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Author Topic: Ground Loops With Ultra Stereo J-200 Trevor Meusx Film Handler Posts: 9 From: Cotati, CA USA Registered: Jan 2019 posted 01-31-2019 01:31 AM                     I grounded the processor to the Doremi thinking that might help... not really. Lost now and wondering what the culprit is in this system. If anyone has time to enlighten me on ground loops in cinema that'd be great.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 01-31-2019 01:59 AM                     J-200? Anyway: If you use the Doremi AUD-D2A it's got unbalanced output, I don't know if the J-200 input is balanced or not. Unbalanced analog audio is definitely prone to ground loops. Odyssey makes adapter boards with isolation transformers for the server input to hopefully eliminate them. Also one theory of amplifier wiring says to connect the cable shield at the amplifier end only, another says connect both ends.. you can try connecting or disconnecting the processor shield, this hum would be on all inputs though not just the server input. Also things change when connecting a balanced processor to an unbalanced amp input and vice-versa and some monitors can introduce hum. Isolate where the problem comes from, the server input or the processor output: hum only on the server input is likely from poor wiring practice or you should add the transformer board. Hum on all inputs is likely the amp wiring or a monitor problem. If it still hums with the processor off and unplugged, the amp(s) may be bad.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 01-31-2019 06:14 AM                     I've successfully used the DTI Dual Transformer/Isolator to eliminate nasty ground loops on unbalanced audio interconnects in the past.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 01-31-2019 06:47 AM                     Trevor - is that a USL JSD-100, or an old JS-200? How do you connect either to the Doremi? Do you know what digital AES audio is? - Carsten  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-31-2019 10:48 AM                     The JSD analog inputs are all unbalanced. The solar cell input is balanced. Mark  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 01-31-2019 11:23 AM                     The JSD-100 analog 8ch inputs are active balanced. - Carsten  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 01-31-2019 04:14 PM                     The analog JS processors have unbalanced inputs except for the solar cell  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-01-2019 06:51 AM                     quote: Carsten Kurz The JSD-100 analog 8ch inputs are active balanced. Carsten... Are you sure you are not thinking of JSX-1000 USL which was THX approved? Mark  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 02-01-2019 12:15 PM                     I made a cable for a colleagues JSD-100, and the manual gave a symmetrical pinout. But I don't think Trevor has a JSD-100, the connection would probably be digital/AES, and he would have no hum from that connection. Unless his Doremi has one of these rare 8ch analog out cards.I guess he uses a JS-200. - Carsten  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-01-2019 01:14 PM                     Also the JS200 was a mono processor that could be upgraded  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 02-01-2019 01:21 PM                     It's somewhat ironic that a company called "Ultra Stereo Labs" sold mono equipment.  |  IP: Logged Bruce Cloutier Expert Film Handler Posts: 161 From: Gibsonia, PA, USA Registered: Aug 2016 posted 02-02-2019 09:06 AM                        I had to isolate the power cord ground on my subwoofer to get rid of hum. This reminds me to look into isolating that LFE audio signal. With audio at least the ground loops make themselves apparent. These can affect serial and other unbalanced data connections. In those cases things may run fine for a long time and then fail for no apparent reason only to work again sometime later. A few years ago when (RS-232 was mainstream) I had a system dependent on communications which would fail on a Friday every two weeks. We had no idea. Turned out that on that schedule in an adjacent room they performed maintenance and would bring in a machine of some kind and plug it in. That created the mysterious reoccurring ground loop. Was fun. I can't take credit for figuring it out.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-02-2019 10:36 AM                     quote: Gordon McLeod Also the JS200 was a mono processor that could be upgraded I would say that is a mischaracterization. The JS200 series were configured as desired at the time of order. Mono only was an option and was upgradable to various forms of stereo. But one did not necessarily order it a monitor and then order upgrade cards. Technically, the CP55/CP65 would be mono processors by the same logic because there were "M" versions. I believe the "stereo" companies chose that name due to Dolby using "Dolby Stereo" to mean any cinema sound system they put their name on. As I understand it Dolby dropped the name "stereo" because there some that thought it was too "'70s" sounding (e.g. archaic). But you had Eprad Stereo Ultra Stereo, Kintek Stereo (though they started as a psudostereo company and even SMART Stereo. Bruce brings up an excellent point of about ground loops. They exist, even if you can't hear them like in an analog system and they are just as bad. A ground "loop" implies that ground is at different potential (and not ground somewhere or everywhere in the system). The real solution is to fix the grounding problem, which wouldn't exist if grounding was carefully designed and everything attached plays by the rules (no current flow on ground). Remember, if there is ANY current flow on the ground conductor, that conductor is no longer at ground potential (can't get around Ohm's Law). The fast solution, that most take, with audio is to float one end of an unbalanced system. This works on lower frequencies, as dealt with audio but doesn't work well on higher frequencies as used in video. A solution there is to apply a capacitor to remove the direct coupling but allow higher frequency noise to still drain to its "nearest" ground. Transformers can also be your friend, if they are high enough quality to not adversely affect your signal and can withstand the power applied. Note, "balanced" is not necessarily the key to noise free. Balanced implies that one has a signal that equally modulates above and below a reference (e.g. ground). The key to it is the differential signal that has a very high CMRR (common mode rejection ratio) since noise/interference that hits the cable during its length will likely hit both leads equally and will sum to zero. One can use a transformer and remove the ground reference and still achieve a differential input and not, technically, be balanced as it is not balanced to a reference. Rane Note 110 is a good reference: https://www.rane.com/note110.html  |  IP: Logged Bruce Cloutier Expert Film Handler Posts: 161 From: Gibsonia, PA, USA Registered: Aug 2016 posted 02-02-2019 04:07 PM                        If you really want to blow your mind you can read about it in the Handbook for Sound Engineers. I have the Fifth Edition and Chapter 36 "Grounding and Interfacing" is written by Bill Whitlock (name not familiar to me) and is like 40+ pages of small print. Steve, the RaneNote was a good read. I especially liked the interconnect reference table of cable assemblies. There are serial port grounding concerns with the way some have employed the JNIOR which is otherwise isolated. That's best held for another topic if anyone wants to hear about it.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-03-2019 11:17 AM                     quote: Gordon McLeod Also the JS200 was a mono processor that could be upgraded Seems to me it was the other way round where it was supplied Stereo as standard but you could order a mono unit if you asked. I never saw a mono unit in service. Mark  |  IP: Logged

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