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In the PASSEQ, SPL revived the concept of the passive equalizer that was used in the 50’s and 60’s. The charming sound of this vintage technology combined with the modern 120V technology results in the PASSEQ.

Only One Filter

All control functions are part of only one passive filter. There are three frequency ranges: Low, Mid and High, each with a cut control on the left and a boost control on the right. Output control is in the middle.


A passive filter has no amplification stages. Therefore, it can only be lowered. If one frequency is to be boosted, all the others must be lowered. Behind the filter, there is a stage that makes up for the lowered overall level. Since low noise is particularly important here, since up to 20 dB can be made up for, the 120V technology comes into its own.


The entire passive filter (variable resistor, capacitor and coil) provides a very nice sound characteristic. Besides the choice of components, the charging behavior of the capacitors and the saturation behavior of the coils play a major role. The resulting relative inertia compared to potentially very fast active filters is the reason for a pleasant, musical sound characteristic. SPL describes the sound as smooth and transparent, as well as strikingly silky in the highs with pithy basses.
During fine-tuning, through component selection, emphasis was placed on achieving the most musical sounding curves possible. For example, you don't have to worry about a comparison with a Pultec EQ from the 1950/60s. PASSEQ comes without all the disadvantages of a 60-year-old original, like the very high background noise, or the very limited frequency selection.


Another highlight of the PASSEQ is the HF+ band, which has been extended by the frequencies 25 kHz and 35 kHz and sounds so incredibly good that you don’t want to switch it off.

SPL PASSEQ Mastering Equalizer

  • SPL PASSEQ Mastering Equalizer
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