greg928gts Posted September 8, 2009 Share Posted September 8, 2009 I'm setting up my EV DX38 with a couple of amplifiers in my living room to test some speakers and I'm getting a bad hum/buzz from the system. I don't remember having this problem when using this setup with my Jubilees in the same living room, same AC source. Although I did have this problem with the same setup with the Jubilees at my shop. I use XLR to RCA adapters in my MCM system at the shop with an analogue crossover and I don't have these problems. I think I've seen some discussions on here about hum/buzz related to the XLR to RCA adapters. Any ideas what could be causing this and/or how to silence it? I've tried lifting the ground at several points without any change. All the components are plugged into the same outlet. Any help would be appreciated. Greg Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 8, 2009 Share Posted September 8, 2009 Greg, There is a grounding "trick" that some of the guys who own the EV units know about. Someone will hopefully jump in and let you know about it. Basically, this wiring change has something to do with providing a ground to one of the pins in the XLR connectors via a bus........so they all receive the ground. It will allow single ended connections (RCA adaptors) to function better. Hopefully, this helps a little. Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 9, 2009 Share Posted September 9, 2009 Regarding Mark's comments: 1. Some of us have opened our box and soldered a ground wire from the #1 input pin to the chassis ground. Seems EV does NOT ground to the chassis since (I guess?) they presume this will be rack mounted and the rack will provide the ground?? 2. Mike B pointed out that this can also be accomplished WITHOUT opening the chassis by getting a XLR plug which would go into the parallel output. This XLR plug would be ...how to say, crosswired such that the #1 pin and the ground pin are shorted together. (don't take my comment there as gospel, that's only going on vague memory) I find I can still have some serious hum in two different situations: 1. If my Peach is sometimes in "HI Z" mode I will get substantially more hum than if I switch it to "Lo Z" mode 2. I admit I've got a rats nest of wires behind my stuff... I find at times I will suffer some hum...and if I wiggle the plugs from my amps (Crown K2's) in their power strip location, the hum will come/go or perhaps at least, become less/more pronounced. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 9, 2009 Share Posted September 9, 2009 Below you will see a schematic of the Input section of the EV DX38 which shows the loop out XLR socket(JS102) is in parallel with the input XLR socket(JS101). You can do the ground modification without going into the DX38 and thus easily reversible if your not using the (Direct Loop Out XLRs next to the Input XLRs :i.e.= this is just a loop through circuit and so the EV DX38's plugs Input/Direct XLRs are wired in parallel) You will need two Female XLR Plugs and you will need to wire Pin1 to the Case Connection Terminal Pin G of the Female XLR( if you haven't noticed there are (4) connections available in the XLR Plugs which are Pins 1, 2, 3 and a Pin G for case ground) which when pluged into the EV DX38 will electrically tie Pin (1) to Case Ground/Earth Ground of the DX38. mike tn Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 9, 2009 Share Posted September 9, 2009 Here is an example of the XLR connections. Note the terminal connections will be marked Pin 1, Pin 2 and Pin 3 of the plug and you will also see a terminal Pin G that makes contact with the metal case of the XLR Plug(the flat looking one with a hole in it in this picture) and this ground terminal and Pin 1 is what you want to tie together. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 9, 2009 Share Posted September 9, 2009 One other comment. Richard mention equipment being rack mounted. What that does is it makes sure that all the various equipment's cases which are often tied to earth ground are very close to the same voltage potential with each other as well as in referenced to earth ground and this can reduce noise and hum issues sometimes. Sometimes it is beneficial to take a wire and find a good point on each piece of equipment (ie: like under a chassis screw and if need be scrape the paint away slightly for a good electrical connection) and experiment connecting each peice of equipment's cases together electrically which is just what rack mounting does mentioned previously. mike tn Quote Link to comment Share on other sites More sharing options...
greg928gts Posted September 9, 2009 Author Share Posted September 9, 2009 Thank you for the resonses everyone. I will have more time to look at this on Friday. Richard - that reminds me of a picture you sent of your DX38 opened up. I think I saved that picture, and I bet it has something to do with this mod. Mike, thanks for the diagrams. I'll look at them more carefully later. Greg Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 10, 2009 Share Posted September 10, 2009 Richard - that reminds me of a picture you sent of your DX38 opened up. I think I saved that picture, and I bet it has something to do with this mod. You're exactly right. Quote Link to comment Share on other sites More sharing options...
greg928gts Posted September 10, 2009 Author Share Posted September 10, 2009 I finally had a few minutes to really read and understand this. Very easy actually. But Richard said that he connected pin 1 from the input to ground, and Mike said I would need two Female XLR connectors. So I assume that Richard connected the pin 1's on both inputs, not just one, and that is why I would need two XLR connectors "cross-wired", one for each input. I'll try it. Nothing else has worked so far. Greg Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 10, 2009 Share Posted September 10, 2009 I may have to do this someday so let me see if I have it right.........If you use RCA-XLR adaptors on an EV DX38 unit without this mod, the ground of the RCA (outside shield) is actually not grounded at all on the EV unit connection because EV does not tie their XLR ground to the case. Correct? So, by tiying the EV ground to the case the RCA receives this connection on its shield and places the EV unit and preamp feeding it at the same or near same potential. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 10, 2009 Share Posted September 10, 2009 But Richard said that he connected pin 1 from the input to ground, and Mike said I would need two Female XLR connectors. So I assume that Richard connected the pin 1's on both inputs, not just one, and that is why I would need two XLR connectors "cross-wired", one for each input. Hey Greg EV's schematic doesn't give me a board layout so I couldn't be sure if the Left and Right channel's input XLR socket's Pin 1 are wired together ( I do believe they are but?) so I played it safe and recommended you use two XLR Plugs. If you want to you can take an ohm meter and measure between the Pin1 of a Left channel input XLR and Pin 1 of a right channel input XLR to see if they measure continuity(ie: a short). If they do then one XLR plug would be sufficient. Also again if you still have issues try wiring the various componet cases together as I mentioned earlier. mike tn Quote Link to comment Share on other sites More sharing options...
greg928gts Posted September 10, 2009 Author Share Posted September 10, 2009 I tried the XLR grounding mod and noticed a slight difference in the buzzing sound. Then I tried turning volume levels up and down and voila! I found the problem. It's my Creek OBH-10 passively attenuated volume control. When the volume knob is all the way up, the buzzing goes away completely. I could swear that I used this attenuator when I had the Jubilees in the living room and I didn't have any noise issues. I guess I can't use that attenuator with the DX38. Greg Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 10, 2009 Share Posted September 10, 2009 If you use RCA-XLR adaptors on an EV DX38 unit without this mod, the ground of the RCA (outside shield) is actually not grounded at all on the EV unit connection because EV does not tie their XLR ground to the case. Correct? Basically Yes the RCA(outside shield) isn't grounded at the EV input directly. The XLR ground PinG is tied to the case(earth ground) but Pin1 (ie: shield connection) isn't tied directly to earth ground or signal ground in the input circuit of the EV,....and although actually....... C101 and C102 for example connected between Pin1 and earth ground do provide a path to ground for some high frequency interference but otherwise yes the Pin1 connection is basically floating when it comes to low frequency issues like 60Hz, 120Hz etc...... So, by tiying the EV ground to the case the RCA receives this connection on its shield and places the EV unit and preamp feeding it at the same or near same potential. Yes by connecting Pin1 to EV's case ground both the unbalanced preamp's case and EV's will possibly be closer to the same voltage potential. mike tn Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 10, 2009 Share Posted September 10, 2009 For anyone interested here is a good paper by Jensen and especially note page 4 (sections 4 and 5 )which might explain why EV doesn't ground it's input circuits XLR's Pin1. Basically in some situations ungrounded can be superior for Balanced Hookup of componets but in the case of some unbalanced componets using 2 prong AC corded equipment especially(ie: equipment without a 3rd prong for earth ground) who's chassis are allowed to float the ungrounded Pin1 of a balanced XLR input circuit can lead to hum/noise problems. Even though I also use unbalanced equipment(all my equipment does use 3 prong grounded AC cords) I have no hum/noise problems in my system whether I ground pin1 or not of the EV but some users with unbalanced equipment should try this modification for optimum hum/noise rejection. This also is why connecting equipment chassis to each other and earth ground could be beneficial and is worth exploring. Greg you might can still try to use the Creek with a litle experimenting with grounding the Creek's case to another piece of equipments case that is grounded. mike tn Jensen-InterconnectionofBalAndUnbalEquip.pdf Quote Link to comment Share on other sites More sharing options...
Guest David H Posted September 11, 2009 Share Posted September 11, 2009 Glad to hear you solved the preoblem. [<)] I was not aware you were using a passive preamp, I have run into that before as well..... Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 11, 2009 Share Posted September 11, 2009 To MikeTN, what I don't understand is how Pin 1 is not grounded in the schematic you posted up top. It clearly shows Pin1 connected to Pin G (which is grounded). What I assumed is that the unit did not follow the schematic you posted and that in reality Pin G's connection to the case did not exist.......and that the mod we have been discussing in this thread was about grounding the case to Pin1 (and thus G). You state that Pin1 is not grounded but that Pin G is tied to the case and thus earth ground............but in the schematic it sure looks like Pin 1 and Pin G are tied together. What am I not getting? [] Edit: Is it because of the caps between Pin 1 and ground that it is not a fully grounded connection.......and just a filter to ground for certain frequencies? Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 11, 2009 Share Posted September 11, 2009 Mark, I'm WAY out of my league here but... Could it be that the pin is grounded to the case BUT...the case itself is not grounded to the ground plug? I know that on mine, I was directed to take the ground wire from pin 1 to the ground wire where the power cord enters. I would personally think that 'ground is ground is ground is ground' so my above suspiction might not hold any water. That said, it does seem reasonable to my ignorance that grounding to the case isn't necessarily the same as grounding to the power cord (???) Mind you, I'm not trying to say that any of this is the answer, I really don't know and am merely speculating. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 11, 2009 Share Posted September 11, 2009 Edit: Is it because of the caps between Pin 1 and ground that it is not a fully grounded connection.......and just a filter to ground for certain frequencies? Exactly! [Y][] Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 11, 2009 Share Posted September 11, 2009 Could it be that the pin is grounded to the case BUT...the case itself is not grounded to the ground plug? Richard the case is electrically connected to the ground prong of the AC plug. The reason any equipment uses a 3 prong AC cord/with ground wire is to make sure that the case or any other exposed metal from the piece of equipment cannot expose anyone to a potential shock hazard should something go wrong in the equipment. Richard grounds can be at different potentials in electronics you will find references to earth ground, signal ground, isolated ground and Hot Ground(which for example in televisions that I use to service could be at a very high volatge potential. mike tn Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 11, 2009 Share Posted September 11, 2009 Richard grounds can be at different potentials in electronics you will find references to earth ground, signal ground, isolated ground and Hot Ground(which for example in televisions that I use to service could be at a very high volatge potential. Aww crimeny Mike... I just got my brain wrapped around understanding esoteric switchplate covers, magic cubes and now you throw me THIS curve? sigh... when will it end... [*-)] Oh well... good thing I know what I don't know and am carefree about admitting it! [Y] Quote Link to comment Share on other sites More sharing options...
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