Isolation Transformers

Without knowing anything about your digital set up one can only generalize; and' I would like to point out I am not in the industry and have no affiliations but I am very fussy after 39 years of record collecting and do enjoy a very revealing and musical system based on reference level Spectral, Goldmund and MIT products. You might want to investigate Equitech's factory blems sale. They have had & will again be selling some model "Q" balanced 'transformers in a box' at a huge discount from the cost of a retail 1.5 or 2Q. One will provide you "dramatic" power line conditioning and isolation for ~$400 and the benefit in sound quality would provide a great foundation for you to more easily & accurately evaluate the benefit of further conditioning items in the future. I bought one and found it to be a stunning value and wouldn't be w/o balanced power ever again. Best of luck. Pete

Bob, each separate (branch) circuit in your house is referenced back to the (transformer on the) pole. The (available) energy at the pole is so enormous compared to that carried by each branch leaving your panel that it's virtually impossible for one branch of a house to "inject noise" onto another branch which is also returning its current to the pole. That's why you don't/can't hear it. This is not strictly true, for example in the case of large apt/condo complexes where you have many, many panels working off of the same transformer, in which case the AC at the transformer itself can be pretty polluted -- but in a typical residential neighborhood, there are no more than a few panels (houses) on each transformer. In fact, when I was a homeowner here in Tucson, lightening severely damaged our (1/2 dozen houses) pole transformer, but it was still working (kind of) and noisy as hell before it finally gave up the ghost and got replaced!

As for your arc welding neighbor, he could cause a slight voltage drop in your local grid if the power transformer capacity has become marginal after a few people in the neighborhood have replaced their panels over the years with higher capacity ones, until the utility company finally has to put in a bigger transformer (or the existing one blows!) But the noise and interference from the welder isn't in the electric grid, it's being broadcast over the air as radio frequency interference from the arc -- causing snow on your TV (and possibly noise in your phono or on your FM tuner.)

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Large iron core isolation transformers are very effective in protecting sensitive equipment from AC voltage transients, spikes, and electrical noise appearing on commercial power lines.

Iso transformers are designed to be exactly opposite to audio transformers. While an audio transformer needs to pass all audio frequency power uniformly, an iso transformer is designed to transfer power only at or near 60Hz. Frequencies below that are attenuated by operating the iso at relatively high flux densities, and frequencies above that are reduced by introducing as much leakage inductance as possible, consistent with good power transfer to the output side.

Power line noise exists in two forms: "common mode", which appears between both sides of the power line (hot and common) and ground, and "transverse mode", which appears from line to line. With good design, and the intelligent use of shielding and grounding, an iso can reduce both by as much as 120dB, and this specification is usually stated by the manufacturer, and sometimes stamped on the faceplate.

If the power line ground is shared on both the input and output sides, excessive ground line noise from other circuits can be transfered. In that case, it is advantageous to run a separate clean ground to the transformer frame and output side.

I am using a 4kva Topaz iso on 4 dedicated circuits, one each for CD, phono, pre and amp, and have realized a noticable overall improvement. I am also using a second 125va iso on the CD to keep its noise from getting back into the other dedicated lines.

I recently bought a Furman Elite 15 and was extremely pleased with the difference it made, especially with my video components. The Furman Elite 15 cost around $300.