Amplifiers

Question 1

what is the tube/ valve

Answer 1

the valve works by placing dc current accorss its plate and heated cathode element

the wire mesh between the two elements acts as a control valve

Question 2

what is a transistor

Answer 2

a component capable of varying in resistance. a small control voltage at the transistors input allows a larger output current flow

Question 3

what is saturation

Answer 3

occurs when the output DC voltage of the amplifier is not sufficient to amplify the input signal

Question 4

what are operational amplifiers

Answer 4

they are high gain and high bandwidth components. they are used in a wide variety of audio and video applications. to reduce the op amps gain to more workable levels a negative feedback loop is required

Question 5

what are amp equalisersd

Answer 5

an eq is a frequency discriminating amplifier. using capacitor/ resistor networks in the op amps negative feedback loop, selected frequencies can be cut or boosted

Question 6

what are summing amplifiers

Answer 6

they are used to provide isolation between various inputs and/ or outputs in a signal chain

Question 7

what are distribution amplifiers

Answer 7

this amplifier does not provide gain as such, but increases the signals current allowing it to be delivered to a number of loads

Question 8

what are VCAs

Answer 8

voltage controlled amplifiers

the output voltage is a function of an external DC voltage
as the voltage goes up the output goes down

Question 9

what are class a power amplifiers

Answer 9

output stag draws a constant high current from supply wether audio is passing or not. this current is constantly bias - they are inefficient due to heat generation but they have a high sound quality

Question 10

what are class b power amplifiers

Answer 10

no current passes through the output transistors when audio is not passing. the driving signal itself is used to bias the transistors. this technique is highly efficient. at low levels sound quality can become distorted

Question 11

what are class d power amplifiers

Answer 11

uses pulse code width modulation. the transistors are driven by an ultrasonic wave whose mark to space ratio is varied by the audio signal. power dissipation in the transistors is minimal, therefore run cool and are efficient

Question 12

what are class g power amplifiers

Answer 12

incorporate several different voltage rails. these progressively come into action as the signal voltage is increased. this gives good efficiency as much of the time only the low voltage rails are in use

Question 13

what are class h power amplifiers

Answer 13

variation of the class g concept, maintains just enough headroom to accomodate the amplifiers output requirements

Question 14

what is an amps sensitivty

Answer 14

how much voltage input is required to produce the amplifiers maximum rated output

sensitivity must be taken into account when considering the equipment driving the amplifier

Question 15

what is an amps power output

Answer 15

A spec might read “200 watts into 8ohms - both channels driven”. This means both channels are capable of delivering this output at the same time.

Question 16

what is bridge operation

Answer 16

this is where both channels are fed the same signal, but one channels polarity is reversed

Question 17

what is power bandwidth

Answer 17

the frequency response bandwidth within which an amp reproduces frequencies at a low power output

Question 18

what is slew rate

Answer 18

a measure of an amps ability to accurately react to high level transients. higher power amps require higher slew rates

Question 19

what is an amps distortion

Answer 19

should be 0.1% total harmonic distortion across the entire audible range

Question 20

what is crosstalk

Answer 20

signal from one channel creeping into another

Question 21

what is signal to floor noise ratio

Answer 21

a measure of the output residual noise voltage expressed as a decibel ratio between that and the maximum output voltage when the input is short circuited

Question 22

what is damping factor

Answer 22

this is a numerical value given to an amps ability to control a speaker. speakers tend to continue to move after the driving signal has stopped

Question 23

what is phase response

Answer 23

this is a measurement of how well the high end low frequency extremes keep in step with the mids

Question 24

what is coupling

Answer 24

the majority of amps have direct coupled, meaning the output power transistors are connected directly to the speakers save for perhaps a low valued resistor and inductor in between