The rail diode, is this a trick, is this a trap or a clever solution? - diyAudio
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Old 19th September 2004, 03:32 PM   #1
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Default The rail diode, is this a trick, is this a trap or a clever solution?

I am a schematic hunter, a schematic colector...have 30231 units.

I am an amplifier tester too... like to assemble and test.... and junk and shot it with .12 gauge.

Some of them makes me happy...JLH, and JLH and the other one is a JLH design...all them class A.... some other makes some impressive sound too...but...99 percent!....BOOOOOOM!

I am a Broadcasting Television Professional, skilled to work in every post inside a TV Station.... from the equipments operation to design, construct, modify, install equipments, repair them, adjust.... one man television... i can do it.

But never studie audio.... i am ignorant...only good years....hearing music (hears, years...do not know)

I am seeing some times...DIODES in the positive rail, sometimes both rails...what are they doing there?

To avoid return patch?
To make some 0.6 constant potencial difference....
To isolation from power to input circuit?

Can you explain me please... this seems to be some trick to my ignorance.

regards,

Carlos
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Old 19th September 2004, 03:37 PM   #2
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In single supply (battery powered) amps sometimes a diode is placed in series with the rail in case the battery gets connected backwards. (thus protecting the circuit from destruction)
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Old 19th September 2004, 03:55 PM   #3
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Default Thank you Hits, this use i already know..but you was kind to inform some.

HELLO people!...... 30 hits in a matter of seconds....
Please...let me know what you think?

Cannot be a trick, despite it smells a trick sometimes...but may have a good and reasonable reason.

Not to discharge some condenser?

To keep 0.6 drop constant?

To avoid some return (of what?....not a radio frequency transmiter...is an audio amplifier!)

Why sometimes only in one of the rails

Why not only resistor...because voltage drop variates with current...but input current variate a little...very small variations!... a cap can control that!


You that is reading..... a lot of hit!...i am seeing people is visiting the thread...PLEASE HELP!

Save big Charlie from the deep ignorance!

regards,

Carlos
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Old 19th September 2004, 03:57 PM   #4
Steven is offline Steven  Netherlands
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Depends on where you put them. Sometimes they are used to isolate an input stage or driver stage from the power stage. The power supply is connected to the power stage, then via a series diode the input stage is powered from the same supply. After the diode an additional elcap is used. If, during transients or just big signals, the power supply of the output stage drops, the diode prevents that the elcap of the input stage is being discharged via the power stage. In this way the input stage keeps a more stable supply voltage.
So, yes, as you suggested, to avoid a return path.

The use of series diodes to create additional voltage drop because the original supply voltage is too low is bad design practice. They do not help a lot, they heat up, efficiency decreases, etc. Then it is better to use a simple pass regulator.

Steven
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 19th September 2004, 04:09 PM   #5
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Default Strongly honored with your presence Steve.

And completely satisfied with your explanation.

No more doubts...it is clear...completely clear to me now!

Thank you very much.

regards,

Carlos
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Old 19th September 2004, 04:20 PM   #6
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Default Interesting, how the difficult things turn simple with a good teacher

Twenty years ago, as a HAM i was working with cable and some instalations, helping friends and someday one question appeared to me.

How the radio frequency energy...voltage.... turns into magnetic?...how the electron... the radio frequency electrons.... in a 30 Megahertz frequency can understand were is the cable and were is the aerial, the antenna.

Because if you separate the cable shild to left side.... and the internal wire to the rigth side....if you respect the wave length, there's one aerial (antenna)

And so simple the answer one enginneer told me.

Insulation.... the electric signal creates some magnetic field..but it is insulated by the shield..... and cannot propagate, cannot irradiate.... when you remove the shield...theres electromagnetical waves free to travel...so easy!.... after some good man has the good will to explain.

regards,...thanks again Steve

Carlos
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Old 19th September 2004, 05:53 PM   #7
Steven is offline Steven  Netherlands
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Hi destroyer X,

Just for fun, thinking about radio frequency energy, areals and loops, turning electromagnetic fields into light:
http://www.rebix.nl/eng/ind-leds.html

The same company is also in Class D, BTW.

Steven
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 19th September 2004, 09:19 PM   #8
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Default This have application as a radio frequency leakage meter

To check the cable leakage and how to show to students the wave length nodules over a transmittion line.

Thank you....magicians can use too...... ligth with the brain energy! ahahah

Good, thanks!

Carlos
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Old 20th September 2004, 01:41 AM   #9
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Wink back to diodes question

Usually they used to put diodes in series with both rails to keep the power "on" in the early stages of an amp for a few seconds after yhou turn it off.
This avoids hearing any "pops" that could also destroy the sepakers.
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Old 20th September 2004, 11:04 PM   #10
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Default Another good information, thank you.

Avoid pop of when turn off.

This is good, a very pratical and real reason.... easy to verify, easy to use, something to put in everyone.

thank you.

Carlos
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