SPL | Passeq

The superior sound qualities and musical characteristics of passive filters ideally meet increasing demands in creating manifold sound colors full of character. In the HiFi domain, the Passeq is the high-end EQ beyond doubt – a perfect tool to solve room acoustical problems by the turn of a knob or improve the sound of old, or inferior, sources.

• The most powerful passive EQ ever made—144 (!) passive filters (72 per channel) in one EQ.
• Individual coils per filter.
• Single core coils, which means that every one is wound individually on its own dedicated core. This excludes sonic degradation from mutual influences while at the same time improving THD values.
• 120V makeup gain amplifiers designed with SPL's unique SUPRA-OPs delivering 141dB dynamic range and 200V/µs slew rate.
• True passive coil filters deliver the genuine, characteristic sound associated with inductive components.
• Distortion elements typical of active filters are ruled out by passive filter design.    
• For any number of reasons stemming from design and component advantages over active filters, passive filters achieve a very natural aural quality and through their harmonic treatment (THD, distortion, phase response, etc.), offering at the very least, a clear sonic alternative, which our ears often perceive as an extremely attractive one.
• All passive filter components (variable resistor, capacitor and coil) work in concert to produce this beautiful sonic result. An important part of this process is played by coil saturation and condenser loading characteristics. The resulting difference in latency from characteristically extremely fast reaction of active filters provides for more pleasant, musical sonic qualities. We tend to perceive these attributes in terms of an increased suppleness and transparency, with perceptibly improved, silky highs and robust basses.
• Fully analog power supply with toroidal transformer
• Made in Germany

With 72 passive filters per channel (36 x Boost, 36 x Cut), the Passeq surpasses all previous designs of this type by a wide margin.

Each channel is divided into three Cut and three Boost bands, each offering 12 switchable frequency ranges. The Cut and Boost ranges are not identical; crossovers are designed to work with like a precise mechanic cogwheel so as to allow the engineer access to the largest possible number of optimal, wide-band S-curves with variable slopes.

A further remarkable Passeq feature is its individual sonic adaptation of each inductive filter through separate coil/condenser/resistor combinations: In stark contrast to other filter design and construction, each Passeq filter is optimized for the frequency assigned.

To insure the best possible signal warmth, richness and musicality in processing, coils for critical voice frequencies are custom-made for the Passeq. This achieves the widest possible range and tonally appealing sound color palette from any passive EQ.

Filter Types: The Passeq employs two distinct filter types: One of these functions much like traditional shelving filters, while the other, as a peak filter, and together, they provide the combined characteristics of wide-band control in low and high ranges with more specific frequency range control in mids. This selection minimizes mutual influences between low, mid and high bands while providing a more selective control in the mids is often useful. Mid boost and cut, as well as HF boost filers have been set up in a peak (bell) configuration, while the hi cut, low cut and low boost filters function in a shelving configuration. The HF boost band offers variable values from Q=1 to 0.1.    

Single Core Coils: Until now design approaches have involved individually wound coils, but multiple coils have nonetheless been placed on a single core. The Passeq design places each coil on separate cores. This eliminates any possible unwanted mutual influence transmitted through common-core windings and thus, among other improvements, results in better THD values.

120V Make-up Amplifiers: With passive filtering comes an unavoidable drop in signal level that requires makeup amplification, and with the Passeq, here SPL’s extraordinary Supra-OPs, with their unique analog 120-volt technology, come into play. With a 116 dB signal-to-noise ratio and +34dB of headroom, the SUPRA-OPs offer a stunning 150dB dynamic range, placing them in an unsurpassed leadership position in either analog or digital signal processing. The tremendously fast SUPRA slew rate of 200V/ms allows for a highest possible precision in filter output signals, particularly in the all-important arena of transient response. These amplifiers effortlessly and without coloration or degradation, transmit all the desired filter characteristics and sonic results an engineer has sought out and in the process, pushing beyond the limits of what has been technically possible to now.

SPL SUPRA Op Amps: The specially designed and for-audio optimized SUPRA OPs are constructed in three stages with high performance, extremely low noise transistors from the modern HF technology sector.

The Sound: 120V Rail Technology is our reference technology developed and manufactured to run on an operating voltage of 120 volts, which corresponds to twice that of discrete operational amplifiers and four-times that of semiconductor operational amplifiers.

120V Rail Technology reaches outstanding technical and sonic performances. Technically especially in terms of dynamic range and headroom and sonically especially in reproducing the finest details and delivering a totally relaxed sounding audio experience. Music sounds absolutely natural and hearing fatigue is drastically reduced.

Even the best audio measuring equipment arrives at the boundaries. In same situations we ended up just measuring the Audio Precision Cascade 2 measuring device and we cannot say how good the 120V Rail Technology actually performs.