System feedback coming thru speakers.....help
A 3-prong to 2-prong adapter will probably still provide a ground, if its metal grounding tab or grounding wire is connected to the screw that holds the faceplate of the outlet in place, and provided that the wiring within the walls is enclosed in metal conduit. If you have a multimeter, or a neon-bulb AC tester, you can verify that by checking for the presence of 120 (or so) volts AC between the AC hot pin of the outlet and that ground screw. From your description of the symptoms, I don't think that AC grounding or feedback have anything to do with the problem. And the fact that it works OK at very low volumes would seem to say that the problem is NOT upstream of the volume control (meaning that it is not being caused by the source component or its interconnect cables, or by preamp circuitry that is ahead of the volume control). Although it would probably be worthwhile to double-check that by trying a different source component, such as the cassette deck. Some things to consider: Are you certain that the new biwire cables are connected correctly, and that there are no shorts in the connections or in the cables themselves? Are you sure that when you heard reasonable sound at low volume settings that you were getting normal stereo separation? It's conceivable to me that a short between channels could produce reasonable sound at low volumes, except that it would be mono, while causing the symptoms you described at higher volumes. Along the lines of one of Lloyd's comments, but specifically with respect to the power amp, I would consider the possibility that the amp's input jacks may have been dislodged as you were connecting things, such that they lost their connection to the amp's circuit ground. And, yes, it does seem conceivable to me that a defective tube, or the wrong tube type, or a tube placed in the wrong socket, could account for what you are describing. Regards, -- Al |
I've plugged the DVD into a different source on the pre amp......same results.What you should try is a different source component, such as the cassette deck. Connecting the same source into a different input of the preamp doesn't prove very much. I made mention Arlie's of it sounding "fine" at lower level......not the case......just at low volumes more difficult to hear the static/thumps.That's different. Given that, I agree with Lloyd that the problem is upstream (ahead) of the volume control in the preamp. Meaning that it is being caused by either the CD/DVD player, the interconnect cable between it and the preamp, or by preamp circuitry (or tubes) that are "ahead" of the volume control. I've included the preamp circuitry that is ahead of the volume control on that list of suspects, even though no symptoms appear when nothing is connected to the preamp inputs, because it is possible that a problem in that circuitry might not manifest itself under zero-signal conditions. Regards, -- Al |
A p.s. to my previous post. Looking at the information on your preamp at the CJ website, although I realize you said that the tube types at locations 4, 5, and 6 are correct, just to be sure I'll mention that if a 12AX7 or 5751 were placed at the V5 and/or V6 locations, instead of the 12AU7's that are supposed to be there, it might result in the symptoms you have described. Also, it can be inferred from that information that V1, V2, V3, and V4 are all only relevant to the phono input, not to the line-level inputs (where the CD/DVD player should be connected, of course). Regards, -- Al |
Try different preamp, or try to see if you can plug the DVD source directly into your amp temporarily...some DVD players have a built-in internal volume control...usually terrible but it should work.Or try the cassette deck straight into the amp. It has a level control on the front panel. Regarding the references to feedback and hum, as I indicated earlier I don't think this is a feedback problem or a hum, ground loop, or grounding problem, based on the sonic descriptions that have been provided. My guess at this point is that it is simply a preamp problem. Regards, -- Al |
So, you believe it might be bad tubes?Seems like a reasonable bet to me. If it is a bad tube, it would figure to be either V5 or V6 (both are 12AU7's), since the other tubes are not involved when line-level sources (CD/DVD or cassette) are being used. Since V4 is also a 12AU7, but only supports phono playback, you might try swapping it with V5 and V6 (one at a time). If either of those substitutions fixes the problem when one of the line-level sources is being used, you've found the bad tube! Regards, -- Al |
