Why does unplugging/replugging TT leads from tube phono pre-amp reset dead channel?
As expected...it couldn't last. So the left channel dropped after a loud passage on Chet Baker's Chet. Great morning tunes. I spun the plug. Wiggled it. Wiggled near the TT. Nothing. Pulled and replaced. Channel returned. I visually inspected the insides of the plugs...the solders look solid. A bit of oxidation inside the ground part (inside the outer part). Thanks for sticking with me on this. Joe |
Jmfawdofile 12-22-2017Joe, the main reason I suggested that you determine what the loading is set to is that it might help in determining the cause of the problem. I’m doubtful that any change you might make to the setting would constitute a solution, although I suppose it’s possible. My original point regarding loading was that when you disconnect and reconnect the cables you are not only physically manipulating the cables and connectors, but in addition when the cables are disconnected you are temporarily changing the impedance presented to the input circuit of the phono stage from a very low value (essentially the cartridge’s impedance) to a significantly higher value (whatever the loading is set to). And it seems conceivable to me that doing so might be allowing the input stage to recover from some abnormal condition. As you can see in the manual resistive loading is set at the factory to 47K, but DIP switches are provided in the unit which can put resistors of 100 ohms, 1K, and 10K in parallel with the 47K, in any combination. There is also provision for paralleling a resistor supplied by the user, which a previous owner may have done if you are not the original purchaser. So the overall load resistance may be somewhat less than 100 ohms, or it can be as high as 47K, or it can be at various settings in between. If it is at the low end of that range, the likelihood that my hypothesis accounts for the problem is minimal, since whether or not the cables are connected would make a relatively small difference in the impedance presented to the input stage. If it is at the other extreme, 47K, the likelihood of my hypothesis being relevant would be significantly greater. But to answer your question, if there is any possibility that changing the loading might be a solution, my guess is that the 47K setting would stand the best chance, if it is not already set that way. If it is not already set that way, changing to 47K would change the impedance presented to the input stage during normal operation in the same direction (i.e., making it higher) as disconnecting the cables has been doing, albeit to a smaller degree. Good luck. Regards, -- Al |
Well, Merry Christmas and Holiday from an LP12 owner here; Joe, I just went through 3 months of a similar problem with an intermittent drop out with my older LP 12/Lingo/Troika/Ekos. One channel would cut in and out with music at times. Then it would stay out for a longer periods; I refitted cables and connectors, which helped for a few weeks and I thought little of it. As the channel dropped out for longer periods of time eventually the cable jostling didn't help as it did on some occasions before. Testing the Troika cartridge leads was not revealing or helpful . Though stored and used little, it may have seen too many years and developed suspension problems. I do not have duplicate components for everything to swap out and check and I could not just put the Troika in another turntable setup. Swapping channels isolated the placed the problem before the preamp. So when I buy a cheap MM cartridge and put it the LP12 and find both channels now working fine the next 3 days I'm convinced the Troika is faulty and need to figure a hefty budget for replacing it, and perhaps going ahead with silver or Cardas front to back TT rewiring for the LP12, which had been one of the potential problems. After weeks of researching cartridges, and tonearm rewiring, etc (and fortunately before buying any) with sporadic listening the channel again starts dropping out, but now it stays out---steady, consistent, predictable---to where it is easy to troubleshoot and isolate--NOT to the LP12 but rather downstream to the American Hybrid Technology phono stage. It turned out that there was a cracked/loose solder joint(s) in the connections power supply umbilical into the board on the main unit. Being 15-20 years old both R and L connections were weak and needed reworked. Whether an initial cold solder joint or just aging and strain from connecting/disconnecting the umbilical was impossible to tell and didn't matter. [btwThe Troika works fine it turns out when the phono stage is working, as is the entire LP 12 setup. I must admit it can be easy to jump to conclusions and blame older gear- especially wading through the dialogue and diatribe between all the Linnies and LP12 Bashers-kinda makes you want to tear your table apart and rewire it...though it might be a good upgrade for a later time it shouldn't be an emotional knee jerk reaction I felt at first...] I came to a reasonable conclusion early on that was entirely wrong when swapping out cartridges because of the intermittent nature of the problem and not being able to confirm the Troika as the problem in another system, and nearly spent thousands to fix a $150 problem. I was lucky to have waited looking at options and have things worsen and declare itself further; it also helped immensely having some duplicate components --so when an older Adcom processor phono stage was substituted in the system and resolved the the drop out for a perfect 10-14 days it was then clear to take the AHT phono stage in for testing in another system. A few dabs of solder and cable anchor and all is well. What a vexing problem from a tiny, inconspicuous spot. Whether the source for your problem ends up similar or not I wish the best of luck, perseverance and much patience. and Happy Holidays. Lary |
