eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) If I understand your situation correctly, you have a preamp output with XLR/ "Cannon" connectors and power amplifiers with RCA/"phono" connectors. Is that right? No. I have only preamps with unbalanced RCA outputs. The previous owner used unbalanced RCA outputs from a VAC preamp to unbalanced inputs on the VAC amps. Edited April 20, 2014 by eth2 Quote Link to comment Share on other sites More sharing options...
Chris Hornbeck Posted April 20, 2014 Share Posted April 20, 2014 Now I'm really confused. I looked for a picture of the VAC PA80/80 and it seems to have (only) RCA inputs. So, you have a third amplifier, a pair of some kind of monoblocks? I've lost track. Can you connect your preamp to any power amp using only RCA-to-RCA cables, no DI box, nothing extra, all electronics plugged into the same power strip, Cable TV disconnected? No powered subwoofer in the system, nothing but preamp, amp(s), speakers. All signal wires from sources disconnected. This stripped down core system is the beginning of trouble shooting. All good fortune, Chris Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) Now I'm really confused. I looked for a picture of the VAC PA80/80 and it seems to have (only) RCA inputs. So, you have a third amplifier, a pair of some kind of monoblocks? I've lost track. Can you connect your preamp to any power amp using only RCA-to-RCA cables, no DI box, nothing extra, all electronics plugged into the same power strip, Cable TV disconnected? No powered subwoofer in the system, nothing but preamp, amp(s), speakers. All signal wires from sources disconnected. This stripped down core system is the beginning of trouble shooting. All good fortune, Chris I am very sorry for confusing things. This thread started with a discussion of the VAC PA90's which are a mono blocks. They are strictly RCA unbalanced inputs (as are the PA80's; I have recently bought both and both have the hum). The 80's do not respond to the DI box, while the 90's do. I realize that there is a ton of information in the thread. With respect to the 90's: 1. With no inputs to the amps, they hum. 2. With the preamp (a Phase Linear) connected they hum louder 3. The preamp does not have a grounded plug. 4. All three pieces are plugged into the same power strip. 5. The PA90 hums coming out of the horns on the K'horns or the Cornscalas. No hum from the woofers. 6. If I connect the DI box between the preamp and amp and lift the ground on the amp side the hum goes away. 7. If I short out the outputs on either amp, the hum goes away (actually you can hear I in a dead quiet room with your ear to the horn). Thanks Edited April 20, 2014 by eth2 Quote Link to comment Share on other sites More sharing options...
Chris Hornbeck Posted April 20, 2014 Share Posted April 20, 2014 (edited) 5. The PA90 hums (coming out of the horns on the K'horns or the Cornscalas. No hum from the woofers. A small hiss is a separate issue, and to some (small) extent inevitable above absolute zero. So, with your preamp to any power amp using only RCA-to-RCA cables, no DI box, nothing extra, all electronics plugged into the same power strip, Cable TV disconnected? No powered subwoofer in the system, nothing but preamp, amp(s), speakers. All signal wires from sources disconnected. Hum? Any condition other than this is filled with confounders, and a waste of your efforts. All good fortune, Chris Edited April 20, 2014 by Chris Hornbeck Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) 5. The PA90 hums (coming out of the horns on the K'horns or the Cornscalas. No hum from the woofers.A small hiss is a separate issue, and to some (small) extent inevitable above absolute zero. So, with your preamp to any power amp using only RCA-to-RCA cables, no DI box, nothing extra, all electronics plugged into the same power strip, Cable TV disconnected? No powered subwoofer in the system, nothing but preamp, amp(s), speakers. All signal wires from sources disconnected. Hum? Any condition other than this is filled with confounders, and a waste of your efforts. All good fortune, Chris This is the current status. There is hum. Also, I replaced inexpensive RCA cables with Monster 850 cables Edited April 20, 2014 by eth2 Quote Link to comment Share on other sites More sharing options...
Chris Hornbeck Posted April 20, 2014 Share Posted April 20, 2014 Cool. Next thing is to listen to just the amplifiers and speakers. You'll need shorting plugs for the amplifiers' inputs. If you don't have a set handy, but have a sacrificable old RCA stereo cable, you can cut it a couple inches long and twist the hot and grounds of each channel of that short stub together. Pop it into the amps' inputs and listen. And just to be very clear, when we're talking about hum, we're meaning a low-pitched sound with a distinct pitch that comes mostly from the woofers? As opposed to a higher pitched hiss without a distinct pitch that comes from the midrange and tweeters (mostly). All good fortune, Chris Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 Cool. Next thing is to listen to just the amplifiers and speakers. You'll need shorting plugs for the amplifiers' inputs. If you don't have a set handy, but have a sacrificable old RCA stereo cable, you can cut it a couple inches long and twist the hot and grounds of each channel of that short stub together. Pop it into the amps' inputs and listen. And just to be very clear, when we're talking about hum, we're meaning a low-pitched sound with a distinct pitch that comes mostly from the woofers? As opposed to a higher pitched hiss without a distinct pitch that comes from the midrange and tweeters (mostly). All good fortune, Chris Chris, I have shorted the amps and they are dead quiet. The "hum" is more like a buzzing and it comes out of the horns on both the Cornscalas and the Klipschorns. The woofers are quiet. The buzzing is fairly soft until I connect both cables from the preamp and then it becomes loud. Attaching only one cable does not greatly increase the buzzing. Also, if I manipulate the grounds between the amp and the power block (e.g., I move the eyelet away from the chassis and rotate a tiny bit on the grounding peg) the buzzing will slightly increase or decrease. It is almost like rotating an antenna (but with less effect). Earl Quote Link to comment Share on other sites More sharing options...
Tarheel Posted April 20, 2014 Share Posted April 20, 2014 Just for you Earl Ballad To My Hum When I plug it in it's here to stay...... When I pull the plug it goes away..... It's a pretty little thing and I love to hear it sing....... Audio bliss is just a little hum away 1 Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) Just for you Earl Ballad To My Hum When I plug it in it's here to stay...... When I pull the plug it goes away..... It's a pretty little thing and I love to hear it sing....... Audio bliss is just a little hum away Hmmm.... Tarheel my friend I feel your lyric up my end Nonetheless, an Easter wish I send Including your very own buzz without mend. Happy Easter. Earl Edited April 20, 2014 by eth2 1 Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted April 20, 2014 Share Posted April 20, 2014 Tarheel it seems has a certain skill. for Earl though, he'd rather take a hurl. This continued hum still has Earl feeling kinda bum. Audio bliss was not born on this Easter morn. 2 Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 Tarheel it seems has a certain skill. for Earl though, he'd rather take a hurl. This continued hum still has Earl feeling kinda bum. Audio bliss was not born on this Easter morn. Sergent, my Sergent Your point is not emergent, Certainly Tarheel's skill, Is far from nil, But of hums be sure, I have had my fill. However you know they will be resurgent. 2 Quote Link to comment Share on other sites More sharing options...
Schu Posted April 20, 2014 Share Posted April 20, 2014 11 pages of this stuff? Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) 11 pages of this stuff? Mr. Shu Don't be no foo. If for you pages are too many, You needn't pay a penny Just skip on to a thread that is new! (Edit: With my regrets to Mr. T) Edited April 20, 2014 by eth2 1 Quote Link to comment Share on other sites More sharing options...
Tarheel Posted April 20, 2014 Share Posted April 20, 2014 Oh Mr. Schu.... you don't have a clue.... what brother Earl may be going through.... he is making a stand..... to get this hum in hand...... So please tell him what to do.... 1 Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 Oh Mr. Schu.... you don't have a clue.... what brother Earl may be going through.... he is making a stand..... to get this hum in hand...... So please tell him what to do.... "And that is all I have to say about that." F. Gump Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted April 20, 2014 Share Posted April 20, 2014 (edited) I actually admire the OP's persistence. That's what it takes to fix a problem like this. I went through a similar thing last fall that spanned about 2 weeks. I finally Killed all of the hum/noise from my system. (I had to, because I went to 114 db Horns). And the addition of 2 more Amps for Bi-amping. I dismantled my entire system, as well as all the electrical work behind the system. I routed one simple dedicated A/C line into a sub-panel. And then hooked all of my gear into 1 outlet via a much quieter Power Strip than I had before. I eliminated 100s of feet of interconnect by removing components that I never use any more (Tuners).... removed RCA interconnects to the TV in favor of Optical into the DAC. My system is as quiet as a mouse now, until those big Oris Horns Explode with a Full Orchestra. I never add anything to my system now, without a thorough evaluation of what noise I'm introducing. Don't give up. In the end it is worth it. You will succeed eventually. Edited April 20, 2014 by Cut-Throat 2 Quote Link to comment Share on other sites More sharing options...
Chris Hornbeck Posted April 20, 2014 Share Posted April 20, 2014 (edited) Quote: I have shorted the amps and they are dead quiet.The "hum" is more like a buzzing and it comes out of the horns on both the Cornscalas and the Klipschorns. The woofers are quiet.The buzzing is fairly soft until I connect both cables from the preamp and then it becomes loud. Attaching only one cable does not greatly increase the buzzing. Also, if I manipulate the grounds between the amp and the power block (e.g., I move the eyelet away from the chassis and rotate a tiny bit on the grounding peg) the buzzing will slightly increase or decrease. It is almost like rotating an antenna (but with less effect). Excellent! VAC makes some really fine amps, and it's good to know that they're blameless in this problem.A buzz, as lots of folks have already suggested, almost always comes from power line borne interference. It's almost always coupled in by a ground loop, but in really pathological cases can even be coupled in as radio waves ("RFI", "EMI"). Tubes amps are pretty immune to this coupling (actually, to the rectification of RF into audible sound), but it's possible in a really tough location. You've proved that your amps are not responding to airborne RF (the RF and the main "antenna", the unshielded speaker wires, are still there in the floating amps test), so coupling must be from a ground loop. As you said in your very first post!You do however have a particularly tough case: your Klipschorns and other Klipsch speakers are very efficient and will play any buzzes Just Fine Thank You. It also sounds like the tiny internal ground loops between power supply and signal chassis in the PA90's may be getting excited by the underlying system ground loop issue. Let's save that for later, because curing the system should cure it too.OK, next test, if you're still up for it, is to connect the grounds (only) of your preamp to the grounds of the amp(s). Here we'll plug the preamp into the same power strip as the amps, have nothing else connected to it. We'll leave the shorting plugs in the amp's inputs, and we'll use any convenient wire to connect from the preamp output jacks' shield (outer connection) to the amps' shield(s). Might be good to try one channel, then the other, then both.All good fortune,ChrisI'm sorry, I can't get the quoting to look like it should (yet). Edited April 20, 2014 by Chris Hornbeck Quote Link to comment Share on other sites More sharing options...
babadono Posted April 20, 2014 Share Posted April 20, 2014 Eth2, Do we have any "dummy plugs" yet? Has your EE friend been able to help at all? I too admire your persistence. Have faith, it will get resolved. Quote Link to comment Share on other sites More sharing options...
LarryC Posted April 20, 2014 Share Posted April 20, 2014 The "hum" is more like a buzzing and it comes out of the horns on both the Cornscalas and the Klipschorns. The woofers are quiet. The buzzing is fairly soft until I connect both cables from the preamp and then it becomes loud. Attaching only one cable does not greatly increase the buzzing. Also, if I manipulate the grounds between the amp and the power block (e.g., I move the eyelet away from the chassis and rotate a tiny bit on the grounding peg) the buzzing will slightly increase or decrease. It is almost like rotating an antenna (but with less effect). I am the least knowledgeable in this, but it sure sounds like a loose connection, perhaps grounding, in your amp or preamp. I guess you have new I/C'a, ao you can rule out those. It seems to me you need a local tech who an open up the pre and the amps and look for loose wires, perhaps near the external connections. It doesn't act like EMI, or the classic RFI coming from the outside, but rather like a broken connection somewhere. Good luck! Quote Link to comment Share on other sites More sharing options...
eth2 Posted April 20, 2014 Author Share Posted April 20, 2014 (edited) OK, next test, if you're still up for it, is to connect the grounds (only) of your preamp to the grounds of the amp(s). Here we'll plug the preamp into the same power strip as the amps, have nothing else connected to it. We'll leave the shorting plugs in the amp's inputs, and we'll use any convenient wire to connect from the preamp output jacks' shield (outer connection) to the amps' shield(s). Might be good to try one channel, then the other, then both. Chris: With the shorting plugs in, the buzz from the horns is almost inaudible. You must have your ear right up to the horn and listen carefully. (Without the shorting plugs the hum is louder and can be heard from 5-10' away). Touching the ground of one channel of the preamp to one channel of the amp does not increase the hum (but it is still there with your ear to the horns and listening carefully). When you touch BOTH grounds on the preamp to BOTH grounds on the amp, the buzz returns to the same level as without the shorting plugs. Bobadano, My friend is in Brazil for 6 weeks. he should return the week after this one. Edited April 20, 2014 by eth2 Quote Link to comment Share on other sites More sharing options...
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