The Amp Garage

Keep in mind that the original issue, noise (hiss?) happens during note decay. That's a big red flag that there may be lurking oscillation/stability issues going on that only happen at certain signal levels. This is a common occurrence in solid state amps, rarer in tube stuff. If I were doing this,...

So I'm clear, when you talk about the PT CT, you're talking about the HT secondary, not the heater CT? Or both? Yes, just the HT secondary. How about this layout? HT CT, heater CT, and filter cap ground go to chassis star point. Not the exact same amp, but a DR504 clone https://ceriatone.com/wp-con...

There is no maybe about it - the CT must go to the negative terminal of the first filter cap. To be clear, I believe it is fine for the PT CT and the negative terminal of the reservoir/first filter to go to the same point on the chassis. You just don't want the high return current pulses traveling ...

You can also see that the PT's HV CT (black) is fused and then grounded right at the chassis under the fuses. Maybe this should go to the negative terminal of that first filter cap as well... This alone will cause 60hz hum. There is no maybe about it - the CT must go to the negative terminal of the...

You can also see that the PT's HV CT (black) is fused and then grounded right at the chassis under the fuses. Maybe this should go to the negative terminal of that first filter cap as well...

Used a tone generator and confirmed the underlying hum is indeed 60hZ. Not a harmonic, like 120hZ, but 60hZ. Volume of hum doesn't change with settings on amp. Preamp tubes are all DC, but power tubes are still AC. Heaters are yellow wires. The CT is green and looks to be grounded at one of the powe...

I didn't see the IEC. I agree the short mains ground is OK. Look at the pic. Do all of the PT wires come through this one hole? I really don't like the primary and secondary bundled like that. But, heck, I'm not saying I know better than Hiwatt, lol. No, that's just the secondaries to the output ja...

That's an OK start, but other issues can remain even with that starting point. A better solution is often to ground the entire amp to the negative terminal of the first filter cap, isolate the input and output jacks from chassis, and run the jacks' "ground" wire to the circuits they connect to. Thi...

Without a schematic and layout diagram, it would be challenging to understand where all the grounds start and end, and where the go in between. You've chosen not to post these. This sets a limit on how much help will be offered. While the build is elegantly tidy, that does not mean tidy = quiet. Al...

You may be using the noise gate to compensate for a ground scheme that doesn't do what it should. Cure the problem. Don't put a bandaid over it. Well yeah. But I can't completely rewire an amp without a concrete game plan. If you'd like to offer some suggestions, I'm all ears. This amp is inherentl...

I think I figured it out. Fortin Zuul+ noise gate. :oops: When running the gate in front of the amp, no problem. When running the gate in the loop, no problem. When running the gate using 4 cable method (as it was designed) in both the loop and out front, using gate's Key input, the gate is causing ...

mhuss wrote: ↑Fri Apr 11, 2025 4:39 pm I may be oscillation, these sometime pop up during note decay on multi-stage high gain preamps. Do you have a scope?

I do not. But it sounds like legit arcing lol, not typical oscillation.