Why does unplugging/replugging TT leads from tube phono pre-amp reset dead channel?

Hi Al,
OK...here is what has happened since your post:
 - I own the adaptors you suggested...supplied by David Lewis Audio upon sale.  They have been un-used out of a concern that it would degrade the sound.  But you provided reason to use them.  (FWIW -  I did not do the tests you suggested.  Is there need for that still?  I do not want to overlook anything....)
- I inserted the adaptors prior to powering up...and both channels worked!
- I listened to a few albums...and then the right channel dropped out...
- Without muting anything...I unplugged the right channel from the balanced adaptors and immediately plugged it back in..and the channel came back!
- and I took a swig of gin...b/c I was stymied!!!  HELP@@!!!

There is no explanation.
You have entered..... The Twilight Zone.

I am thinking of a mismatch between the male RCA plugs at the ends of the ICs coming from the Linn and the female RCA jacks on the BAT, such that the hot contact is intermittent. This can happen if the male RCA pin is not long enough quite to reach the contact point inside the female or the male is too thin in diameter. I apologize for the myriad of sexual connotations. 

Lew, not sure you saw that shortly before you posted the OP indicated that he tried connecting the RCA plugs to the BAT’s XLR input connectors via adapters, with the problem nevertheless presenting itself subsequently.

Joe, no problem re not having done the measurements I suggested. I made that suggestion mostly because I thought it might provide me with some insight into how the input circuit is implemented, which in turn might have triggered further ideas.

At this point, if you haven’t already done so I would suggest that while music is playing you very gently wiggle and tug on the cables, near the turntable end as well as at the phono stage end. If that doesn’t precipitate a dropout, and given that the problem has occurred with both the RCA and XLR inputs, I would have to think that the cables and connectors are exonerated, and the culprit is something in the circuitry of the phono stage. As to specifically what that may be, I’m at a loss at this point.

Per one of my earlier suggestions, though, it might prove useful to know what the resistive loading is set to, since as I had mentioned the act of disconnecting the turntable cables changes the impedance presented to the input stage from essentially the cartridge’s impedance to whatever value the loading is set to. I realize that in order to determine that you would have to open up the phono stage. But who knows, when you do that you might spot a burned resistor, a leaking capacitor, or some other visual evidence of something that might account for the problem!

Regards,
-- Al

Al, I did see that.  Perhaps the male pins in question are just thinner than most. Thus, they are not only a misfit for the BAT but also for the adaptors.  You could have a snug ground fitting and never know whether the hot pin is also snug, just due to the nature of an RCA connector.

To the OP
You said in one post that BAT cannot replicate the issue.
Did you mean they cannot get the problem to occur on a similar unit or that they have had your actual unit in for test and could not get this peculiar problem to manifest?


Do you access to another TT to test by any chance as I appreciate the fixed leads syndrome!