Hi Glenn,
Thanks for your message. I am now almost certain the issue lies with the LP-2 based on the following diagnoses I have run through:

If I flip the input switch on the Decware Torii to the other inputs (to which nothing is connected), there is no hum, even if I turn the volume pot all the way up, so it seems to be somehow related to an interaction between the LP-2 and the Torii.

If I switch the preamp to the other set of inputs on the Torii, the hum follows the preamp - now the other input on the Torii (with nothing attached) is silent.

The hum persists irrespective of which set of inputs or outputs I use on the LP-2 (I only have one source – my Mojo Audio DAC).

I disconnected all power cords and interconnects and reattached them to see if there was a loose connection somewhere, but the hum persists.

If it helps at all, this hum started after I installed my new Sophia Princess 274b meshplate rectifier in the LP-2, but it only began after listening for about 2 hours.

Swapping out the 274b for the original 5Y3GT does not solve the problem. I have also tried swapping out all 3 6FM7 tubes to no avail.

The system is on a dedicated 20A circuit, and all gear is plugged into a Puritan PSM156 line conditioner that is grounded to a Puritan GroundMaster City. If it helps in diagnosis, the Puritan also filters any DC that might, for some reason, be on the line.

This is most frustrating, as it occurred with no warning, and I can’t figure out what is causing it or how to make it stop.

If I take the LP-2 out of the loop and just listen to my DAC directly into the Torii, the system is dead silent, so I have to conclude that the issue is with the LP-2.

Any thoughts/suggestions would be greatly appreciated.

Thanks again,
Chris

Have you tried different cables between the preamp & amp?

Hi Glenn,
I did; it does not make any difference; the hum persists

Time for Analog Addict to come to your aide. As a subscriber you can PM him.

Thanks, Glenn! PM sent to Analog Addict

Hello cporada

I once had a similar humming problem that I could not explain. All tubes and cables submerged But the noise did not want to go away. The solution to the riddle was a device similar to the Ground Master. this caused problems after a few days of use. I used a different product and the humming was gone.

Give it a try.

That's an interesting variable I had not considered.
I can give that a try, but I'd be very surprised if that's causing the issue, as the GroundMaster has been in my system for over a year, and the system with the LP-2 had been dead silent since I received it for Christmas. I thought the point of these types of devices are to ensure that you cannot have ground issues, as they create a "pristine" ground path for all components that are attached to the power conditioner; isn't it?

cgn-dt-n,
Out of curiosity, what product did you switch to?
Thanks,
Chris

Hi cporada,
I tried a lot of things.
I had problems with AFTERDARK. PROJECT CLAYX BLACKICE GROUND BOX.
The products of Audioquest, Telos, FABER'S CABLES GROUNDING BOX, Nordost, IsoTek and Kecs did not cause any problems.

Each was more or less good, there were slight differences in sound. a bit softer but spatial, controlled bass but slimmer in the midrange, better differentiation in the treble but somehow lifeless.

All in all, I tried all the products and decided on none.

In the large setup I operate a socket strip and power cable from phonosopie in the silver version and only one Vortex HiFi Power Optimizer 2 P.I.

In the smal setup everything is from Supra Cables and the Vortex HiFi Power Optimizer 2 P.I.

I was more concerned with resonance optimization and found the results achieved better than those with the power supply.

Thanks for the info, cgn-dt-n!
Does the Vortex come in a version for the US? All of the websites I can find show the European power plug.

So, the problem is not the GroundMaster. If i remove that, the hum is actually a bit louder.

Also, the hum occurs if I disconnect all sources from the LP-2 and simply attach the LP-2 to my Decware Torii and turn the two units on; with just the Decware, there is silence.

I can only conclude that the hum is coming from the LP-2, but I have no idea why, as it didn't hum until a few days ago