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

None of the glitches you discovered leads to an easy explanation for what you experienced, in my opinion, but it's good that you found them.  And it's even better that you are now able to listen for longer periods without that aggravating problem, no matter what the cause.  I don't think that, because your unit was at BAT a year ago, we can rule out a cold solder joint that is intermittent.  If the unit functioned flawlessly at BAT on the workbench, they would never have had cause to look for such a problem.  And such problems can be near to invisible by inspection.  Sometimes you just have to bite the bullet and re-solder everything, in order to get rid of an intermittent solder fault.  (I don't suggest you need to do that, since you are doing fine as is.) Happy New Year.

Hi All,
Thanks for your patience with the silence during the holidays.  I have a few things to report.
- First, I'm grateful for the suggestion to look at the load on the Shelter 901.  The recommended loading is 100.  I had it set at 47K.  I dropped it down from 10K, to 1K, to 100.  Seems to balance the treble/mids so much better...but also, the dropouts seem to have stopped.  This may have been the cause of the issue, Al.  Thanks.

- I also examined each tube carefully.  One of the 6N7Ss had a hairline crack on the base.  I replaced it.  Could this have caused BOTH channels to be randomly dropping??

- I have been listening all week...and the drop out occurred only once after those changes.  I did notice a big dustball on the stylus.  Removed it, did the unplug/replug...and no more issues.  Could that be a factor??

- I appreciate the LP12 support.  I like the table...other than the click in the bb at the bottom of the sub platter spindle. ( I can hear it on very soft passages or before the music starts.)  I think in your situation, the MM change from MC might point to Al's solution.  

- I don't know what a cold solder crack would even look like.  But the Phono preA was at BAT about a year ago...so I assume they would have noticed.

- The system sounds the best it ever has.  I'll keep you posted.

Happy New Year.

Joe

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

No advice, only a comment. I’m surprised that when mentioned your TT was an LP12, that everyone didn’t  immediately blame the TT. I have an LP12 and just it’s mention seems to bring out all sorts of haters. It’s gotten comical. Seriously, good luck resolving your issue. 

Jmfawdofile 12-22-2017
Suggestions on loading to address this issue? It sounds fine as it’s currently set.

Joe, 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

I'd be surprised if the problem isn't resolved after a good cleaning of all connectors from the cartridge pins to the RCAs.

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

Good news?   I have not been able to replicate the issue of late.  Perhaps this post will remedy that. I've ordered from Amazon a tube of DeOxit. Just in cast that's the culprit.  Next steps are to check loading on cartridge.  Suggestions on loading to address this issue? It sounds fine as it's currently set.  Also...will be interested in seeing what else I discover with the hood open. 
Lewm- The male RCAs from Linn simply screw open- very easy. How do I know by visual inspection if there is "an intermittent or cold solder joint to the hot pin."  I'm not sure what that means. Thanks. 
Thanks all.  

Or by the way, have you ever unscrewed the protective barrels of the male RCAs at the ends of the ICs, to see whether there is an intermittent or cold solder joint to the hot pin?

You really don't need to upgrade the cable so much as you need to try a different pair of male RCA plugs at the ends of the cables coming from your Linn. If you have soldering skills, you can buy any pair of aftermarket male RCAs and do it yourself.  I recommend Cardas, for ease of use or WBT. (I am guessing that you have one continuous set of wires from the cartridge all the way to the phono stage, so it would be a big job to change out the wires.  If you are using a traditional pair of ICs with RCA connections at each end, then of course you need to attend to the connectors at the turntable end, as well. Or maybe the wires terminate in a DIN plug at the tonearm end.  DIN plugs can be maddening too.)

Hi All...
Lewm -- the male end of the Linn RCA is split, so I gently expanded it...that was a while ago in response to advice from a dealer a few months back.  It has not helped.  Length, though, I cannot change.  I have considered upgrading the cable on the TT.  It might resolve issue. I cannot believe the adaptors also have the issue with the Linn cable.  But who knows.  Thanks.

Al -- I will try that test next time the issue presents.  Thanks.  As to opening the phono stage...that will be done over the weekend...as it has 14 zillion screws and is a major hassle to open.  

Uber -- BAT had the unit in for an upgrade (superpak) and new tubes...the issue existed prior, I believe, and they could not replicate it. (Which is why they say its my TT, not their unit. However, I have another phono preamp...and never had this issue with that unit.)  I don't have access to another TT...but that is worth pursuing.  Especially if I can get it to happen with a different TT!  Thanks for the suggestion.

A mystery.

Joe

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!

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.

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

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. 

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@@!!!

Thanks for the additional info.  It doesn't sound like a grounding issue, as there's no hum involved.

If by any chance you have a multimeter, it might be helpful if you could perform the following experiment:  Remove one of the XLR shorting plugs.  On that plug, measure the resistances between pins 1 and 2; between pins 1 and 3; and between pins 2 and 3.

Depending on whether all three pins are shorted together, or just pins 1 and 3 (or possibly 1 and 2) are shorted together, or if there is some significant resistance between the pins, I might have some further ideas.  Such as perhaps trying the XLR inputs using RCA-to-XLR adapters.

If you don't have a multimeter, you might ask BAT if using an adapter, such as this one, would be ok.  Like most such adapters, it connects XLR pins 1 and 3 and the RCA ground shell together, while connecting the RCA center pin to XLR pin 2.

Good luck.  Regards,
-- Al
 

Thanks for the suggestions. I have a Linn LP12. Only one set of RCA leads. Can’t remove them.

Al- I’ve had the unit for years. This is a new issue...I think...perhaps since the upgrade to the Superpak. BAT can’t replicate the issue.

1- I have the shorting plugs.
2- not sure on the loading...it was set when the cartridge was put in years ago.
3- no sounds...no clicks....It just gets quiet. I can listen for hours before that happens.
4- " When it powers up, it will not be working." That is after the initial mute has concluded it’s cycle. I wait. I hear the click that it’s on. I get music on one channel and I hear nothing in the other channel. I just pull the dead lead, put it back. I’m good to go.

Think it’s a grounding issue? It switches from one side to the other randomly. Does that info help? Thanks everyone.

Layniesdad83, thanks, but both the description and the manual of the VK P-10SE, as well as various rear panel photos that can be found online, indicate that it provides RCA as well as XLR inputs.  And the manual states the following in bold-face type:

When connecting your cartridge to the VK-P10SE RCA inputs, it is necessary to install the supplied shorting plugs into the unused XLR inputs.

Regards,
-- Al

BAT--balanced audio technology--no RCA's, period. strictly xlr.

Some questions, that might be relevant if the problem turns out to not be a connection intermittency as the others have suggested:

1)Assuming the turntable is connected via RCAs, are the XLR input shorting plugs that were originally supplied with the unit installed?

2)What do you have the resistive loading set to? The reason I ask is that when you disconnect one of the turntable cables you are changing the impedance that is presented to the input stage for that channel from a low value (essentially the cartridge’s impedance) to a higher value (whatever the input loading is set to).  And perhaps that change is allowing the input stage to recover from some abnormal condition.

3)When the dropouts occur, do you hear a relay clicking?

4)When you said "it actually is out when the system powers up" are you referring to before or after the approximately 45 seconds following turn-on during which the phono stage is designed to mute its output?

Regards,
-- Al

As others have said, clearly the movement (wiggling) caused when you attach or detach RCA plugs to the sockets is causing something to touch and hence reconnect.

Maybe there is a member of our group in your area who would be willing to allow you to connect your phono preamp to their system and rule out that possibility

Cold solder on one channel, but alternating right and left?

Have you tried another set of phono leads?

It's more likely the preamp has a loose RCA plug / cold solder joint.

I have spoken to Victor several times.  He is not sure the problem isn't my TT. Or the leads. 

Call victor, the chief over at BAT.  I used to have BAT power amp. I had a service question and he was easily accessible and very helpful. You can’t beat that!