[BUILD]CAPI 2-ACA-Bo~Official Support Thread

[Hansblooey Ribbon]

The 2ACA-Bo is an excellent modification to my Trident 65. I know there’s several issues with this console but fixing the weak ass mix bus has made a light years difference in headroom and sound.
AAAA++++

 

[beezer4]

Hi there. I'm working through how to add the 2-ACA-Bo to my MCI JH618. I attached the master module schematic. I indicated in red where I would pull signal to run to and from the ACA-Bo board. Badly circled in yellow the parts of the circuit that would be removed or severed. Could someone spot check me on this and the mute CTL location?

Also I believe my stereo L/R patch points for the patch bay are unbalanced. What's the best way to wire output transformer for the ACA? Pin 3 to ground and 6 to the patch point?

Thanks for the help!

 

[Brian Roth]

It's late and I may be in error.....but I think you'll need to invert the control signal to the mute FETs. It appears on the MCI, the FET is switched "on" to mute. On the CAPI, the FET is turned "off" to mute,

Bri

 

[Brian Roth]

@beezer4 .... I have a couple of JH-6xx manuals around here but I would have to dig around to find them. Looking at the schemo you posted, I am guessing that "slate mute command" pin 41 normally "sits" at a negative voltage and is "pulled" to 0V to activate the muting.

You probably don't have one of the MCI extender modules....they are made of Unobtanium. So I would suggest you "tack" an insulated wire to that node so you can bring it out of the guts to measure that voltage and verify what I think is going on.

I've worked with JH-6xx desks since 1980 (and onward)....One JH-618, one 652, and multiple 636's. I never tried to modify the LR summing buses with an external PC board. Interesting idea, though. Where do you plan to "park" the CAPI board (with all those transformers) into the frame? Just curious.....

For grins, I attached a couple pix of the extender which was owned by a client.

Bri

 

[beezer4]

@beezer4 .... I have a couple of JH-6xx manuals around here but I would have to dig around to find them. Looking at the schemo you posted, I am guessing that "slate mute command" pin 41 normally "sits" at a negative voltage and is "pulled" to 0V to activate the muting.

You probably don't have one of the MCI extender modules....they are made of Unobtanium. So I would suggest you "tack" an insulated wire to that node so you can bring it out of the guts to measure that voltage and verify what I think is going on.

I've worked with JH-6xx desks since 1980 (and onward)....One JH-618, one 652, and multiple 636's. I never tried to modify the LR summing buses with an external PC board. Interesting idea, though. Where do you plan to "park" the CAPI board (with all those transformers) into the frame? Just curious.....

For grins, I attached a couple pix of the extender which was owned by a client.

Bri

Hey Brian,
Thanks for the info. I do have the extender card. Luckily it came with console, so I can measure the voltages for slate mute command. I need to measure for a location to mount the CAPI board... I think there is a enough space against the right hand panel sitting against the patch bay. Mounting it vertically. Then I'll slide my panel with my monitor faders over one, since they are cable connected and not on a PCB. The key piece will be where to run the wiring.

I did think of another question... for the ACA output portion... since it will go to the patch bay that is already unbalanced (from what I can tell) do I even need to add those transformers to CAPI PCB and can I just run the output from after C12 and C16 respectively?

 

[Brian Roth]

Hiya James. LOL...making a joke here....that extender is probably worth more the the desk! KIDDING!!

OK I'm working from memory here because of too many years since I dug around in the "deep guts" of a 6xx. So, I'm "spit balling".

Picking the "easy one" first....the muting. If I'm correct and you verify my idea about how the muting functions, it will require a bit of simple circuitry to dim/mute the CAPI card to avoid blasting your monitors when pressing the Slate button.

Next....mounting the CAPI card "far" away from the bus board means you have to extend the LR buses via shielded cable.

There is a belly pan beneath which held the optional automation stuff on the 636 and perhaps other versions. I worry about extending the LR buses to another destination.....but I worry a lot. <g>

If your desk lacks the belly pan, perhaps consider concocting your own "mini belly pan" directly underneath the master section. A suitably sized metal box to comfortably contain the CAPI. You'll need to poke a hole (s) into the MCI sheet metal to drag audio and power wiring.

Regardless, you will have to do some hacking around in the Belly of the Beast to insert the CAPI. I am certain the insert sends were wired with balanced cables, even though the sends were unbalanced to/from the patchbay. MCI didn't suddenly decide to use unbalanced/shielded cable for that feature. Now you have to dig through the harness to find those two send and return cables so you can connect them to the CAPI card.

If it was me, I'd leave the transformers everywhere on the CAPI....just because? <g>
Not trying to discourage you at all....just tossing out 2-cents-worth thoughts regarding what I consider a less-than-trivial mod to a factory made desk.

1. You have to hack onto the LR summing buses on the motherboard and also remove the OEM summer....as in chop a pair of circuit board traces?

2. You have to locate the wire harness sends from the summers on the master module that feed and the patch inserts and master fader and then back into the line out drivers.


Bri

PS, if possible when working in the Belly, set the desk on it's side or totally upside down. You'll thank me later. <g>

 

[beezer4]

Hiya James. LOL...making a joke here....that extender is probably worth more the the desk! KIDDING!!

OK I'm working from memory here because of too many years since I dug around in the "deep guts" of a 6xx. So, I'm "spit balling".

Picking the "easy one" first....the muting. If I'm correct and you verify my idea about how the muting functions, it will require a bit of simple circuitry to dim/mute the CAPI card to avoid blasting your monitors when pressing the Slate button.

Next....mounting the CAPI card "far" away from the bus board means you have to extend the LR buses via shielded cable.

There is a belly pan beneath which held the optional automation stuff on the 636 and perhaps other versions. I worry about extending the LR buses to another destination.....but I worry a lot. <g>

If your desk lacks the belly pan, perhaps consider concocting your own "mini belly pan" directly underneath the master section. A suitably sized metal box to comfortably contain the CAPI. You'll need to poke a hole (s) into the MCI sheet metal to drag audio and power wiring.

Regardless, you will have to do some hacking around in the Belly of the Beast to insert the CAPI. I am certain the insert sends were wired with balanced cables, even though the sends were unbalanced to/from the patchbay. MCI didn't suddenly decide to use unbalanced/shielded cable for that feature. Now you have to dig through the harness to find those two send and return cables so you can connect them to the CAPI card.

If it was me, I'd leave the transformers everywhere on the CAPI....just because? <g>
Not trying to discourage you at all....just tossing out 2-cents-worth thoughts regarding what I consider a less-than-trivial mod to a factory made desk.

1. You have to hack onto the LR summing buses on the motherboard and also remove the OEM summer....as in chop a pair of circuit board traces?

2. You have to locate the wire harness sends from the summers on the master module that feed and the patch inserts and master fader and then back into the line out drivers.


Bri

PS, if possible when working in the Belly, set the desk on it's side or totally upside down. You'll thank me later. <g>

Hey Brian,
Thanks for all the details. That extender is a rarity for sure haha. Was able to measure the dim/mute at pin 41 and it is sitting at -V. Can you recommend tweaks to be made to the CAPI board?

There seems to be enough space to mount the board on the wall near that patch bay. That means runs of balanced cable will be about 10-12 inches to get to the master module. I assume introducing noise with wiring is what gives you worry.

Going to start digging around in the belly pan. I was hoping to find a less invasive way than chopping traces, but I need to look closer at the schematic to see if there are just components I can pull to create the separation.

 

[Brian Roth]

James, just for grins, measure that pin 41 again when the LR bus mute is triggered. It's been too long for my memory, but I believe it is only triggered when you press the Slate button and with the selected slate destination is something like "2 mix" or similar. I think pin 41 will toggle from V- to 0 VDC. If so, I'll think about a simple method to "invert" that command for the CAPI's FETs.

I found some pics online for a JH-618:

https://reverb.com/item/4133601-1984-sony-mci-jh-618-console

There are two blank filler plates to the left of the patchbay and several (fader sized) blanks below the patchbay. Perhaps those would be possible locations for the CAPI card?

Bri

 

[Brenaudio]

Hey all,
After a few years of having set this project aside, I decided to jump into it again. I had built the ACA a few years ago and never got it incorporated into my desk before a big move, etc put this on the shelf.
I had the ACA on my bench today to see if I could run some tones through it and it's got some funky power rail behavior.
This is all with a single DOA in any of the four sockets, and I've tried 5 different DOAs. With no DOA in a socket the rails are rock solid, this only happens under load.
Bench DC supply running around +/-15VDC. I did some process of elimination and removed the 33/50v power rail filter caps one at a time from each rail with no change. With only the -15VDC attached, I'm getting a voltage drop on the negative rail of about 5V, from -15VDC to -10VDC. It gets really weird when I attach the +15V supply and the neg rail jumps to -2VDC. This suggest some short or bleed from the positive supply, but I'm not sure where. The -v and +v pins read no continuity, but when there's a DOA in place they read ~800k. Nothing gets hot or smokes. All 10R resistors measure good.
Wondering where to try next...

Thanks

*EDIT - could be my power supply, which I found out doesn't have a regulated Neg supply, but uses a ref voltage which doesn't work well under load.

 

[beezer4]

James, just for grins, measure that pin 41 again when the LR bus mute is triggered. It's been too long for my memory, but I believe it is only triggered when you press the Slate button and with the selected slate destination is something like "2 mix" or similar. I think pin 41 will toggle from V- to 0 VDC. If so, I'll think about a simple method to "invert" that command for the CAPI's FETs.

I found some pics online for a JH-618:

https://reverb.com/item/4133601-1984-sony-mci-jh-618-console

There are two blank filler plates to the left of the patchbay and several (fader sized) blanks below the patchbay. Perhaps those would be possible locations for the CAPI card?

Bri

Brian,
It's interesting... when activating the slate button pin 41 doesn't toggle to 0VDC, but instead stays at the same -V. The dimming of the monitors still happens with 2Mix activated. I can hear a relay switching... I think I'll need to dig a bit deeper into that circuit.

Good call on location, that's the exactly place I'm hoping to mount the CAPI board, in the area left of the patchbay. I'm working now to get in there to drill holes for mounting.

 

[Brian Roth]

@beezer4 Interesting. Obviously some feature uses pin 41 for some function. Maybe the 2 mix is muted when the oscillator is sent to the multitrack buses?

I'll find my JH-6xx manuals and see what is going on. It's been eons since I did any work in that portion of those desks.

Bri

 

[Brian Roth]

@beezer4 Found my MCI 6xx manual and I have a headache following through the "logic" design for that portion of the MCI circuitry! lol

A real world test. Patch something (external oscillator, whatever but NOT the desk's internal oscillator) into a line input, bring up the fader so you have signal on the 2 Mix meters and can hear it in the CR monitors.

Be sure the desk oscillator is switched off. Select "Slate/Oscillator" to 2 Mix. Press the Slate switch. Monitors should mute, but what happens on the 2 Mix meters?

Turn on the oscillator. What happens on the 2 mix?

Next, deselect the "slate/oscillator" from 2 Mix and select "TKS" (tracks) and then turn on the oscillator. What happens? And what happens when you press Slate?

I used to know this.....<g>

Bri

 

[Brian Roth]

@beezer4 Apologies for not getting back to your project. I literally had a headache looking through the diagrams in my MCI manual. It's a real MCI binder as delivered with the desk. However, several of the 11 x 17" fold-out pages are obviously greatly photo-reduced from an original diagram as drawn by a MCI draftsman.....I'm guessing the original was 2x at 22 x 34" or 24 x 36".

Hence my literal problem squinting at a variety of tiny, partially illegible, details in my manual. I found a magnifying glass here to help my aging eyeballs, and I'll return to it. Still need to determine the exact muting logic, signal path for slate and oscillator .... which all "snake" through 3 or 4 pages in the MCI manual. Unsure of the ramifications of muting the CAPI output booster vs. MCI's design of muting/dimming the summing amplifier.

Bri

 

[beezer4]

@beezer4 Apologies for not getting back to your project. I literally had a headache looking through the diagrams in my MCI manual. It's a real MCI binder as delivered with the desk. However, several of the 11 x 17" fold-out pages are obviously greatly photo-reduced from an original diagram as drawn by a MCI draftsman.....I'm guessing the original was 2x at 22 x 34" or 24 x 36".

Hence my literal problem squinting at a variety of tiny, partially illegible, details in my manual. I found a magnifying glass here to help my aging eyeballs, and I'll return to it. Still need to determine the exact muting logic, signal path for slate and oscillator .... which all "snake" through 3 or 4 pages in the MCI manual. Unsure of the ramifications of muting the CAPI output booster vs. MCI's design of muting/dimming the summing amplifier.

Bri

Hey Brian,
No worries at all. I also got busy with my day job. I'm hoping to test out your above requests from last Wednesday at some point today. I'll report back.

 

[MidnightArrakis]

I'm guessing the original was 2x at 22 x 34" or 24 x 36".

[I'm guessing the original was 2x at 22 x 34" or 24 x 36"] -- Those are called "D-Size" sheets in the drafting world.

If you either still have these and/or are still available to you, I could "Reverse-Engineer" them both mechanically and PCB-wise for anybody/you, if I had them physically in my hands!!! Just sayin'.....



/

 

[beezer4]

@beezer4 Found my MCI 6xx manual and I have a headache following through the "logic" design for that portion of the MCI circuitry! lol

A real world test. Patch something (external oscillator, whatever but NOT the desk's internal oscillator) into a line input, bring up the fader so you have signal on the 2 Mix meters and can hear it in the CR monitors.

Be sure the desk oscillator is switched off. Select "Slate/Oscillator" to 2 Mix. Press the Slate switch. Monitors should mute, but what happens on the 2 Mix meters?

Turn on the oscillator. What happens on the 2 mix?

Next, deselect the "slate/oscillator" from 2 Mix and select "TKS" (tracks) and then turn on the oscillator. What happens? And what happens when you press Slate?

I used to know this.....<g>

Bri

Real world test:

Be sure the desk oscillator is switched off. Select "Slate/Oscillator" to 2 Mix. Press the Slate switch. Monitors should mute, but what happens on the 2 Mix meters? --- Monitors mute but the 2 Mix meters continue to show level. No voltage change at pin 41 sitting at -17.2 vdc

Turn on the oscillator. What happens on the 2 mix? --- "MIX" button does not dim the CR monitor or 2 Mix levels, the oscillator is just fed into the 2 Mix signal path. No voltage change at pin 41

Next, deselect the "slate/oscillator" from 2 Mix and select "TKS" (tracks) and then turn on the oscillator. What happens? And what happens when you press Slate? --- Once I select the TKS button the CR monitors dim and 2 Mix meters dim and there is a voltage drop at pin 41 to .721vdc / pressing the slate button mutes the CR speakers as before but doesn't affect pin 41

It appears the only function affecting the voltage at pin 41 is the TKS button for the internal oscillator.

 

[Brian Roth]

@beezer4 Interesting....but it's kinda what I was guessing. Dimming/muting 2Mix when the oscillator is sent to tracks is logical; if you have several (or more) faders up and monitoring the track sends, the additive signal from multiple tracks with tone present will sum in the stereo bus and slam that!

I figured the 2 mix would also dim/mute when slating to tracks for the same reason. IIRC, any slate mode feeds a 20 Hz tone to whatever destination as well as the talkback mic. Shrug <g>.

Now I'll check to see if there is a simple mod to the comm module to "invert" the control voltage. With the CAPI we need 0 VDC (or that slightly positive value) as "normal" mode and the negative 17 to mute the 2 mix output. Otherwise an "outboard" inverter will be needed.

I hope @jsteiger (CAPI Jeff <g>) will see this thread and verify my thinking.

Bri

 

[Brian Roth]

[I'm guessing the original was 2x at 22 x 34" or 24 x 36"] -- Those are called "D-Size" sheets in the drafting world.

If you either still have these and/or are still available to you, I could "Reverse-Engineer" them both mechanically and PCB-wise for anybody/you, if I had them physically in my hands!!! Just sayin'....

Yeah, I know those are "D" and the 11 x 17" sheets are "C", but many folks don't have any drafting knowledge. That's why I used dimensions versus the letters. <g>

The extender in the pictures I posted belongs to a client located hundreds of miles from where I now reside. However, those extenders are pretty rare, especially nowadays! They were an option when the desks were new back in the late 1970's/1980's and I'd say a majority of the buyers were "penny-wise, pound-foolish" and didn't buy one. So, today they are pretty rare. Someone could start a small Cottage Industry selling a modern clone. I would guess at least a dozen might be easily sold...maybe a lot more. MCI sold a BUNCH of JH-6xx desks with many still in service.

Bri

/EDIT:

PS...we should move this extender discussion elsewhere, like drawing board or machine shop so this CAPI thread doesn't get bogged down.

 

[MidnightArrakis]

and the 11 x 17" sheets are "C", but many folks don't have any drafting knowledge. That's why I used dimensions versus the letters.

[the 11 x 17" sheets are "C"] -- >> INCORRECTO!!! << My Friend!!! 11" X 17" is a "B-Size" Sheet!!! An ANSI B piece of paper measures 279 × 432 mm or 11 × 17 inches. ANSI B is part of the American National Standards Institute series, with an aspect ratio of 1:1.5455. ANSI B is also known as 'Ledger' or 'Tabloid'.

However, an ANSI C piece of paper measures 432 × 559 mm or 17 × 22 inches. ANSI C is part of the American National Standards Institute series, with an aspect ratio of 1:1.2941.

The extender in the pictures I posted belongs to a client located hundreds of miles from where I now reside.

Is this person "contactable"? Do you own a bicycle? Can you hitch-hike???

However, those extenders are pretty rare! Someone could start a small Cottage Industry selling a modern clone. I would guess at least a dozen might be easily sold...maybe a lot more.

WELL.....OK, NOW!!! -- Let's start a "Small Cottage Industry"!!! WHO'S WITH ME???.....

If you could contact this person you know and convince them to relinquish their "Extender Board" long enough for me to completely "Reverse-Engineer" it into a set of 3D CAD-models and fabrication drawings, then perhaps this could help out countless numbers of aging recording engineers around-the-world who are still clinging onto their beloved vintage analog equipment!!! I believe all that it takes is just a bit of some positive momentum to "get the show on-the-road"!!!

And.....from what I have also seen here on this forum is kind of the same thing with vintage AMPEX tape-decks!!! There are all sorts of PCB's and simple sheet-metal parts that are vital in keeping these machines operational, but there are no available spare parts that anyone can just go out and buy!!! So, again.....if I were to actually have these old sheet-metal parts for me to measure from and aging PCB's that I could copy off of.....then I could "Reverse-Engineer" these old parts well enough in order to create modern fabrication files so they could be made again!!!

However, my doing this doesn't mean that I would be going into business manufacturing old equipment parts, NO!!! But, by my going through the "Reverse-Engineering" process and creating 3D CAD-model files and mechanical detail fabrication drawings does mean that anyone with these data files -- COULD -- take them to most any competent PCB or sheet-metal fabrication shop and have these parts made on their own for themselves.

The initial and -- MAJOR -- hurdle towards resolving this issue.....is in physically getting me the actual vintage pieces of equipment and PCB's!!! Once that is overcome, the rest of the issue is relatively easy. As I have made mention in other threads scattered about this forum.....I have already "Reverse-Engineered" PCB's ranging from those in an original 1974 API mixing console to a PCB designed in 1979 for a U.S. fighter jet to the PCB for an ALLISON-RESEARCH "Gain-Brain" comp/limiter. Mechanically, I have done all sorts of chassis, brackets, panels, etc. No BIGGIE!!!

/

 

[Brian Roth]

Hey Dude...I am branching this thread to here....not trying to mess up a specialized discussion about a CAPI project:

https://groupdiy.com/threads/mci-extender.87493/post-1149337


Bri