Bettermaker EQ 502P - Manual (Page 14)

14
VII. EQ Filter Sections in Depth
We’ve put a large amount of time, effort, money, and listening tests into the research and development of the
analog stages of the Bettermaker EQ502P. We feel that it represents one of the best values, highest fidelity, and
newest methods of working available in audio today. We set out to make a product that broke new ground, an
equalizer with the highest sonic quality, ease of use, and a full pallet of sound shaping tools to allow engineers to
make the best-sounding record. In the following pages, we’ll share this knowledge, show how the filters work and
interact to provide a complete sound-sculpting system.
The following measurements illustrate a precision of filter implementation rarely seen in any analog equalizer.
These were taken at 96 K sample rate so they do not extend to the full 100 kHz bandwidth of the EQ502P. As
the curves approach the Nyquist frequency of 48 kHz they will appear slightly deformed (though in real life they
extend symmetrically and smoothly to 100 kHz). Also, since human hearing is generally limited to under 20 kHz,
you should pay attention to how the curves look within the audible spectrum. For viewing clarity, we began our
measurement sweep at around 20 Hz and stopped it at 20 kHz or as high as 40 kHz.
PEQ Filter Section
History / Theory of Operation
The P-filter section is an homage to a classic Pultec™ EQ from the 1950s which has attenuation (cut) and
addition (boost) controls on separate knobs. This design is unique in that identical boosts and cuts do not cancel,
but rather deform the filter response in a special way. However we did not set out to make an exact replica.
We wanted to update this classic design and make it even better while maintaining its somewhat quirky feel,
so original users can feel right at home. The P section is a passive filter, and we have included a make-up gain
stage which has slightly more gain than in the originals. It is also built with modern components which create a
faster response, resulting in sharper and more detailed transient reproduction. Our implementation of this filter
retains the original’s classic warm, resonant quality while still being lively and transparent for classical music or
audiophile jazz.
P Section Topology/ Implementation
The P-filter low frequency section is a first order RC filter network with additional resonance. The P-Filter
high frequency boost is built with an LC filter network. The inductor in this network is hand-wound for superior
sonics and custom sound characteristics. Both RC and LC filter networks are passive filters. The make-up gain
of the P-filter section is performed by a high-speed operational amplifier to give clean, accurate, and consistently
reproducible gain. Since the digital encoders are speed-dependent, turning them slower results in a finer gain shift,
so it is possible to be very exact with this EQ, and our true-stereo implementation is perfectly matched channel-to-
channel with single control ergonomics.
PEQ Bandwidth/ Gain Ranges
The P-filter section is in four parts:
Low Frequency
1) Boost: a fixed bandwidth shelf with a maximum boost of +14 dB
2) Cut: a fixed bandwidth shelf with a maximum cut of -14 dB
High Frequency
3) Boost: a bell with adjustable slope. At its middle bandwidth of 7 its maximum gain is +14 dB.
As the bandwidth is increased, its maximum boost is reduced.
4) Cut: a fixed bandwidth shelf with a maximum cut of -14 dB.