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Term 2 Theory Prep > Amps > Flashcards

Amps Flashcards

1
Q

DEF:

amps

A

electronic device for increasing amplitude of electrical signals, mainly used for sound reproduction

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2
Q

how does tube/valve amp work?

A

cathode (-) is heated and generates electrodes which are filtered by the triode (grid) and are pulled toward to plate

the grid is given charge and depending on + or - will either repel - electrons and stop them passing through or increse the number of + electrons, amplifying the sound

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3
Q

why is it important to bias the tube?

A

operating at the extremes will cause the output to be non-linear and distorted

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4
Q

DEF:

transistor (amp)

A

component capable of varying its resistance

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5
Q

how does a transistor work (amp)

A

“valve” placed across the collector and emitter

small control voltage placed at transistor’s input allows larger output current

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6
Q

Where is DC bias voltage applied?

A

base (valve) of the transistor

grid (triode) of valve/tube

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7
Q

DEF:

saturation (amp)

A

occurs when output DC voltage isn’t sufficient to amplify the input signal

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8
Q

harmonics from tube clipping vs transistor clipping

A

transistor - odd-order harmonics

tube - even-order harmonics (more musical)

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9
Q

DEF:

cutoff

A

when there is not enough electrons being generated by the cathode to be pulled by the anode/plate

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10
Q

what is an op amp?

A

operational amplifier with high gain and high bandwidth, used for a variety of audio and video applications

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11
Q

howis the op-amp’s gain reduced so it’s at a level you can work with

A

uses a negative feedback loop where a portion of it’s output is fed, through a resistor, back into it’s input out of phase, reducing the op amps output

varying value of resistor gives different output levels controlling the op amp’s gain

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12
Q

DEF:

equalizers (amp)

A

a frequency discriminating amplifier using capacitor/resistor networks in the op amp’s negative feedback loop allowing selected frequencies to be cut or boosted

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13
Q

DEF:

summing amplifiers

A

used to provide isolations between various inputs/outputs in a signal chain

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14
Q

DEF:

distribution amplifiers

A

amp that does not provide gain but increases current signals allowing it to be delivered to multiple loads

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15
Q

DEF:

VCA / DCA

A

voltage/digitally controlled amplifier

output voltage decreases as the control voltage increases

DCA - digitally controlled DC control voltage

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16
Q

Power amplifier classes

A

A

B

AB

C

D

T

EF

G

H

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17
Q

Class A power Amplifiers

A

output draws a constant high current from supply regardless of audio passing through or not

current used to bias transistors

inneficient due to heat generation from constant bias current, but transistors have a constant steady temperature

very high sound quality

low current class A used widely in audio circuits

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18
Q

Class B power Amplifiers

“pull-push” amps

A

no current passes through output unless audio is passing

driving signal is what biases transistors

very efficient and great for battery powered equp but at low signal levels they operate near cutoff point making sound quality distorted/degraded

pairs of transistors are used to handle separate halves (+/-) of waveform, as signal hits zero crossing amp gets crossover distortion

used when you don’t need high sound quality

19
Q

Class AB amps

A

relatively low bias current flows at all times (Class A amp)

as input signal is increased transistors are biased w/ higher current to deliver more power to speakers but since transistors are constantly biased crossover distortion is avoided

majority of high quality amplifiers are AB

20
Q

Class C amps

A

used for driving narrow band frequencies into resonant load

used for radio to drive signal to aerial

21
Q

Class D amps

A

uses PWM

transistors are driven by ultrasonic wave w/ mark to space ratio varied by audio signal

power dissipation in transistors is minimal

run cool and highly efficient

low pass filtering required to remove square wave component of signal

22
Q

Class T amps

A

from the Tripath Company

ultrasonic fequency is continually varied in accordance with input amplitude

very high efficiency

23
Q

Class G amps

A

incorporates several different voltage rails that are used progressively as signal voltage increases

very efficient (usually use low rails only) and can be smaller than Class AB amps

24
Q

Class H amps

A

variation on Class G but supply voltage rails track input signal continuously maintaining just enough headroom to accommodate the amps output requirements

25
Q

Characteristics of MOSFET amp

A

low distortion

good thermal tracking

simple output design

greater tolerance of adverse speaker loads without complex protection circuitry

26
Q

MOSFET

A

Metal Oxide Field Effect Transistor widetly used since 80’s in output stages of power amps

27
Q

power amp sensitivity

A

how much voltage input is required to produce the amp’s max rated output

must be taken into account when considering what equip will drive the amp, must not be able to deliver more voltage than the sensitiity rating or clipping will occur

28
Q

what is ‘bridged operation’

A

where both channels are fed same signal (usually L) but one channel’s polarity is reversed (usually R)

both channels process same signal and load is connected to draw power from both channels

will be refelcted in specs

mono will be double amt of W than stereo

29
Q

DEF:

power bandwidth (power amp specs)

A

freq response bandwidth within which an amp can sustain a specified output

must be considered when matching amps to loades (ie. subs, HF horns)

30
Q

DEF:

frequency response (power amp spec)

A

a measuer of the limits within which an amp can reproduce frequencies at a low power output

usually measured w/ amp delivering 1W into 8Ω load

31
Q

DEF:

slew rate

A

a measure of amp’s ability to accurate react to high level transients

defined as Vus (volts per microsecond)

32
Q

Slew Rate rule of thumb

A

Amps of 100 W shoul dhave slew rate of 10 Vus

amps of 200 watts should have slew rate of 30 Vus (min.)

higher power amps require higher slew rates as wattage swings are more severe

Excessively high slew rates should be treated w/ caution as they can be associated with too high a bandwidth which can allow amps to pass RF signals

33
Q

distortion (power amp specs)

A

should be 0.1 THD across entire audible range

34
Q

crosstak (amp specs)

A

should be at least -70 dB between channels in mid frequencies

  • 50 dB at freq. extremes
35
Q

DEF:

signal to noise ratio (amps)

A

how much hiss the amp has when it’s cranked up all the way

100 dB is common for moder amps

36
Q

DEF:

damping factor (amps)

A

numerical value indicating how well an amp can control a speaker

the ratio between the amp’s output impedance and speaker’s impedance

damping factor is more useful when frequency is given

37
Q

DEF:

phase response

A

measurement of how well the high and low freq extremes keep in step with mids

15 degree phase lag at 20Hz and 20Khz is common

38
Q

DEF:

direct coupled (amps)

A

output power transistors are directly connected to the speakers, except maybe low valued resistor and inductor in-between

39
Q

DEF:

transformer coupled amp

A

transformer buffers the output and the amp uses split voltage rails of opposite polarity to have no DC output present at output terminals

+/- 40m V is acceptable max

15mV > is common

40
Q

speakers connected in series

A

current flows serially from one speaker to next

impedance of series is equal to impedance of each speaker added together

41
Q

speakers wired in parallel (impedance)

A

impedance is calculated like this:

42
Q

pro/cons of speakers wired in series

A

pro:

if individual loads are low, series increases impedance

con:

if one speaker goes, series stops working

damping effect is greatly reduced

interaction between speakers is higher = more distortion

43
Q

pro/con speakers wired in parallel

A

pro:

one speaker fail, the rest still work

con:

limited number of speakers can be connected before impedance drops below amp’s operating load

44
Q
A

Term 2 Theory Prep (11 decks)

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