SPL Passeq Passive Equalizer Stereo EQ
The SPL Passeq is one of the most powerful passive EQ units ever made, featuring an amazing 144 passive filters! The Passeq is built to fulfill the highest professional expectations and is a useful tool throughout all areas of audio processing, from recording, to mixing, to mastering. The SPL Passeq makes use of true passive filtering for maximum sound character and minimum distortion and features a number of controls for detailed sound sculpting.
- 144 true passive filters: 72 per channel
- Individual design and component specificity for each filter
- Single core coils, helping to excludes sonic degradation and improve THD values
- 120V makeup amplifiers based upon SPL unique SUPRA-OPs
- Switches and potentiometers from Elma and ALPS
- 14 dial controls per channel: 28 in total
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With 72 passive filters per channel, 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 like a precise mechanical 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 earlier filter design and construction, each Passeq filter is optimised 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 helps to achieve the widest possible range and tonally appealing sound colour palette from any passive EQ.
Advantages of Passive Filtering
Typically, coil inductance in virtually all active filters is achieved through simulation. True passive coil filters, on the contrary, can only 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, offer at the very least, a clear sonic alternative, which our ears often perceive as an extremely attractive one.
All passive filter components 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 the 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.
The Passeq employs two distinct filter types. One of these functions much like traditional shelving filters, while the other functions 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 minimises 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 also offers variable Q values.
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, SPL's extraordinary Supra-OPs, with their unique analogue 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 analogueue or digital signal processing. The tremendously fast SUPRA slew rate of 200V/ms allows for the highest possible precision in filter output signals, particularly in the all-important arena of transient response.
SPL SUPRA Op Amps
The specially designed and for-audio optimised SUPRA OPs are constructed in three stages with high performance, extremely low noise transistors from the modern HF technology sector.
The Full Range
The Passeq is the first passive EQ to provide three separate frequency ranges for both amplifier and cut stages. One famous, if not the most famous, passive design was the Pulteq EQ from the decades of the 1950's and 60's. This EQ sported two frequency bands (low and high frequencies) and had only a few switchable frequencies to offer. In contrast, the Passeq has 12 switchable frequencies per band, totalling 36 boost and 36 cut frequencies. Boost and cut frequencies are NOT identical, thus the resultant 72 frequencies per channel offer an enormous choice for the most elaborate EQ curves.
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UK Non-Mainland: £ 12
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