No announcement yet.

Building "the perfect Champ"

  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    a capacitance multiplier on the screen supply.
    YEah, what he said! I'm very interested too.....


    • #17
      In this schematic
      (which I've posted before) the MOSFET Q3 forms a capacitance multiplier together with C16, R20 and the output impedance of VR4.

      VR4 is a front panel control labelled "wattage": it is a combined capacitance multiplier and power scaling circuit.

      R20 could do with being bigger, as the hum increases quite a bit when VR4 is turned all the way up. I didn't bother changing it out, though. I never use the "all the way up" setting because it also red-plates the power tube. At the settings I normally use, the hum is about the same level as the preamp noise floor.
      "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"


      • #18
        If turning the volume control down also turns the hum down, that means the hum you are hearing was coming THROUGH that volume control. SO the source of the hum is before that control. When I ask if pulling the preamp tube kills the hum, and it does, then we know that tube either IS the source of the hum or it is amplifying the hum from someplace earlier in the circuit.

        If the hum is 120Hz (or 100Hz for you folks with 50Hz mains) that means power supply ripple is the cause, but not necessarily from lack of filtration. It could also be charging currents and the preamp tube is sharing a ground path with the main filter cap.

        I think fancy MOSFET circuits could be interesting here, but considering the OP is trying to understand power supply filters, isn;t that really above the level of this thread.
        Education is what you're left with after you have forgotten what you have learned.


        • #19
          Hello folks,

          while I was building, I discovered that a bad connection of the jack with the ground gave a lot of ground hum. It was for this amp is not necessary to build the filter in the PT section. Just the CT 6VAC on the cathode of the 6V6 and an the adjustment to the jack was enough.

          Anyway thanks for the information. I will definitely use them in future DIY projects.

          Results in this video:

          Hum reduction by single ended amplifiers - YouTube

          Regards, Scartube.


          • #20
            Mabe off topic (should I start a new one?)

            I also want to build a Line-in, a line-out (headphone) and a external cabinet output jack on my next build... Could someone help me out with drawing the right adaptation on the 5C1 schematic?

            Click image for larger version

Name:	champ-5c1-schem (1).gif
Views:	1
Size:	58.5 KB
ID:	826772



            • #21
              Most amp hum problems stem from improper grounding . I just keep the input and preamp near in a hole in the chassis as well as the pot grounds all with their own leads sort of one star ground and then the cathode resister on a PT stud along with the 1st two filter caps and the power tube pin 8 and the other filter cap ater the second dropping resister which feeds the preamp and pots and inputs go to the same star ground with another lead. Never had a SE or Push/Pull hum . The line green ground goes to the closest stud on the PT where it enters the chassis . I always use the heater center tap and two heater leads to each tube socket and ground the center tap as far away for the filter caps and line but still on one of the PT studs. Works for me. Just section off the three stages of the amp and ground them so they don't share the same ground lead . OT to speaker near or on the same ground as the Cathode pin 8 .