearing that mess up.

 

[audioguru]

For the amplifier in the buffer amplifier I was going to use an LM386.

It has a flea power output. People use it to drive headphones. With a 9V supply its output at clipping into 8 ohms is only 0.45W.

 

[Space Varmint]

For the amplifier in the buffer amplifier I was going to use an LM386. The amplifier on the board already is the Sanyo amplifier.
I thought that the inputs may be wrong on the VU meter, thanks for clearing that mess up.

No don't use a '386 as a buffer. It might make a good driver if you want a more powerful amp on the output. Use a common collector amplifier as a buffer of a Darlington pair is even better.

 

[Dragon Tamer]

As long as we're at it, I thought that I might throw a wrentch into the works here; I stumbled across this circuit and was wondering if it was legit or just another load of BS.
**broken link removed**

 

[audioguru]

Here is a better way described in the datasheet to get much more gain (and distortion and hiss) and reduced high frequencies out of an LM386:
**broken link removed**

 

[Dragon Tamer]

I am going to go home and make that! I've got a LM386 amp in a card box set to 200 gain and this would be so much better!!!

 

[Space Varmint]

As long as we're at it, I thought that I might throw a wrentch into the works here; I stumbled across this circuit and was wondering if it was legit or just another load of BS.
**broken link removed**

Yeah that should work fine.

 

[audioguru]

I am going to go home and make that! I've got a LM386 amp in a card box set to 200 gain and this would be so much better!!!

It has a high amount of gain but its max output before distortion is the same as before (only 0.45W).
The high gain amplifies its own hiss 5 times more.
The distortion is increased 5 times more.
The reduced bandwidth is to about only 4kHz now like a telephone or AM radio.
The original amplifier with a gain of 200 already had too much gain and now it will be 5 times more.

 

[Dragon Tamer]

Makes sense, although it surprises me that nobody picked up on the recuring trend (I have a thing with boxes). I also had another idea for the box, add a clock! Space Varmint showed me a really nice schematic for a pic clock, the problem is... it's just a little over my head. So I was thinking of taking an old alarm clock an completely gutting it and rebuilding the circuit so that it's a "learning experience". ( LOL) This way I can have the clock run off of the battery when the box is not pluged in (which it may be for an extended period of time, posibly months)

 

[Space Varmint]

Hey, well Dragon Tamer. If you want some help with the clock, just feel free to ask. Oh by the way. I just happened to be looking into or actually designing a regenerative receiver. I just want to get a handle on the concept. But this type of radio would do nicely in the shoe box because they a very simplistic in their design and therefore require just a very few parts. Its a good candidate for battery operation due to the low part count.

 

[audioguru]

A super-regen "radio" overloads easily by strong local stations.
Its bandwidth is either too wide or too narrow since it has only a single tuned LC instead of many LCs and crystal filters in a real radio.
It squegs at an ultrasonic frequency that beats with the 19kHz pilot of an FM stereo radio station and beats with the 23kHz to 53kHz stereo subcarrier. Its squegging oscillaton also beats with 67kHz SCA restaurant music and digital identification subcarriers. The beats are a hum, a squeal or both.

It has an AM detector that receives very distorted FM by tuning to one side of an FM signal and letting it slope-detect. Since it is an AM detector then it picks up all kinds of interference.

It causes interference to other radios since it oscillates at the frequency it is receiving.

 

[Space Varmint]

A super-regen "radio" overloads easily by strong local stations.
Its bandwidth is either too wide or too narrow since it has only a single tuned LC instead of many LCs and crystal filters in a real radio.
It squegs at an ultrasonic frequency that beats with the 19kHz pilot of an FM stereo radio station and beats with the 23kHz to 53kHz stereo subcarrier. Its squegging oscillaton also beats with 67kHz SCA restaurant music and digital identification subcarriers. The beats are a hum, a squeal or both.

It has an AM detector that receives very distorted FM by tuning to one side of an FM signal and letting it slope-detect. Since it is an AM detector then it picks up all kinds of interference.

It causes interference to other radios since it oscillates at the frequency it is receiving.

Well, if I put a Foster Seeley discriminator in it, it should receive a good FM signal. The other draw backs just need to be dealt with appropriately. I am impressed that it does have such a high degree of selectivity with no crystal filter. This I must see! Much of what youy are talking about can be altered by the amount of feedback used. What is also impressive is that by leaving a certain amount of feedback it can receive SSB & CW. This is amazing! It would also appear that no tuning of a BFO is required or no offset crystals for upper & lower sideband.

 

[Roff]

Regenerative and superregenerative receivers are two totally different breeds.

 

[Space Varmint]

Regenerative and superregenerative receivers are two totally different breeds.

In deed they are. I'm having fun with this one. Right now I got it on the short-wave band. It has 3 transistors and an LM386 to drive the head phones. It's working pretty good but that feedback adjustment is kinda touchy. I might try some rf AGC on it to help keep it in it's window of operation. Do not want too many active devices because I want the power consumtion to be low. I went to Walmart and bought one of those outside night lights that run on solar for 3 bucks. I want to gut it out and use the parts for the power.

 

[audioguru]

A super-regen radio automatically sets its RF positive feedback to the point of barely oscillating in waves so the gain is very high and the bandwidth at -3dB is very narrow. Since there is only a single tuned circuit then the bandwidth further down the slopes is pretty wide which might cause multiple stations to be heard at the same time. The waves of feedback occur at an ultrasonic rate.

A solar night light uses a voltage stepup circuit similar to a "joule-thief". It draws about 40mA from a solar-charged 1.2V Ni-Cad cell and has an output that is 10mA at 3.2V.

Here is a simple project:

 

[Space Varmint]

A super-regen radio automatically sets its RF positive feedback to the point of barely oscillating in waves so the gain is very high and the bandwidth at -3dB is very narrow. Since there is only a single tuned circuit then the bandwidth further down the slopes is pretty wide which might cause multiple stations to be heard at the same time. The waves of feedback occur at an ultrasonic rate.

A solar night light uses a voltage stepup circuit similar to a "joule-thief". It draws about 40mA from a solar-charged 1.2V Ni-Cad cell and has an output that is 10mA at 3.2V.

Here is a simple project:

Thanks Audioguru! So it has rf AGC? I was just getting ready to put mine in.

 

[audioguru]

A super-regen has a RF oscillator that turns on and off. Its positive feedback causes its gain to increase until it begins oscillating then a capacitor charges and cuts it off so its oscillation stops, then it builds up its gain again and oscillates again and stops again. It does not have AGC so it is overloaded easily by a strong local station.
It probably will not work if it has AGC unless the AGC is applied to another RF amplifier at its input. But then how would you detect the signal strength to control the AGC?

 

[Space Varmint]

A super-regen has a RF oscillator that turns on and off. Its positive feedback causes its gain to increase until it begins oscillating then a capacitor charges and cuts it off so its oscillation stops, then it builds up its gain again and oscillates again and stops again. It does not have AGC so it is overloaded easily by a strong local station.
It probably will not work if it has AGC unless the AGC is applied to another RF amplifier at its input. But then how would you detect the signal strength to control the AGC?

One very good way is to use the audio output. Being the loop is so small I'm thinking of taking it right to the front end.

Question for you. When they make these cheap radios with nothing but a whip antenna. What do they do to bring down the front end impedance? Use an attenuator?

 

[audioguru]

The base of a transistor has a medium impedance. They don't match the low impedance of the antenna on a radio.