SPL is constantly pushing analog signal processing to its limits by combining the best possible components with perfectly optimized circuit design. As our latest achievement in this ongoing process, SPL‘s High Gain Series surpasses the hitherto accepted limits of audio signal processing and combines truly unparalleled analog sound quality with the control and convenience of digital units.
Further High Gain projects are in planning, including a microphone preamplifier and a compressor, although no availability projections can be made for these currently.

PQ 2050

The PQ is a fully parametric, dual-channel 5-band equalizer. As with all SPL High Gain units, the PQ has an operating voltage of 124 V and is constructed with the best analog components available.

The Filter Stages

The individually switchable filter bands are self-contained on separate circuit boards. Contrary to most conventional equalizers, the bands are not summed via a central stage, so that the signal passes only through those filter stages which are activated.

Constant Q and proportional Q modes
Each frequency band consists essentially of two fully parametric equalizers: one for constant Q mode and one for proportional (or variable) Q mode, selectable per band. The PQ is the first equalizer to offer both modes, endowing it with double equalization power for demanding corrective and creative applications.
In constant Q mode, the selected bandwidth remains unaffected by the amplitude setting, making it the better choice for corrective applications (e.g. to eliminate unwanted frequencies). In proportional Q mode, the bandwidth is reduced as the amplitude is raised and vice versa. This more „musical“ operating mode is better suited for creative, sound-shaping applications.

Controls

All variable controls are motorized and all keys are digitally controlled to provide the same programmability and repeatability of digital units. Individual settings can be stored in up to 24,000 presets.
Motorized potentiometers
The adjustment range of the Frequency, Bandwidth and Amplitude potentiometers is evenly dispersed throughout the 300-degree movement area, ensuring smooth and continuous adjustments and extreme operational security. The high resolution of each respective value (e.g. Q from 0.1-3.7, evenly distributed over 300 degrees) allows extremely precise adjustments as well as accurate repeatability.
We intentionally avoided unnecessary or confusing functions such as frequency range switching or frequency, bandwidth or amplitude multiplicators.

LINK Mode
Channel 1 and 2 can be linked for coherent stereo operation and either channel can be designated as master. In link mode, coupled bands can be activated/deactivated simultaneously, while single bands may also be released from link mode if required for individual adjustment.

Master/Slave (unit link) mode
FThe PQ offers a Master/Slave mode for surround applications or subgroup processing, in which the settings on the master unit are precisely duplicated on the slave units. Thus the PQ is the first EQ system that provides up to eight channels for coherent analog equalization of surround recordings.

Remote Control Unit
SPL is developing a remote control unit with an identical user interface to the PQ, which will be able to control up to four units—individually or in common.

Display
A central display clearly indicates all information relating to preset, storage and control functions. The control logic is clear and intuitive without menu layers, guaranteeing quick and easy operation and a minimal learning curve.

Frequency
Each channel provides five fully parametric frequency bands covering 10 Hz to 28 kHz. Each band overlaps its neighbor by one octave and can be independently activated and deactivated.
The following frequency bands are provided:
LF (Low Frequencies): 10 Hz-235 Hz
LMF (Low Mid Frequencies): 35 Hz-720 Hz
MF (Mid Frequencies): 330 Hz-7.1 kHz
HMF (High Mid Frequencies): 670 Hz-16 kHz
HF (High Frequencies): 1.2 kHz- 28 kHz

Amplitude
Amplitude settings are freely adjustable from -11.5 to + 11.5 dB. The lower range between 0 and 2.5 dB offers extremely high resolution, allowing delicate adjustments with maximum precision.

Bandwidth
Bandwidth is adjustable between 0.1 and 3.6 Q in proportional Q mode and between 0.7 and 15 Q in constant Q mode. The extremely high maximum bandwidth in constant Q mode enables tight, selective control in precision applications.

Illuminated keys
The PQ features illuminated keys that illuminate brightly when activated.

LF, LMF, MF, HMF and HF keys
These keys activate (key lamps lit) or deactivate (lamps off) the 10 filter bands.

Con. Q key
This key switches the 10 filter bands between proportional Q mode (lamps off) and constant Q mode (lamps lit).

Additional construction features

All crucial resistors in the I/O and filter circuits are subject to ultra-tight tolerances of 0.001% to ensure clean and accurate amplifier stage performance. All circuit board tracks are double-width (1 mm) and double-thickness (70 micrometers), guaranteeing stable high-gain operation with minimum resistivity. A separate grounding track is placed between signal track pairs, virtually eliminating crosstalk for maximum signal separation.

Connections: The PQ is fitted with XLR I/O connectors.

Power for sound: SPL SUPRA components

The central component of the PQ is a fundamentally new amplification design: discrete, custom made Class A audio operational amplifiers which run on a 120V operating voltage (+/- 60 V). This amounts to over three times the operating voltage found in most high quality audio gear (+/- 15-20 V) and about twice as much as the highest voltages used in the best units currently available.
This extremely high voltage allows the circuitry to process an astonishing dynamic range of ca. 150 dB and an amazing +34 dB of headroom, virtually eliminating overloading of individual filter stages—even when processing extremely high-level signals.
For the first time, transistor circuits with such an impressive degree of stability and freedom from harmonic distortion can be realized. After the revival of tube units in the early ‘90s, we feel that the time may be ripe for a revival of the „transistor sound“ in the near future.

Input stages of the SUPRA components
Wolfgang Neumann, founder of SPL and developer of the High Gain Series, has paid the highest attention to realizing components with high loop amplification, extremely low phase shifting and THD, combined with maximum amplification and a frequency response up to 100 kHz.
A main and obvious advantage of the discrete SUPRA components is the exclusion of those parts often found in industrially manufactured standard components that are not necessary for audio processing.
The SUPRA input stages are designed as symmetrical differential stages and comprise six matched high voltage transistors switched in parallel.
The concept of the input stage is based on the established principle that parallel circuits are not correlated noise sources, but the wanted signals are added geometrically which decreases the overall noise. The input stages are free of coupling capacitors to exclude additional capacitor noise. The symmetrical operation voltage of +/- 60 V is delivered from a linear -80 dB high voltage power supply.

Intermediate stages of the SUPRA components
The audio signal is lead to a further differential stage and from there through further processing stages to the Class-A output stage. All passive components have been tested for the highest fidelity.

Output stages of the SUPRA components
Extremely low noise, high voltage output transistors are set up with a high quiescent current and excessive heat is dissipated via special cooling plates.