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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2011/
Module Title: Audio Electronics
Module Code: ELTR
School: Electrical and Electronic Engineering
Programme Title: MA in Music & Technology
Programme Code: GMUTE_9_Y
External Examiner(s): Mr D. O’Connell, Mr M. Kelleher, Mr D. Heffernan
Internal Examiner(s): Mr Patrick Collins
Instructions: Answer all questions.
Q1 = 25% , Q2 = 25% , Q3 = 35% , Q4 = 15%
( M = 10
6
, k = 10
3
-
, n = 10
-
, p = 10
-
Duration: 2 hours
Sitting: Autumn 2012
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
a) A 15V supply is connected to 3 resistors in series : R1 = 1.8k , R2 = 2.2k. The total current flowing is 2mA. Find the value of the 3rd^ resistor. [ 5 marks ]
b) Too much current is being drawn by a load of 16 ( a speaker input ). A resistor of 144 is added in series to limit the current. The speaker output drops to a fraction of its expected value. Calculate this fraction. [ 5 marks ]
c) Three resistors in parallel are connected to a 20V supply. One carries a current of 1mA. The other carries a current of 2mA. The total current flowing is 7mA. Calculate each resistor value and the total resistance. [ 5 marks ]
d) If a 100W speaker has a resistance of 8 then how much current will flow when 100W is being consumed? [ 5 marks ]
Fig Q1e.
e) In Fig Q1e : V7 = 15V. R27 = 1k. R23 = 2k. R25 = 3k. R24 = 4k. R25 = 5k.
i. Find the total resistance and current. ii. Find current through and voltage across each resistor. [ 5 marks ]
a) Explain how a Shure SM58 dynamic microphone can be connected to a phantom power circuit and not be affected or damaged. Include a circuit diagram in your answer. [ 8 marks ]
Fig Q3b.
b) Explain the function of an audio output transformer. Use the numbers in Fig Q3b above in your explanation. The 10 resistor represents a speaker. The 100V signal comes from an amplifier. [ 11 marks ]
Fig Q3c.
c) For the DI box shown above in Fig Q3c,
i. What function do R5 and C4 perform? ii. Why are C1 and C2 in parallel? iii. How does the unit divide down the input signal by -10dB when this option is chosen? Show calculations that prove that the output signal is reduced by roughly 10dB. iv. Show calculations that prove the output signal is reduced by roughly 20dB when this option is chose. [ 8 marks ]
d) What is a “ground loop”? How can a DI box solve the problem of having a ground loop in the system? [ 8 marks ]
a) An 8-bit ADC has an input voltage range of 0V to 5V. Initially the output is 10101010. It then changes to 11001100. What was the change in the input voltage that caused the ADC output code to change? [ 2 marks ]
b) An ADC has an input voltage range of 0V to 3.3V. If you want to be able to detect an input change as small as 20V , what is the minimum numbers of bits needed in the ADC? [ 3 marks ]
c) Explain the principle of operation of a SAR ADC. Draw a circuit block diagram as part of your explanation. [ 10 marks ]
