tgourlie Posted January 23, 2006 Share Posted January 23, 2006 I just re-tubed my amp. Audio research D-76A. I now have this loud hiss coming from my speakers. EH tubes all around. Whats up? HELP!!! Quote Link to comment Share on other sites More sharing options...
garymd Posted January 23, 2006 Share Posted January 23, 2006 You could replace them one at a time with your old tubes to see which is causing the problem. Folks will tell you to let them burn in for a while. It may quiet down but in my experience, probably not. I'm guessing one or more is bad. Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 23, 2006 Author Share Posted January 23, 2006 I was "luckY" enough to get 5 12AX7's when I only need 4. I started moving them around, the hiss came out of different speakers, I finally narrowed it down and got rid of it. But the noise that made me buy new tube still remains... a buzzing type sound coming from all drivers. It actually got louder [:@] Would the AC balance have any affect on the sound? I just bias my power tubes the other day. Quote Link to comment Share on other sites More sharing options...
garymd Posted January 23, 2006 Share Posted January 23, 2006 Then I doubt it's the tubes. You need to talk to someone who knows something. Sorry but I'm not that person. Email Craig. He'll get you straightened out. Quote Link to comment Share on other sites More sharing options...
JBryan Posted January 24, 2006 Share Posted January 24, 2006 "... a buzzing type sound coming from all drivers." Is it a mechanical-sounding buzz or more like a hum? Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 It's a hum. Sounds kind of like a buzz in the high frequency drivers. This is really driving me nuts. I thought I was getting a filament to cathode hum, so I bought the Electro Harmonix 12AX7 that are designed to eliminate that type of hum. But it is still there haunting me. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 24, 2006 Share Posted January 24, 2006 AC balance will have no effect and its not advisable you play with that type of control you have no way too accurately adjust it. 1) Does the amp have a three wire power cord? If so lift it from ground with a cheater plug and see if the noise is gone. 2) unhook all inputs to the amp and see if the noise changes. Its helpfull on this test to have some RCA shorting plugs since the amp could pickup stray noise from the RCA inputs being left open. You can make a set from an old cheapo set of IC's buy cutting the ends off 4" back and stripping the insulation off the outer shield and inner conductor and twist the wires together. If the amps are near silent with the inputs shorted the amp is amplifying something your preamp or sources are presenting it. If the amp is still noisy with the shorting plugs in place then the amp has a problem and needs service. Craig Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 amp does not have a 3 prong plug, just two. The buzz is pretty much the same at both speakers as far as pitch and loudness. I have tried different outlets, only one piece of gear in the system is three prong grounded (preamp). So for test #2, I just short the inputs on the amp? + to -? I have unplugged the inputs to the amp, and the sound does not change pitch or loudness. Thanks for the time guys, this is really frustrating. TG Just to keep you guys/gals posted, -I will be checking potential from 3rd ground on wall outlet, to chassis on amp. -Also will be adding a better power line filter (Pure AV PF60). -I will also be checking to see if pitch/vol changes while physically moving the amp around while operating to see if it changes. -short the amp inputs All of these will be checked as while I was biasing my power tubes, I had it hooked to an oscillascope at my shop, and I did not see any resemblence of this noise. Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted January 24, 2006 Share Posted January 24, 2006 TG, Just a wild thought. Do you have a lamp on the same electrical circuit with a dimmer on it? I had the same buzzing sound when my wife came in a put the lamp on a dimmer without me knowing it. She turned it 1/3 of the way down and the HF section just buzzed like a bee. If it buzzes with the volume all the way down, you're getting something extraeneous to the system, but I'm no electrical expert. Chris Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 yes it happens when the gain on the amp is at zero.... or eleven... my goes 1 louder and I do have a lamp on a dimmer switch. TG Quote Link to comment Share on other sites More sharing options...
garymd Posted January 24, 2006 Share Posted January 24, 2006 Unplug the lamp.[] Wouldn't that be a kick if you spent all this time troubleshooting and it turns out to be a dimmer switch.[][] Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 eww that would really get me. But I would be happy none the less. As long as I can fix it I will be happy in 2channel land. [ip] Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 24, 2006 Share Posted January 24, 2006 Try the dimmer switch but it sounds to me like the amp could need work. Isn't this model over 20 years old? As far as the shorting plug goes yes the positive (inner conductor) of the RCA input to the outer shell of the RCA will rule out any external noise pickup. But if having nothing attached to amp made no change what so ever it sounds like the nose is coming form the amp. You can also reverse the way you plug in the AC cord but that is a stretch. Craig Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 When we hooked it to the oscilloscope we did not get any sign of a hum from the output. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 24, 2006 Share Posted January 24, 2006 Well if you can hear it obviously it has to be present. It doesn't take much to hear it out of a Klipsch speaker anything above 2mv on the output gets pretty audible without music playing or during quiet passages in a song. Buzzing type hum is the worse! Craig Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 24, 2006 Author Share Posted January 24, 2006 I know what you mean! I tried it all now, and nothing changed. Dimmer out of all. Pure AV PF60 power filter, Moved the amp to a different location same outlet. moved the amp to a different outlet. Checked potential from 3rd ground to chassis. Unplugged pretty much every device in the home. Had the amp on an osculloscope with no sign of any noise. Could this be normal noise coming from a tube amp at idle? Is dead silence too much to ask for out of a tube amp? Right now I am ready to throw it out of the window, at least then it will be silent. I have noticed that valve #1 on the preamp stage of the amp does not glow at all. No matter which tube I put into that socket. Hear is a simplified schematic of the amp. http://arcdb.ws/D76/ARC_D76_schematic2.JPG I sure do appreciate any help on this. I would be willing to try anything you suggest. Thanks TG Quote Link to comment Share on other sites More sharing options...
mark1101 Posted January 24, 2006 Share Posted January 24, 2006 When you retubed did you set the DC balance to minimize the hum? Quote Link to comment Share on other sites More sharing options...
joshnich Posted January 25, 2006 Share Posted January 25, 2006 Is your cell phone on in the room? I dont know why but if I walk into the room with my stereo gear with my cell phone on, the system buzzes! Josh Quote Link to comment Share on other sites More sharing options...
tgourlie Posted January 25, 2006 Author Share Posted January 25, 2006 tried with cell phone off, no dice. When I biased the tubes (actually done by a technician I know very well) DC balance was used in conjunction with the bias adjustment in order to get the reading within the range specified on the amp chassis. I have not biased it with an IM yet. I am setting that up with him as well. Mostly around his schedule. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted January 25, 2006 Share Posted January 25, 2006 I would stop right there, find myself a nice box and proper packing material, and ship it off to NosValves. Something's up with it and Craig should be able to fix it. Quote Link to comment Share on other sites More sharing options...
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