FX Audio 6j1 tube preamp - a $31 wonder

Discussion in 'New Gear - Values' started by Poultrygeist, Dec 9, 2018.

  1. Dadbeh

    Dadbeh Schrodinger's meerkat Subscriber

    Messages:
    596
    I am by no means an expert but based on my experience two tubes might reach their optimal operating point a few seconds apart. as in, it is possible that when you turn on the amp the two channels have different ouptut levels and after a few seconds the imbalance goes away. this is not just due to the tubes themselves but also due to the circuit requiring a few serconds to bring the tubes to the operating point. but I have never seen or heard about this taking more than a minute. usually 15 to 30 seconds. in your case you already know that it is the tube that is the source of the problem so if you already gave it a good amount of playback time and the problem it still there, id say send it back and get your money.
     
    Last edited: Mar 11, 2019
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  2. Pio1980

    Pio1980 AK Member Subscriber

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    The heaters are wired in series, if they are not warming up evenly, one gets hot before the other comes up.
     
  3. cuchu

    cuchu New Member

    Messages:
    20
    I have had a problem with some GE JAN 5654w. The fact is that after a week of using my Fx Audio Tube 01 with those tubes, my Pioneer VSX 324 amplifier suddenly went out. The first few times it turned off after 20 or 30 minutes of use. Later the blackouts were more and more frequent. At first, I think that they were cooling problems of the amplifier. I put the amplifier in a more ventilated area and kept going off. Then, I disconnected the Fx Audio Tube 01 and the blackouts disappeared. Next I tried the Fx Audio Tube 01 with a pair of Voskhod 6j1p-ev tubes and it did not turn off. I'll keep watching, but I think there is no doubt that these GE JAN 5654w tubes are not right. I will request the refund from the seller.
     
  4. petemcfc

    petemcfc Well-Known Member

    Messages:
    758
    Location:
    Gt. Manchester UK
    An update on my problem with the FX,the humming is on both channels,swapped around the supplied tubes to no avail,the signal path is CD>FX>Amp,there is no hum when the FX is taken out of its path.
    There was no power supply,I have used one off a PC monitor,I assume it is of the switching kind,the rating of it is, Input 220-240v~ 50Hz 200mA
    Output 12V-1000mA.
    I have contacted the seller the reply is.
    bestg61 sent you a message about your request:

    dear friend so sorry for all trouble Could you plz keep it and then we will refund you 30%as a compensation without return? Could you plz repair it in your local repair shop? Plz do not worry i just want help you and protect your profit. waiting for your repl.

    I cannot see how I can fix it,it should be working correct in the first place,unless I have done something wrong.
     
  5. Pio1980

    Pio1980 AK Member Subscriber

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    It could be a ground loop problem rather than a source problem. Does it happen with the CD player disconnected from the FX?
     
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  6. MiamiEd

    MiamiEd Member

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    52
    Location:
    Miami, FL
    The least the guy could have done is send the stock power supply. If you are getting sound out of both channels but with hum, the power supply is a likely cause. Try a regulated power supply.

    Ed
     
    Last edited: Mar 12, 2019
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  7. petemcfc

    petemcfc Well-Known Member

    Messages:
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    Location:
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    With the CD player disconnected from the FX and connected to the amp there is no hum.
    I am getting sound out of the CD player but with hum,I do not own a regulated power supply nor do I know anyone who has which is a stumbling block.
     
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  8. petemcfc

    petemcfc Well-Known Member

    Messages:
    758
    Location:
    Gt. Manchester UK
    I have a desktop PC with a very old M Audio analogue soundcard,I've just connected the FX between that and the amp using another power supply still non regulated.
    No hum.
    Could you please explain a ground loop problem,I understand ground loop issues on a turntable but not digital.
     
  9. Pio1980

    Pio1980 AK Member Subscriber

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    This usually follows a problem related to an AC differential showing up on the ground planes of interconnected components, due to inadequate power supply line isolation somewhere.
     
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  10. petemcfc

    petemcfc Well-Known Member

    Messages:
    758
    Location:
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    Though I've been speaking fluent English since my inception to this world,what the bloody hell does that mean?

    :):):eek:
     
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  11. Poultrygeist

    Poultrygeist Lunatic Member

    It may not be FR hum but by moving it to different locations on your rack you could at least rule that out.
     
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  12. Bicyclist

    Bicyclist Member

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    I had an issue with my unit having a tube fail with a loud cracking noise. I am lucky it didnt take a tweeter out. I have since replaced the tubes with sylvanias and it seems to work fine. At this point i dont have it in the circuit because i am enjoying the passive pre on its own.
     
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  13. Poultrygeist

    Poultrygeist Lunatic Member

    Is your passive a DACT?
     
  14. Bicyclist

    Bicyclist Member

    Messages:
    82
    Its a tc-754.
     
  15. Seppo

    Seppo AK Subscriber Subscriber

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    Got my batch of matching November 1985 Voskhod's!

    20190314_181710.jpg

    All four make this distortion buzz/cracking, like dripping at 3 Hz frequency. The loudness of the buzz is independent of the position of volume knob, and is present more or less symmetrically on both channels. Sometimes this distortion escalates to a constant even louder buzz (I could imagine some leak current) that then changes back to "dripping" after 15s or so. Is this something that 'burning the tubes in' will resolve? Or did I get a bad batch?

    The original Chinese tubes do not have any issues (anymore), although I remember that very early on there was some (less loud) cracking sounds with them that went away quickly.
     
  16. Poultrygeist

    Poultrygeist Lunatic Member

    I have one of those but it's not passive. A $30 Pyramid power supply is also a monster upgrade for that puppy.
     
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  17. Poultrygeist

    Poultrygeist Lunatic Member

    Did you buy them on eBay? If so you can get your money back. FWIW I only buy from sellers with high feedback numbers and scores.
     
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  18. Seppo

    Seppo AK Subscriber Subscriber

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    Yes, from eBay. The seller has over 4k transactions and 100% positive. So you think this is something that will not go away?
     
  19. Dadbeh

    Dadbeh Schrodinger's meerkat Subscriber

    Messages:
    596
    it id strange that all 4 would have the same problem. I have bought 10 pairs and none had this issue. the only time I had an issue was one pair that was supposed to be matched had noticable channel imbalance. they simply were not a matched pair. i just kept them as backup.
     
  20. Seppo

    Seppo AK Subscriber Subscriber

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    Location:
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    I switched back to the original Chinese tubes, and the crackling is gone...except that I now realize that it is still present, but just much much fainter than with the Voskhod's. I can still here very similar cracking, but only if I put my ear next to the speaker and everything is otherwise absolutely quiet.

    So it sounds like that this crackling is a property of the Dilvpoetry pre-amp itself, and then the Voskhod's are somehow more sensitive to it, or amplify it more. To the degree that they are not usable in my pre-amp. Weird...
     

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