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dazzdax wrote:

what is your experience with passive transformer based preamps? Is this the ultimate way to get a perfect variable gain? Or do you prefer to use an active preamp?

I think the terms of ultimate might be applied only in context of the specific requirements when the definition of success would be a match between the demands and accomplishments. All those passive transformers-based preamps along with the inner-stage transformers are very much should be approached from those positions: in context of what requirements the passive preamps should be observed.

If you have bookshelf, ported or juts in any way LF challenged loudspeakers or for instance not really demanding LF electronics (courtesy to the SET amps) then the passive resistors of transformer attenuators might work perfectly fine for you.

Certainly a resistive attenuation will not drive cables but it you locate them right at the power amp input then the resistors network works juts fine. Once again: they will work fine… depends of the demands of your loudspeaker in your room, primary depends of dynamic and LF demands… Sometimes, going up with your demand and up with your expectations you will reach a point when a passive attenuation extended further form the input stage of your amp will not satisfy you anyhow, primary because it will compress dynamic and truncate LF. Still, my estimate the is that 70% of audiophile systems out there should not worry, or will not able to detect the remote resistors network problems.

With the transformer attenuation everything more completed. It is possible to make a transformer that would preserve or even enrich dynamic range. I said possible not because you can go to store and buy it but because if you chase them for years and years, spending thousands dollars then you might eventually discover one. Also, it is practically imposable to custom order anything serous in magnetics because the manufacturers do not do what it necessary or demanded but what they feel is “comfy” to manufacture…. However, even if you did succeed to preserve dynamics in your line-level transformer then the LF cut off of this transformer will “get” you. The solution is very simple: do not run any transformer attenuators within a really LF capable installations….  I said the “LF capable” and I wonder… how about the LF modulations that must be within any amplification channel? Absents of real bass within amplifier means no properly auditable HF, no proper harmonic modulations… no Sound as far as I concern. (Remember, I did not advised to high pass the HF channel of the supper Milq).

Would it be theoretically possible to bult a properly operating full-range capable innerstge transformer? I did not see any. I am sure Bud, Chris from UK or Torthen if they read it would be violently disagree to my assessments, but I do agree with myself: a line level transformer has more problems then solution, beside that fact that it never sound LF capable, or something that I usually call “good only for Lowther-based systems”....

... there is no really LF potent/transparent line-level transformers.

Rgs,
The Cat

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