HUM in Tube Amp (I Tried My Best)

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  1. StanD
    Your power transformer's secondary with the two diodes looks like there is no ground return. Usually one uses a bridge rectifier (4 diodes - full wave) and grounds the centertap of the secondary for +/- railes or uses one side of the bridge rectifier output to ground. Why is there a ground coming from the primary of the IEC transformer?
    Is that the mains ground going to your chassis ground?
    Does the Pete Millet Regulator have rectifier diodes or have they been omitted?
  2. DutchGFX
    The IEC earth is connected to the amp ground at the filter cap negative.
    The secondary is actually a separate transformer, and is no referenced to ground. It is a floating DC regulated supply, it has a bridge rectifier. It has 2 terminals on each side, one side says AC IN, the other has + and -. Here is the page. You are correct in that there is no ground return. Grounding the center tap creates a HUGE amount of hum. Since it is a bridge rectifier and a floating supply, I don't think grounding the CT is advised.
  3. StanD
    Your circuit shows two diodes and no path for the negative, that is NOT going to work. You need to use 4 diodes as seen in the first drawing without the grounded centertap that I linked to.
    The secondary has to get power inductively from the primary, there is no magic.
    What exactly is the IEC earth and what does IEC mean? This looks suspect.
    You didn't answer - Does the Pete Millet Regulator have rectifier diodes or have they been omitted?
  4. DutchGFX
    I am using a full-wave center tapped rectifier for my B+, into the Maida Regulator.
    IEC is what I was taught to call the inlet that the power chord plugs into. It has the three prongs, it's the standard power connector.
    The millet uses a diode bridge.
    The path to negative is connected to the signal negative (the end of the cathode resistor) and connected to earth.
  5. StanD
    Your diagram shows only two diodes, not a bridge rectifier to the Maida regulator and no path for the negative due to the missing diodes. What you show in your schematic will not work, period. Look below. There is no path to ground for current from the secondary. That is why one needs to use a bridge rectifier as in the diagram I showed you. This basic stuff.
  6. DutchGFX
    Well I am an idiot. My diagram SHOULD have looked like this. I forgot the wire, sorry. In the actual build there is a path to ground. My build is wired as shown in the image below. The CT goes to the filter cap negative, which is connected to 0V earth at the cable.
  7. DutchGFX
    I also tried adding additional filtering after the regulators, which had no effect on the noise
    I'm still wondering if it is the issue that my 5ft cable is dropping 1.6mV on the ground line
    Grounding one end of the cathode/filament supply completely kills the hum. Not sure if that is useful info but I think that, along with the fact that if I disconnect the b+ the hum goes away, proves that the hum is most likely NOT from the filament supply
  8. dsavitsk
    Your regulator seems to have different connections for input and output ground? If that's the case, that could be your problem. The amp's ground needs to be the same ground as every other ground. Ground is ground.

    Otherwise, at this point I'd say that either something is hooked up wrong or broken. Were it me, the next step would be to return to first principles and draw a careful and well planned out schematic. Then draw a careful and well planned layout based on it, then get back to soldering. But I think in a haste to build you skipped a few necessary steps.
  9. Gandes
    Pete Millet Regulator this have rectifier diode in structure. I think you should use integrated rectifier IC.
  10. DutchGFX
    Thanks for input, but this was fixed some time ago! Thanks all
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