Inductors are wires wound around a coil that provide a form of frequency-dependant resistance. When they saturate, they bring out beautifully musical harmonics that give your tracks the smooth, polished sound that has made Rupert’s consoles and equipment so desirable for over fifty years. This is what makes them different from capacitor-based EQ designs, which do a great job at surgical equalization. But inductors provide the tone.
While it is certainly possible to create a functioning EQ using off-the-shelf inductors, we choose to use our own custom inductors for the 551. This attention to detail in controlling variables such as the winding and core materials in relation to the surrounding circuitry allows the 551 to capture the vitality and personality of Rupert’s classic designs.
EQ IN
Engages all bands of the equalizer except the high-pass filter.
8K / 16K + HF LEVEL
With the switch out, the center or corner frequency of the high band is 8 kHz. With the button pressed, the center or corner frequency changes to 16 kHz. Between this switch and the HI PEAK switch, you have 4 different EQ curves to finesse the high frequency content. The HF knob adjusts up to 15 dB of boost or cut at the selected high frequency.
HI PEAK
When the button is out, the high frequency band operates in shelf mode, boosting or cutting above the corner frequency at approximately 6 dB/octave. Below the corner frequency the amount of boost or cut gradually diminishes. With the HI PEAK button pressed, the high frequency band changes to peak mode with a bell shaped boost or cut curve. The peak mode utilizes an inductor and capacitor circuit to create the bell-shaped curve.
MID FREQ + MID LEVEL
The MID FREQ rotary switch has 6 positions to select the center frequency of the mid band EQ stage. This circuit utilizes an inductor and capacitors to shape the EQ curve, in the same way as Rupert Neve’s console designs of the 70’s. The frequencies chosen are 200 Hz, 350 Hz, 700 Hz, 1.5kHz, 3 kHz and 6 kHz. 200 Hz is especially useful for cuts on individual tracks within a dense mix. The MID knob adjusts up to 15 dB of boost or cut at the selected mid frequency.
MID HI Q
The resonance (or Q) of the mid band at maximum boost is typically 2 when the button is out. When the MID HI Q is pressed at maximum boost, the Q narrows to approximately 3.5. The Q widens nicely with less boost or cut, as is typical for passive EQ circuits.
HPF
Engages an 12dB per octave High Pass Filter with an 80Hz corner frequency.
LOW FREQ + LF LEVEL
The LOW FREQ rotary switch has 4 positions for selecting one of four corner or center frequencies for the low band EQ section. The frequencies are 35 Hz, 60 Hz, 100 Hz and 220 Hz. The LF knob adjusts up to 15 dB of boost or cut at the selected low frequency. Cut can be used as a variable (and perhaps more gentle) alternative to using the HPF.
LO PEAK
When the button is out, the low frequency band operates in shelf mode, boosting or cutting below the corner frequency. Above the corner frequency the amount of boost or cut gradually diminishes at approximately 6 dB/octave. With the LO PEAK button pressed the low frequency band changes to peak mode with a bell shaped boost or cut curve.
EQUALIZER BYPASSED
NOISE
Measured at Main Output, un-weighted, 22Hz-22kHz, source impedance 40 Ohm balanced. Noise specifications may vary depending on which 500 series chassis is being used, and / or interference from stray magnetic fields.
Better than -102 dBV
FREQUENCY RESPONSE
Main output, no load: +/- 0.1 dBu from 20 Hz to 31.5 kHz, -1 dB @ 120 kHz
MAXIMUM OUTPUT LEVEL
23.25 dBu
TOTAL HARMONIC DISTORTION AND NOISE
@ 1 kHz, +20 dBu output level, no load: Better than 0.0025%
@ 20 Hz, +20 dBu output level, no load: 0.13% Typical (2nd and 3rd harmonic)
HIGH PASS FILTER
-2.7 dB @ 80 Hz
Slope: 12 dB/Octave
EQUALIZER ENGAGED
NOISE
Measured at Main Output, un-weighted, 22 Hz - 22 kHz, source impedance 40 Ohm balanced.
Better than -94 dBV
FREQUENCY RESPONSE
Main output, no load: +/- 0.25 dBu from 20 Hz to 45 kHz, -2 dB @ 120 kHz
MAXIMUM OUTPUT LEVEL
23 dBu
TOTAL HARMONIC DISTORTION AND NOISE
@ 1 kHz, +20 dBu output level, no load: Better than 0.009%
@ 20 Hz, +20 dBu output level, no load: 0.13% Typical (2nd and 3rd harmonic)
POWER REQUIREMENTS
120mA on +16VDC
110ma on -16VDC
UNIT DIMENSIONS
1x 500 Series Module: 1.5” W x 5.9” D x 5.25” H
(3.8 cm W x 15 cm D x 13.3 cm H)
UNIT WEIGHT
1.5 lbs. (0.7 kg)
SHIPPING DIMENSIONS
10” W x 8” D x 3” H
(25.4 cm W x 20.3 cm D x 7.6 cm H)
SHIPPING WEIGHT
3 lbs. (1.4 kg)
