Classic Dolby remote control fader?

[Tj Hopland]

What sort of voltage is the classic Dolby fader? I know there was some electronic options available, Pennywise maybe? I know that was planned for the Dolby NA10 automation but never implemented in the software. Is it just a DC voltage? So could you use something like a 0-10 dimmer module? Or does it have to be its own power so you have to more simulate the original pot? What was that called an E pot? Where you basically commanded the device what the resistance was to be so the commands and what was being controlled was electrically isolated.

The goal would be to remote / automate the fader so in the case of commercial cinema have the server send commands or in a home application maybe integrate into some sort of modern home automation system. Just think of the potential for sales of such a product today? Has to be 10's of people worldwide! Probably why even Dolby never got around to implementing it in their own hardware even 15 years ago.

Could something like an Arduino or Pico be made to work? If those don't have the right onboard options there are tons of add on modules available, seems like there would have to have been some other similar application that used this sort of control scheme.

[Tony Bandiera Jr]

What processor are you talking about? The CP50, 65, 200 and possibly CP45 all used a more or less standard pot, (100k linear taper if memory serves) and the processor supplied a 10v dc bias. So yes, the legacy processors are more or less 0-10v controlled. You CAN drive it externally using using a 0-10v source, but you MUST use an external series resistor (It was 2.2k ohms) and you feed the positive voltage (through the series resistor) to the "REM" terminal and the negative voltage to the "ground". With AMX or Crestron hardware I'd use a voltage generator card set to max out at 10 volts and drive the fader that way. Format selections and muting were done with relay cards.

As for the CP500 and 650 and later, the remotes used a proprietary data bus protocol. Dolby (to my knowledge) never made that protocol available to anyone other than one other manufacturer to build the remotes. For the 500 and 650, I used AMX/Crestron connected to the serial data port to send fader, muting and format commands. Dolby did make the serial commands available to select dealers and techs. (I was lucky enough to have good rapport with my local Dolby office at the time, so I got the serial command info from them.)

I have not dealt with the CP850 and later so perhaps Steve Guttag can chime in on those.

So yes, it is possible to control legacy Dolby processors with automation, if you have the know how and the right interface capabilities.

[Tj Hopland]

Yes I am talking about the processors that used or had the 100k linear option. Or was it 10k? Zeros are never important right? I think up to and even the 500 supported the pot so CP100, 50 (with the optional 117 or later 517 fader card), 200, 55, 65, 500, 45. I think many of the other brands had something similar too just don't remember if it was the same value and linear. Not trying to show / test my memory with that processor list just putting it in there for future people finding this tread because they want to do this. I do believe you are correct that they never published the protocol for the data based remotes of the 650 and 750 likely because as you say those had serial and or Ethernet options that were published.

0-10v still being used for light dimming should give several options to integrate into what ever control scheme or hardware one has since lighting is often one of the things home or pro would possibly want to remote control. And if 0-10 was the actual range that should mean you can't have a hiccup in your programming and overdrive it. Was it even 12v since that was one of the rails? So you can't remotely hit 100%? Not that you would want to so no big deal if it is. Or is the 2.2k dropping it so its more like a 0-5 sort of thing? I obviously don't really know the inner workings of VCA circuits.

Either way how the inner workings work its good to hear that 0-10 with a 2.2k in the remote line has been done and works. Not sure if this will ever be that useful to me these days but maybe will be useful to others that are still working with or are thinking about working with this old stuff.

Question to anyone that has done this are we lucky enough that 5v=5.0 and 7v is 7.0? I would guess not since that wasn't the intent of the design at the time and if the venue needed to switch between the analog and new remote and or still think in Dolby terms one would have to do some calibration tests to be able to accurately represent the Dolby numbers in what ever the new user interface is?

[Marco Giustini]

If I remember right the 500 and 650 also use the same 100k pot (below is the 650 wiring diagram) - what was removed was the ability to select local/remote with an automation which sucked as you couldn't have a "dual volume" control as with a CP65/55 etc.
If you wanted to use the digital remote then yes, there is no documentation on how that works.

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[Tj Hopland]

I was thinking that that connector on the 650 had more than 3 pins but could not remember why, that explains it. I almost never had to use it just likely stared at it while wiring up the ones I was using. So the 750 apparently the first to not have the analog pot option. I do remember with the 650 it was common to get panic calls saying the volume was stuck at 0.0. That was due to the Auditorium vs Local fader selection being the first menu option and it being really easy trying to figure out how to advance to the next option switching the mode. My first question was always is there a A or L in the display. The nice thing about the digital remotes was it wasn't an either or thing they were both live all the time and with the display on both either person could tell what the current setting was or if the other location (or an automation) had changed it.

I never did many remote faders but I heard it was a very common thing in the studio screening game and the techs that traveled around carried one so they wanted something that was universal so they didn't have to carry something different that may require different cabling for the newer at the time processors.

I remember there used to be the Cat 122 and 123 remotes. I think it was the 122 was the end one or if you just had a single. 123 was a middle unit and had some switching logic in it so it would either patch itself in as the active one or the other depending on what was selected.and they had an LED that lit when it was the active unit. I think you would often tie it to the change over and have one by each projector but I think you could trigger it other ways so it could have been a booth or auditorium thing. Its been just a few years since I had to wire one of those.

[Tj Hopland]

I didn't finish my thought about the 122, 123 fader boxes, I had at one time considered that concept for remote control. You could take what ever relay automation you had and as long as you had the 'latching' mode for relays program them to patch in multiple analog pots. You could have one for trailer mode set to 5.5 then one for feature mode set to 7.0. Not as nifty as being able to fire a 6.7 direct from the server to the CP but would have been an improvement over no change at all.

I guess if you had enough relays you could just use a ladder arrangement with resistors and patch in and out resistors to simulate the pot in steps. Lots of possible ways to do it but back in the roll out if someone didn't want to spend the money on a new audio processor at the time which was nothing on top of the cost of the projector and server they didn't likely spring for much if any automation either so you probably didn't have a bunch of extra relays to play with which is why I never took it past the I wonder if it could be done stage back then.

[Steve Guttag]

I'm not sure that Dolby used a set voltage level across all products. In fact, I'd think that they didn't. The used a 100KΩ (linear) pot across all products. You need to consider that the CP50-CP200 utilized discrete components for the VCA and part of why 7.0 was chosen as reference was to ensure channel-to-channel tracking was in the "sweet spot" of both the pot and the components. The CP50 used a crude voltage reference using +24/-12 and a zener with a resistor on the +24. And, mind you, on a CP50, those voltages are incredibly "nominal." A CAT114 was doing well to hit +/-10.5VDC with some ripple.

Later processors used integrated circuits for VCAs and even mixed and matched (the 441 used THAT corp, as I recall while the 242 used TDA stuff). They just had to ensure that the 100K pot would work with with the VCA scheme, including on the digitally based processors, the CP500 and CP650.

FYI, Pennywise did make the "DF-1" box that allowed for adding serial commands to otherwise analog processors. The DF-1 (I believe it was called Digital Fader) did allow control over the fader as well as having otto-isolated I/O to monitor/control formats and such. One did have to set jumpers/dip switches based on the processor being used as well as calibrate the fader. It was a pretty cool little box. They developed it for their automation system, the CA-21 (which also went by the name of EMK-1 for Kinoton and FT-21 for Film-Tech).

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[Tj Hopland]

Yep that's the device I remember hearing about. Never got to use one. Best I was able to do after we started running trailers in stereo was if it was a USL with the JFM-20 format card they had that volume pad feature you could activate with a contact closure. It was a fixed offset set by a pot on the card only accessible with the card out but it did the job. Never saw anyone else use that feature other than me but I thought it was useful.

Which way did the Dolby pots work? lower resistance louder? High quiet?

[Steve Guttag]

High resistance was off, short was full output.

[Marco Giustini]

makes sense: nothing connected to it => no sound. You don't want the level to jump to 10.0 if the wiring fails