300b lovers

This is getting dangerously close to an infommercial😉   Really, I have enjoyed the thread and never expected it to have this sort of life.   I just received the final version of the preamp output transformers from Dave Geren at Cinemag yesterday and installed them.  They are the next level up.  I expected a subtle improvement, but I am quite shocked.  The prototypes were the best I had heard, but the final version has improvements to the core material to give even more detail and even better bass response.   You can hear it right away.   These will be in Seattle and again, I hope to get everyone's opinion who can stop by and listen.

I will state again that there are many paths to audio nirvana and I would never claim that Lynn and I are on the only true path.  For those who love SETs please come hear these amps and let us know what you think.  You may be surprised.  My own personal bias (pun intended) is towards an all tube system.  I can hear any solid state device in the signal path and don't like it.   Yes, my Lampizator Pacific DAC has a solid state chip set doing the DAC part of the job, but that feeds the output tube grids directly and from that DAC chip set to the speaker is all tubes.  I would always choose a tube friendly speaker so that I can use a tube amp.  I realize there are those folks who love speakers that are difficult loads and require big solid state amps to drive them.  So be it.  There is no right or wrong.  There is what we like.  If you can visit the Pacific Audio Fest in Seattle you will hear the sort of system I favor.   All tubes, these amps and preamp, and some wonderful all passive open baffle speakers from Spatial Audio Labs.  There will be no DSP or powered subs or anything like that in the signal path.   The only solid state device in the chain will be the DAC portion of the Lampizator Pacific, then it is all tubes and passive speakers.  We hope you like it!

This thread has been informative and inspiring and I’m looking forward to hearing these amps at the PAF next month.

This thread has also caused me to reflect on the question of "what should I do" or "what should we do?" given the fact that Don & Lynn’s new amps are not available to purchase at this time and that, when they are, they are likely to be out of my budget.

My guess is that many of us who have followed this thread with great interest already have equipment that reflects the performance goals, priorities and values of Don and Lynn. I'm grateful that there are so many options out there right now - we seem to be living in a new "golden age" of hi-fi and music. So I'm not actually discontented with my equipment right now. But I've learned a lot on this thread that has provoked some new ideas and questions and for that I'm grateful.

The interesting thing is that "conventional" amps like PP KT88’s can be substantially improved as well. For example, floating paraphase phase inverters instead of split-load inverters or Mullard long-tail pairs. The phase division isn’t as precise, which is why they dropped out of favor, but the drive capability is much stronger than the other two types. And they really sound better. That’s one thing.

Another is dual B+ power supplies per channel, and is especially worthwhile in any PP amp, more so than SE. Isolating the noise and distortion of the final section from the driver + input is very worthwhile and lifts the amp into another class. This applies to solid-state as well. That’s another thing.

The third thing is scaling up driver current two or three times, and choosing the most linear driver tube that is available. Typically, this will be a medium-power tube, not a video amplifier out of a 1958 color TV. Video amps are powerful but linearity was not a major consideration in the tube design. You might get a linear one, but you might not. And you really want matched pairs for equal and symmetric distortion spectra.

Combine these three things, and the PP KT88 is now on a different level, but still has the same power as before. The slew rate goes up, and the noise and distortion go down.

Am I going to design this? Nope. But folks in the medium to high-power PP KT88 arena should check it out. You can’t keep making copies of Marantz amplifiers forever.

So, Lynn, given your comments, would an experienced technician know where to start to make these kinds of modifications? Or are they too obscure for the average tech to understand and execute...

Unfortunately, revising the driver away from the usual single 12AU7 means another hole in the chassis, and a pair of octal sockets at that. And split power supplies means another power transformer and rectifiers, although it relaxes the endless search for Holy Grail rectifiers. When an amp is that sensitive to rectifier choice, frankly, there is a design error lurking in there somewhere.

Somewhat counter-intuitively, splitting the power supplies front to back sounds better than isolated stereo power supplies, where the gain is fairly minor. The front to back isolation is not minor. Another counter-intuitive thing is PP amps benefit more from power supply isolation than SE amps.

As for inverters, the split-load inverter plus input tube uses two sections, while Mullard and the floating paraphase use three sections. And the last two sections can be octal medium-power tubes, not a single 12AU7.

This will change the forward gain of the amplifier, not by by much, but some. Probably a few dB less gain thanks to different and lower-mu drivers. Maybe a small trim in the feedback network, but less gain is easy to adjust for (unlike more gain).

In practical terms, a new chassis. Sorry. Those old amps were engineered down to the last inch, with no room to spare, and not one part wasted. Flip one upside-down and the parts in there are really, really tight. Too tight, and prone to overheating, which does no favors to the capacitors.

Most of the engineering effort in the Golden Age, even for Marantz and McIntosh, was simply watts-per-dollar, and keeping chassis size down as a secondary goal. In the late Sixties, the Crown DC300 and Phase Linear 700 blew the watts-per-dollar tube amps out of the water, and forced them into the audiophile market, where they remain today.