Kaiju build complete – light transformer hum and residual speaker hum [resolved]

[RdDgWest]

Hi all,

I’ve recently completed a Kaiju build and wanted to share a few photos of the finished amp. The build went smoothly, voltages are within spec, and the amp is operating normally from an electrical standpoint.

What I’m more concerned about at this point is a mechanical hum from the power transformer that is audible in the room, not just with my ear near the chassis. This is present with no music playing and is completely independent of the volume controls.

Separately, there is a very light residual hum at the speakers. Hum pots are adjusted after warm-up, and the lowest measurable residual hum I could achieve was ~6.1 mVrms at the speaker terminals, with further adjustment increasing hum again. Channel balance was set using a 1 kHz mono test tone (~200 mVrms at the speaker terminals), and balance is solid.

Given that the transformer hum is audible in the room, I wanted to sanity-check whether this level of mechanical transformer noise is considered typical for the Kaiju, or whether there are specific things I should double-check. I've rechecked mounting and mains voltage.

My build does not yet include the DC filament upgrade. I understand that it would not address the mechanical transformer noise, which is my primary concern at the moment.

Appreciate any guidance or confirmation from others who have built or lived with a Kaiju.


Thank you

 

[Thermioniclife]

Check that the mounting hardware for the power transformer are as tight as you can get them. But having said that I do not have a Kaiju. IF you use the DC filament should get your speaker hum lower than what you have. BTW all power supply trans formers have a certain degree of mechanical hum, It's inherent.

 

[hmbscott]

My Stereomour, had similar hum levels after trimming the hum pots, and it was quite audible too. The DC filament option completely eliminated it.

 

[Paul Birkeland]

The DC filament will take that hum to below 1mV. Some power transformer noise isn't particularly abnormal, and tight hardware is helpful for minimizing it.

 

[RdDgWest]

Thank you all, this is very insightful.

I’ll recheck the transformer mounting hardware to make sure everything is evenly snug, and see if there’s any reduction in the audible hum in the room. For context, the mechanical hum from the transformer is audible from roughly 15 feet away in a quiet room.

It’s good confirmation that the DC filament upgrade should take the speaker hum down further.

I’ll report back once I’ve done a bit more mechanical isolation testing. Appreciate the guidance.

 

[Paul Joppa]

I'd say 5mV to 8mV is typical of AC-powered 300B amps. For those with especially high efficiency speakers and/or quiet background noise, that's why we have the DC filament kit.

As Thermioniclife said, all transformers will vibrate at least a little according to the signal current. If there is a little DC on the power line, it willl be worse - that could be worth checking out.

 

[RdDgWest]

Thank you everyone for the guidance.

I went back and rechecked the power transformer mounting hardware. Each nut took roughly 1–2 additional turns before reaching a point I could no longer tighten. After doing so, the mechanical hum dropped significantly. At this point the transformer noise is no longer audible from the listening position and can only be heard when standing very close to the amplifier in a quiet room.

Just a low level hum in the speakers. Next up DC filament upgrade.

Appreciate the help, this was very useful.

 

[RdDgWest]

Quick update: I’ve now installed the DC filament upgrade, and the speaker hum is completely gone, the system is dead silent even with my ear right at the drivers.

Thanks again for the guidance. Very happy with the result.