SteelerFan Posted April 9, 2004 Share Posted April 9, 2004 If I hook up my speakers to the amp I have no hum. As soon as I hook up the pre-amp to the amp I get the hum. It doesn't matter if the pre-amp is plugged in or not, I still get the hum. Does this mean there is a problem with the pre-amp? I've tried cheater plugs, switching interconnects, using different electrical circuits and isolating the pre-amp from all other sources. Do I have anything left to blame it on other than the pre-amp? Quote Link to comment Share on other sites More sharing options...
D-MAN Posted April 9, 2004 Share Posted April 9, 2004 Try different interconnects for the amp. The preamp turned off has nothing to do with the humming. Sounds like a bad cable. DM Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 10, 2004 Author Share Posted April 10, 2004 I've done the interconnect thing already. I bought 7 Cobalt interconnects and I don't think they would all be bad. Never the less I then tried some of the interconnects that came with other equipment I've bought over the years with the same result. I also find it odd that I get the humming whether the pre-amp is plugged in or not. I just bought a B&K PT5 2ch pre-amp the other evening. I was planning on updgrading my 2ch rig next year anyway so I just moved up the schedule. I should have it by Monday and will try it first in my HT. I am very interested to see if I get the humming with it. Quote Link to comment Share on other sites More sharing options...
lynnm Posted April 10, 2004 Share Posted April 10, 2004 There is a possibility that the problem is with the amp itself rather than the preamp or interconnects. Hopefully the new pre amp will not hum but I wouldn't be suprised if it does. Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 10, 2004 Author Share Posted April 10, 2004 I hope it's not the amp either. Both amps I bought, NAD S250 and Cary HTA-2 are humming although the hum through the Cary is much softer. And I'll add if I can ignore the humming, the sound from the Cary is stunning. I'd hate to discover it's part of the problem. I did as suggested on the hum busters section of the PS audio forum and unplugged the pre-amp from the amp and when I do the hum goes away. That supposedly rules out the amps as the cause. Once the B&K arrives and I get it installed maybe I'll find out what gives. Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 10, 2004 Author Share Posted April 10, 2004 ---------------- On 4/9/2004 6:47:13 PM D-MAN wrote: Try different interconnects for the amp. The preamp turned off has nothing to do with the humming. Sounds like a bad cable. DM ---------------- DM, you're the man. It's got something to do with the cables. Thought I'd tried everything but I took your advice and kept playing with it and discovered that if I plug any interconnect into the amp, even without plugging the other end into the pre-amp, I get the hum from the corresponding speaker. I've tried it with the expensive Cobalts, a pair of Tsunamis I have and the EL Cheapo one's I've collected over the years that were included with various other equipment I've bought. They all have the same result. The bad news is what the heck do I do now? Can't use it without interconnects. I don't have the option of trying balanced with the NAD stuff, they are single ended only. The new B&K pre-amp I bought has balanced connections along with the Cary amp, but I'm screwed with the NAD. Any ideas? Quote Link to comment Share on other sites More sharing options...
lynnm Posted April 10, 2004 Share Posted April 10, 2004 "kept playing with it and discovered that if I plug any interconnect into the amp, even without plugging the other end into the pre-amp, I get the hum from the corresponding speaker" Unfortunately I think that points rather more precisely to the amp than either the preamp or the interconnects. That amp is quiet with nothing plugged into it but hums if "any interconnect" is plugged into it. I hope the new pre amp clears up the problem but I doubt it will. Best guess is that the amp has a bad ground connection somewhere. Many amps use a common ground for the input ( ie. the signal lines are fed separately to the the gain stages but the grounded side of the individual inputs are connected together and then are grounded to the chassis as if they were a single connection. It is that connection point that I would be suspicious of. Quote Link to comment Share on other sites More sharing options...
lynnm Posted April 10, 2004 Share Posted April 10, 2004 A couple of questions for you. How loud is the hum ? Is the sound really a hum or is it more of a hiss ? When the preamp is connected does the hum increase in volume as the preamp's volume control is increased ? Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 11, 2004 Author Share Posted April 11, 2004 ---------------- On 4/10/2004 5:33:01 PM lynnm wrote: A couple of questions for you. How loud is the hum ? Is the sound really a hum or is it more of a hiss ? When the preamp is connected does the hum increase in volume as the preamp's volume control is increased ? ---------------- The hum with the Cary amp is fairly soft. I sit about 9' from the speakers and can just barely hear it. The hum from the NAD amp is much louder. It's definately a hum. I've always had a slight hiss from both my Forte's and RF-7's, even when I was using them with my old Yamaha DSP-A1000. The hiss is only detectable if I put my ear up against the horn. This hum is coming from the woofers. The hum does not seem to increase when I turn up the volume as far as I can tell. You must be right about the amps not being grounded right. I pulled the NAD out and hooked the Yamaha back up to use as just an amp for the center and surrounds. There is no hum. Is this a problem that is easily fixed? I'd really hate to give the Cary amp up. Other than a slight hum it's a fantastic sounding amp and is no longer available. I really haven't bothered evaluating the NAD amp and it wouldn't break my heart to see it go. Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted April 12, 2004 Share Posted April 12, 2004 I have always had a slight hiss out of my system, but after replacing my NAD T163 with another one I too seem to have developed a hum. Sometimes it is more noticeable than others. I have tried a variety of things to silence it to no avail. I am not using NAD amplification however, but I don't ever remember the noise being that prominent. If I lower the volume knob on the NAD to "infinity" or off the noise will drop to about inaudible unless you put your ear right to the speaker. But the second I move it to the first increment which is like -74 I get the noise right back. Is this indicating that the preamp is obviously introducing the noise? I have a Denon AVR-3300 in the bedroom that I can drag back in and try but damn that is alot of connections to undo and redo to test it and I did not feel like going through all that. I called the dealer last week and let him know. I will call today and see if I can get any answers. This is annoying I should have just kept my Denon AVR-4800 that worked fine. Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 13, 2004 Author Share Posted April 13, 2004 I've always had a slight hiss also, even with the DSP-A1000. Never bothered me because the only way to hear it was put my ear up against the horn. The hum was a different story, I could hear that even from my seating position. And let me tell you, a hum from the surround will drive you nuts, it's not something you would get used to. My hum always stayed at the same level. I could turn the volume all the way down or turn it all the way up, it didn't matter. I guess that's a classic ground loop? Whatever, I gave up and am sending it all back. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted April 13, 2004 Share Posted April 13, 2004 Grounding could be an issue with the amp hum, but you should not actually hear any hum resulting from an unconnected interconnect being "connected" to the amp. I agree that it is unlikely that there would be a problem with multiple interconnects. This indicates an internal problem in the amp itself... is it one channel or both? what happens when you connect only one interconnect to an input? Is it on one channel or both, etc.? It doesn't bode well, I'm sorry to say... DM Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 13, 2004 Share Posted April 13, 2004 I have not been blessed with hum problems. I don't know why. Or maybe my hearing has a notch at 60 and 120 Hz. Smile. If I had your problem, I'd take a lead with allegator clips on both ends and find the chassis ground on each component. Then connect them together. If that didn't work, I'd disconnect the shield on the power amp side of the connector with the chassis grounds still connected through the allegator clip set. Of course the latter can be done with some ordinary speaker wire (one lead) connected to chassis (plural) grounds. Gil Quote Link to comment Share on other sites More sharing options...
formica Posted April 13, 2004 Share Posted April 13, 2004 ---------------- On 4/10/2004 7:37:38 AM SteelerFan wrote: I also find it odd that I get the humming whether the pre-amp is plugged in or not. ---------------- Ummmm Im assuming you are talking only about the power plug? Im asking because ground loop hum may come from other sources other than the power plug. Do you have cable or DSS plugged into the unit? To correctly troubleshoot, you should unplug all the interconnects feeding into the preamp (except the amp), and see if it still hums. - If it does, probably EMI/RFI interference in the interconnects or the preamp. Interconnects can be swapped... preamps, well... - If it doesnt hum... plug back one item at the time till the hum reappears... and youll have your culprit. Good luck... Rob Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 14, 2004 Author Share Posted April 14, 2004 Trust me on this, I tried EVERYTHING I could think of to try. I never even thought about hooking up my cable to it just to avoid the problem I ended up having. Couldn't have been something else in the system....I had no system. I not only unplugged and disconnected everything else, I went to the trouble of actually pulling everything else completely out of my audio rack! I mean out and set aside. Just in case I was getting some kind of screwy magnetic field. I drove myself nuts. As far as working on the grounding myself, if that means opening up the amp...forget it. I'm not very handy like that. They did send me a second NAD amp they had opened up and worked on the grounding of. They told me to turn down the channel levels. That helped somewhat, but doesn't that mean I wasn't getting my whole 125 watts per channel I paid for? I discovered I could hook up channels 3&4 of the second NAD amp and not get a hum. If I tried to hook up all 5 channels then all of them except channel 3 would hum. I give up. That's 3 amps with a hum for me. Next time if I go seperates I'll buy locally and pay them to set it up and if there are any problems, they can figure it out. Better yet, when I'm sure I've got my money back I'll pick up the B&K 507 and be done with it. Quote Link to comment Share on other sites More sharing options...
iXtreme Posted April 16, 2004 Share Posted April 16, 2004 don't they sell adaptors that change digital coax rca to toslikn, use one properly and one backwars to break the rca to toslink for a bit ending the metal electrical connection and killing the hum?? yes, no? Quote Link to comment Share on other sites More sharing options...
SteelerFan Posted April 16, 2004 Author Share Posted April 16, 2004 ---------------- On 4/16/2004 12:02:11 AM iXtreme wrote: don't they sell adaptors that change digital coax rca to toslikn, use one properly and one backwars to break the rca to toslink for a bit ending the metal electrical connection and killing the hum?? yes, no? ---------------- I'm about 99.9% positive my problem was with the amps and not the pre-amp or DVD. I can use my DSP-A1000 as an amp with the NAD pre-amp and it works perfectly, no hum at all. Quote Link to comment Share on other sites More sharing options...
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