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Post by abacus9900 on Sept 22, 2010 14:35:14 GMT 1
How does an audio amplifier work? (Broad brush strokes please).
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Post by pumblechook on Sept 22, 2010 15:26:01 GMT 1
Big subject. What do you know about electronics or even basic electricity? Where does one start?
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Post by abacus9900 on Sept 22, 2010 16:49:34 GMT 1
Big subject. What do you know about electronics or even basic electricity? Where does one start? I am familiar with simple circuits. |
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Post by pumblechook on Sept 22, 2010 17:46:32 GMT 1
Start with Class A triode valve amplifiers. A variable voltage on the grid causes a large swing in anode current. You put a negative dc bias on the grid such that the anode current with no signal applied sits about half way between the max and minimum anode current swing you require. Class A amplifiers a are fine for low lvel signals but when you get into the few hundred mW and higher region of output they are inefficient. They consume a lot of dc power. Almost all high level audio amplifiers are Class B (or AB) where two separate devices (two valves or two transistors handle different parts of the waveform). The devices are biased so that they have only a small current flowing when there is no signal. One of the pair of devices handles the rising waveform (above 0 Volts) and the other handles the falling waveform (below 0 volts input) . Amplifiers used to use two indentical devices in a push-pull arrangement and had a transformer on the output an one on the output. Bipolar transistors are used mainly these days and the transformers have been designed out by using a 'complementary pair' with similar electrical parameters but one is NPN and the other is PNP.
Key words to look up.
Triode amplifier.
Class A
Push-Pull
Class B
Complementary pair.
MOSFET amplifier.
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Post by abacus9900 on Sept 22, 2010 18:50:53 GMT 1
Start with Class A triode valve amplifiers. A variable voltage on the grid causes a large swing in anode current. You put a negative dc bias on the grid such that the anode current with no signal applied sits about half way between the max and minimum anode current swing you require. Class A amplifiers a are fine for low lvel signals but when you get into the few hundred mW and higher region of output they are inefficient. They consume a lot of dc power. Almost all high level audio amplifiers are Class B (or AB) where two separate devices (two valves or two transistors handle different parts of the waveform). The devices are biased so that they have only a small current flowing when there is no signal. One of the pair of devices handles the rising waveform (above 0 Volts) and the other handles the falling waveform (below 0 volts input) . Amplifiers used to use two indentical devices in a push-pull arrangement and had a transformer on the output an one on the output. Bipolar transistors are used mainly these days and the transformers have been designed out by using a 'complementary pair' with similar electrical parameters but one is NPN and the other is PNP. Key words to look up. Triode amplifier. Class A Push-Pull Class B Complementary pair. MOSFET amplifier. Thank you, pumblechook, for that interesting explanation.  |
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Post by StuartG on Sept 22, 2010 20:53:50 GMT 1
Here's a really interesting video of 'Make your own vacuum tubes?' blog.makezine.com/archive/2008/01/make_your_own_vacuum_tube.htmlor paillard.claude.free.fr/or www.youtube.com/watch?v=gl-QMuUQhVM&feature=relatedThe first bit he makes is the anode 'pied' foot the glass base of the envelope les traversees wire conductors between valve electrodes and base pins. l'ampoule lamp, in this case the heater assembly, filament, cathode. le queusot 'vacuum tube' [connects to vacuum pump to evacuate the glass envelope] c'est l'heure du bain. literally this is the hour of the bath, bathtime or in this case to 'acid bath to make electrodes chemically clean' monter le pied sur l'ampoule mount/fix the cathode/heater assy to the the 'foot' of the glass envelope. faire le vide evacuate the glass envelope remove the air from the assy the vacuum pump voici le nouveau ne here is the new valve [envelope complete with electrodes] le coulot....et son moule fit the new valve to the base premier essai test the new valve check the gain retour en arriere recap on events, and show gas discharge tube [something else he makes] vacuum pump to evacuate envelope, the 'man' at the vertical milling machine and not doing the tool up properly! Fin [ish] |
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Post by alanseago on Sept 22, 2010 21:34:06 GMT 1
Félicitations. That is the best piece of nonsense I have heard in many a moon.
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Post by StuartG on Sept 22, 2010 21:43:52 GMT 1
Que?
To wit?
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Post by Progenitor A on Sept 23, 2010 7:22:43 GMT 1
Start with Class A triode valve amplifiers. A variable voltage on the grid causes a large swing in anode current. You put a negative dc bias on the grid such that the anode current with no signal applied sits about half way between the max and minimum anode current swing you require. Class A amplifiers a are fine for low lvel signals but when you get into the few hundred mW and higher region of output they are inefficient. They consume a lot of dc power. Almost all high level audio amplifiers are Class B (or AB) where two separate devices (two valves or two transistors handle different parts of the waveform). The devices are biased so that they have only a small current flowing when there is no signal. One of the pair of devices handles the rising waveform (above 0 Volts) and the other handles the falling waveform (below 0 volts input) . Amplifiers used to use two indentical devices in a push-pull arrangement and had a transformer on the output an one on the output. Bipolar transistors are used mainly these days and the transformers have been designed out by using a 'complementary pair' with similar electrical parameters but one is NPN and the other is PNP. Key words to look up. Triode amplifier. Class A Push-Pull Class B Complementary pair. MOSFET amplifier. An admirable atttempt Pumlechook, but a triode! Methinks you show your age.  Is your PC a 3-valve superhet? |
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Post by pumblechook on Sept 23, 2010 10:19:53 GMT 1
A triode is a simple device and a good starting point. Bipolar transistors, holes and electrons, are a bit more complicated.
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Post by Progenitor A on Sept 23, 2010 11:50:02 GMT 1
A triode is a simple device and a good starting point. Bipolar transistors, holes and electrons, are a bit more complicated. I see your point, but then again, is describing how a horse and cart works a good starting point for the IC engine? Just joking |
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Post by pumblechook on Sept 23, 2010 14:08:44 GMT 1
Valves (and varients) are still used you know. And for some applications they will never be replaced. There is your microwave and your satellite TV. Audio-nuts still swear by them.
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Post by Progenitor A on Sept 23, 2010 14:13:46 GMT 1
Valves (and varients) are still used you know. And for some applications they will never be replaced. There is your microwave and your satellite TV. Audio-nuts still swear by them. Oh yes! And don't forget the 50kW amplifiers that super-groups use! |
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Post by Mr Red on Nov 1, 2010 11:40:38 GMT 1
Satellite TV? where is the valve?
CRT's are valves, Plasma displays are valveish
Up in the exosphere the satellites use valves - or traveling wave tubes for microwave frequencies.
At microwave frequencies - above a few watts semi-conductors get a bit fiddly due to poorer efficiency and heat dissipation problems.
Oh and 50Kw audio amplifiers - but then how much do you value your hearing?
Basically if your ears ring 5 minutes after - damage is occuring, if ringing persists a day later - permanent damage has occured. The ear is logarithmic - you find out properly when it is too late.
You are not the judge!
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