PQ is a fully parametric, dual-channel five-band equalizer. The PQ Mastering Equalizer – Model 1540/1544 is a new revised edition of the well-known SPL PQ Mastering Equalizer – Model 2050. All five bands can each be activated or deactivated and you got the possibility (for every single band) to seperately switch between Constant Q and Proportional Q. This kind of circuit has not yet been achieved in any other equalizer.  

Another highlight is the possibility to boost or cut the amplitude to 20 dB. If you only wish minor changes of the music material, you can reduce the intensity of the boost or cut by using the 1/4 Gain-Switch, which regulates the potentiometer from max +/-20dB to +/-5dB cut. This gives you the possibility to perform small corrections, as common in Mastering or higher amplitudes in Proportional-Q mode. 
Thanks to detent potentiometers, a precise recall is very easy to realize. You can adjust parameters Gain, Frequency and Q in 41 steps with detent potentiometers.