Chapter 6: Audio Systems

Question 1

What are examples of input sources

Answer 1

Microphones, Mp3, Instruments, CD

Question 2

What is a pre-amp

Answer 2

Voltage amplifier. Non-inverting op amp due to high input impedance

Question 3

What is a mixer

Answer 3

Combine input signals from a number of sources and allow music instruments to be faded in or out. Based on a summing amp

Question 4

What is tone control?

Answer 4

Emphasis high (treble) or low (bass) notes

Question 5

What is a power amp

Answer 5

Produces current and voltage signals to drive the loudspeaker. Composed of emitter follower or push-pull power amps

Question 6

For a pre amp, the bigger the gain, the lower the bandwidth. How can this problem be overcome?

Answer 6

Using a multi-stage amplfier. Bigger gain with higher bandwidth

Question 7

What do capacitors do in audio systems?

Answer 7

Block DC signals

Question 8

What does the variable resistor on each channel do for an Audio Mixer?

Answer 8

Gain for each channel to be varied. This changes how the audio sounds

Question 9

Why is it important to design an audio mixer with a feedback resistor?

Answer 9

So the output doesn’t saturate

Question 10

State a disadvantage of an audio mixer and how it can be fixed

Answer 10

Signal can’t be faded out completely, use potentiometers instead so the signals can be varied from 0 to full amplitude

Question 11

Difference between passive filters and active filters

Answer 11

Passive only cut signals
Active filters cut and boost and can have a gain bigger or smaller than 1

Question 12

Draw the 4 active filters

Answer 12

see notes

Question 13

When does distortion occur?

Answer 13

In frequencies above the break frequencies

Question 14

How to remember how to draw the filters

Answer 14

Treble=Capacitor parallel
Bass=Capacitor series
Bass boost=treble cut
Bass cut= Treble cut

Question 15

State the advantage of an emitter follower (transistor)

Answer 15

good for matching impedances as it has a high input impedance and a low output impedance

Question 16

State the disadvantage of an emitter follower

Answer 16

amplifier only works for positive input voltages greater than 0.7 V. Biasing with resistors is the solution.

Question 17

State the advantage of an source follower (mosfet)

Answer 17

good for matching impedances as it has a high input impedance and a low output impedance.

Question 18

State the disadvantage of an source follower (mosfet)

Answer 18

amplifier only works for positive input voltages greater than 3.0 V. Biasing with resistors is the solution.

Question 19

State the disadvantage of an source follower (mosfet) with added DC

Answer 19

there is always a current flowing through the biasing resistors.
The transistor is always conducting so always dissipating heat.

Question 20

How would you solve the problem of crossover distortion of a push-pull amp

Answer 20

Op amp with negative feedback