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The CAPI 2-ACA-Bo Rev B.1 printed circuit board has two channels of two different vintage style amplifiers on board. The two right side of the PCB channels are simple and basic inverting style summing amplifiers or ACA's, short for "Active Combining Amplifiers". The circuit is a recreation of the vintage API ACA circuit including the use of two PCB mount EA2623-4 balancing output transformers. The output signal can be taken from here and normalled to a patchbay. This point will provide a -2db insert point for the 2-mix, just as it was done on the vintage API consoles. The returning signal needs to be routed to a user supplied stereo potentiometer, rotary or slide-fader type. The potentiometer wiper signals will be returned to the left pair of channels on the PCB. The two channels on the left side of the PCB are the post fader "booster amplifiers". These channels are accurate recreations of the way API used the 325 cards in their vintage recording consoles. They are slightly different that a stock 325 card. Provisions have been made for a Program Mute Circuit in conjunction with a talkback signal. This can be used for slate/tone signals. An optional N-channel switch is activated when it receives a -16 volt logic signal, which mutes the program feed, allowing the slate/tone audio to be the booster's only input. The output of the booster amplifiers is balanced with the EA2503 transformers. Provisions are on the board for multiple transformer outputs. The slate/tone logic circuit along with the talkback feed, can simply be left unpopulated for normal operation. The N-channel switch should be jumpered over with a 24.9ohm resistor for consistent levels as compared to the originals. If you are adding on to a vintage API console, these can be used as additional submaster group buses. Program Mute will work seamlessly with your existing system. A support-build thread for the CAPI 2-ACA-Bo project can be found here in the Prodigy Lab forum. This new release is the Rev B version. Nothing has been changed as far as the signal path. The changes are mostly layout and silkscreen related. Besides top and bottom ground planes, I have added PSU damping resistors and individual PSU decoupling capacitors for each opamp. Designed for Molex .156" KK headers Simple daisy-chain power to other CAPI PCB's Standard 2520 footprint with .09" plated thru holes to accept Mill-Max #0322015013427100 sockets to makes for easy swap of different discrete opamps Signals being combined thru these ACA channels should be routed thru 47K bus resistors EA2503's are mounted with our L Bracket Kit Use the J111 for optional N-channel chopper switch A 104mm, 1K stereo log fader can be found here A pair of Elma 1K stepped switches is also an excellent choice Successfully stands up to the vintage 2-mix in my API desk Board is 5.5" long by 6" wide ***Please note: This item is a raw, unpopulated PCB only. All other components in pictures are for informational purposes only. The board in the below pics is a Rev B.

Additional information and photos:

Stuffed

Transformers

Opamp Area

Block Diagram