As the title states, this is the official support thread for the 2-ACA-Bo, PCB build that can be found at here http://capi-gear.com/catalog/index.php?cPath=22_46. Per a request in the BM, I felt I should start this thread.
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September 21st, 2015 Update:
All support docs for this project can be found on the recently added Support Docs page at www.capi-gear.com
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Anyhow, here is a brief history of the creation of this board. Like many projects, I created this for my own personal needs in the rebuild of my console. I am using this board as the 2-mix summing/booster stage of the custom discrete monitor bucket that I'm building. I wanted to match the exact process that API used to complete this task on the main or "input" side of my desk. My board, unlike some others, used the 4 channel ACA's for summing and 325 cards for the post fader booster amps. So, that is what the 2-ACA-Bo is comprised of. This is the exact same method used for summing all the group buses as well.
Per a behind the scenes discussion with Dennis (Prodigy member "API"), here are a few back-side pictures of my desk before my furniture/frame rebuild.
All the 4 channel ACA's are in the middle section. 300 series card cage is on the right.
And another...cage closed
The 4 boards to the right are ACA's for summing the 16 sub-groups. The 5th board is 2 channels for Input Cue 1 & 2 summing, and 2 channels for stereo 2-mix, Left and Right of course. These output transformers are the AP2623-4, PCB mount version of the 2623.
From here, the each summed signal goes to normalled points at the patchbay where they create an insert point that is -2db. The return signal is directly wired to the respective fader (group or 2-mix), which were originally 600ohm in my board. That's right, the returns are all unbalanced, and the insert device (if any) is directly driving the fader. The fader output is then wired back to the 300 series card cage.
In the card cage, you see an ass-load of beautiful and underrated 325 cards. These cards are the post fader, booster amps. These are not exactly the 325 circuit that you've all seen the schemo for. They have an obsolete TIS73 that was used to switch between the program source and a slate/tone signal. There is a 10uf input coupling cap and they use the inverting input of the 2520.
In the cage you also see 4-325's that were quad boosters for the control room, 4-325's that were the quad boosters for the studio amps and a single mono program booster.
The output of each sub-group 325 booster goes to the patchbay were it normals to the tape machine inputs. A mult is on this output that feeds a meter buffer as well. The input/group meter buffers are on the monitor cards, where you can switch the metering from input channel or monitor channel. The "direct" switch on each input channel determines if you are metering sub-group or input channel. ??? Might sound a little confusing but it's really pretty simple.
Besides the 2-mix output, 2 mults are on the 2-mix booster card outputs. The first feeds the L-R meter buffer amps and the 2nd is the feed to the control room module. Of course there, you select 2 track return, CD player or "program" for the source you are listening to in the control room.
This 2-ACA-Bo board is an exact replication of 2 stereo ACA amps and 2 of the 325 amps, with three exceptions. The original ACA input coupling caps were 250uf, mine are 220uf. The output coupling caps are 470uf instead of the 250uf on the ACA's and the 400uf originally found on the 325 cards.
I am happy to help with anything I can on these.
Cheers, Jeff
--------------------------------------------------------------------------------------------------------
September 21st, 2015 Update:
All support docs for this project can be found on the recently added Support Docs page at www.capi-gear.com
--------------------------------------------------------------------------------------------------------
Anyhow, here is a brief history of the creation of this board. Like many projects, I created this for my own personal needs in the rebuild of my console. I am using this board as the 2-mix summing/booster stage of the custom discrete monitor bucket that I'm building. I wanted to match the exact process that API used to complete this task on the main or "input" side of my desk. My board, unlike some others, used the 4 channel ACA's for summing and 325 cards for the post fader booster amps. So, that is what the 2-ACA-Bo is comprised of. This is the exact same method used for summing all the group buses as well.
Per a behind the scenes discussion with Dennis (Prodigy member "API"), here are a few back-side pictures of my desk before my furniture/frame rebuild.
All the 4 channel ACA's are in the middle section. 300 series card cage is on the right.
And another...cage closed
The 4 boards to the right are ACA's for summing the 16 sub-groups. The 5th board is 2 channels for Input Cue 1 & 2 summing, and 2 channels for stereo 2-mix, Left and Right of course. These output transformers are the AP2623-4, PCB mount version of the 2623.
From here, the each summed signal goes to normalled points at the patchbay where they create an insert point that is -2db. The return signal is directly wired to the respective fader (group or 2-mix), which were originally 600ohm in my board. That's right, the returns are all unbalanced, and the insert device (if any) is directly driving the fader. The fader output is then wired back to the 300 series card cage.
In the card cage, you see an ass-load of beautiful and underrated 325 cards. These cards are the post fader, booster amps. These are not exactly the 325 circuit that you've all seen the schemo for. They have an obsolete TIS73 that was used to switch between the program source and a slate/tone signal. There is a 10uf input coupling cap and they use the inverting input of the 2520.
In the cage you also see 4-325's that were quad boosters for the control room, 4-325's that were the quad boosters for the studio amps and a single mono program booster.
The output of each sub-group 325 booster goes to the patchbay were it normals to the tape machine inputs. A mult is on this output that feeds a meter buffer as well. The input/group meter buffers are on the monitor cards, where you can switch the metering from input channel or monitor channel. The "direct" switch on each input channel determines if you are metering sub-group or input channel. ??? Might sound a little confusing but it's really pretty simple.
Besides the 2-mix output, 2 mults are on the 2-mix booster card outputs. The first feeds the L-R meter buffer amps and the 2nd is the feed to the control room module. Of course there, you select 2 track return, CD player or "program" for the source you are listening to in the control room.
This 2-ACA-Bo board is an exact replication of 2 stereo ACA amps and 2 of the 325 amps, with three exceptions. The original ACA input coupling caps were 250uf, mine are 220uf. The output coupling caps are 470uf instead of the 250uf on the ACA's and the 400uf originally found on the 325 cards.
I am happy to help with anything I can on these.
Cheers, Jeff