Hi Luigi -
I now use Lundahl amorphous-core transformers in my amp upgrades (and in my VRE-1 preamp). I started with Jensen transformers, but switched a few years ago when I found the Lundahls offered better transparency. I originally used input transformers to provide a balanced option, but I then found that I preferred the sound of my amps with them, regardless of which input (balanced or unbalanced) I was using. First of all they provide complete immunity from DC and RFI, and well-designed units have outstanding common-mode noise rejection (CMRR). This allowed me to simplify my amp's input stage, and the net result was sound that I hear as cleaner, clearer, smoother, and more "pure" if you will excuse the expression. And keep in mind that my design handles both balanced and unbalanced signals via the same path (the only difference being the input jacks) so you get the benefit of the transformer either way. Of course this only works well with great transformers, but that is the only kind I use ;-)
In short, I feel the input transformers are a sonic benefit even if you use only the unbalanced inputs. The only downside is the relatively low 10KOhm input impedance, but this is an issue with only a small number of preamps.
Best regards,
Steve McCormack
SMc Audio
