It looks like the "default" amperage for USB 3.1 is .9 amps. A complaint USB-c to USB-a cable is supposed to use a 56 kΩ resistor, limiting it to .9 amps. A USB-c to USB-c cable uses a 10 kΩ resistor, which allows for up to 3 amps. I would assume the cables that have been found to work by Ted either dont have resistors or have a 22 kΩ, allowing for 1.5amps, which is presumably the minimum needed for the mixpre.
http://www.cypress.com/knowledge-base-article/termination-resistors-required-usb-type-c-connector-kba97180https://www.chromium.org/chromium-os/cable-and-adapter-tips-and-trickshttps://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphonehttps://www.amazon.com/Manhattan-353298-USB-CABLE-C-M/product-reviews/B015MGH0RM Manhattan USB Type-C cable is not spec compliant. May cause damage to charger, hub or PC USB ports.
ByBenson Leung
Manhattan USB Type-C cable is not spec compliant. May cause damage to charger, hub or PC USB ports.
ByBenson LeungTOP 100 REVIEWERon February 29, 2016
Benson again continuing my reviews of USB Type-C legacy cables. This time, I'm reviewing Manhattan's "353298 MH USB C CABLE C-M TO A-M"
This cable does not correctly follow the USB Type C specification Release 1.1. To find the specification, please go to usb.org, and look under developers/usbtypec.
Specifically, using this charging cable, the Chromebook Pixel will attempt to draw 1.5A of current over the cable, potentially damaging the USB hub or charger on the A side, which is not guaranteed to be rated at 1.5A.
Please see Section 4.11 of the Type-C specification and the following note :
1. For Rp when implemented in the USB Type-C plug on a USB Type-C to USB 3.1 Standard-A Cable
Assembly, a USB Type-C to USB 2.0 Standard-A Cable Assembly, a USB Type-C to USB 2.0 Micro-B
Receptacle Adapter Assembly or a USB Type-C captive cable connected to a USB host, a value of 56 kΩ
± 5% shall be used, in order to provide tolerance to IR drop on V BUS and GND in the cable assembly.
In other words, since you are creating a USB Type-C plug to a USB 2.0 Type-A Plug assembly, you must use a resistor of value 56kΩ as a pull-up on CC (configuration channel). According to my testing, your cable uses a 22kΩ pull-up, which is not legal when the other end of the cable or adapter is a legacy Type-A or Type-B connector or receptacle.