UA 610-A Tube Preamp and EQ

The 610-A models the vintage module in Wally Heider's Green Board console. Both its tube gain stages, transformer components, and feedback-style EQ are part of the emulation. It is not the expanded modern 610-B: the A has simpler gain switching, a fixed mic impedance, and fixed shelf frequencies with fewer gain choices.

Tone depends on where gain is developed. Input settings change the first tube stage, while the large Level control drives the tube output stage. The EQ sits within a feedback-style design and can affect the output stage's distortion, so equalization and saturation are not entirely separate decisions. A final clean Output control allows compensation without undoing the chosen drive.

Start in Line mode for a less driven DAW treatment, or carefully compare Mic when stronger coloration is wanted. Establish input gain, shape the broad shelves, and balance Level against Output. In the Apollo Unison version, supported controls and the 600-ohm mic impedance interact with hardware; ordinary or native inserts do not provide physical impedance switching. The current manual also restricts pad availability in the native version.

Manual — sections: Vintage 610-A; Tonal Range; Input Controls; EQ Controls; Output Controls.

• Input Select: Line uses the attenuated line path; Mic applies approximately 30 dB more unattenuated tube gain to an existing DAW-level signal. Reduce monitoring or downstream level before switching. The A's mic impedance is fixed at 600 ohms, unlike the B's two choices.
• Input Gain / LO–OFF–HI: Select LO or HI to change the first tube-stage operating gain. HI adds approximately 8 dB and changes distortion character. The center OFF position bypasses processing; it is not a neutral zero-gain setting. These exposed gain-jumper options distinguish the A from the B's five-step gain knob.
• Mic Input Pad: Provides 20 dB attenuation for Mic, reducing drive when the input overloads. It is unavailable in Line, unavailable for Unison Line/Hi-Z inputs, and fixed off in the native plug-in according to the linked manual. Do not rely on it as an always-available DAW attenuation control.
• Polarity: Up inverts polarity; down is normal. Compare it when combining microphones, remembering that this is not continuously variable phase adjustment.
• L.F. Gain: Fixed 100 Hz shelf with −6, 0, or +6 dB choices. Zero disables that band. Use it for broad low-frequency weight or reduction rather than precise low-mid correction.
• H.F. Gain: Fixed 10 kHz shelf with −6, 0, +3, or +6 dB choices. Zero disables the band. These are the A's actual options; the B's selectable frequencies and finer gain steps do not apply.
• Level: Controls the second, tube output gain stage, with approximately 61 dB available gain. Raising it adds coloration, so it is not interchangeable with the clean Output trim. Revisit it after EQ changes because the feedback-style EQ can affect output-stage distortion.
• Output: Clean final gain from −infinity to +12 dB. Use it to normalize level after increasing Input Gain or Level. Rotating to silence leaves processing loaded; this differs from bypass.
• OFF: Click the Output OFF label to disable the plug-in. Ordinary knob rotation does not reach that bypass position unless Gain Stage Mode is active. In Unison Gain Stage Mode, supported input, Level, and Output controls can be selected for hardware adjustment.

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