BRUEL & KJAER 2706 - Distortion; Noise and Hum

Due to the generous feedback in the power section, output impedance is
very low. Fig.4.5 shows the variation of the output impedance with
frequency.
100
90
80
///
///
/
70
/
60
/
I
/
I
V/ /// //
/ Sp~fic/io/ /
// //
V/ /
/
/
50
40
30
20
10
0
10 20
50 100 200
500
1K 2K
5K 10K 20K
Fig.4.5. Output Impedance
4.5.2. Distortion
Frequence (Hz)
"r72ool
Heavy feedback in the power section and use of complementary power
transistors
working in class AB have resulted in very low harmonic
distortion.
At full capacity, it will be less than 0.5% over the frequency
range 20 Hz to 20 kHz and wi II be less than 0.2% between 20 Hz and
10kHz. Typical values at 500Hz are -66 dB referred to the fundamental
for both the second and third harmonics.
4.5.3. Noise and Hum
Careful design has resulted in low noise and hum levels, which 'should be
at least 70 dB below full output (i.e. <4.75 mV).
A
typical frequency analysis of noise and hum with short-circuited input
on the 2706 is given in Fig.4.6.
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