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Woo Audio Amp Owner Unite

Discussion in 'Headphone Amps (full-size)' started by dannie01, Jun 9, 2009.
  1. TheGrumpyOldMan
    Welcome to the fickleness of tube amps...
    There is a possibility it could be the rectifier tube since it determines the amount of power getting to the driver tubes, thus how strongly they can drive each channel. Not sure about the exact topology of the WA6SE, but the 274B can provide voltage to each side separately and if there is an issue with one of the cathode/anode pairs (even with a new tube like yours) that may cause this imbalance problem.
    Another thing could be a mechanical contact issue, maybe use a flashlight and check the sockets (tubes should be OK since you swapped them without swapping the imbalance), to make sure nothing is bent, obstructed or loose in the pinholes. It could also be a faulty cap etc. inside the amp. If either of these things go wrong, you'll have most likely have to send it in for repair.
    But hopefully it's just a tube issue. Since you tried the driver left/right swap, definitely try the rectifier tube. And since the SE uses an umbilical cord between the two halves, disconnect it completely, check for bent pins/pinhole damage that may cause a contact problem, then tightly reconnect.
    P.S.: Also be aware the a 274B provides less voltage/power than the 5U4G usually provided by Woo. Shouldn't matter, but if there's one thing I've learned with my own tube-rolling experience it's that there are many parameters and characteristics to tubes, even within the same compatible family, and these interactions are not always as simple. I.e. the drivers may not be well matched, though with sufficient power they will be OK, but in an edge case it may just be enough for one tube but not the other. Though since the issue didn't switch after the tube swap, it's not likely in this particular case.
    P.P.S.: While swapping tubes with the amp off is a good way to check things, I would NOT advise to wiggle them while ON; if there is a contact issue and it is lost and thus the circuit interrupted, then even maybe reconnected, very bad things can happen. Most people wouldn't open a powered-on solid-state amp and pulling on/plugging the live components or shorting out the wires either, and just because on many tube amps part of the circuitry is on the outside (the tubes) that doesn't make any more a good idea...
    ninjapirate9901 likes this.
  2. bbophead
    I thought the driver tubes were also the power tubes (dual triode) or is that what you just said?
  3. TheGrumpyOldMan

    Yup, though it's a special case in that these specific tubes combine the driver & power sections in one tube for each channel.
    But it's the rectifier (ex. 274B), turning the AC current into DC current at high voltage, that said tubes directly depend on. So if it is faulty, everything down the chain will be affected.
  4. bbophead
    So a rectifier could screw up one channel but not the other?
  5. TheGrumpyOldMan
    So I had to really dig in a bit and look into this in more detail since I'm still learning too (beyond having experienced the differences when swapping rectifiers myself).
    And: probably not... As it turns out, a full-wave rectifier (like the one discussed here) has two sections not for L/R, but for making use of the positive & negative cycle of alternating current. So it would not cause problems in the sense of having one section affecting only one channel.
    However, if one section is defective, it would probably still cause audible problems because of the ensuing voltage fluctuation. And the other possibility remains as well, that in an edge case combined with mismatched L/R driver/power tubes, one side may be more affected than the other.
    At this point, someone more experienced should probably chime in with this. Anyway this wasn't supposed to turn into a technical discussion of tubes, but more about some suggestions for troubleshooting ninjapirate9901's problem.
    The bottomline is that the rectifier can affect audio quality, possibly one channel more than the other, and when troubleshooting it is worth swapping it out as one of the checks. Though I'd say in this case, most likely it's more circuit related, on that side/channel, bad contact, bad cap or loosened wire during shipping (since it's a point-to-point wiring but Woo usually has very good build quality)
  6. bbophead
    Thanks for your efforts.
  7. deanorthk
    I'm totally decided, I'm going to sell my fostex HPA8, and get the WA6SE.
    As I've ordered a cypher labs theorem 720 dac/amp, I think that I'm really going to just let the WA6SE on my desk and pair it with the cypher as a dac, when I'm home, and unplug it when I'm away.
  8. ninjapirate9901
    Thanks for the help!
    I did some further testing last night and it doesn't seem like changing the rectifier makes any difference to the channel imbalance. I think I have found the issue though.
    It seems to be related to the socket for the left channel. The position of the tube seems to be quite important as it seems I can make the left channel louder or quieter depending on how the tube is seated in the socket. A quick inspection with a flashlight doesn't really show anything particularly out of whack when compared with the socket for the right channel. I'm guessing some of the internal pin sockets are worn out to some degree.
    Maybe I just need to replace the socket completely...
  9. Justin_Time

    Did you try swapping the 300B and 6SN7 from left to right? The tubes may not be well matched. If that does not help, It sounds like ( no pun intended) you have poor contacts. You can open the back of the amp or PSU very easily and have a complete access to the back of the sockets--do turn off the power first. He! He!

    Then you can see the status of the sockets. You can easily clean the copper springs if needed (Detoxit D100) or bend them slightly with a pair of needle-nose pliers to make sure they are aligned with the holes and provide even and sufficient pressure on the tube pins.

    Replacing the sockets--get the Teflon upgrade if you do--will require significant surgery-- multiple solder joints--and will set you back quite a few clams.

    I hope this helps.
  10. ninjapirate9901
    It's a WA6 SE so the 300B and 6SN7 don't really apply in this case. I have swapped the driver tubes around to little effect (see an older post), so my thinking is that it's most likely socket related. I may have to crack the underside off and see if the pins are bent.
  11. BoxBoxBox
    How do I replace a blown fuse in a woo audio amp? Is it difficult? 
  12. Justin_Time
    No, it is usually quite easy.
    The fuse holder in many models are right below the AC plug. Just pop it out and you usually find a short slow-blow fuse of 2.5 to 3 amps. 
    It is a lot more difficult to figure out why you blew the fuse.  If the problem is not fix you will blow the next fuse or worse, you could damage the amp or the tubes.
    Good luck.
  13. Stealer

    I am coming from Little Dot mk 6+
    And wondering what will I be expecting if I were to upgrade to wa22.
    Beside leaving a big hole in my pocket.

    Been wanting to go for and audition but the shop had just shipped its unit to US for an upgrade.
    No.. I had to listen to a Woo yet..
  14. koiloco
    Whatever you do, just do not listen to the WA22 with stock tubes and with unbalanced inputs...You will not be very impressed.
  15. givemevinyl
    I'm interested in buying a used WES.  Please let me know if anyone is willing to sell.

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