Universal PreAmp grounding of signal circuits

Home › Forums › Forum › Universal PreAmp grounding of signal circuits

Viewing 9 posts - 1 through 9 (of 9 total)
  • Author
    Posts
  • February 25, 2023 at 12:03 pm #15461
    Dinx
    Participant

    Just wondering if all the signal ground cables should be shielded? Shield bonded to conductor one end only? I am presently experiencing a slight hum using non shielded ground cabling and 93db efficient speakers… almost not noticeable from 6ft.

    February 25, 2023 at 6:14 pm #15463
    clambton29
    Keymaster

    Hi Dinx,

    Can you describe your setup for us? The way the universal preamp is designed, is so that the grounds between the input and output stay isolated from each other to prevent ground loops. This should work in the majority of the situations, but let’s see how you have things setup and go from there.

    Charles

    February 28, 2023 at 4:51 am #15473
    Dinx
    Participant

    Thank you for your response. Setup: Larger sized Hammond steel enclosure with R-core x-fo, chokes, large caps installed on top. Power and preamp boards inside. All components from either Valvesnmore, PartsConnexion, or Digikey. Rubycons, and Solen caps, Vishay resistors. When preamp hooked up to Pre-In on R8, sound is just wonderful, with more separation and clarity…but annoying hum=buzz faintly in background. Grounding: #1: Ground pin from receptacle to chassis (1 1/2 in. away, paint scared off) #2: 2 from J1 on power boards #3: (all shielded) 1 each for pre-amp boards; 1 for 2 switched inputs; 1 for Alps volume pot; 1 from SMPS input (for tube heaters and feeding remote control board … only Chinese component, LED’s on knob (from remote control board and switch… would forget on otherwise…) 1 for 2 outputs, Of note: 6 volt difference side to side from B+, buzzing present when music paused and SMPS unplugged. 1 volt difference on pin #6 13-14 Volts. R8 is completely silent at speakers when used with other inputs, no preamp. I am considering bringing it to a tech who has a scope if I can find one… My wife of 50 years is fed up with me trying to find a fix since October. Thanks for you help. Can send pictures.

    February 28, 2023 at 12:46 pm #15476
    Dinx
    Participant

    Trying to send you image of frequency plot I just took with Audio Spectrum Analyser app on my iPad. Cannot attach, but biggest spike is 301Hz, then 60 then 120. (From what I can tell. The 301 is constant both channels 6 inches away. This might help.
    I just sent the attachment to your dad. This was with no music, volume down to minimum. Thanks again. Gilbert Lessard

    March 2, 2023 at 9:01 am #15481
    clambton29
    Keymaster

    Hi Gilbert,

    Sorry for the late reply here, we’ve had a busy few days. I would first try a different SMPS if possible and see if that eliminates the issue. If you could share some photos of the build as well for us to review, that could help us track down any issues.

    Thanks!
    Charles

    March 4, 2023 at 12:36 pm #15489
    Dinx
    Participant

    Thank you Charles. Latest update: Brought it Friday to have the preamp looked at and worked on by some one that was recommended on canuckaudiomart, an older gentleman who has been in tube radio repair since 1960. He redid all of the signal wiring with bigger shielded cable (nice looking job actually) went over grounding etc, and ‘tested’ before giving it back to me $300+ later… Got home. Plugged unit in. After 3-5 minutes low volume hum started. Same as before. Called, him and asked it he put it on a scope. Not not necessary he said. FYI: This most recent (third) SMPS was shipped from your store to me. I have decided to ‘Throw in the towel’ for now. Frustrating because it sounds just marvellous, except on near silent passages. Time for me to move on… for now anyway. Thanks again. Wish the best to you and your dad.

    January 1, 2024 at 2:10 pm #16374
    Dinx
    Participant

    Final update. I just finished building a class D power amplifier and decided that I would try the universal preamp that continues to hum with the Wilsenton R8. (R8 is fine as is…) Guess what… completely silent! Sounds quite incredible actually. Interestingly, I built your preamp with the remote controlled volume as you show in your latest update, except that I replaced the motorized pot with a genuine Alps unit. (Measures much better with both sides being even resistance wise). I use a 9 volt battery to power it up. Works just fine. Looks like my problem from the start was the incompatibility of the pre-in on the Wilsenton R8, not the quality of my build, parts used nor your design. Thanks to you both. PS: lots of ´stuff’ on the internet about the R8. Mine has been working for 3 years with no problems at all. Sounds great with Totem Bison Twin Towers I just purchased. Bye for now…

    January 3, 2024 at 10:29 am #16376
    clambton29
    Keymaster

    Thanks for the update Dinx, we’re glad you can finally enjoy your universal.

    We’d love to see a picture of your motorized pot, we actually had the same idea and ordered in a genuine alps to replace the generic one. Does it last long on the 9v cell?

    Cheers!
    Charles

    January 6, 2024 at 5:18 am #16382
    Dinx
    Participant

    Will take some pictures shortly and send them along. Warning: I must have taken everything apart 10 or more times and rearranged and resoldered. Not pretty… but works fine. Still on my first 9 volt battery. You don’t use much energy changing volumes levels once and a while. I put the LED on the volume knob to remind me to shut it off when I turn off the main power and tube heaters. So far so good. Thanks for your interest.

  • Author
    Posts
Viewing 9 posts - 1 through 9 (of 9 total)
  • You must be logged in to reply to this topic.