Solid state Amplifiers, Physics tutorial

Solid state amplifiers:

Solid State amplifiers have better technical specifications as compared to valve amplifiers. But when solid state amplifiers were initial launched it was noticed that they sounded flat and unresponsive in comparison to well made valve amplifiers. Also solid state amplifier had to be twice as powerful as the valve amplifier to sound as loud.

Amplifiers and speakers have usually been marketed independently of each other. There has been little attention in how amplifiers and speakers interrelate.  Valve technology was tiresomely assembled with manual labor while Solid state technology is mass produced at the fraction of cost. Economical rationalism and modern marketing easily pushed aside the older valve technology.

Basic technical principles:

Several professional audio providers and audiophiles have misconceptions about how the solid state (transistor) amplifier functions. Misconceptions take place as basic principles aren't understood.  

The solid state amplifier comprises of three sections:

1) Input driver circuit amplifies small input signal to the larger size, about x20 to x50.

2) Large output transistors add current to amplified signal to be sent to speaker.

3) Power supply converts 110V / 22OV AC mains to 2 DC supply Voltages that power amplifier.

Output stage comprises of 2 or more large output transistors bolted to the heat sink (NPN and PNP).

The solid state amplifier has 2 (DC) power supplies (+V and -V).  2 power supplies are connected in series. Middle is connected to chassis. One terminal of speaker is connected to middle chassis and other speaker terminal is switched between 2 supplies.

  • As speaker is joined from chassis across +V supply the cone moves out.
  • As speaker is joined from chassis across -V supply cone moves in.

Speaker is joined across one power supply at a time. Thus maximum Voltage across speaker can be no greater than 1V5 at any one point in time.

Solid state devices:

Solid-state electronic devices are part of our everyday lives. Transistor was the first solid-state device to come in commercial use in 1960s. Solid-state electronic devices have replaced vacuum tubes in just about all electronics devices. Vacuum tubes are still utilized in transmitters of radio stations, several guitar amplifiers and some audiophile equipment.

One of the first solid-state devices was the crystal radio. In the crystal radio, piece of wire positioned on crystal's surface is capable to divide lower-frequency audio from higher-frequency transmitted radio carrier wave. This form of signal detection is because of crystal's ability to pass a current in only one direction.

Solid-state derived its name from path which electrical signals take through solid pieces of semi-conductor material. Before use of solid-state devices, like common transistor, electricity passed through different elements inside of heated vacuum tube. Solid-state devices, like a transistor, use conductors to manage flow of signals through the circuit.

Solid state devices called diodes have the replaced rectifier vacuum tubes, utilized to transform alternating current (AC) to direct current (DC). Cool-running light-emitting diodes (LEDs), another solid-state device utilized for indicators on front panel of computer and monitor, have replaced earlier incandescent bulbs. Multiple bright LEDs are also utilized for third stoplight on several U.S. vehicles and for traffic signals.

Solid-state miniature electronic components are in many places:

  • Mounted on flexible thin film printed circuits in cameras and disk drives.
  • Beeping sound made by the cell phone, page or auto dashboard alarm.
  • Voice chip in the answering machine.
  • TV remote control.
  • Laser pointer.
  • Inside of MP3 player.
  • The quartz watch.
  • Image sensor in the digital camera and camcorder.
  • Computer monitor you are viewing.

Advantages of Vacuum tubes:

  • Highly linear without negative feedback, particularly some small-signal types
  • Clipping is smooth, that is extensively considered more musical than transistors
  • Tolerant of overloads and voltage spikes
  • Characteristics highly independent of temperature, really simplifies biasing
  • Wider dynamic range than typical transistor circuits, thanks to higher operating voltages
  • Device capacitances differ only somewhat with signal voltages

Disadvantages of Vacuum tubes:

  • Bulky, therefore less appropriate for moveable products
  • High operating voltages needed
  • High power consumption, requires heater supply
  • Produce lots of waste heat
  • Lower power efficiency than transistors in small-signal circuits
  • Low-cost glass tubes are physically brittle

Advantages of transistors:

  • Generally lower cost than tubes, particularly in small-signal circuits.
  • Smaller than equivalent tubes.
  • Can be combined in one die to make integrated circuit.
  • Lower power consumption than equivalent tubes, particularly in small-signal circuits.
  • Less waste heat than equivalent tubes.
  • Can operate on low-voltage supplies, lower component costs, smaller clearances, greater safety.

Disadvantages Transistors:

  • Complex circuits and considerable negative feedback needed for low distortion.
  • Sharp clipping, in the manner extensively considered non-musical, because of considerable negative feedback usually utilized.
  • Device capacitances tend to differ with applied voltages.
  • Large unit-to-unit variations in main parameters, like gain and threshold voltage.
  • Stored-charge effects add signal delay, that complicates high-frequency and feedback amplifier design.
  • Tendency toward higher distortion than equivalent tubes.
  • Device parameters differ significantly with temperature, complicating biasing and raising possibility of thermal runaway.
  • Cooling is less efficient than with tubes, as lower operating temperature is needed for reliability.

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