Made to Order CAPI SumBus ACA 8x2 Discrete Analog Summing Mixer

Classic Audio Products, Inc. has taken the analog outboard summing game to the next level. You can bring the warmth, detail, depth, and punch of a classic 70’s API console to your pro (or home!) studio in a 2RU space.

Unlike any other unit on the market at the moment: The audio paths are fully discrete and come complete with input transformers (2622 style) and discrete op amps on every single channel input.  

Each SumBus ACA is expandable up to 32 input channels (in banks of 8 at a time) and up to 2 stereo output buses. Even after being assembled, it can still be expanded! It’s modular! If you do go this route, please note that the lid needs to be removed from the unit In order to install the additional input cards properly. Removing the lid is not hard to do and just requires the removal of a palmful of screws on the top, front, and rear. The output bus cards can be removed and inserted without taking off the lid.

Each output bus utilizes a pair of output transformers (2503 style) and just about any 2520 footprint op amps. The second output bus gives you the chance to use different op amps or transformer combos either on mixes or any other outboard summing you might need to do in order to condense several mic signals into a mono or stereo signal with that distinctive API console sound.

Any pair of op amps provided by the CAPI website come with the purchase of each unit. Please let me know which op amps you will want before or at the time of your order.

This version of the SumBus (known as the SumBus32) can only take the SB-2T input cards. These cards feature pushbutton switches for routing. 2 output selection switches left and right to both output buses A+B. Naturally the B output bus switches will not route any signal if there is no specific B bus output card present. There is nothing variable about the controls on this version of the SumBus, making recall a breeze especially if you send mixes straight from your sessions in your DAW of preference.

Taken straight from CAPI’s website:

“The gain staging of the SumBus is overall based on [Jeff Steiger’s] vintage console and the 2-ACA-Bo card. The 2-ACA-Bo is a 2-stage mix bus. This means the ACA (active combing amplifier) stage is followed by an active booster stage. 6dB of gain is provided by the booster stage. The SumBus only contains the first half of the 2-ACA-Bo's signal path so technically the SumBus should be followed by a pair of line amps to makeup this 6dB.”

Every input channel has its own LED VU meter. 0VU is calibrated for the standard +4dBu signal and is the nominal input signal strength. However! It still has tons of headroom and the meter peaks at +24 VU. Just keep in mind that the output stage is 6 dB down as noted by Jeff above.

The inputs are fed into the unit by 2 pairs of Dsub 25 connectors wired to TASCAM standard pin outs. As pictured, the first 16 channels are shared by 2 connectors. They are divided across the top planes of the stereo input cards, so if you are using 8 channels, the first four inputs of both the A and C connectors are what will feed across the first half of the top and bottom planes of the input cards, so at least 2 Dsub snakes will be required for operation even with only 8 channels installed. A small sacrifice in the face of owning an API console in a 2RU space!

The chassis is made from US steel. Its dimensions are 14”x19”x3” and the fully built chassis weighs in at 21 lbs. Each 8 channel expansion adds 4 lbs. and each pair of output cards adds 1.5 lbs.

Please allow up to 3-4 weeks depending on CAPI’s stock levels, number of input channels requested, and my current workload.

I ship via FedEx ground within the continental US. The unit comes fully assembled. The packages I send are fully insured and will require an adult signature for delivery. If you will need it expedited or if you live outside of the continental US please contact me and we can work something out!

Due to the cost of this piece these units are considered Special Order only. Once the kit has been ordered from CAPI, it will be non-returnable. You are still protected against receiving a defective unit. We will fix any potential issues and ship it back.

Thank you for checking out my builds! Let me know if you have any questions at all :D