Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER Instruction Manual - page 48
The QPAUT composed of the preamplifier itself and the microphone power supply, is intended for
the Mike input No 1, whereas the QPUT intended for the Mike input No 2 is composed of the
preamplifier only, then it cannot be installed alone without the QPAUT.
The QPAUT is externally switchable and the QPUT internally.
Dynamic microphones: Impedance 200 Ohm, frequency response ±1dB 80 Hz to 20 kHz, sensitivity
0.2 mV/µbar, max. input level producing 1% distortion 50 mV.
Condenser microphone: "Phantom" +12 V or +48 V, "T" powered (+10 V), same frequency
response as dynamic ones, sensitivity 1.5 mV/µbar, max. input level producing 1% distortion 640
mV.
SPECIAL PLUG-IN PREAMPLIFIERS
Filtering Versions of the QPSE
On special request, it is possible to supply "Standard" preamplifiers having a bass attenuation up to
as much as 18 dB at 50 Hz or whose gain is different from the normal value.
Cable Preamplifiers
These preamplifiers are placed near a dynamic microphone. Their power supply is derived from the
Nagra and is transmitted along the same cable as the signal. The Nagra should be equipped with a
condenser microphone preamplifier (see above).
"CABLE SEN 5-200" Code: QPLE 200 and "CABLE SEN 5-50" Code: QPLE 50 (for 50 ?
microphone)
These preamplifiers function in conjunction with the "Static 5" incorporated within the Nagra. The
overall results are equivalent to using the "Standard 200 and 50" (see above)
The low frequency attenuation can be adjusted on the incorporated "Static 5" preamplifier.
LOW FREQUENCY ROLL-OFF ATTENUATORS
Why Filter?
Sound engineers have long known that in certain cases an attenuation of the low frequencies can
improve the subjective quality of the recording, because:
A)
Certain microphones (e.g. ribbon) have a frequency response which is very linear, but
only if it is sufficiently distant from the sound source. Placed close to the latter (10 cm),
the bass frequencies are accentuated. This gives, for example, a very "warm" voice, a
phenomenon which certain singers exploit, but which diminishes the intelligibility.
B)
A sound studio is constructed and treated in such a manner as to reflect, in the same
proportion, both low and high frequency sounds. When the sound recording is made in
any other room, often the low frequencies are exaggerated, the carpets, curtains and
other absorbent surfaces attenuating essentially the high frequencies, whereas the low
frequencies are integrally reflected.
In the two cases above, the attenuation of the low frequencies only re-establishes the linearity. In
case A) this is clear, but in B) isn't the reality that which we would have heard if the ear was put in
place of the microphone? The ear, however, has the facility of selecting the sounds in function of
their direction and to subjectively attenuate reflected sounds. When recording in mono (and even in
stereo), the microphone captures, without discrimination, all sound which reaches it. Of course, the
directional properties of the microphone can be used, but the reflected bass frequencies can be
behind the sound source and reach the microphone from exactly the same direction as the useful
sound.