Instruction Manual

frequency cut-off is accomp1ished by placing a capacitor directly across the
signal input terminals of the circuit card connector, again allowing inter-
changeability of amplifiers irrespective of response differences in various
amplifier locations. The extreme stability of the amplifier allows a
capacitive shunt without any change to amplifier performance other than high
frequency response. With a 600 ohm source impedance to the amplifier, as an
example,
a .012 MFD capacitor would provide an amplifier response that is -3 dB at 40
kHz. Any desired frequency response below 1 MHz may be obtained in this
manner.
IMPEDANCE MATCHING
There exists no requirement to match input and output impedance with the
Model 10l Audio Amplifier, since the amplifier is purely resistive in nature.
The amplifier may be terminated with any source resistance, O ohms to
infinity, with the only performance change being one of noise. Noise output
further decreases below the -127 dBm specification as the source impedance
decreases (see Noise section).
The output of the amplifier may be loaded with 600 ohms to infinity with
no performance change. Loadings 600 ohms or greater should be observed for
amp1ifier maximum power capability considerations (output stage current).
NOISE
Noise output, referred to the input, varies from -132 dB to -125.5 dB for
input sources of O ohms to infinity, respective1y. Typical sources of 50 ohms
and 600 ohms give -l30 dB and -l27 dBm, respectively. In order to maintain the
specified noise figure, the amp1ifier should not be located in or near strong
magnetic fields produced by transformers, motors, etc.
As an example, the unequaled low equiva1ent input noise measurement of -
127 dBm is based on: Unweighted response; 20 Hz to 20 kHz bandpass filter; and
input terminated with 600 ohm low noise (eg. meta1 film) resistor.
Note: A1l measurements specified in dB are measured with respect to O dB =
0.775 volts. Al1 data in dBm are with respect to O dBm = l mW dissipated into
a 600 ohm resistive 1oad = 0.775 volts across 600 ohms.
INPUT TERMINATION/MICROPHONE LOADING APPLICATIONS
Microphone loading normally falls into two categories: Power matching and
voltage loading. Most American dynamics, etc. fa11 into power matching and are
loaded with their source impedance. Voltage source microphones, such as
condensor microphones, however, may not be 1oaded in this manner or distortion
and frequency discrimination will occur. All such microphones should see at
least 5 times their source impedance - or operate unloaded.
Termination into the Model lO1 Audio Amplifier, therefore, is simply a
matter of selecting a transformer tap that reflects the proper 1oading to the
microphone to be used.