2. amps-preamps
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Preamp Quandary - sonics vs. ergonomics??

I have been auditioning (buying and selling) preamps for over a year now. My only absolute criteria is that the preamp must be a fully balanced design that has low enough output impedance to effectively drive my McCormack DNA 500 amp (10K input impedance). However, since my system is in the living room, there are some ergonomic considerations including the potential for other users. After trying several, I currently have two pretty good but different preamps, an Atma-Sphere MP3 that is maxed out with teflon caps, regulated power upgrade, caddock resistor package, and user-applied 3M constrained layer damping sheets. It also has Jensen transformers for phono that I do not use. My other preamp is an Ayre K-5xe which is an outstanding ergonomic match with my CX-7e source. The comparisons are;

Ayre K-5xe - very user friendly, stays on all the time, uses the same remote as my CX-7e source, no heat issues, dead quiet, smooth sounding with tight punchy bass and adequate decay for a SS unit, no turn-on/off issues, heat, DC worries or other tube related concerns. In other words a competant performer which is the perfect operational match for my situation.

Atma-Sphere MP3; deep bass, dynamics that you can feel in your chest, well-extended for a tube unit and has that "rightness" only tubes seem to be able to provide, outstanding 3-dimensionality, and an outstanding midrange that puts the performers in the room with you. In short, this is the best sounding preamp I have heard in my system, but not the easiest to use.

Have any of you made a similar choice, and did you have any regrets?
mitch2
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unsound
7,341 posts
 
Perhaps a Sonic Frontiers Line 3 will satisfy all your needs?
herman
2,277 posts
 
The input impedance of each channel is usually detetermined by a single resistor on the amp's input. If this is the case with your amp then any competent tech could change that resistor and raise the input impedance.

Why not check with the manufacturer? They choose such a low value to minimize noise that the amp can pick up through the inputs, but unless you live in an extremely electrically noisy enviroment (unlikely) then increasing it doesn't affect the performance.
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mitch2 OP
4,166 posts
 
Can't do that with the DNA 500, per Steve McCormack -
"I usually design my amps with a 100K input impedance for maximum compatibility, but using the Jensen (or Lundahl) input transformers forces a shift to 10K (at least for the 1:1 types I prefer). It would be nice if I could offer all of the advantages of the transformer input topology along with high input impedance, but I feel strongly that the strength of this approach more than outweighs this small disadvantage. Using these transformers allows me to simplify my input stage somewhat, and provides a “brickwall” filter against DC and RFI – without the need for blocking capacitors or additional filters. Like many audiophiles, I used to look askance at the use of transformers, but I must say that I have become very fond of them. Used properly, I feel they offer a lot of advantages, and their main drawback is high cost."

the whole thread is at;
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1140406847&read&keyw&zzjensen+transformers
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