Walker Posted January 7, 2013 Share Posted January 7, 2013 Would splitting my rig into a few smaller rack cases cause grounding issues? I'm thinking Furman, wireless in one case, Pre and amp in another, tuner and effects unit in a third. Cheers Chris Quote Link to comment Share on other sites More sharing options...
Monckyman Posted January 7, 2013 Share Posted January 7, 2013 Shouldn`t be any different to being in the one case if they are all on the same mains feed. Might even be better, as units grounded together by the rack strip in a case can cause problems, and so Humfrees (isolating rubber washers for the rack bolts) are often used to prevent a ground loop. Quote Link to comment Share on other sites More sharing options...
BigRedX Posted January 7, 2013 Share Posted January 7, 2013 Grounding issues can be so complex that breaking your components up in to separate racks might improve the situation or it may make it even worse. Can I ask why you are think ing about doing this? For me the beauty of a rack system is that everything is all wired up permanently and correctly. I can have my rig up on stage set up and ready to use in under five minutes - one speaker cab on to of the other and the rack case on top of that. Take off the front a back rack lids, pull out the speaker leads, mains lead and footswitch cable out of the back and plug them in. Plug the bass into the front and I'm ready to go. The drummer will still only be setting up his bass drum and the guitarists will be messing about with their pedal boards. Quote Link to comment Share on other sites More sharing options...
Walker Posted January 7, 2013 Author Share Posted January 7, 2013 Thanks gents. Weight is the major thing. A full 8U is a bugger to carry from the car! But I've been trying to solved a buzzing problem ALL weekend. I [url="http://basschat.co.uk/topic/191203-multi-preamp-switch-box-project-wiring-help/"]built a switchbox[/url] that lets me connect different pre amps to my poweramp (the power stage of a GB Shuttle 9.2). Pre No.1 is my Ampeg SVP Pro, No.2 is a Pod XT Pro. The Pod is quiet when switched, the SVP buzzes when switched, but stops buzzing if I unplug the Pod. I have both pre's going into my switchbox via a 2 channel hum destroyer. Without the hum destroyer, everything is unusable. The Pod is in its own 2U case, the rest of my gear is in a 6U. Grounding issues are a nightmare - that's a weekend I'll never get back and It's still not solved! Quote Link to comment Share on other sites More sharing options...
BigRedX Posted January 7, 2013 Share Posted January 7, 2013 Just had a quick flick through your switchbox thread, and my initial reaction is that because the ground is constant whatever connections are made this is the culprit, and separating the components into different rack cases is unlikely to solve your problem. I'd try wiring up as much as you can without the switchbox in place and then test each signal path with everything in the rack turned on and as many of the connection made as possible without the switchbox being present. If that gives you hum-free operation for each signal path, then you either need to switch the ground as well as the hot connection, or you need to make up some special ground lift cables for some of the connections. Which ones you'll only be able to find out by trial and error. Quote Link to comment Share on other sites More sharing options...
Walker Posted January 7, 2013 Author Share Posted January 7, 2013 [quote name='BigRedX' timestamp='1357577215' post='1924759'] ...then you either need to switch the ground as well as the hot connection... [/quote] Thanks so much for this, I've been trying to learn about ground loops all afternoon and what you say makes complete sense. The point you make about switching the ground too is something I considered this weekend, but didnt know if it was technically possible - I'm a total newb at this electronics lark - but learning fast. Quote Link to comment Share on other sites More sharing options...
Walker Posted January 7, 2013 Author Share Posted January 7, 2013 (edited) I've had my rack in bits this evening. In my switch box, I have the grounds of all the 'ins' joined and the grounds of all the 'outs' joined (serial). Then I join them to the case. When i disconnect them from the case and disconnect the ins and out from each other, my hum stops. Is this dangerous? Or OK. But if I add the 2nd preamp to my switchbox, back it comes! Edited January 7, 2013 by Walker Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted January 7, 2013 Share Posted January 7, 2013 Walker, Going back to the original switchbox build thread, the capacitor&resistor combination marked 'A' is designed to damp down hum loops so they are not a problem. I'd suggest putting one of those in one of your signal earth paths and then checking each preamp in turn on that input/output, to see if it still hums or buzzes. If it seems to help, then put more of them in, until all the circuits that hum are connected to earth via these modules - hopefully, that should clear it. In your previous post, you ask if it is dangerous to disconnect earths - no, providing that they are signal earths, and nothing to do with mains earths. You also mentioned joining earths (serial) - if you are joining them all together, that is parallel. Joining them like daisy chains would be serial. David Quote Link to comment Share on other sites More sharing options...
Walker Posted January 8, 2013 Author Share Posted January 8, 2013 Thanks for your help David. I did try the capacitor/resistor combo you suggested, but it didn’t seem to make any difference. I’ve included a few photos of what I did so you may be able to spot where I went wrong! Ignore the random bits of heatshrink, I was experimenting! The photo of the box below shows where I am now. It’s deadly quiet until I add a second preamp into the mix. The in’s and out’s grounds have been disconnected from each other and the box. To keep things simples I’ve decided to only use 2 preamps now, with no mute or tune, so would switching the grounds using a different switch now be a better idea? Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted January 8, 2013 Share Posted January 8, 2013 Looking at your photographs, I can't see anything obviously wrong - The original star earth with resistor/capacitor 'modules' is supposed to stop most problems, but didn't. Your current earthing wires ought to work, and I am not convinced that switching earths as well should be necessary Your earlier posts refer to both a buzz and a hum, so the first thing we need to be clear about is which problem we are trying to solve. Deep bass-tone hum is mains 50Hz or 100Hz, and we need to keep it out. A buzz is more likely to be caused by a digital piece of kit, and it can often be suppressed by putting a load on it. Take a resistor of about 1K ohms and put it across the output connections of the pod, and see if that gets rid of the buzz. If it does make a difference, see if it still works on the output of your box, reducing the input impedance of your amp. Since each preamp is a buffer between your instrument and your amp, this should have no impact on your tone. If one resistor on the output works, that is what to do - if it does not, try one resistor per preamp output. If you still have a hum problem, my next step would be to try and find out where it is coming from: Start with the obvious - check that all your jack to jacks are correctly connected, to make sure that you have not lost an earth connection somewhere. Next, connect in preamps until you get hum, then disconnect and reconnect in a different order to see if it is always that socket that gives problems, or always that preamp that gives problems - you have probably already done this. Next, check whether you get the hum with one preamp powered up and the others powered down, but connected - this may identify one preamp as the culprit. If that does not provide some clues, then I'm afraid anything else I suggest would be guesswork. David Quote Link to comment Share on other sites More sharing options...
Walker Posted January 9, 2013 Author Share Posted January 9, 2013 Thank you David, I'll work through this over the next few days and let you know when I get to the bottom of it all! As ever, your help is really appreciated. Thanks again, Chris Quote Link to comment Share on other sites More sharing options...
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