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Cork Institute of Technology
Bachelor of Engineering in Applied Electronic Design – Award
(NFQ - Level 7)
December 2006
Audio-Visual Electronics
(Time: 1.5 Hours)
Answer THREE questions. All questions marked out of 100 marks
Examiners: Dr B.V.Donovan Mr. D. Denieffe Dr. R. O Dubhghaill
Q1. Write a brief account of the development of audio recording on magnetic materials up to the development of DAT technology. (30 Marks)
Why did ‘Tape recording’ remain less significant, commercially, than Vinyl records while still being a vital component of any recording studio? (30 Marks)
How did Henry Ford stimulate the tape recorder industry? (20 Marks)
What did Dolby do to improve tape recording technology (and become very wealthy in the process)? (20 Marks)
Q2. A mixer /pre-amplifier circuit is shown in Fig Q2.
If the Microphone output is in order of 10mV rms, what would be the approximate gain of the stage to provide ‘line’ o/p level? Hence evaluate R (^) feedback. (30 Marks) If a S/N ratio of >100dB is required (at the output), what is the maximum rms noise voltage would one measure for a signal level of 1V rms out? (30 Marks) If one wanted to mix/combine two separate audio signals of 20mVrms each, from similar microphones, what would be the equivalent total, input signal level to the amp.? (20 Marks) In the absence of any external source, evaluate the total rms noise voltage on a 600Ω transmission line for a typical HiFi system. (20 Marks)
{Take Er.m.s. (f 1 → f 2 ) = 0.13 √[R (f 2 - f 1 )] μV (R is in Meg-Ohms and ∆f is in Hz).}
4.7k
47k R feedback
47k
V cc
C
C
Fig Q
4.7k
C
600R
