Voltron Posted August 23, 2009 Report Posted August 23, 2009 So, I have owned the Moth 300B for years and have never once experienced what is happening right now. I was playing speakers through it earlier just fine, and was putting records on shelves, etc., so not being too critical. Wanted to switch to K1000s out the back so switched the speaker cables for the pigtail and went out on the porch. In order to adjust volume on the lousy recording I was listening to, I went into the room again and was thinking that the K1000s were really loud through the window and 10 feet away. But even after unplugging them from the pigtail, music played on quite audibly... So for some reason, this straight up power amp with now speakers attached is "playing" music. It is not a slight "singing" of tubes. I called JP who just recently borrowed the Moth (and obviously got is possessed by some spirtit at his place), and he could easily hear it over the phone. I have never once heard this and cannot understand what parts of the amp are projecting the tunes. Listening right now, the K1000s sound fine, too, so it does not seem to be "damaged." Well, I have to go make dinner and then see Inglorious Bastards with my wife. I hope somebody will have some kind of genius solution for the mystery later when I check back in. Thanks in advance.
luvdunhill Posted August 23, 2009 Report Posted August 23, 2009 perhaps you were hearing your phono cartridge?
Voltron Posted August 23, 2009 Author Report Posted August 23, 2009 No cartridge in the CD player I was using.
guzziguy Posted August 23, 2009 Report Posted August 23, 2009 Shouldn't this have been posted in the "What are you drinking?" thread?
dsavitsk Posted August 23, 2009 Report Posted August 23, 2009 I went into the room again and was thinking that the K1000s were really loud through the window and 10 feet away. It is probably the OPTs. They do this, though it is usually inaudible over speakers. It is similar to a power transformer humming from 60Hz AC. But even after unplugging them from the pigtail, music played on quite audibly... This is a good way to destroy your OPTs. Don't do it.
tkam Posted August 23, 2009 Report Posted August 23, 2009 Yeah that's a good point it's bad to have OPTs with no load on them.
recstar24 Posted August 23, 2009 Report Posted August 23, 2009 Yeah that's a good point it's bad to have OPTs with no load on them. Not simply no load, but no load and playing music through them. I think the fact that Al was able to hear music being played through his OPTs with no load is not a good sign...I have never heard of such a thing, but I guess it does make sense since the iron would resonate and those magnetic fields could actually produce a low acoustic output.
dsavitsk Posted August 23, 2009 Report Posted August 23, 2009 I have never heard of such a thing, but I guess it does make sense since the iron would resonate and those magnetic fields could actually produce a low acoustic output. It can be quite loud. Hook up resistors across the speaker terminals and turn your amps up to see what happens.
guzziguy Posted August 23, 2009 Report Posted August 23, 2009 Did Mikhail ever work on this amp? Instead of wallwarts, maybe he stuck an iPod in it.
Dusty Chalk Posted August 23, 2009 Report Posted August 23, 2009 It is similar to a power transformer humming from 60Hz AC.My usual joke response to this is, "maybe it doesn't know the words"? So...maybe it knows the words?
crappyjones123 Posted August 23, 2009 Report Posted August 23, 2009 im not sure i follow whats going on here...the amp itself was playing music? with no speakers/headphones attached? if yes, thats WEIRD!
Voltron Posted August 23, 2009 Author Report Posted August 23, 2009 When I first heard the music playing out of the amp, the K1000s were still plugged in and I only unplugged them for a moment or two in order to confirm that it wasn't them I was hearing. The amp was playing the music out loud, not humming, and the best comparison was what JP said while he heard it over the phone: it was like the AM radio version through a transistor radio. Weird. I just disconnected the pigtail and reattached the speaker cables. With no volume there is no sound coming from the amp. With low volume, there is no sound coming from the amp, and the same with higher volume. I put my ear right next to the trafos and the tubes (concerned about scorching my lobe) and there was no sound coming from them that I could hear. What I heard before, I would easily have heard again even with the speakers playing, but it wasn't there. Weirder. Maybe the higher load of the speakers has an impact? I think that earlier today when it happened was the first time I had used the pigtail, which is Equinox cable with silvered wire ends an 4-pin XLR. Last night and recently, I was using a APS pigtail that has banana plugs and 2x3-pin XLRs. No haunted music was playing when I used that pigtail and I was sitting on the ground right next to the amp last night. Super weird.
cclragnarok Posted August 23, 2009 Report Posted August 23, 2009 I can also hear music coming out from the output transformers of my Sound Quest SQ-84 that JP nums used to own. I was kind of surprised when I first heard it, but it makes sense that output transformers would generate some sound. It's not very loud on the SQ-84, but that's compared to regular headphones like the K701. Since the K1000 is much less efficient, it probably makes the transformers much louder by comparison. I can also see the higher impedance of the K1000 (compared to speakers) to be a factor, but I don't know enough to make any guesses there.
Voltron Posted August 23, 2009 Author Report Posted August 23, 2009 See, JP is the common denominator. Now I know what I need.
cclragnarok Posted August 23, 2009 Report Posted August 23, 2009 See, JP is the common denominator. Now I know what I need. Everything he touches comes alive?! Maybe he can also resurrect dead drivers? That'd be pretty useful.
Torpedo Posted August 23, 2009 Report Posted August 23, 2009 Music playing from "the amp" even with no load (which I completely agree is very harmful for tube amps) is due to mechanical resonance of the OPTs. They vibrate harmonically with the signal they're fed. This can get worse if you play music through the amp with no load. This happens because the primary becomes a too low impedance for the tubes output, then a very high current demand happens which is what may end up damaging the amp. This high current going through the OPT primary excites the resonance of the core even more, then the music coming from the trafo sounds louder. Just make this test. Get a test CD with some high frequency tones from 10KHz and up. You'll notice that these are usually the ones that produce the loudest sounds. I've witnessed this many times when I've visited a friend of mine who builds amps, and he's testing them. Kind of scary hehehehe. Some OPT "sing" more than others, it depends on the core materials and shape, also how they're shielded, etc. EI core trafos are said to have this resonant effect more than others, specially if they have those metal caps attached with bolts, leaving an air chamber beneath, which acts as a resonance one. The metal cap, if has the appropriate size and thickness, becomes a sound radiator increasing the level of the sound.
jp11801 Posted August 23, 2009 Report Posted August 23, 2009 Al, you should give Craig a ring on Monday maybe? You could get evil and have him drop in c-cores
blessingx Posted August 24, 2009 Report Posted August 24, 2009 More importantly what did you think of Basterds?
Voltron Posted August 24, 2009 Author Report Posted August 24, 2009 More importantly what did you think of Basterds? I love the Basterds. The Jew Hunter was a great actor and there were far fewer scalpings than I had imagined.
matt fury Posted August 24, 2009 Report Posted August 24, 2009 I also enjoyed Basterds. It wasn't quite what I was expecting, so it was a pleasant surprise. Pitt was awesome too.
Voltron Posted August 24, 2009 Author Report Posted August 24, 2009 As Grahame so aptly posted elsewhere, all you need to say is "Bon Jour No" and I bust up laughing.
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