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Author Topic: Ground Loops With Ultra Stereo J-200 Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-03-2019 01:57 PM                     If you recall, there were three series in the analog life... the 5/95, the very short lived 105/195 and the 205/295. The second and third digit defined what its capabilities were. It is the same frame in each case. The only differences were what cards were stuffed in. One could add a JSYN-05 to a processor to get Synth stereo too. However, most used that slot for their "pink card" for testing. There was a VERY VERY close variant to the JS-200 series the JSX-1000A for THX people and, officially, only approved for Dolby-A noise reduction though there was a JSX-1000S that had the SR module too. I saw the JS series in mono, Center-Surround, the very goofy Left-Surround, Center, Right-Surround (Left was played out of Left-Surround and likewise on Right to Right-Surround). as well as the more popular JS-280, which was a full stereo unit. The lesser decoders were a simple L-R for surround rather than actual audio steering.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-03-2019 04:59 PM                     Yea, I did have Center-Surround and Left-Right-Surround in a few places. All those went away for Digital.  |  IP: Logged Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 02-07-2019 12:17 AM                     Thanks guys sorry for the delay. Wasn't getting email notifications for some reason. Apologize for the typo it is a js200. Dave: the doremi is not an AUD, im pretty sure its a DCP 2000. it's all the way in fortuna and I'm in Sonoma. The processor is unbalanced. Ive been troubleshooting cp 50s and 65s that have shielding to disconnect, and it's where I go first with ground loops. so the first thing I noticed was that I had no audio grounds to disconnect on a js200. Thank you very much for the ideas. Carsten: the doremi connects to the processor with serial pin. Definitely digital. I understand AES to be a digital audio signal as opposed to good old analog. Correct me if I'm wrong or elaborate, I'd love to learn everything I can. Thanks. Bruce: yeah I was wondering. So you're saying that the bad ground in your sub amp presented hum across all your outputs? Or just the sub? It's an old building and I wonder if there is some ancient projector vent causing it somewhere in the circuit whenever it turns on. Cool story. Steve: thanks I've noticed floating one end of the input never seems to fix it completely. Where and how does one apply this capacitance you speak of in a circuit? I have trouble picturing what that looks like.  |  IP: Logged Bruce Cloutier Expert Film Handler Posts: 161 From: Gibsonia, PA, USA Registered: Aug 2016 posted 02-07-2019 07:54 AM                        The hum was just the sub. I had meant to pull the amp back out to see how chassis and signal ground are handled internally. I haven't yet. Guess I do have the schematics someplace. I rebuilt that Klipsch subwoofer after a lightning strike some years ago. The hum existed before then. Basically I had to replace all of the ICs and most caps but didn't want to invest in another sub at the time. Klipsch was very helpful even to the point of discussing the apparent manufacturing line changes to filters that I discovered. I probably just found the right guy at the time. But as a result now everything is Klipsch. And, without asking the insurance company included compensation for my time in performing the repair in the settlement.  |  IP: Logged Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 02-07-2019 08:59 AM                     Carsten: I am mistaken. It's serial pin out of the analog output on the back of the doremi  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 02-07-2019 05:41 PM                     Trevor - Doremis have serial out, but that is a control interface (typically, a 9pin, DSUB, computer type connector). That could be used to issue commands towards the JS200 (switch formats). No idea wether a JS200 has a serial interface, I am not familiar with that processor. Now, the audio needs either an analog multichannel, or a digital (AES/EBU) interface, usually on a larger connector (typically 25pin DSUB). Maybe you could show us some pictures of the back of the Doremi? In many digital installations which reuse film age processors, a digital to analog converter was placed between server and processor - one common type is the Doremi AUD-D2A (see a picture here: https://www.dolby.com/us/en/professional/cinema/products/aud-d2a.html ). Another common type was the USL ECI-60, or the Dolby DMA8(+). However, I think some older Doremis also offered a server-internal 8ch analog output card, so, it may be that your installation can output analog audio from the server directly. I don't know if there is any technical reference available about this analog audio card. - Carsten  |  IP: Logged Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 02-07-2019 11:30 PM                     On the back of the DCP 2000, is two 25 pin outs. One is AES and the other is analog. The JS has no serial interface built in but adaptors exist that mount above the screw terminals. or it just gets hardwire. split and fanned out to the appropriate screws. Sorry the processor is like 200 miles away, so I don't have pictures of it. But here's what the Doremi looks like. http://www.film-tech.com/ubb/f2/t004863.html  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 02-08-2019 03:17 AM                     Yes, that's one of the old Doremis with a rev.B Dolphin (4 BNC), GPIO on DB25, AES AND analog out on DB25. I can imagine that you get ground loop problems using this analog out. I guess I don't have a pinout description for the old analog out card that could help with that. If I remember right, there were balanced and unbalanced out versions of that audio card. If we can't figure out a different wiring solving the issue, I would suggest a set of isolation transformers or 'DI boxes'. You can also find them rack mounted in 8ch configurations, although these are usually more expensive than a set of 6 single channel or 3 stereo DI boxes. There's a bit of rewiring involved, as these typically use XLR connectors at least on one side. edit: I found the analog pinout in the Doremi audio wiring document. There is also a suggested wiring guide towards some common audio processors in that document. Not towards a JS-200, but some towards e.g. the JSD80 or DTS6AD may help. I would NOT connect DCP2000 chassis ground towards the JS-200. Also, do not connect cable shield/connector to audio ground. You may connect cable shield only on one side of the cable. Full document: http://www.manualsdir.com/manuals/751530/doremi-dcp-2000.html?page=9 - Carsten  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 02-08-2019 09:57 AM                     quote: Steve Guttag If you recall, there were three series in the analog life... the 5/95, the very short lived 105/195 and the 205/295. The second and third digit defined what its capabilities were. It is the same frame in each case. The only differences were what cards were stuffed in. One could add a JSYN-05 to a processor to get Synth stereo too. However, most used that slot for their "pink card" for testing. There was also the very first Ultra*Stereo analog processor, the one with the taller cards and the full plexi faceplate, the series numbers escape me at the moment. I had one of those, loved the look of it but compared to the later JS Series it was somewhat lacking in performance. (Not in a bad way really, just the NR seemed a bit off and it had higher noise floor.) I also recall it took me a while to scare up a format card with remote fader ability. One flaw that IIRC all of them had, was that it was possible to force the Surround decoder card into the SYN slot, which always fried a few resistors on the backplane and sometimes the Surround decoder card. (On second thought, it might have been the other way around, I think this location only had center-surround, so it would be the SYN card into the surround slot.) I had a theatre I serviced with a notoriously sleazy owner who had that problem constantly at one location, due to a popcorn kid who fancied himself a tech (or fancied me, I was young and pretty then). The owner was one of those guys who, if you fixed the rectifier on lamp #1, blamed you for theatre #4 losing sound the next day. He quickly became a cash-only, 4 hour minimum UP FRONT customer. He only did it because I was the only one dumb enough to show up. He had bought a really bad location (4 screens, with Cinecitas (or as I called them, Sorry-to-see-yas), CFS consoles, and the Ultra*Stereo processors). The late Conrad Button had a field day riling that guy up. Back to the main topic: Trevor, you really need to check out the Rane document that Steve linked to on the first page. It offers detailed explanations about balanced vs. unbalanced, and has several options (with illustrations) on how to make up cables with balanced to unbalanced connections. The balanced connection (usually shown as the XLR connector on the diagrams, pin 2 is +, pin 3 is - ) would be on the server side, and the unbalanced would be the JS 200 side. They also show the capacitive shield coupling.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-08-2019 12:16 PM                     The original USL was the CS serries but it had a predecessor that had a solid blue cover the matrix was very smooth in it  |  IP: Logged Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 02-08-2019 07:42 PM                     Carsten: yeah grounding to the doremi doesn't seem to cut it. Does the audio ground on the amps link to the chassis? Cause the bit of Steve's note I read mentioned connecting the shielding of a balanced cable to the chassis. very helpful thanks man. Tony: I started to give it a read last night. Feels like I found the dead sea scroll. Thanks.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 02-08-2019 08:21 PM                     quote: Trevor Meusx Does the audio ground on the amps link to the chassis? That's usually an important safety requirement. So, the answer should be: Yes A ground loop essentially occurs when you have two grounds in your system. There will be a difference in potential between those grounds and even if it's just a few volts, there will be a current between those systems over the ground loop you created. It's this current that introduces the hum on your system. A ground loop can also occur if equipment is connected to the same ground, but with one of the devices having a problem with the grounding, introducing some level of resistance. In those cases, it can help to give those devices a new ground, by connecting the chassis directly to the ground. If you cannot connect all devices to the same ground, I strongly advice a transformer, like I mentioned before. That will not only get rid of hums produced by ground loops, but will also make your setup safer, since it will introduce a Galvanic isolation between both systems.  |  IP: Logged Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 02-18-2019 09:28 PM                     Anyone ever had luck isolating the hum with an in line xlr iso block?  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 02-19-2019 04:14 AM                     Like I and others mentioned before, if this "Iso Block" is an isolation transformer and your issue is a ground loop and the device you're eying is any good, then it should work.  |  IP: Logged

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