Helios Type 69 Preamp and EQ

This is the newer end-to-end Helios model, based on two Olympic-era modules and their associated output fader. It includes the Lustraphone input transformer, feedback-style triple-amplifier input stage, and nonlinear behavior of the passive EQ inductors. Those modeled stages distinguish it from the EQ-only Legacy plug-in.

The preamp and EQ can each shape character. Input gain changes the amplification structure, while the EQ's broad shelves and peak/trough midrange provide assertive tonal moves. The bass section is unusual: its selector alternates between boost frequencies and fixed-frequency shelf-cut amounts, so the Bass Gain knob is not active in every position.

Set input mode and drive before equalizing, then use the clean final Level fader to compare at consistent loudness. EQ IN lets you separate tonal shaping from the remaining channel coloration; Power is the full bypass. In an Apollo Unison slot, mic input impedance and supported controls interact with the physical preamp. Outside that slot, the software model remains useful, but it does not change hardware loading.

Manual — sections: Operational Overview; Unison™ Integration (Apollo only); Type 69 Control Differences.

• Input Select / LINE–MIC: Chooses the input path governed by Gain. Feeding a line-level track through the virtual mic path can produce a large gain increase and more distortion, so lower downstream level before switching. In Unison, connected Hi-Z input forces Mic operation.
• Gain: Six steps—20, 30, 40, 50, 60, and 70 dB—adjust the triple-amplifier feedback network. Use the interaction of input mode, gain, and pad to establish clean or driven character.
• −20 Pad: Attenuates the input by 20 dB in Mic mode only. It does not function in Line mode. This preamp control is absent from Legacy.
• High Shelf Gain: Fixed 10 kHz shelf with −16 to +12 dB available in 4 dB increments. Use it to change overall upper-frequency balance rather than isolate a narrow resonance.
• Mid Freq / Mid Gain: Frequency choices are 700 Hz, 1, 1.4, 2, 2.8, 3.5, 4.5, and 6 kHz. Gain offers up to 15 dB boost or 9.9 dB cut; increasing its setting narrows the response.
• PK/TR: Selects midrange Peak boost or Trough cut. Trough also introduces the modeled approximately 1 dB overall level loss, so compare at compensated level.
• Bass: Frequency positions select peak boosts at 60, 100, 200, or 400 Hz. Alternatively, choose −3, −6, −9, −12, or −15 dB for a fixed 50 Hz shelving cut. The modern top boost frequency is 400 Hz, unlike Legacy's 300 Hz.
• Bass Gain: Controls only peak-boost mode, up to 15 dB. At its minimum the bass EQ circuit is bypassed; moving up engages the modeled boost starting around 3.3 dB. The manual also warns that choosing a boost-frequency position can change gain even at zero. It has no effect in shelf-cut mode.
• EQ IN / Polarity: EQ IN enables equalization; EQ bypass retains circuit coloration. Polarity flips the signal when switched up.
• Level: Final clean attenuation/boost from −infinity to +10 dB, modeled around the Danner fader with added boost convenience. Use it to compensate preamp drive and EQ gain.
• Power: Full processing bypass, distinct from EQ IN. Unison Gain Stage Mode can expose Gain and Level to the hardware control.

Manual — sections: Preamp Controls; EQ Controls; Global Controls.