The further development of the RIAA stage of the HP 700 (SE) increases the signal-to-noise ratio while reducing system-related equalization errors. Increasing the bandwidth enables precise RIAA equalization and explores the full potential of analog playback. The Phono RIAA is equipped with a switchable subsonic filter.
The principle of the record is based on mechanical scanning: music signals are cut into the record as an audio track and mechanically sampled by the pickup. In order to be able to integrate the entire frequency range from 20 Hz to 20 kHz into a sound track, low frequencies must be reduced and the upper frequency range must be increased. The ratio of boost or cut is defined and is referred to as RIAA equalization.
A phono amplifier must therefore be able to reproduce the RIAA equalization exactly in order to avoid tonal distortions. An accuracy of 0.5 dB across the entire frequency range and channel equality of 0.1 dB are minimum requirements.
We realized the phono RIAA circuit of the HP 700 SE with three tubes:
ECC 83 (12 AX 7)
ECC 81 (12 AT 7)
ECC 88 (6922, 6DJ 8)
The phono RIAA amplifier of the HP 700 SE must always be supplemented with an input module. A maximum of two phono input modules can be installed. The function of the input modules corresponds to an input amplifier, which raises the different signals from the pickup to a constantly high level that the RIAA amplifier can optimally process. Phono is then selected via IN 1 to IN 2.
Subsonic filters
In addition, the Phono RIAA is equipped with a switchable subsonic filter (-3 dB at 15 Hz).
Wavy records and unfavorable pickup/tonearm combinations can lead to significant low-frequency interference that affects bass reproduction. These low-frequency levels can be attenuated with the switchable subsonic filter. The corner frequency is outside the audible range at 15 Hz.
Delivery condition: Subsonic filter on