Licensed EMS Trapezoid Generator and VCA

The RS-510N is an authentic licensed recreation of the classic EMS envelope shaper and integrated VCA found in the Synthi A, VCS3, and AKS synthesizers.

This module diverges from standard ADSR envelopes by shaping control voltages around four stages: Attack, On, Decay, and Off. Instead of waiting for a gate signal to end, the internal trapezoid shape sustains for a fixed hold period dialed in by the On control, while the Off knob sets a mandatory delay window before the module can accept a new trigger.

In practice, the module doubles as an unusual low-frequency oscillator. Setting the Off time to its minimum value forces the circuit into an automatic repeating loop, generating asymmetric trapezoidal or triangular modulation waves. The dual signal outputs feature a bipolar level control, letting you attenuate and invert the generated shape directly from the front panel.

The onboard VCA is internally normaled to the trapezoid voltage, providing complete dynamic voice shaping without extra patch cables. Because the Off parameter intentionally ignores incoming gates until its delay cycle completes, the envelope can feel restrictive if you expect traditional keyboard tracking, but this unique behavior is what gives classic EMS rhythms their distinct feel.