Dear all,
I am wondering if anyone can help me troubleshoot a problem that just suddenly appeared in my system. I have a Dennis Had LP-2 preamp feeding a Decware Torii MK3, which until about an hour ago, was making glorious and truly magical music. This combo was dead silent; I could turn the gain all the way up on the LP-2 and the volume all the way up on the Torii with no music playing, and I could put my ear inches from my speakers and not hear even a whisper. Suddenly, a hum started coming out of the mid/woofer on my speakers. The loudness of the hum is independent of the gain on the LP-2, but it increases as I turn up the volume on the Torii. The hum becomes audible when the Torii’s volume pot is at around 10 o’clock and gets louder and louder as I increase the volume, even if the gain pot on the LP-2 is turned all the way down. If I flip the input switch on the 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. 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.
I would be very grateful for any thoughts/suggestions.
Thanks so much,
Chris

My MKIII has only one fuse, at the IEC, and without it there will be no power. This sounds mysterious for sure... no noise with the other input channels of the MKIII on, and noise only from the pre Torii inputs with the Pre hooked up. The abrupt shift seems to be a pointer, quiet to noise, but not sure why.

I think I have had similar when my ground between pre and amp is not great, which can happen since I use KLE IC ends which have a little bitty ground connector in only one position, and using WBT RCAs in the amps with the spiral connection, I can sometimes turn the IC end to where the two are connecting better and reduce hum. The quick night and day shift is confusing for this, but it might be worth trying to reconnect all your cables, power and IC, and see if anything changes. Also, could it be something else increasing line noise that was not on before the hum, that came on, system or room?

I have also had tubes make a hum .... can't recall details. But that does not make a lot of sense to me with the Torii anyway since your amp is quiet when switched to the non-pre Torii inputs. Did you try moving the ICs from the pre to the other Torii inputs to see if the noise follows?

Is the hum from both speakers? If not, might be worth changing left/right with each tube in the pre. If the hum moves sides, it will show a bad tube. Maybe try a spare rectifier there also.

Hum can be such a drag! I feel for you.

Thanks everyone!  I tried swapping the rectifier on the preamp; that did not fix the issue. I will try swapping in other tubes (the pre takes one 5Y3GT rectifier and three 6FM7 tubes) to see if that helps.
I also tried swapping interconnects, but this did not help (which should have fixed a bad connection issue).
I don't think anything else turned on in the house that could have caused the issue, but that is an intereresting possibility.
Thanks, Will, for the idea to try swapping the pre to the other set of inputs on the Torii to see if the noise follows it. I will do so and report back.
Thanks again,
Chris

OK; so the hum comes from both speakers equally.
I switched out all the tubes in the preamp - the hum persists.
I switched the preamp to the other set of inputs on the Torii, and the hum follows the preamp - now the other input on the Torii (with nothing attached) is silent.
I disconnected all power cords and interconnects and reattached them, but the hum persists.
Nothing new is attached to the system, and nothing else is running in the house.
The system is on a dedicated 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.
Any thoughts?
This is driving me crazy...
Thanks,
Chris

That's right. Your last test eliminated the Torii as the problem.

That's a good point Will. I had (ahem) assumed all this was with no sources attached but in rereading I don't see that mentioned. I would disconnect all sources from the preamp and confirm or deny the hum persists.

In light of the problem disappearing wihout the pre, is there still something I can learn from trying the pre into the Torii with no source connected to the pre?

Yes, after fully ruling out source and source cables, sounds like a call to Dennis Had is indeed needed. Bummer, but hopefully a simple fix. I get missing gain tuning and pre potential for soundstage tuning, but glad you have a good listening path in the meantime! Does your DAC have variable output? If you have not tried yet, you may be able to gain tune with it and the Torii to get a little better soundstage effect??? Different because it raises the voltage out of my DAC, but this works with a ZBIT and my DAC, the balanced out of the DAC 6 as opposed to 3 volts through the RCAs. Then turning up or down the added voltage is a nice tool. Who knows, though not increasing voltage overall, you may find a nicer balance with gain tuning between DAC and amp.???

Good Luck Chris, and looking forward to the word on new things.

It's not the ICs...

Chris, I know soldering is not new to you, and if you are OK with opening it, draining caps, etc, a look around in there could possibly help you fix it yourself. It is all a bit of a blur for me on specific details, but I have had a hum show up in the CSP3 when I had a solder joint on some big resistors associated with the power tubes get weak to where they were partially connected. Could be worth pulling out your little needle noses and taking a trip around in there to see that all joints of parts, connectors and wires are solid??? Guessing it is probably not that complicated in there.

Hi Lon,
I had thought the same and tried the fuse, but that didn't do it
Best,
Chris

CAJames,
I tried just connecting the preamp to the Torii with no source devices attached to the preamp - the hum is still there at the same level, so I guess that rules out anything upstream of the preamp.  If only Dennis were as responsive as everyone on this forum, I could get this resolved  ;D
Thanks for everyone's help!
Chris

I took a look around inside and nothing seems to be loose or disconnected.
The unit is hand-signed by Dennis in 2014
From what I can tell from internet searches, his units don't come with any sort of manual.
I bought it secondhand from the Music Room before Christmas, so it's past its 30 day return period, plus it sounds fantastic, so I'd really like to fix the issue to be able to use it.

Thanks, CAJames; I'll see if I can find anyone locally.  The funny thing is, I live only about 2 hours from Cary, NC where Dennis is located...

Hi Kamran,
Thank you so much for your help; PM sent with my contact info.
Best,
Chris