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4 Channel Inverting ACA
[Classic Inv-ACA Rev B]
Number of Products in stock: 104

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The CAPI Inv-ACA Rev B printed circuit board is a simple and basic inverting style summing amplifier or ACA, short for "Active Combining Amplifier". Actually, it is four independent ACA's. By selectively populating jumpers JP1- JP3, you can achieve two independent 2 into 1 circuits or a 4 into 1 configuration. By using 28K feedback resistors, the discrete opamps will provide no additional gain within the console's 2-mix signal path (unity). The circuit is essentially a copy or clone of the vintage API ACA circuit, up to the balancing output transformer. Each board has 3 auxiliary inputs to provide easy access to the input of the 2-mix bus. You can take the summed monitor section or any outboard mixer's unbalanced outputs through 47K bus resistors and simply "inject" them into your 2-mix ACA.

By removing each channel's 47K output bus resistor and adding any of our 2623 transformers, you will have 4 independent channels of classic, vintage style summing. 2623-1-CF's are a good versatile mount for use with that application.

The purpose for this PCB in my desk is basically shown in the block diagram below. The idea is to sum the channels in smaller groups, then sum again into the 2-mix ACA. This will help when the 32 summed monitor channels and the 16 summed group buses are also dumped to the main 2-mix. Plus, I want the signal path to be the same between the discrete monitor channels and the input channels. The idea is not new and was used on the massive, custom O'Henry API console. It is common practice for some of the other major console manufactures, past and present.

This new release is the Rev B version. The only signal path related changes are the adding of the footprints for Vishay/BC axial coupling caps. The bulk of 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.

Compact layout, designed to daughter mount on vintage style API ACA boards with four strategically placed holes and 1-1/2" standoffs

Designed for Molex .156" KK headers, like the vintage ACA

Simple daisy-chain power to ACA board below

Standard 2520 footprint with .09" plated thru holes to accept Mill-Max #0322015013427100 sockets to makes for easy swap of different discrete opamps

Board is 6" long by 3-1/8" wide

Excel BOM and mounting hole pattern will be provided via email after purchase

***Please note: The polarity of the original balanced ACA output must be flipped to maintain proper phase. This should be done after the output transformer.

***Please note: This item is a raw, unpopulated PCB only. All other components in pictures are for informational purposes only.

***Please note: The pics below of the installed PCB are of the original Rev which was green.

Additional information and photos:

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No Opamps

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Vintage ACA Top

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Vintage ACA Bottom

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Installed 1

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Installed 2

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Installed 3

Block Diagram

This product was added to our catalog on Sunday December 01, 2013.
Classic Audio Products, Inc.
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Classic Audio Products, Inc. is not affiliated with API. Customers and fans should not refer to Classic Audio Products, Inc. as "Classic API." API is a registered trademark of Automated Processes Incorporated. Classic Audio Products, Inc. has no affiliation with Automated Processes Incorporated.
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