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9
Noise
The output noise contains a low frequency component (0.03 Hz to 20 Hz) that is independent of the
load capacitance; and a high frequency component (20 Hz to 1 MHz) that is inversely related to the
load capacitance. Many manufacturers quote only the AC noise measured in the 20 Hz to 100 kHz
range, which is usually a gross underestimate.
The noise is measured with an SR560 low-noise amplifier (Gain = 1000), oscilloscope, and Agilent
34461A Voltmeter. The low-frequency noise is measured to be 50 uV RMS with a peak-to-peak
voltage of 300 uV. This noise level is significantly less than the least significant bit of an 18-bit
digital-to-analog converter.
The high frequency noise (20 Hz to 1 MHz) is listed in the table below versus load capacitance. The
total noise from 0.03 Hz to 1 MHz is found by summing the RMS values of the low and high
frequency components, that is �� = √��
Load Cap.
No Load
3 nF
10 nF
30 nF
100 nF
300 nF
1 uF
Table 2. RMS noise versus load capacitance (0.03 Hz to 1 MHz)
10 Overload Protection
Each channel is independently protected against average and peak current overload. Exceeding
these limits will result in signal distortion.
The front-panel overload indicator will illuminate when the total power supplied to all channels is
greater than 25W. This can occur when all channels are simultaneously operated at full power or
when there is a failure of one or more channels. During a maximum power overload, the power
supply is temporarily disabled and will reset once the power drops below 25W.
When the amplifier is first turned on, the overload protection circuit is engaged by default and will
require approximately two seconds to reset.
2
2
+ ��
.
����
����
Bandwidth
HF Noise RMS
100 kHz
39 kHz
14 kHz
5.1 Hz
1.5 Hz
520 Hz
150 Hz
11
Total Noise RMS
130 uV
80 uV
50 uV
30 uV
40 uV
50 uV
70 uV
139 uV
94 uV
71 uV
58 uV
64 uV
71 uV
86 uV
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