Charles Turner Posted February 2, 2002 Share Posted February 2, 2002 I recently moved my stereo to a smaller room and now I notice my old Mac 225 tube amp is emitting a low level hum through the cornwalls. I've tried switching cables etc and the only thing that reduces the hum is reseating the tubes but doing so does not completely eliminate the noise. The amp sounds wonderful except for the hum. Is this just a part of having an old tube amp? thanks for any suggestions. Quote Link to comment Share on other sites More sharing options...
MacKlipsch Posted February 2, 2002 Share Posted February 2, 2002 Charles, It shouldn't hum at all....Could it be AC noise???....It didn't make any noise in the bigger room?....Way back when (before the redo at Audio Classics) it would hum when the refrig cycled on...Changed to a dedicated circuit and that solved it, but didn't get any hum since....Is it worse when turned up?....Do you have any sort of power conditioner?? If you can't solve it, call Ryan at Audio Classics and ask him wassup...tell him it's the one you got from me Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 2, 2002 Share Posted February 2, 2002 Charles, I agree, a Mac amp shouldn't hum! Try turning the input level controls on the amp itself down. If the hum stays there, the amp may need new filters capacitors or something like that. If the hum goes down with the knob you probably have a ground loop or a bad cable. Al K. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted February 2, 2002 Share Posted February 2, 2002 Given that your tube amp did not hum in the other room, and your moving of the tubes removes a smattering of the offending noice, I would assume it really has to do with your wiring or a ground loop of some sort. Try getting a cheater plug if need be and plugging in your amp with the ground floating. REverse the plug polarity and see what happens. The outlet could be wired differently than your previous outlet. Float the ground. See if this does anything. Also, disconnect the sources/preamp to see if hum persists. My bet is that it lies in the wiring. And after that, just to test, do the below as described by J. Scull. Let's now turn our attention to plug orientation. As revealed last month, hot and neutral are connected to a component's power transformer, and some current leakage is common. Usually one orientation of the AC plug causes less leakage than the other, and finding out which is which is relatively easy. First, disconnect all cables from the component; you want to eliminate all other paths to ground. Plug the unit into the wall and grab your trusty RadioShack voltmeter. Touch the negative probe to ground and the hot probe to a chassis screw. A good ground to use might be at the preamp, the hub of your system. Or you can touch the negative probe to the screw securing the faceplate of the outlet into which the unit is plugged. Check the reading, then reverse the plug's orientation, using a cheater plug if necessary. Whichever AC plug orientation measures the lowest voltage is usually the better sounding. However, using cheater plugs in your system may result in other problems, which I'll go into next month. Once you've done this with all the components in your system, the cumulative effect might surprise you. f>s>My right Moondog is actually wired so that I need to use a reverse polarity cable or the cheater plug. The amp also happens to be far more quiet. Instead of the meter, I use an Elfix Polarity tester I purchased years ago. They dont make it anymore but it was a good little device. Does amazing things for hte noise floor. kh ------------------ Phono Linn LP-12 Vahalla / Linn Basic Plus / Sumiko Blue Point CD Player Rega Planet Preamp Cary Audio SLP-70 w/Phono Modified Amplifier Welborne Labs 2A3 Moondog Monoblocks Cable DIYCable Superlative / Twisted Cross Connect Speaker 1977 Klipsch Cornwall I w/Alnico & Type B Crossover system one online / alternate components / Asylum Listing f>s> Quote Link to comment Share on other sites More sharing options...
Charles Turner Posted February 3, 2002 Author Share Posted February 3, 2002 Lots of really good suggestions here...I'll check them out and let you know what I find. Sincere thanks Quote Link to comment Share on other sites More sharing options...
Charles Turner Posted February 3, 2002 Author Share Posted February 3, 2002 Just tried a couple of the ideas posted here and the results are probably diagnostic. In response to your question, the amp was seldom played in the larger room because other family members complained...and the room was at least 5 times larger in physical volume and the distance between the cornwalls and listener much greater. 1) Changing the gain on the amp does not affect the hum 2) Reversing the plug does not affect the hum 3) The hum is the same with or without the Monster HTS2000 ($200) line filter 4) The hum begins approximately 5 seconds after the amp is plugged in 5) Unplugging the amp and replugging it causes a significant movement of the woofer and dump dump (techo jargon) sound then it quickly returns to the dull steady hum More research later Quote Link to comment Share on other sites More sharing options...
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