Thermionic Culture Swift 2-Channel All-Valve Equalizer

The Thermionic Culture Swift is a 2-channel all-valve equalizer equally suited to tracking individual instruments and processing a stereo mix bus. The design draws from two classic references: a 1950s EMI desk, which contributes a Baxandall-type active EQ with extended top and bass response, and the Pultec, which informs the passive mid-lift section with 4 selectable frequencies and 3 Q settings. A Presence switch based on a Vic Keary design from 1963 provides a broad mid/high frequency lift, and passive controls handle HPF, Mid Cut, and AIR. All pots are continuously variable for subtle, stepless adjustment. The electronics can be completely disconnected by a Bypass switch for transparent A/B comparison, and the Swift is capable of +20dBu output without noticeable distortion. Each channel uses only two valves with modern Sowter transformers, keeping valve colouration minimal while achieving specifications well beyond the original reference designs.

Key Features

• Baxandall-type active EQ — based on 1950s EMI desk topology with extended top and bass response beyond the original; classic shelving-style active EQ character
• Presence switch — broad mid/high frequency lift; based on a design by Vic Keary from 1963, as used in his mixing desks; adds presence without harshness
• Passive mid lift (Pultec-inspired) — 4 selectable frequencies; 3 Q settings; passive design provides the natural, musical quality associated with classic passive equalization
• Passive HPF, Mid Cut, and AIR — all passive; HPF last-position provides a shelving bass cut combined with a very low frequency filter—combine with bass lift at 50Hz or 100Hz for a Pultec-type simultaneous boost and cut effect; AIR adds high-frequency clarity
• Gain on switches — gain stages selected by switch for accurate recall and comparison purposes; all other controls continuously variable
• Bypass switch — completely disconnects the electronics for accurate comparison with the unprocessed signal
• Two valves per channel — minimal valve colouration; modern Sowter transformers (designed specifically for the Swift); technically superior to the original reference designs
• +20dBu output without noticeable distortion — no metering (deemed a distraction from the listening process)

Specifications

• Channels: 2
• Active EQ: Baxandall type (1950s EMI-inspired; extended top and bass)
• Presence Switch: Yes (broad mid/high lift; Keary design, 1963)
• Passive Mid Lift: Pultec-inspired; 4 frequencies; 3 Q settings
• Passive HPF: Yes (last position: shelving bass cut + very low frequency filter)
• Passive Mid Cut: Yes
• Passive AIR: Yes (high-frequency clarity)
• Bass Lift Frequencies (for Pultec effect): 50Hz; 100Hz
• Gain: Switched
• Controls: Continuously variable pots (not indented)
• Bypass: Hard bypass switch
• Valves per Channel: 2
• Transformers: Sowter (modern, custom design)
• Max Output: +20dBu
• Metering: None
• Construction: Handcrafted in England