• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tubes4HiFi SP14 really noisy!

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Here is a photo of the Hiraga

IEC ground goes to chassis, and from chassis to the star ground.

Star ground is isolated from the chassis

RCA input grounds are tied together, and go to start ground.

Center of each of the two power supply boards go to the star ground, and to the power supply in on the amp boards from the power supply boards. It’s difficult to see from the closeup, but there are two wires from the center - yellow and green

Shield around the power supply boards is grounded to the chassis

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".. using the DIY Audio VFet, with the supplied SMPS and a non grounded power cord has provided the sound w the least noise, only barely audible with ear pressed up against speaker (102db sensitive…)"

Doe it mean the hum is low enough in this case ?
It does indeed mean that! Problem is, the other amp - Hiraga - sounds better w the preamp.

I pulled the Cornwalls out of the basement so I could better hear the noise.

Speakers I normally have in place are small, 3ohm 79db efficient speakers…. So not nearly as noisy as the Cornwalls, but they require a lot more power to play at any kind of volume.
So the DIY Audio VFet amp has a power cord without safety ground.
This leads to the assumption you have a safety ground loop.

It may be safe to use your "noisy preamp" without power ground connection,
because the cabinet is made of wood. But perhaps you want to keep this ground
connection to the metal face plate, back plate etc. In this case remove all signal
ground from the metal parts, in other words keep your star ground or whatever
signal ground wiring you have isolated from the metal and safety ground. Then
connect these (power cord safety ground on metal and signal ground) with a
resistor of say 22 ohms. This way you break the ground loop.
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If I use the same power cord that is on the VFet (no ground) on the Hiraga, the noise returns at the same level as with a regular power cable.

Going to take me a second to digest the preamp grounding protocol you’re suggesting. As a visual thinker, I need to draw it out :)

If I use my Adcom GFA545 with the preamp, I have the same issue w noise - and it only has a two prong power cord.
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The signal ground is attached to the PCB in two places. The ground bus wire of the RCA input/output (single wire from bus to board), and the ground from the volume pot goes to the signal input on the PCB

The power ground is connected to the PCB from the chassis/star ground. The star ground has the front, top and rear panels connected to it, as well as the power/earth, the transformer grounds and the PCB ground.
Not interested to read the whole thread again, but it is bad practice to connect signal
ground and safety ground. Of course it is useful to keep metal parts connected to safety
earth, but not the signal ground (in more than one unit of the stereo set). But i you say
the noise remains without safety ground on the preamp the problem may be somewhere
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Just tried connecting my Fosi V3 up to the preamp, and it’s dead quiet.

Tried the Adcom GFA 545, and it hums. Tried my Vista Spark, and it’s dead quiet.

Going to order the ground lift board today and see if it helps.

So, Fosi V3, VFet (with ground lifted cord) and Vista Spark II (with grounded cord) are all quiet.

Hiraga and Adcom both hum
This is a rather expensive way of lifting the signal ground.
The schematic is freely there, and one can do it diy pretty easily ptp. I think Broski provides all parts, pcb, shipping, etc...I have a few pcb gerbers that are similar to this that I use for my personal use ordered from a chinese fab, which needs to be done in multiples not singletons.

That's why I wrote "CONSIDER", on post #228, not "YOU MUST."

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Between work and kids, time has not been my friend …

Tried the ground lift, didn’t make a difference to the noise unfortunately.

Removed all the signal wires, picked up some new wire and about to replace them all with twisted pairs. Fingers crossed this helps.

If this doesn’t help, then I’m going to remove the steel top plate and see if that makes a difference. If it does, I’ll be rebuilding it in a Hammond Aluminum chassis.