Sonic Farm Star Treq is a dual-channel tube equaliser with a fully discrete signal path and a hybrid topology. Pentodes provide the majority of the gain, delivering smooth yet precise equalisation, while transistors act as buffers to drive the output transformer and subsequent units in the signal chain.
Each channel features five filter boards that are entirely passive, utilising real inductors and capacitors to create bell-shaped EQ curves. The first and last bands can be switched to shelving mode for added flexibility.
The bandwidth (Q factor) is adjustable from approximately 0.2 to 9, with 12 frequency steps per band selected via rotary switches. Gain and Shape controls are detented for precise recall. Thanks to dual 150V supply rails, the Star Treq operates with an industry-leading 300VDC on its main EQ boards, ensuring exceptionally high headroom.
Tonally, the Star Treq is both sweet and transparent, adding subtle coloration while maintaining clarity and definition. It is suitable for tracking, mixing, and mastering, offering versatility in any studio application. As with all Sonic Farm units, all supply rails are fully regulated for smooth, noise-free operation.
The design of the Sonic Farm Star TrEQ was driven by the goal of creating a versatile, tube-based 5-band equaliser suitable for tracking, mixing, and mastering. Tubes were chosen for their subtle colouration, while real inductors were used to introduce a touch of saturation, as long as they operated within their near-linear range. However, these choices came with design challenges and necessary compromises.
To balance the natural non-linearity of tubes, the circuit had to limit their effect to a pleasing degree. Since a good preamp already adds character, the EQ itself needed to impart less colour. The solution was a hybrid topology featuring an OP-amp stage preceded by two pentodes. A dual 150V supply was implemented to fully utilise the headroom, ensuring the tubes operated at 300V. Solid-state components support the tubes by adding minor gain and reducing impedance for proper signal drive.
One of the biggest challenges was managing gain variation in the tubes. Unlike conventional solid-state discrete OP-amps that use matched transistor pairs for minimal DC offset, tubes degrade over time and require replacement, making perfect matching impractical. This posed a risk of significant DC offset, potentially damaging the unit. After nearly two years of development, a sophisticated servo circuit was designed to correct DC offset, ensuring stability with any tube pair. While matched tubes maximise headroom, they are not required for proper operation.
Inductors presented another design hurdle. Real-world inductors introduce complexities such as parasitic capacitance, frequency-dependent inductance, hum sensitivity, and wire resistance. Though solid-state gyrator circuits could offer more precision, they lack the natural saturation of real inductors. Ferrite core tolerances and capacitor inaccuracies added further challenges, making precise tuning necessary. Each inductor and capacitor had to be carefully adjusted per frequency, and shielding the power transformer was critical to eliminating hum.
As a result, the Sonic Farm Star TrEQ is not a surgical EQ. If pinpoint adjustments – such as boosting 1kHz while cutting 1.3kHz – are required, a different design would be more suitable. However, this precision would come at the expense of the organic sonic character imparted by the unit’s analogue imperfections. The Sonic Farm Star TrEQ embraces these trade-offs to deliver a rich and musical equalisation experience.
