EM-301 | Twin Blackmer VCAs

ST. TROPEZ is a dual-channel voltage-controlled amplifier built around two independent THAT2181A precision monolithic VCAs, each derived from the Blackmer gain-control architecture. The devices employ complementary dielectric-isolated transistor structures, providing wide dynamic range, low distortion, and minimal control-voltage feedthrough while preserving signal integrity across a broad range of gain-control applications.

Each channel features independent bias and modulation-depth controls, together with a continuously variable response characteristic spanning exponential, linear, and logarithmic control laws. Rather than switching between fixed response curves, the control permits continuous interpolation, allowing the relationship between incoming control voltage and output amplitude to be shaped with precision.

Both channels maintain independent signal paths, with Channel I's output internally normalled to Channel II when the first output jack is unoccupied. This configuration routes both signals through an active summing stage built around precision operational amplifiers, producing a high-fidelity mix at Output II without requiring an external mixer. Inserting a cable into Output I breaks the normalled connection, restoring fully independent output operation.

The architecture is deliberately restrained: precise voltage-to-gain conversion, wide dynamic range, and minimal coloration. From conventional envelope-driven amplitude shaping to layered modulation and complex dynamic control, ST. TROPEZ maintains a consistent emphasis on accurate gain behavior and transparency throughout the signal path.

01 / AMPLIFIER ARCHITECTURE

Dual independent Blackmer-topology voltage-controlled amplifiers
Precision THAT2181A monolithic VCA architecture
Low distortion and control-voltage feedthrough
Wide dynamic range and precision gain control

02 / VOLTAGE & RESPONSE CONTROL

Continuously variable exponential / linear / logarithmic response
Independent bias and CV modulation-depth controls per channel

03 / SIGNAL ROUTING

Independent channel outputs with active precision op-amp summing at Channel II

POWER & CONNECTIVITY

±12 V. 10-Pin IDC / Keyed headers. Red Stripe: −12 V.

LA CIRCUITS, INC.

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