I found an error on the Parasound A21 manual page 8:
" 2. Plug the other end of this wire into the external DC source. "
the picture shown the control component plug into the " INPUT "
The correct connection should be connect the 3.5mm 12V trigger cable to P5 preamp 12V Out, Turn on options switch to manual.
On the A21 plug the trigger cable to 12V Input and switch position at 12V.
This setting will allow the preamp to control the power amp.
" 2. Plug the other end of this wire into the external DC source. "
the picture shown the control component plug into the " INPUT "
The correct connection should be connect the 3.5mm 12V trigger cable to P5 preamp 12V Out, Turn on options switch to manual.
On the A21 plug the trigger cable to 12V Input and switch position at 12V.
This setting will allow the preamp to control the power amp.