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Do you still listen to AM/FM radio?

I think you need at least 60 Khz, because you's like to reproduce a 20 kHz SQUARE wave, not a sine wave and Fourier theory suggests more. The bone heads used sine waves and hearing ability. Shape of the waveform is missing. The Nyquest criteria only applies to sine waves, I believe.

The speaker can reduce the bandwidth, but the amplifier has to try, Rolled off to 40 kHz is the minimum. With an amp capable of a slew rate of 100 V/us and and unrolled off bandwidth of 0-800 kHz, it's outside the normal bounds or nearly any stereo amplifer and it sounds good. It is intentionally rolled off from 0.5 to 40 Khz. The pre-amp is good from 0 to 100 kHz.

I live in the Far East where there are a few AM stations (especially the 500KW religious broadcasters in the Philippines) and the host countries where their version of the truth is broadcast. (Funny thing is most locals only use FM receivers - so the religious outfits are simply wasting their time and energy.)

My monitoring includes HF and Medium bands.

These days, in order to get a balanced view of the news, it is necessary to listen to several stations as they all, including the BBC and Voice of America, never give you ALL the straight goods.
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When young I liked to listen to a small amount of "voice of Cuba".
A long long distance. 2600 miles The skip had to be just right.
Back when AM was king, I worked through high school in a TV repair shop. At the end of the afternoon pickup and deliver run, 5-6 pm in winter, dark in Ohio, sometimes I could get Seattle rock stations KOL or KJR on the car radio.


Active Member
At about 8 years new, dad passed me his Sanyo :

Which gave me shortwave and medium wave. Kept always at my bed side, nightly heard news, music and radio 'soap operas'

Later by 11, built a crystal radio that awoke the electronics in me. Helped at a TV service shop by 13, 14.

Maaany years later, worked in broadcast audio processing factories (Orban, Dolby) building, testing, configuring, servicing broadcast audio equipment.
These were my children :

With 2 amateur radio licenses, I can say radio has been a large part of my life.


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For your benefit. Reconstruction of a square wave from the sum of add harmonics of sine waves.

At 7 * 3khz (voice) is 21 kHz. I'm sure you can tell the difference of a square and sine wave with 7x the fundamental.
So, I do believe it's way to low in terms of 0.5 Hz to 2 kHz. 40 kHz/7 ~ 5700 Hz, 100 kHz/7 = 14.2 k=kHz.

I've heard an amplifier croak when fed a high slew rate signal. It sounded awful. The 4bx is capable of increasing the slew rate of a signal which translates to being able to hear the hammer hit on a song with a hammer dulcimer or a piano. It's a very different experience.

The type of music influences the behavior too. A friend had a Macintosh amp (tube) and the Voice of the Theater speakers which had horns for the high frequency. The tube amp with the horns really did well with the classical music.
I would need more voltage and equalization, probably (or more power) to achieve the loudness of the horns

On the other hand the tube amp could not match the base of the solid state amp. My amp is a variation of The Leach Amp described here: http://leachlegacy.ece.gatech.edu/lowtim/

Biggest differences are 4 x 9600 uF capacitors for the dual independent 2 x 50 vDC @ less than 3A power rails for each amp. 3 A is inadequate. At home I also run the amp with a 500 Watt sine wave voltage regulator which improves the bass even more. The construction article (Appeared in Audio magazine) the amp was driving electrostatic speakers.

I have speakers with dome tweeters rates at 35 W and the woofers rated at 100 W.

My friend agreed that the solid state amp rivaled the Leach amp with the Leach providing more bass and the horns sounded better and louder with tube drive. There was no comparison with speakers. So, we believe that the music type influences the speaker type. No signal processing was done.

I screwed up the power supply design. At one point I had an 18 A constant voltage transformer for the power supply and the bass was really good. The transformer was custom.

Besides component choices metal film resistors, a 10 turn pot for bias and a better power supply (but not good enough) there is in-rush protection, exponential audio ramping and thump protection.

The in-rush protection could be better. If any power supply fuse blows a resistor in the AC line will blow.

I was thinking about adding a clipping indicator and high temperature protection. The clipping indicator would be really useful.



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Your hearing rolls off high frequencies. Then if you have excellent young hearing a 20kHz sinewave sounds exactly the same as a 20kHz squarewave or 20kHz trianglewave. You do not need hundreds of kHz (AM radio?).

Some audio amplifiers misbehave when fed very high frequencies. But audio has no very high frequencies, a microphone rolls off the very high frequencies of anything, even a cymbal.

An old horn high frequency speaker sounds awful today because its output is full of resonances. But in the old days that is all they had.


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I have not listened to radio in 25 years. Advertisements were so bad it was 90% advertisements.

I don't watch TV anymore either pay TV has advertisements. I cancelled pay TV 10 years ago.
@ gary350
I am with you on TV. My landlord provided a 36" wall TV - which has never seen a TV program even though cable is only $5/month for 200 channels, most Western advertising is better than the programming.

But for PCB design, the TV set set is great!


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I wrote this in December, 2006, and sent it out to family and friends on Christmas Eve.



'Tis the season to write about religious holidays.

Invisible airwaves crackle with life;
Bright antennae bristle with the energy.
Emotional feedback on timeless wavelength,
Bearing a gift beyond price, almost free.

- Neil Peart, "The Spirit of Radio"

Mass Communication

Greek Runners

Roman Mail

1450 - Printing Press

European Rail System

1837 - Telegraph

1876 - Telephone

1892 - Long Distance

1899 - Fax Machine

1929 - Television

1962 - Telstar

1972 - eMail

1973 - Cellular Telephone

1974 - The Internet

1991 - The World Wide Web

1999 - Wireless Broadband


No matter which criteria you use to chart the "evolution of society," there is no question but that things change, the pace of change always has changed, and the technologies of mass communication both enable and engender change. By the early 19th century, the latest batch of technologies had reached a state of equilibrium with society. With publishing, horses, trains, and trans-oceanic ships working in concert, the first era of mass communication was winding down, almost 400 years after its start in 1450.

The next chapter was short, maybe as a forward to what was to come, and began with a click. The telegraph was a tantalizing peek into the future, instantly made "instant" a new part of the nature of communication, and sparked a paradigm shift of intercontinental proportions. But it was the telephone which altered the core of personal communication for the first time: Instant, Two-way, Personal, Voice - a long-distance grand slam 10,000 years in the making. Now, if we could just get rid of all those wires...

Missing from the historical list above is the thing which began the second era of mass communication - radio. It removed the physical limitations of all previous communication structures. From Caruso and Sinatra to The Mercury Theatre of the Air and "Oh, the humanity!", radio unlocked (or unleashed) the power of the shared experience.

The hard-wired telephone survived for 97 years because the technology was so elagantly simple. Television was neither elegant nor simple, and was useless unless wireless. "See It Now" with Edward R. Murrow, "...one small step for (a) man...", M-TV with The Buggles, and Tienneman Square with the faxes vs. the tanks - these images made the 20th century the "television century." But it is the science of radio which carries the ideas that move the world.

On April 3rd, 1973, Martin Cooper of Motorola placed the world's first portable, non-automotive cell phone call to his car-phone rival at ATT, Joel Engel. Practical cell phones were ten years away, but this one phone call was the beginning of the end for the wire and all it represented. In the same way Edison's light bulb broke the millennia-old bond between light and fire, Cooper's cell phone used radio to sever the last bond between communication and location.

Cell phones introduced this year (2006) have high-resolution color cameras and can record several minutes of full-motion video with sound. The video can be transmitted instantly to anyone, anywhere in the world, or uploaded instantly to a web page where it is available to *everyone* in the world, from a device which is completely wireless, smaller than a paperback book, and can run all day on one battery charge. While I'm sure there are many improvements to come, this convergence of wireless, text, voice, image, personal, and mass communication is the end of this chapter in the evolution of communication, and will both report and shape the next phase in the evolution of society.

"... Which brings us here." - James Burke
(image of David bowing down in the general direction of England)

100 years ago, Reginald Aubrey Fessenden was a smart guy. Early on he was the principal, and the sole teacher, at the Whitney Institute in Bermuda. Later, he was a Professor of Electrical Engineering at Purdue, and the first department Chair of Electrical Engineering at what is now Pitt. A one-time Edison assistant, he quit because he couldn't stand Edison's non-science approach to, well, science. With over 500 patents (second only to Edison), his achievements remain almost completely unknown even in technological circles, except for one.

On December 24th, 1906, at 10:30 PM EST, at Brant Rock, Massachusetts, Reginald Fessenden made the first voice radio broadcast.

His transmission was picked up by numerous ships at sea. Fantastic claims of "voices" coming from the radio sets led captains to suspect their radiomen of being drunk on duty. Reggie introduced himself, spoke briefly about his invention, read from the Bible, and played "O Holy Night" on his violin. Thus, at sea, began the second era of mass communication, "... a sea-change into something rich and strange."

So this Christmas Eve, at 10:30 PM EST, take out your cell phone, use it to track down an electrical engineer, and go kiss him right on the face.

Happy Birthday.
Merry Christmas.



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Thought provoking.



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The marvel of communications, ak, you left the poster above, speechless. WOW :woot::troll:

Credit goes all to you! :D

Merry Christmas

schmitt trigger

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Thread starter #60
Invisible airwaves crackle with life
Bright antenna bristle with the energy
Emotional feedback on timeless wavelength
Bearing a gift beyond price, almost free

- Neil Peart
A fabulous song from one of Rock's most accomplished groups. I love Rush.

Having said that, the song's final verse ends on a sadder note:

"For the words of the profits were written on the studio wall.....Concert hall
And echoes with the sound of salesmen...of salesmen...of salesmen."

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