WHY most of DACs (if not all) with USB interface have the USB-B type socket?

[krowaklara]

hmm?
instead of let`s say - widely used USB-A type?
anyone knows?

 

[Fio]

Cable with A-A is a non-standard configuration and for specific proprietary purposes only.
This can end up in short circuit and is not compliant with USB-IF (as far as i know).
With the exception of usb type c ...

Type A receptacle is a host / power source, like a pc or a charger.

 

[krowaklara]

Thanks for giving a hint, it seems you are right;
i found a document called Universal Bus Spec and it says

To minimize end user termination problems, USB uses a “keyed connector” protocol. The physical difference in the Series “A” and “B” connectors insures proper end user connectivity. The “A” connector is the principle means of connecting USB devices directly to a host or to the downstream port of a hub.
Series "A" plugs are always oriented upstream towards the Host System
Series "B" plugs are always oriented downstream towards the USB Device

This specification describes three USB cable assemblies: standard detachable cable, high-/full-speed captive cable, and low-speed captive cable.
A standard detachable cable is a high-/full-speed cable that is terminated on one end with a Series “A” plug and terminated on the opposite end with a series “B” plug. A high-/full-speed captive cable is terminated on one end with a Series “A” plug and has a vendor-specific connect means (hardwired or custom detachable) on the opposite end for the high-/full-speed peripheral. The low-speed captive cable is terminated on one end with a Series “A” plug and has a vendor-specific connect means (hardwired or custom detachable) on the opposite end for the low-speed peripheral. Any other cable assemblies areprohibited.

But.... lets assume i have USB A-A cable, would adaptor A-B do?
YES nad NO, it all depends on cable construction and shielding

 

[Fio]

I know of some "A-A" cables for a direct link between two hosts.
BUT this is not a simple A-A cable, there is a transceiver chip in the line, in the end this is more a A-B(transceiver)B-A cable.