How to Record an EP-133 K.O. II into Your iPhone

This is the step that catches everyone. USB audio was added to the EP-133 K.O. II in the OS 2.5 update, which landed in June 2026. If your unit is on 2.4 or earlier its USB-C port only does data and charging, so the phone gets no audio at all no matter what you plug in.

Update it first. The firmware is a free download from Teenage Engineering's EP-133 downloads page, installed over USB. Once it is on 2.5 or later, the USB audio is there and you are ready.

Not much and no interface.

• An EP-133 K.O. II on firmware 2.5 or later.
• Fresh AAA batteries for it. More on why below.
• An iPhone, plus the right cable. The EP-133 has a USB-C port.
• A recording app. Reel, which we make, is what we record these into, but any class-compliant iOS app works.

If your iPhone is USB-C (iPhone 15 or later) you need a single USB-C to USB-C cable. Plug one end into the EP-133 and the other into the phone. That is the whole connection.

If your iPhone is Lightning (iPhone 14 or earlier) a plain cable will not do it. You need an Apple USB camera adapter in between and the Lightning to USB 3 Camera Adapter is the one to get because its extra power port keeps the phone charged. Run a USB cable from the adapter to the EP-133 and plug a charger into the adapter's power port.

The EP-133 can take power over USB-C, but an iPhone is a weak power host and asking it to feed the EP-133 tends to be unreliable. The steady setup is to run the EP-133 on its own AAA batteries and let the USB cable carry audio only.

Batteries have a second benefit. Some people hit a faint hum or USB noise when recording over USB and it is almost always a power or ground issue. Running the EP-133 on batteries and trying a different cable or phone port usually clears it.

Once it is updated and connected, there is no menu mode to switch on to send audio out. The EP-133 simply appears as an input. Open your app, pick the K.O. II as the input and record. In Reel it shows up automatically and each take lands as a clean capture, because Reel follows the K.O. II's rate for you. If you want to check it, the rate picker in Settings shows what is actually running. One more thing that matters if you play audio from the phone back into the K.O. II to resample: Reel's metronome no longer feeds back through a K.O. II that is monitoring it, which used to be a real nuisance.

You capture the stereo master mix, so set your levels and balance on the EP-133 before you record rather than expecting separate tracks. One thing not to touch: the SMP to USB setting with its MON option is for sending audio the other way, into the EP-133, so leave it alone when you are recording out to the phone.

Here is the OS 2.5 USB audio going straight from a K.O. II into Reel, no interface in the chain.

The 2.5 update made USB audio work both ways, so as well as recording the K.O. II into the phone you can send audio from the phone into the K.O. II. Plug in, pick the K.O. II as your output and Reel plays straight into it, ready to resample. This is what the SMP to USB setting is for.

The same update added an arpeggiator that a lot of people could not find at first. It lives in KEYS mode. Hold TIMING and press a few pads and it arpeggiates them. The catch is the sample has to be a oneshot or legato sound for it to work, and you set that with SHIFT then SOUND on the pad. If your arp does nothing, that sound mode is almost always why.

The short below runs through both, the USB audio going into the K.O. II and getting the arpeggiator going.