Please uninstall the UAD software. It is important to delete the preference files as stated in the article:
UAD Uninstall / Reinstall Procedure (Windows)
This will also delete any presets you have created. Backup them if necessary.
Reset your device:
Apollo Twin MkII Hardware Reset (Please turn your Speakers off first!)
Download and reinstall the latest UAD software:
https://www.uaudio.com/
If the issue persists please perform a manual firmware update:
UAD Firmware Update Instructions
Navigate to Windows: C:\Program Files (x86)\Universal Audio\Powered Plugins\Firmware\UAD-2\
to find following file:
Drag and drop this file on your Apollo Twin MKII DUO in the System Info window of the UAD Meter:
Important: A complete power down (external UAD devices) or computer restart (UAD-2 PCIe cards in INTERNAL PCIe slots) is critical to complete any firmware change.
Important: Do not interrupt system power during any firmware change routines.
Now please take these steps to test your device in standalone mode (disconnected from the computer). Note that the Thunderbolt cable needs to be disconnected from the computer for the entire test.
- Disconnect the Thunderbolt lead from the Apollo and turn off your speakers.
- Follow this process to reset your device: Apollo Twin MkII Hardware Reset
Make sure the Thunderbolt cable is not reconnected - Power cycle the device.
- Plug in a microphone via XLR cable to channel 1
- Power on your speakers, ensure they are connected to MON L/R on the Apollo.
- Use the hardware controls on the Apollo to increase the gain of the microphone (phantom power if needed), and see if you can see signal on the Apollo? If you can, can you hear it on the speakers? Also check to see if you can hear it on headphones? Is the sound distorted in this scenario?
Please confirm the test results for these questions.
If you are successfully getting sound from the Apollo, reconnect the Thunderbolt and test to see if it now works with your computer.