Amps Flashcards
DEF:
amps
electronic device for increasing amplitude of electrical signals, mainly used for sound reproduction
how does tube/valve amp work?
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
why is it important to bias the tube?
operating at the extremes will cause the output to be non-linear and distorted
DEF:
transistor (amp)
component capable of varying its resistance
how does a transistor work (amp)
“valve” placed across the collector and emitter
small control voltage placed at transistor’s input allows larger output current
Where is DC bias voltage applied?
base (valve) of the transistor
grid (triode) of valve/tube
DEF:
saturation (amp)
occurs when output DC voltage isn’t sufficient to amplify the input signal
harmonics from tube clipping vs transistor clipping
transistor - odd-order harmonics
tube - even-order harmonics (more musical)
DEF:
cutoff
when there is not enough electrons being generated by the cathode to be pulled by the anode/plate
what is an op amp?
operational amplifier with high gain and high bandwidth, used for a variety of audio and video applications
howis the op-amp’s gain reduced so it’s at a level you can work with
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
DEF:
equalizers (amp)
a frequency discriminating amplifier using capacitor/resistor networks in the op amp’s negative feedback loop allowing selected frequencies to be cut or boosted
DEF:
summing amplifiers
used to provide isolations between various inputs/outputs in a signal chain
DEF:
distribution amplifiers
amp that does not provide gain but increases current signals allowing it to be delivered to multiple loads
DEF:
VCA / DCA
voltage/digitally controlled amplifier
output voltage decreases as the control voltage increases
DCA - digitally controlled DC control voltage
Power amplifier classes
A
B
AB
C
D
T
EF
G
H
Class A power Amplifiers
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
Class B power Amplifiers
“pull-push” amps
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
Class AB amps
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
Class C amps
used for driving narrow band frequencies into resonant load
used for radio to drive signal to aerial
Class D amps
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
Class T amps
from the Tripath Company
ultrasonic fequency is continually varied in accordance with input amplitude
very high efficiency
Class G amps
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
Class H amps
variation on Class G but supply voltage rails track input signal continuously maintaining just enough headroom to accommodate the amps output requirements
