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Chris Hornbeck

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  1. 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. Excellent! and pretty interesting too. The fact that you can induce the noise with only grounds connected confirms that we're seeing a ground loop. An interesting test at this point would be to disconnect the preamp completely and to connect the two amplifier grounds to each other (only). Amplifier shorting plugs in place, nothing else connected except speakers, both amps plugged into same power strip. Noises with inputs open don't mean anything at all - they're a confounder that just distracts us. Do you have an outlet tester? One of those little plug-in guys with three lights? They're not infallable (they can be fooled by reversed neutral and safety grounds) but they're a quick check of more dangerous issues. Also, do you have a voltmeter of some sort? We're heading there. Happy Ishtar, Chris
  2. 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, Chris I'm sorry, I can't get the quoting to look like it should (yet).
  3. 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
  4. 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
  5. 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
  6. It's just sunk in that you're using a real DI box. I'm sorry, I'd thought that you were just using a non-standard term, as so often seen in technical threads. (Nobody's born knowing the names of every gadget in the Universe, and sometimes folks will disagree.) A DI box isn't really appropriate, or even wanted. For one thing, it's designed to reduce line level signals down to microphone level, and for another, it provides "galvanic isolation" which isn't needed when all the pieces are together at one location. 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? If so, my next question will be about the details of the preamp's output. These vary in sometimes surprising ways, but are all completely workable and understandable. What we really want to determine is the exact best way to connect the preamp and power amp. It will not require anything but connectors and shielded wire. I promise. All good fortune, Chris
  7. There's another solution that might be easier for you. If you have a lightning protection power strip that includes cable protection (with F-connectors on board) just run your cable and all electronics' power through that. Within the lightning protection strip the cable's shield is connected to power's safety ground. This will also force a small local loop, and the large loops back and forth to panel won't matter. The same thing can be done with a grounding block, as used outdoors before the cable enters your residence, with its earthing wire plugged into a safety ground (third wire) hole of your outlet strip - BUT this is not safe and not code, so don't do it. For clarity and info only. All good fortune, Chris
  8. The CATV line is earth grounded (by code) before it enters your residence, usually but not always to panel. It forms a ground loop through the cable box chassis, through interconnect cables, through other electronics chassis, through their safety grounds, and back to panel and cable safety earth. In future, this is always the first thing to look at. To solve the problem permanently, you can buy a widget that passes cable signal but blocks audio and slightly above audio band. They're commonly called "cable ground lifters", and get one that advertizes that it can pass Internet and talk-back to the cable company. (Both are lower in frequency than the cable TV stuff). It connects in the cable line (in series). All good fortune, Chris
  9. It may not help much, but you can check that your AVR is set up as two channels only, and that any Zone 2 stuff is either off or turned all the way down. In setup, you'd tell it "no center channel" and "no surround channels". If it's still clipping off, you're listening too hard! All good fortune, Chris
  10. You have a ground loop. Plain and apparently not so simple. This is called a "loop" because current can travel around a completed loop, typically on the safety earth (safety ground, third wire, etc.) path. The typical path would go something like: preamp through interconnects to power amp to panel (through safety ground) to preamp (through safety ground). Real systems are more complicated, but the problem is similar. A path through the house is one turn of a poor quality but large transformer, and inductively picks up whatever stray fields it finds. Easy to fix. First: plug all of your electronics into a single power strip. Second: disconnect any other earth grounded wires (including cable TV, etc.) Third: plug the single power strip into the wall and enjoy. There will still be a local ground loop, but it will be small enough to not matter. All good fortune, Chris
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