Marakanetz stated: "If roll-off touches too much an audiable freequency we can apply a small feedback and make tranny's load responce much wider."
This sounds like you are taking one negative ( transformer induced frequency response errors ) and trying to correct it with another negative ( increased negative feedback ). In most instances, at least when it comes to audio, two negatives don't make a positive.
Audio Xpress had an interesting article about an amp that was somewhat similar in design to the Marantz 8 / 8B and the trade-offs that they had to make when building that amp. The unit built & described in this article showed the differences in bandwidth / linearity using various amount of negative feedback, etc.. while making use of what were supposed to be "high tech" wide-bandwidth toroidal output transformers. None of the results looked real good to me as each approach seemed to solve one problem and create another. As a side note, the measured distortion on this amp was pretty attrocious too.
Having said all of that, much of this does not really apply to interstage or "coupling" transformers due to the low current levels in use.
Clueless stated: " 2) There has been lots of talk about caps and their sonic signature. One way of thinking is that any cap is a bad cap. Using IT coupling may allow you to get rid of a cap in the signal path and the sonic degradation some associate with it.
My thoughts about this are that you have simply traded one sonic signature for another. While every cap made will have its' own characteristics, so will a transformer. The ease of changing a cap within a circuit is FAR easier than doing the same with a transformer. This is not to mention that one literally has dozens upon dozens of caps to choose from / manipulate whereas the options with transformers are rather limited ( in most cases ).
Clueless stated: "4) ITs do not do well with lots of non local negative-feedback.
Personally, i don't know of any gear that uses a lot of global feedback that sounds real good. It might measure quite well in specific areas, but sonically, it is a mess. Can you say "sterile & lifeless" ???
Clueless also stated: "7.) Other things: They break the signal ground, isolate RF trash from the input stage,"
My thoughts about this are that any transformer that is not well designed / shielded becomes a source to pick up / pass on RFI. Transformers work by creating a magnetic field and varying the energy transferred within that field. RF based signals are nothing more than "floating fields" and can easily find their way into such designs. Obviously, a poor design combined with high levels of RF would become pretty obvious and HIGHLY annoying. Once again, it is not so much the design as it is the quality of parts used and how well the design is implimented.
Other than that, i thought that some of the points that he covered in parts 4, 5, 6 & 7 were very fair and even-handed. All designs / products have trade-offs and i thought he did a very nice job of highlighting both the pro's and con's of IT's. Sean
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