Rerurn to Romy the Cat's Site

Hi Romy,

I just want to add my experience I had last year with a transformer based (actually it was an autoformer based) "passive" preamp.  I thought that this could be the final solution in my preamp quest.  Alas, it was not the case.  Here I will give you some specific reasons why the unit I tried (the Sonic Euphoria passive) did not live up to my hopes.

1) Loss of dynamic contrast.  I am sure you are aware of this problem.  It should not have been such a problem on my system with a 100kOhm input impedance but there it was.  This lack of contrast gave the sound a bland sameness that quickly became boring.

2) Loss of drive to the sound.  This I blame on problems in the low frequencies.  With time-coherent speakers (pair of Stax ELS F81s) it was easy to hear the bass was now lagging behind the rest of the music spectrum.  I think there must be a phase shift occurring to result in such behavior. 

In order to assess the problems more clearly I put an active preamp between the source (cd or vinyl) and the passive preamp.  This made the active preamp a "virtual" source or an output stage with much better driving capabilities than the source by itself. The result was that the sound took on much of the same character as I heard with only the "passive" preamp in the system.   I also tried it the other way around (essentially giving the source a volume control) and found that dynamics were improved but the bass rhythmic problem persisted.  I haven't tried other transformer based preamps so I don't want to over generalize.  However, it occurred to me that anyone who is using a non-time coherent speaker (especially a vented system with a high order and thus high phase shift in the bass) might not be as sensitive to these problems.  Their speaker already makes a mess of this information.   It seems you have had a similar finding with these so called "passive" devices...

If the output transformers cause so much trouble have you thought about remaking the Super M. amp as a Single Ended OTL?  You will need more tubes and generate a lot more heat but the sound should improve.  I recently purchased a pair of Silvaweld OTL monoblocks that use 4 6C33C-b tubes in a SEPP configuration.  It is running Class AB but the sound is really a cut above most of what I have heard (including IMO the Lamm ML2).   Another amazing sounding amp and preamp  that I heard recently is from a German company called Einstein.  Their 6C33C based OTL amps called "The Final Cut" are loosely based on a circlotron theme but the details are not forthcoming from the company except to say that it is a new variation. The preamp called simply "The Tube" is fully differential and interestingly has no input selector switch in the signal path.  It simply activates the filament and heater of the input tube to whichever channel was selected. So each input has its own input tube and the others are simply deactivated.  This gear is definitely worth your investigation as is the top gear from Silvaweld.

Rerurn to Romy the Cat's Site