Special Functions - Violectric HPA V90 User Manual

Special functions

Please note:
In the following, the internal settings of the HPA V90 are discussed. For
changing these, a TORX T10 screwdriver is required and you should
by all means
PULL THE MAINS PLUG !!!
Only thereafter the settings can be altered without any hazard.
Frequency bandwidth limiting
Your HPA V90's upper frequency limit is 200 kHz - the so-called "3-dB
point" - at which signal level drops by 3dB. This limit is high enough to
exclude any effect on the audible spectrum on the one hand, but low
enough to provide sufficient rejection of possible radio-frequency
interference.
Towards the low end, your HPA V90's frequency response is not
restricted at all. This means that even extremely low frequencies - right
down to DC - will be amplified. "DC-coupling" as this technique is called,
is not necessarily useful since neither DC nor very low frequencies are
audible, but may damage your headphones on the other hand.
Therefore, the HPA V90 offers a low-frequency limiting option as well.
For this purpose, the two "LO-CUT" jumpers to the left and right of the
"VOLUME" control can be swapped from "DC" to "AC" position. When
set to "AC", low frequency response is limited to 12Hz, again referred to
the "3-dB point".
See also: technical appendix, page 22.
Ex-works, the HPA V90 is set to "AC" response (12Hz).
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