CECAA850 Posted April 8, 2014 Share Posted April 8, 2014 Cheater plugs are the 3/2 prong adapters that you've already tried on the power cord. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 8, 2014 Author Share Posted April 8, 2014 (edited) I want to be sure I have the right picture here: You have one circuit turned on at the panel. You have two mono amps that are plugged into that one circuit The amps are connected to the speakers The preamp is NOT in any WAY connected to these amps, and is NOT plugged into the wall ...and there is a loud amount of noise using either 3:2 or 3:3 plugs. Right? Mark, I have tried a variety of options. (No Preamp but speakers plugged in) 1) Two cheater plugs plugged into same circuit - LOUD hum 2) Two power cables plugged into same circuit w/o cheater plugs - LOUD hum 3) Same scenarios as 1 &2 but plugging each mono block into different circuits - LOUD hum 4) One with cheater/one without cheater - soft hum When I plug the preamp in it dampens the hum when the preamp is powered on. Edited April 8, 2014 by eth2 Quote Link to comment Share on other sites More sharing options...
LarryC Posted April 8, 2014 Share Posted April 8, 2014 Anything described as coming out of the mid horn or tweeter would not be considered hum. 60hz and 120hz Hum comes out of the woofer only. I work through this type f problem with Craig, While I can't disagree re 60 and 120, I had a low-level hum from one of my K-horns that apparently was/is due to its being right on the other side of an exterior wall from the house electrical service entrance. It must have involved higher frequencies, since I could hear it, extremely faintly, from the midrange and tweeter as well. Interestingly, the hum continued even after disconnecting the wires from the speaker. From what I've read, this is because EMI goes airborne to the crossover coils, by-passing the speaker wire. It is then magnified to audibility by the horn efficiency. I finally decided the 3-way hum was too faint to bother with, and did nothing further about it. Fixing the dimmer switch solved my bigger problems. Quote Link to comment Share on other sites More sharing options...
muel Posted April 8, 2014 Share Posted April 8, 2014 The cure for my ground loop trouble was to lift the ground on both mono blocks and ground the preamp. OR If you would just teach your amps the words they wouldn't have to hum! Quote Link to comment Share on other sites More sharing options...
Schu Posted April 9, 2014 Share Posted April 9, 2014 Post #1 was a buzz... on this most recent page we're now into a hum. I am wondering which it is and if you have swapped out interconnects as yet. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 OK - I have once again gone through the steps. I have replaced all dimmers with regular switches. I have all circuits disable except the one in the living room; no change I have also run a cord to another part of the house and turned that circuit on; no change Interestingly, when I use either both 3:2 plug adapters or no plug adapters the hum is very loud. When I use only one 3:2 adapter it is still present, but perhaps 1/10th the loudness. Flipping all breakers back on has no effect. Turning the preamp on increases the volume of the hum buy by about 50%, but still far lower than with both plugs using 3:2 adapters or no adapters at all. I have tried using different RCA cables without effect. Increasing the volume on the preamp has no effect. If I turn the right amp off the hum stops completely. Hmmmmm?.........Is this with the cheater plug or no?... or either way? This amp connected to either speaker with nothing else makes noise?(Hum or buzz or whatever). You need a dummy input plug to confirm this. If I turn the left amp off it decreases markedly (but does not stop) Eth2, Have you obtained or made a dummy plug per the Jensen Transformer doc? It will save you a lot of guess work. There is no connection between the chassis of these mono blocks except the power cord ground? Is that correct? Until you plug them into the preamp with RCA cables then they get tied together at the preamp. Does the preamp have a 3 prong cord also? You are almost going to have to draw us all a schematic. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted April 9, 2014 Share Posted April 9, 2014 The cure for my ground loop trouble was to lift the ground on both mono blocks and ground the preamp. OR If you would just teach your amps the words they wouldn't have to hum! Hey you stole my joke! Quote Link to comment Share on other sites More sharing options...
mustang guy Posted April 9, 2014 Share Posted April 9, 2014 OK - I have once again gone through the steps. I have replaced all dimmers with regular switches. I have all circuits disable except the one in the living room; no change I have also run a cord to another part of the house and turned that circuit on; no change Interestingly, when I use either both 3:2 plug adapters or no plug adapters the hum is very loud. When I use only one 3:2 adapter it is still present, but perhaps 1/10th the loudness. Flipping all breakers back on has no effect. Turning the preamp on increases the volume of the hum buy by about 50%, but still far lower than with both plugs using 3:2 adapters or no adapters at all. I have tried using different RCA cables without effect. Increasing the volume on the preamp has no effect. If I turn the right amp off the hum stops completely. Hmmmmm?.........Is this with the cheater plug or no?... or either way? This amp connected to either speaker with nothing else makes noise?(Hum or buzz or whatever). You need a dummy input plug to confirm this. If I turn the left amp off it decreases markedly (but does not stop) Eth2, Have you obtained or made a dummy plug per the Jensen Transformer doc? It will save you a lot of guess work. There is no connection between the chassis of these mono blocks except the power cord ground? Is that correct? Until you plug them into the preamp with RCA cables then they get tied together at the preamp. Does the preamp have a 3 prong cord also? You are almost going to have to draw us all a schematic. I was thinking along those lines. If the preamp is a 2 prong, could reversing the polarity affect this? Perhaps the best thing would be to have a 3 prong installed on the preamp so all units are not only the same polarity but all grounded.. 1 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted April 9, 2014 Share Posted April 9, 2014 I do not know what "cheater plugs" are but will get them if you tell me what to look for. http://en.m.wikipedia.org/wiki/Cheater_plug Quote Link to comment Share on other sites More sharing options...
NOSValves Posted April 9, 2014 Share Posted April 9, 2014 I think the main problem here is we have too many Chiefs instructing one Indian and its causing confusion. This type of problem needs to be handled methodically one step at a time. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 9, 2014 Author Share Posted April 9, 2014 You have to solve the noise problem with the two amps before introducing a preamp into the mix. A preamp will make things more complicated. A few things come to mind... 1. Do you have another amp (and I mean JUST amp) to connect to the Khorns? What happens? 2. When you have been experimenting with these two mono amps, how are they physically arranged? Side by side? How close? Vertically? 3. When they are exhibiting this noise, have you ever grabbed one and rotated it, move it? What happens? 1. Do you have another amp (and I mean JUST amp) to connect to the Khorns? What happens? Yes. The problem goes away with either the other VAC or the B&K. VAC told me that the PA90 was the only VAC amp that did not have circuitry to prevent ground loop problems. 2. When you have been experimenting with these two mono amps, how are they physically arranged? Side by side? How close? Vertically? 3. When they are exhibiting this noise, have you ever grabbed one and rotated it, move it? What happens? I have had them vertically placed in the rack and side by side. I have even moved them 5 feet apart. MORE INFORMATION: I think I have two problems: 1. I believe I have a ground loop because when I move the amps to the den or library the problem remains if I do not have one (or both) connected to cheater plugs. Once connected the problem goes away. 2. Additionally, there must be some form of interference coming from somewhere else and affecting the living room. If there was not, the cheater plugs would solve the problem in living room as well. However, since I have shut power off to EVERYTHING except the living room (where nothing other than the amps are connected), the problem would go away by using the cheater plugs. The confusing part of all of this is why, if there is another form of interference affecting the living room, does it not affect the B&K or the VAC 80/80? I have also used a Pioneer integrated 7.1 in the living room and there is no problem. Quote Link to comment Share on other sites More sharing options...
Schu Posted April 9, 2014 Share Posted April 9, 2014 can I ask another simple question... can a bad tube cause the sound you are hearing? Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 9, 2014 Author Share Posted April 9, 2014 Shu, If it was a bad tube, it would seem that moving the amps or using a cheater plug would have no effect. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 I think the main problem here is we have too many Chiefs instructing one Indian and its causing confusion. This type of problem needs to be handled methodically one step at a time. And the METHOD is in the Jensen Transformer doc. I'm sure it is probably documented other places as well. I will resist the temptation to add my suggestions if that is what Eth2 wants. Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 9, 2014 Author Share Posted April 9, 2014 Bobadono, I am not sure why you keep intimating that I do not want you to comment. I have printed the document you provided and I thank you for it. Please remember, I am a lawyer not an engineer or technician. This stuff is way outside of my experience. I have tried all the things in that document that I was capable of performing. I have sent it to a friend who is an EE and asked him to come over this weekend if he is available. In the mean time, I will continue to try everything you all suggest, given my limited technical abilities. Thanks, Earl Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 9, 2014 Author Share Posted April 9, 2014 Eth2, Have you obtained or made a dummy plug per the Jensen Transformer doc? It will save you a lot of guess work. There is no connection between the chassis of these mono blocks except the power cord ground? Is that correct? Until you plug them into the preamp with RCA cables then they get tied together at the preamp. Does the preamp have a 3 prong cord also? You are almost going to have to draw us all a schematic. I have not made a dummy plug, but have asked a friend to help me do so this weekend. The connections are as follows: Each amp has a separate power block. They are attached by an XLR connection and a grounding strap. They have RCA in and XLR in connectors. However, my preamp is only RCA. There are no connections between each set of front ends/power blocks. The preamp has a three prong cord. The preamp is old (a Phase Linear). Next Monday I should receive Mike's Peach. Any schematic I was to draw would not be helpful. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 Eth2, No worries mate. Sounds like you still want all ideas/input. I was just offering to bow out if that was your desire. Do you understand the "dummy plug" from the doc? Can you make one (or better yet 2 for stereo). Or could your EE friend make one or two? Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 Sorry, must have been typing as you posted. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 Ok so each power amp has a separate power supply unit. Each chassis is grounded through the third prong on the power plug(with no cheater) and then the two power supply chassis are strapped together? Or are the power supplies strapped to their respective amp units? Just for clarification. Quote Link to comment Share on other sites More sharing options...
babadono Posted April 9, 2014 Share Posted April 9, 2014 Isn't it possible that one of the power supply units filtering is not up to snuff? Or the ground connection in the power supply, wherever that is on the chassis is getting a wee bit resistive? Quote Link to comment Share on other sites More sharing options...
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