Click to enlarge

The SumBus32 8x2 Summing Mixer Bundle [No Skins] is a product bundle that will give you a 8x2 version of the SumBus ACA summing mixer. A 2520 style opamp is needed for each ACA output card. Those can be added at the bottom of this page. Besides the opamps and front panel skins, this bundle contains everything else needed to complete a 8x2 summing mixer. Product pics are for information only. This bundle does not include any of the front panel skins. The logic behind this option is the user can purchase other skins if the future plan is to expand with more channels. Following is a list of additional components that are required to complete this build: (2) 2520 style discrete operational amplifier PS: DOA's can be added to this kit at the bottom of this page. Please note: This kit is not for the beginner. The build for the SumBus is a pretty major task. Support docs will not be step-by-step from a newbie perspective. If you do not have extensive DIY experience, please DO NOT buy this product. If you are interested but can't DIY, there are many experienced CAPI kit builders around the globe that can be found on Facebook, Instagram, Reverb etc. The audio path of the SumBus is quite unique. In fact, I don't think this type of circuit has every been done before especially in a compact summing mixer style format. Each input channel contains a CA2622 input transformer and our own DTO5 discrete opamp. Each ACA is a 2520 style opamp and a quadfilar 2503 wired 1:3. The sound of this box is like no other. I would say that is due to the iron in the audio path. It's not just about the actual summing process itself but more about the additional circuitry that comes before and after those little bus resistors. The SumBus is a semi-modular design meaning the channel count can be expanded as work flow requires or funds permit. The input channels are on individual cards which plug into a PCB backplane. The top cover of the carcass needs to be removed for the input channel cards to be properly inserted, hence "semi-modular". The ACA cards are also inserted into PCB backplane card edge connectors. These can be removed and reinserted without removing the top of the carcass. The gain staging of the SumBus is overall based on my 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. The SumBus inputs are at +4dBu nominal and the outputs are -2dBu nominal. We do have a MasterACA in the works that will be a perfect solution for providing the 6dB of gain as well as mixing the four ACA outputs...and more! Addition 2-channel ACA cards and kits can be purchased separately to fill out the unit to 4 bus outputs. Following is a list of tools that will help in the assembly of the SumBus: 1/4W Lead Forming Tool IC Pin Straightener IDC Ribbon Crimping Tool The Pictorial Build Guide and Support Documents can be found here

Additional information and photos:

Click to enlarge

Click to enlarge