Redphu
I read your post with interest as I had a similar experience with my Lampi GG2. I’d like to provide some background and context. My system prior to the addition of the GG2 (which you can view here
https://www.whatsbestforum.com/members/marty.11/#about) was perfectly quiet and had no 60 Hz hum whatsoever for any input source. Much to my chagrin, when I substituted the GG2 for the Meitner DA-2, I had 60 cycle hum that was very disturbing. As many audiophiles know, hum and noise can be the bane of our existence. I thus tried all the usual solutions including 2 prong cheater plugs, the well-regarded Iso-Tek Synchro Uni, praying to unnamed spirits, reciting incantations, lighting frankencense and myrrh and other nonsensical solutions since nothing worked.
Before going any further, let me state that hum can be caused by several things which include the obvious ones such as ground loops, but also some less considered etiologies such as proximity effect. This occurs when the transformers in individual components are placed close enough for them to have an interaction that results in induced hum. This plagued me for quite a while in my phono system when I was using a different phono stage other than my present Zanden 1200, and it took me over a year to find that the solution was simply moving the phono stage to a different shelf! Drove me nuts for far too long when all it took was a simple gear placement change to solve the proximity effect.
So all was humming along beautifully (no pun intended) until the GG2 was installed. And with it, 60 cycle hum returned in all its glory. When I played a CD or if I streamed and suddenly hit the pause button at listening volume, the hum was obvious. My handy spectrum analyzer app “Analyze” on my iPhone confirmed that I had a huge amount of not only 60 Hz, but 120Hz and 180Hz hum as well.
Enter the Furman IT-Ref 20i.
https://www.furmanpower.com/product/discrete-symmetrical-power-filter-20-amp-IT-REF 20I
There have been many discussions on this topic elsewhere in this forum that need not be repeated here, but isolation transformers can be highly useful for eliminating 60 Hz ground loop hum which is caused by common mode noise in many AC installations. This is often caused by stray capacitance leakage to ground in the gear that is the source of the ground loop.
I’m certainly no expert in this area, but the following is from Furman literature:
“In much the same way that balanced audio lines can reduce the pickup of hum and other types of electromagnetic interference (EMI), the use of balanced AC power lines in sensitive audio, video, or computer installations can make an enormous difference in system noise and signal integrity. But power distribution in North America, unfortunately, is not balanced. The distribution standards currently in use were derived from practices established over a century ago, when electric power use was limited to lighting and motors, long before any AC noise sensitive applications existed. The emphasis then was on convenience and safety, but not noise cancellation. The result was a three-wire distribution scheme in which 120V branch circuits have a hot wire and a neutral wire, with the neutral tied to a third wire connected for safety to an earth ground. The third wire does not carry any current unless there is a fault. This unbalanced scheme can create hum in audio circuits for two main reasons. First, the current flowing in the hot wire induces hum in any other nearby wires, which may carry vulnerable low-level audio or video signals. Second, because the impedance of chassis and cable shielding to ground is always greater than zero ohms, ground current flowing from power supply capacitors and from EMI pickup causes a voltage drop at 60 Hz and its harmonics. This low level noise becomes part of the audio signals.
Furman’s Discrete Symmetrically Balanced Power is achieved by running the incoming AC into a 1:1 isolation transformer with a precisely placed center tap on the transformer’s secondary. The incoming voltage (120V on the line terminal and 0V on the neutral and ground) is split into perfect halves on the transformer’s output. The AC line now has 60V on the line and 60V on the neutral when referenced to the new center-tapped ground, which remains at 0V AC. What is significant about this is that the two 60V AC terminals are now in opposite polarity. This completely cancels all common mode noise from the incoming AC line. This noise reduction is extraordinarily efficient and linear across a huge frequency range, and the result is perfectly clean power devoid of ground loops and AC hum noise.”
Since employing the Furman, my ground loop and hum disappeared as by magic. (It’s not magic of course, it’s science!). A few additional noteworthy comments. First, I use the Furman only for the Lampi GG2. I do not need it for any other component. One may read the Furman literature and come away thinking, why not use it for all of one’s gear? Well, that is a hot debate topic that will trigger a range of responses among WBF members. There are some users who use isolation transformers for their entire AC supply before AC distribution in their rooms, and others who eschew these devices because they feel they may have a “downside” since common wisdom suggests there is no free lunch including what may happen when power goes through any type of transformer. Me? It’s simple. If there is a downside of using the Furman, all I would say in response is that it’s not even close to the obvious downside of not using it and accepting 60Hz hum in return. Even if your 60Hz hm is nominal (mine was not), I think you would be shocked at how much better the sound is when it is banished in its entirety. The bass in particular is the greatest beneficiary, but the SQ improves throughout the frequency spectrum. 60Hz hum is pernicious and bad. I’ll gladly use the Furman because the alternative is just untenable in my system. Academic arguments to the contrary don’t interest me. Results do and in my rig, they speak for themselves. I should add I bought my unit on ebay and it included a 30 day return policy. That sort of made it a no brainer for me to try.
In retrospect, I bought the 20 amp version because I had no idea what I would hook up to the Furman. However, now that I know it's just the Lampi, I probably could have saved some money by buying the 15 amp version IT-Ref 15i instead.
One final comment. The Furman was designed by Garth Powell, who also designed the well-regarded Niagra 7000 Power conditioner (which uses an isolation transformer as well for the same purpose of supplying balanced power). The difference is that the Niagra was conceived as an “audiophile component” where as the Furman was designed as a work horse for recording studios. The Niagra retails for 7K; the Furman retails for 4.5K (actual cost was about $2200 new on ebay). We had the opportunity to compare the Furman IT-20i to the Niagra 7000 in a friend's system recently. (In this case, the 60 cycle hum was in the phono stage, not the DAC pathway.) Much to our amazement, the Furman sounded better. Go figure…..
Marty