New tube Phono preamp, hiss-like noise and crackling on left channel. (with pictures and schematics)

Discussion in 'Audio Hardware' started by EddieVanHalen, Sep 13, 2017.

  1. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    Hello to all forum members. I received yesterday a new tube Phono preamp which is a clone of the EAR 834.
    It came without tubes as I got a deal with the Ebay seller to do a discount for meby not sending me the three 12AX7 it includes as I have around 12 of them or so.
    I opened the Phono pre, insert the 3 tubes, closed it and connected to my TT and Pioneer A/V receiver. First thing I noticed was some hiss-like noise on the left channel and intermitent crackling noise on the same channel. First thing I did was swap tubes, I tried all the different combination possible with the 16 tubes I have both NOS and new production. No luck, same noise and crackling was there.
    Then I cleaned the pins of ALL my tubes with alcohol and also the tube sockets with a cotton swab with alcohol and a very thin brush. Put the tubes in again trying with different combinations, and no luck again, noise and crackling was there.
    Then I removed the tubes and with a very thin and flat screwdriver I tighten the contacts of the tubes sockets, but no luck, noise and crackling was still there.
    With the top cover off I softly tapped the three tubes with the rubber of a pen (wearing headphones to monitor the resulting sound), and I could only hear ticking on the left channel along with the hiss-like noise and crackling. Using a microfiber cloth I touched some of the components of the audio board (I didn't touch the power supply board or the toroidal) including the tubes, not touching anything with my bare fingers, and sometimes a loud hum was heard, but only on the left channel.
    Three things to keep in mind:
    1- The Phono preamp is brand new, I received it yesterday and has been on for around 5 hours.
    2- When listenning some records using my usual Goldring GR-1 TT with a Denon DL-110 cart, at normal listenning levels sound is great in both channels, it's just that the left channel has the hiss-like noise and crackling.
    3- This Phono preamp doesn't use one tube per channel, it haskind of a peculiar arrangement. Tube one, on the right, does the amp. Tube two, at the center, does RIAA de-eq and does some more amp. Tube three, on the left, is used as a buffer to keep impedance low.
    What may be the problem with this Phono preamp? It's obviously defective but if the problem is easy to solve it may be better to take it to the local electronics technician than to ship it back to China, wait for the seller (best case scenario) to ship a new one, get it home and pay import fees again, around 60 $.
    I'd appreciate your help. Thanks in advance.[​IMG] [​IMG] [​IMG]
     
  2. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

  3. Daily Nightly

    Daily Nightly Well-Known Member

    Location:
    New Jersey, USA
    The hissing/crackling sounds like faulty and/or underrated voltage capacitors were used...which, if you're talking tube gear, always have to be 400vdc *minimum*. That China stuff cuts corners to suit the bottom line and the internal components are not reliable.
     
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  4. tiller

    tiller Active Member

    Location:
    Montreal
    Could just as easily be a bum tube. It happens. I'm not entirely familiar with that circuit but you might try swapping around tubes and see if the problem changes.
     
  5. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    Thanks for your reply. Which are on the pics the capacitors? Why this would only affect only one channel? The noise and crackling is on the left channel, the right one sounds clean.
    Do you think if I take it to a Hi-Fi repairman I know this would be very hard to fix?
     
  6. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    Thank you for your reply. It's not a bad tube as I have tried 16 different tubes on different combinations as each tube does something to both channels, half of the triode on the first tube amplifies one channel while the other half triode does the same for the other channel. On the second tube, half triode does RIAA re-eq for one channel, and the other half triode does the same for the other channel. And the same for the third tube which works as a buffer to keep impedance low.
    I got the same result with all 16 different tubes I tried on different combinations, same hiss-like noise and crackling on the same channel, the left one. So it's not the tubes which by the way they all work flawlessly on my previous Phono preamp.
    At first I thought it could be the components which would need to break in and settle down, but at this point I doubt it's this.
     
  7. tiller

    tiller Active Member

    Location:
    Montreal
    Sounds like you have a good grasp of troubleshooting. I assume you've tried reversing both inputs and outputs to see if it follows cables? Apologies if this tip is obvious.

    Beyond that I can't offer much in the way of help. Perhaps it's something as simple as a cold solder joint somewhere. Good luck!
     
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  8. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    Thanks for your reply. Do you mean connecting the right output coming from the TT to the left input of the Phono preamp and viceversa? And also doing the same with the outputs? No, I haven't tried that, but I did try to disconnect the turntable from the Phono preamp and the noises were still there.
     
  9. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    I've tried reversing both input and outputs and other than the noise and crackling showing up on the right channel nothing has changed, same noises at the same levels.
     
  10. tiller

    tiller Active Member

    Location:
    Montreal
    Yes that's what I meant. Right phono into left input and vice versa. If the noise had've moved it's safe to say that it was coming from upstream of the preamp. Sadly it hasn't. The fact that it exists without the phono input at all is a good sign that it's coming from your preamp, like you'd originally suggested.

    Wish I could help you more!
     
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  11. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    The noise has indeed changed from the left channel to the right channel coming out from my A/V receiver, that is no surprise as the left output from the Phono preamp is now on the right input on the A/V receiver, same noise and crakling coming from the opposite channel as I swapped connections.
     
    tiller likes this.
  12. Salectric

    Salectric Member

    Location:
    Maryland
    I would suspect some carbon resistors are the culprit. The most likely candidates are the 300K plate resistors for V1 and V2 but the 47K input load resistor is another possibility. A tech who is used to within with tube equipment should be able to track it down without too much effort. There is nothing unusual or complicated about the circuit.
     
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  13. Davey

    Davey very clever with maracas

    I'd first try to get help from the seller and/or designer, this may be a common problem they are having, and could tell you what needs to be fixed. It sounds like you had a conversation with them before buying, so presumably they are communicative, and can speak English.
     
    EddieVanHalen likes this.
  14. EddieVanHalen

    EddieVanHalen Forum Resident Thread Starter

    Thank you both for your replies and help. I opened a dispute (bought the Phono pre on Ebay) with the seller yesterday but I haven't had any answer yet. Ebay told me that if I don't get any answer from the seller by the 16th, that it in 3 days, they'll step in. Usually when they step in on a dispute between seller and buyer because of a damaged item, buyer uses to win getting a full refund and usually the seller doesn't want the item back due to high price for shipping and customs. If I get a new and fully working Phono preamp and the shipping back for the damaged item is paid by the seller I'll be a happy guy.
    One thing I noticed on this Phono preamp is its insane gain, even with a Denon DL-110 High Output MC cart like the one I'm using. May this have something to do with the noise and crackling noise?
     

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