Apollo Solo

Plug your electric guitar or bass straight in here with a standard guitar cable — no amp needed. The moment you plug in, channel 1 switches to listen to your instrument.

tip: Use a regular guitar (TS) cable, not a balanced (TRS) cable — the troubleshooting guide notes TRS cables won't work here. To go back to a mic on channel 1, you must unplug the guitar.

Plug your headphones in here. UA touts this as an unusually loud, clean, detailed headphone amp — good enough to mix on. Set its volume with the big knob after pressing MONITOR to select headphones.

tip: Muting the speakers (pressing the LEVEL knob) does NOT mute the headphones — so you can silence your room speakers and keep listening privately.

This is the one big dial that does almost everything. Turn it right to make things louder — either how much your mic/instrument is boosted, or how loud your speakers/headphones play. What it's controlling depends on which mode button you pressed last. Push the knob in to mute your speakers, or (in preamp mode) to jump between your two input channels.

tip: Since one knob does double duty, always glance at the display first to confirm whether you're adjusting an input's gain or an output's volume before you turn it — otherwise you might crank the wrong thing.

Press this to make the big knob control your listening volume. Press it again to switch between controlling your speaker volume and your headphone volume — check the display to see which one is lit.

tip: You may need to press it twice to land on Headphone control; the display's MONITOR and HEADPHONE indicators tell you which output the knob is currently driving.

Press this to make the big knob and the option buttons control your inputs (mics/instruments) instead of your speakers. Press again to switch which of the two inputs you're adjusting.

tip: You can also press the LEVEL knob itself to flip between channels 1 and 2 while in preamp mode — often quicker than reaching for this button.

Tells the unit whether you plugged a microphone (XLR) or a line-level device (1/4-inch) into the rear combo jack. Press to switch between MIC and LINE. This matters — if it's set wrong, you won't hear your source correctly.

tip: If you plug a guitar into the front Hi-Z jack on channel 1, the unit ignores this button and auto-selects the instrument input; unplug the front jack to use the rear mic/line input on channel 1 again.

Turns on a filter that trims away deep, rumbly low-frequency noise below 75 Hz — great for cutting out things like mic-stand thumps, footsteps, air conditioning hum, and pop-filter breath rumble.

tip: Leave it on for vocals and most spoken-word recording; those deep frequencies rarely help and usually just muddy things up.

Sends power up the mic cable to run a condenser microphone (the studio-style mics that need electricity to work). Dynamic mics and instruments don't need it.

tip: Always turn this OFF before plugging or unplugging an XLR microphone — connecting a mic with phantom power live can damage equipment. Also, don't enable it for ribbon mics unless the manufacturer says it's safe.

Knocks the microphone signal down by a fixed amount so very loud sources (a screaming vocalist, a close-miked snare drum, a loud amp) don't overload the input. Use it when the sound distorts even with the gain knob turned all the way down.

tip: If your input meter shows the red clip light even at minimum gain, press PAD — that's exactly the problem it solves.

Flips the signal upside-down electrically. This helps when you're using two microphones on one source and they sound thin or hollow together — flipping one can restore a full, solid sound.

tip: Handy for a snare drum miked top and bottom, or a guitar amp with two mics: try flipping one channel's polarity and keep whichever sounds fuller.

Ties both inputs together so they act as one, matching their settings — perfect when recording a stereo source like a keyboard or a stereo pair of room mics. Adjust one and both follow.

tip: You can't link when a plug is in the front Hi-Z instrument jack, because the guitar input can't be paired with a mic or line input.

The glowing ring of lights around the big knob shows you how high you've turned it. If the ring goes red, it means your speakers are muted.

tip: A red ring is your quick visual reminder that you've muted the monitors — no sound is a feature, not a fault, in that moment.

Tells you which of your two inputs you're about to change. Whichever channel name is lit is the one the knob and buttons will affect.

tip: Always check this before adjusting anything in preamp mode — it's easy to accidentally tweak the wrong channel.

Bar-graph lights that show how strong your incoming sound is. Aim for the meter climbing near the top on the loudest parts, but never lighting the red clip light — that means distortion.

tip: Set levels while performing your loudest passage, then back off a touch so you have headroom for surprises.

Confirms whether the unit is listening to a microphone, a line device, or your guitar. If this doesn't match what you actually plugged in, you'll get no sound or the wrong sound.

tip: If you plug into the front instrument jack and don't hear it, make sure the display shows HI-Z — it should switch automatically.

Lights up to tell you the big knob is now controlling your speaker volume. If it's red, your speakers are muted.

Shows how strong the sound leaving the unit is (going to your speakers/computer). If the red clip light lights, something feeding the output is too loud — turn down whatever's sending signal.

tip: These meters read the signal level, not your listening volume — so they can show clipping even if you've turned your speakers down.

Lights up to tell you the big knob is now controlling your headphone volume.

tip: If it won't light, press the MONITOR button again — you sometimes need two presses to reach headphone control.

A little row of labels (INPUT, filter, +48V, PAD, Ø, LINK) that light up brightly when that option is on, dim when it's off, and go dark when it can't be used with your current input.

tip: A dark (unlit) option isn't broken — it just doesn't apply to what you've plugged in (for example, +48V and PAD go dark on the guitar input).

The single lifeline to your computer. This one cable carries your audio in both directions AND powers the unit — there's no separate power supply. It must go to a real Thunderbolt 3 port, not just any USB-C socket.

tip: Not all USB-C ports or cables are Thunderbolt 3 — look for the lightning-bolt icon on the port and cable. On a laptop, keep it plugged into wall power so the interface doesn't drain your battery.

Connect your studio speakers here (left and right). This is the sound your room hears. Volume is controlled by the big knob after pressing MONITOR.

tip: Always turn these down before powering up or plugging things in. Balanced (TRS) cables are best for keeping the signal quiet over longer runs.

Your two main input sockets. Each hole takes either a microphone cable (the three-pin XLR) or a 1/4-inch cable from something like a keyboard or synth. Just remember to tell the unit which you're using with the INPUT button.

tip: Turn off +48V phantom power before connecting or disconnecting a microphone's XLR cable to avoid damaging your gear.