UA 610-B Tube Preamp and EQ

The 610-B is modeled from UA's 2-610 hardware and represents the modern branch of the 610 design. It shares the two tube gain stages and transformer-based architecture with the family, but offers more detailed input-gain choices, switchable mic impedance, and selectable shelf frequencies than the vintage A.

The signal's color depends on both Input Gain and the large Level control. One changes drive at the first tube stage; the other sets the tube output stage. Because the shelving EQ is feedback-based, tonal changes can also affect distortion in that output stage. The separate Output control is clean, allowing loudness compensation without removing the chosen saturation.

For an ordinary mix insert, begin with Line, set gain structure, and apply broad shelves before final output matching. Mic settings can produce much greater drive from a line-level track, so approach them carefully. In a dedicated Apollo Unison insert, the mic impedance choices and supported controls interact with the physical preamp. The linked current manual distinguishes that hardware behavior from standard inserts and notes that the native version's input pad is fixed off.

Manual — sections: Modern 610-B; Tonal Range; Input Controls; EQ Controls; Output Controls.

• Input Select / Impedance: Choose Line, 500-ohm Mic, or 2-kilohm Mic. Mic introduces approximately 30 dB more unattenuated tube gain than the line path for a DAW-level source; switching can cause a large level jump. In Unison, the Mic setting also changes actual Apollo input impedance. Hi-Z connection overrides source switching.
• Input Gain: Five positions provide −10, −5, 0, +5, and +10 dB at the first tube stage. These settings alter both level and distortion behavior. Zero is an active neutral gain setting, unlike the 610-A's central OFF position.
• Mic Input Pad: Attenuates Mic by 15 dB when engaged. It does not work in Line and is unavailable for Unison Line/Hi-Z inputs. The manual states that it is fixed off in the native plug-in. This is the B's 15 dB pad, not the A's 20 dB pad.
• Polarity: Up inverts polarity, down preserves it. Use for microphone-combination checks rather than as a substitute for time alignment.
• LO Frequency / LO Gain: Choose a 70, 100, or 200 Hz low shelf. Gain options are 0 and ±1.5, ±3, ±4.5, ±6, or ±9 dB. At zero gain the band is inactive, so frequency selection has no audible effect.
• HI Frequency / HI Gain: Choose 4.5, 7, or 10 kHz, with the same 0 and ±1.5, ±3, ±4.5, ±6, ±9 dB gain choices. These shelves support broad tone changes, not narrow corrective bells.
• Level: Drives the tube output stage, with approximately 61 dB of available gain. More Level can add color. Listen again after EQ adjustment because the feedback-style EQ influences the output-stage distortion character.
• Output: Clean final trim from −infinity to +12 dB. Lower it when driving the tube stages harder to compare at equal loudness. Minimum output silences the signal but does not itself unload processing.
• OFF: Click the OFF text associated with Output for plug-in bypass. Outside Gain Stage Mode, rotating the knob does not select that bypass position. Apollo Unison Gain Stage Mode can provide tactile access to input gain, Level, and clean Output as separate stages.

Manual — sections: 610-B Mic Impedance; 610-B Input Gain; Mic Input Pad; 610-B EQ; Level; Output / Off.