300b lovers

My first experience of a 300B amplifier was back when I was writing reviews for Positive Feedback magazine back in 1993. It had grown from a 4-page mimeographed club magazine for the Oregon Triode Society to a fat 100-page periodical with cartoons, editorials, and a staff of reviewers.

I was one of them, after submitting a series of construction articles for the Ariel twin transmission line loudspeaker. I was listening to a whole string of amplifiers when David Robinson, the magazine editor, dropped off not just the Audio Note Ongaku (which cost three times the price of my car) and the Reichert Silver 300B’s. So now I’m in the reviewing business, too. Oh well, not one to look a gift horse in the mouth, away I go, with a month’s free use of entirely new amplifiers on my brand-new speakers.

Which was quite a revelation. When you design a speaker, and you’ve been doing it for decades, you get to know them pretty well. What they can and can’t do, and what the overall character of the speaker sounds like. Nothing new to me, and the Ariel was my eighth speaker design, after my time at Audionics during the Seventies.

One of the last stages of a near-commercial design is auditioning the speaker on many different amplifiers, keeping in mind the impact of output impedance (damping factor) on the bass alignment and the crossover. The Ariels are designed to have low sensitivity to output impedance: transmission line bass with no impedance peaks, low-Q 2nd-order crossovers, very flat drivers that don’t need equalization, and a tweeter that is running flat out, with no attenuation, since the paired midbass drivers have matching sensitivity. So all amplifiers see an equal playing field, with a minimum of power disappearing in resistors.

The shock with both DHT amplifiers was a radically different sound than Class A transistor, Class AB transistor (with high slew rate), and push-pull pentode. Much higher transparency and much more vivid tone color ... out of a speaker that I knew very well, and was my own brainchild. This is what led me to design my own DHT amplifier, but not following the path of either the 211-based Ongaku or the Reichert Silver 300B. But definitely using the 300B for sure; no 2A3 came close, and 211’s and 845’s (with plates running at 1 kV) are extremely difficult to use.

Don has brought me up to speed on modern power supply design, things I didn’t know about in 2003, when the Karna was designed. That takes the Karna to a new level, and reduced it from a ridiculous four chassis setup with high-voltage Amphenol connectors to a much more sensible pair of monoblock chassis. One pleasure of working with Don is he will chase down every possible variant, build it, audition it, and let me know how it measures and compares to all the rest. Fortunately, we have gone full circle and have arrived at a Karna Mark II with far superior transformers and power supplies.

Yes, we are pretty much back to an updated Karna circuit with more modern power supply topology, and custom wound iron everywhere.  I listened to every possible variant of the circuit and it is obvious that removing all coupling caps and going with all transformer coupling walks all over any other variant in pretty much every way.  We are now using custom wound Monolith Magnetics iron for power and output transformers, and Cinemag interstage transformers.  The chassis is much wider than the shoebox amps displayed at the Pacific Audio Fest in Seattle.   Spatial will change the look slightly, but the layout and size will be the same.  There are reasons for the layout, which makes for very short signal path at all sections and also has complete isolation of the power supply from the signal part of the amp.  They are just about ready to build in quantity and I would expect them to be available in November or December if all the vendors meet their production schedules for parts.  I will say that I cannot listen to anything else now.  I am spoiled.....  everything else sounds dull and coloured to me now and I have pretty much cleared my house of all other amps and preamps.  We shall see what others think!

I cannot seem to post a photo of the final prototype, but will upload to my old website and see if I can post a link to that photo eventually.

This thread, with over 500 posts I think, has allowed interested people to understand the evolution of their 300b amps design compared to other designs.  A rare insight into the machinations of amplifier design, which to be honest Roger Modjeski from RAM was stellar at doing as well.   Lynn astounded me with an earlier post that some designers, maybe it was with speakers, design to specs and that's it.  What Don and Lynn have done is an endless process of swapping not only components, but topologies, a very interactive process, subject to both measurements and equally or more important, endless comparative listening observations.  This to me is the optimum process to design gear and the process has to be exhaustive, but both Don and Lynn have done  this for decades... this iterative process.   And, to wit, they have shared their excursion on this thread in masterful detail to inform all of us.   

My pre-pro 300b amps are a glimpse of heaven with my Cube Audio speakers and it is hard to imagine how much better they will sound when Don updates them to the final version, but  I am certain his promises will be fulfilled.  

I managed to update my ancient website with the beginnings of 300b project page.  There is a photo of the final prototype of the Blackbird 300b monoblock amp at the bottom of this page.  Spatial will change the look a bit, but dimensions and layout will be the same.  The amps are optimized for sonics and short signal path.