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Posted: Mon Oct 16, 2006 12:01 pm
by Robert Reed
I still don't see the reasoning behind this LED circuit. Any diode introduced into the signal path could only degrade the input, even if minimally. A high fidelity amplifier has only one job to do and that is to boost the signal levels voltage or power without introducing any other noise or distortion. In other words, extreme fidelity in-extreme fidelity out; garbage in-garbage out; etc. AGC wuld not be helpful in hi-fi circuitry as far as the input signal goes, as this would be almost similar to compression. A type of AGC in controlling DC bias shifts affecting amplifier gain would be helpful, but now we are talking about two different things.
I mentioned companders only in reference to the advertised wording of attack,decay . I realize that compressing signal content would be detrimental to the hi-fi content. But companders also expand and these were somewhat popular during the dying days of vinyl albums. It seems that so many heavy rock albums were being produced at this time, that record manufacturers were no longer concerned with dynamic range, due to the fact that loud rock had practically no range, just constant loud. Unfortunately other styles of music suffered such as classical, where dynamic range is everything. Because of this many peole were purchasing expander units to overcome this (I designed and built my own at the time). Again , in respect to consumer audio equipment, this is the only place I have seen these terms attack and decay used and relates to the actual ressponse of the expander to progam material (millisecs to secs).

I hope I havn't missed the point here, but I still don't see where the attack and decay is utilized in this amp.

Posted: Mon Oct 16, 2006 12:53 pm
by Chris Smith
Actually through out the history of the diode, many did glow and were encased in black plastic to stop this affect.

That’s how the principal of the LED was found and formed.

The 914 is in clear plastic for the reverse effect. It responds to bright light signals quite fine. [Just use a pico or nano amp]

I recall reading many years ago about the effects of diodes and light emitting [as well as other frequencies like MW] and while some thought it to be a disadvantage, others felt a new poroduct line was about to be in place.

The latter won out.


The only advantage of the Led is its response curve. However, there are soo many other diodes to do the same trick, thus it is most likely just a gimmick rather than a actual advantage, other than cost or availability.

Posted: Mon Oct 16, 2006 5:44 pm
by Dean Huster
Actually through out the history of the diode, many did glow and were encased in black plastic to stop this affect.
Sorry, Chris, I'll have to take exception to that statement. The little glass signal diodes where painted black because the little buggers were light-sensitive and really screwed up circuits if they were bare. The black epoxy case is pretty much an economic thing. The Heathkit Optoelectronics course of the 1980s used one of these with the paint scraped off in one of their experiments.

Many diodes did emit light, but most folks didn't know about it because it was IR. The first LEDs were IR and as technology developed, so did the colors, climbing the color-temperature chart until we finally have violet and ultraviolet LEDs. For most of that growing period, the higher the color temp, the lower the efficiency.


Posted: Mon Oct 16, 2006 7:05 pm
by Chris Smith
Thank you Dean for exactly re writing my statement.

Read it again, that’s what I said.

"Sorry, Chris, I'll have to take exception to that statement. The little glass signal diodes where painted black because the little buggers were light-sensitive and really screwed up circuits if they were bare"

The 914 is still light sensitive.

The 914 is made of clear epoxy, its still light sensitive, and its still used as a light trigger even today. [pico op amp needed]

The Glow was mainly visual, IR, UV, and MW.

Efficiency was never stated as useful or wanted.

Posted: Tue Oct 17, 2006 12:23 pm
by haklesup
Actually Chris, you implied that the diodes were painted black to keep in the light, Dean reversed your statement making it correct by saying the opaque encapsulant is to keep light out.

Glass (not clear epoxy) is actually used to encapsulate the smallest dice because it has an excellent thermal match to Si and is completely hermetic and inexpensive. For larger Dice with different bonding, glass filled epoxy encapsulant becomes more economical (and satisfies other requirements like excluding light). The transparency of a given package is mainly incidental though some creative designs may have occasionally made use of the light sensitive properties. You still need a pretty bright light to excite the small junction and moderate doping of the 914. Fortunately most electronics boards are inside a box of some sort. Though mostly small signal diodes, I do have a few zeners with glass packages. I have to think a little legacy (tradition) plays a part in what is used.

It is well known that Si diodes are light sensitive. I experienced it while viewing biased IC devices under a microscope, sometimes the light from the scope would make the supply current go way up. It basically causes a reverse biased junction to leak lots of current.

If any diodes did emit a visible glow (way back when) they were not silicon. Only in the last few years with great effort have researchers been able to make visible light Si structures. It's just as well, light represents inefficiency in the blocking or switching of the structure. If Si structures were strong emitters of photons, the speed of computing would be slowed and power consumption would be much more significant. Stray photons emitted from one structure would interfere with the operation of others requiring additional procession steps to prevent that. Even at the rate it does happen, it is a concern to IC designers of deep submicron structures.

Also MW is not considered an optical frequency (except perhaps by radio-astronomers who know the difference better than anyone). I also don't believe anything but IR is generated by a DC biased diode or transistor.

Posted: Tue Oct 17, 2006 2:48 pm
by Chris Smith
Reading between the lines where nothing exists, make one a fool.

I made no implications or statements to any contrary, and I mentioned the 914 up front which is, and always was clear.

The 914 and the Pico amp is used because of its excellent speed response, [tiny mass] often used in the night scope or other the pieces of equipment to shut down the power if light is detected.

From memory the response is in the sub nano seconds which is why it is used.

Also it has no/low saturation values to screw up its response in this fashion.

The history of diode from the early 50s states all the faults of clear diode packages, and goes on to tell why black was chosen. The advantages of the dark diode package was obvious at reducing transmitting and receiving. A lot of circuits had “Noiseâ€

Posted: Tue Oct 17, 2006 4:24 pm
by Robert Reed
Thank you - you answered all the questions I was going to post. Its like the TV show "Jeopady". You gave the answers first before I posted the questions. Kind of neat.

Change of subject
I still don't get the correlation between LEDs and the so called 'attack, decay' wording. Even marketing hype wouldn't apply here, as it makes no sense at all.

Posted: Tue Oct 17, 2006 5:16 pm
by Chris Smith
Sounds like English 101 is needed here.

Reading between the lines is an American favorite, one I love to bait just to see just who fell down the well.

Do Try to change, its almost as smart as an athlete.

Rich and dumb. Their actually not compatible!

But, if your soo smart, do your best to tie your lies to my words?

Wont happen, today or any other. duhhh

Cant wait.

Posted: Tue Oct 17, 2006 6:58 pm
by Dean Huster
We'll never figure out the trigger.


Posted: Tue Oct 17, 2006 7:10 pm
by Chris Smith
Id concentrate on the English, it eludes too many.

You could actually become educated in the language and get a degree? [gawd help us?]

Too much huddling, squeezes the brain for air?

Posted: Thu Oct 19, 2006 10:11 am
by Ron H
Give it up, guys. Have you ever known him to admit he was wrong?

Posted: Thu Oct 19, 2006 5:34 pm
by Chris Smith
Has any one at all here shown anything to be anything but wrong, or just more "pretense, deflect, hide, whine, and lie"?


Grow up Armature pipsqueak, shut up, learn, and don’t argue with those who have been there, done that, and know far more that you will ever.

Pip squeaks like you are noisy, boring, wrong, and nothing more!

Like child telling a parent,..but but but?

Go soak your head.

Posted: Thu Oct 19, 2006 7:36 pm
by MicroRem
Armature pipsqueak?

Wow, That's a phrase I never expected


Posted: Thu Oct 19, 2006 7:52 pm
by Chris Smith
Such silence and errors, over and over and over. Duhhhaa

Not one with the balls to claim anything other than being bottom dog, bow wow, and such pathetic rhetoric.

So much silence and no corrections at all??? woff woff?

Gee, who could have guessed these continued lies, other than one who has been there, done that and listened to these piss squeaks whine and moan, empty with out squat.

Must be time for a snooze, the amateurs speaking.

Do Wake me when you find your ass?

Grow up little child of naieve,....Getting it wrong must be soo right, said the resident in the WH, just like you?

Feel good, getting it all wrong? duhhh

Huddle, its your only savior,...little sheep

Posted: Thu Oct 19, 2006 8:14 pm
by Ron H
usteservice wrote:Armature pipsqueak?

Wow, That's a phrase I never expected

I think that's the noise your motor makes when the brushes wear down to their carriers. :D
I wonder if he was addressing me? I probably have more experience and education than he does. He also assumed I was talking about him. Maybe I was talking about Dean. He has a huge ego, and flies off the handle when anyone catches one of his slip-ups. :)