300b lovers

Don, Lynn

Like many have said, there is a lot here that is technically beyond me...so, I'd like to see if I've understood the essence of what you are saying..which I believe is....

That by eliminating all harmonic distortion above 3rd...and by driving 2nd and 3rd harmonics to extremely low levels you have achieved an amplifier that is not "tubey" in the classical sense but absolutely open and clear that gets out of the way resulting in truthful musicality.

Obviously, this is an extreme simplification of what you've achieved and how you've achieve it...but is this a correct interpretation or have I over simplified or missed some key discoveries?

To simplify.. All tubes have distortion. The higher orders are what are like fingernails on a blackboard to your ear. DHTs have lower levels of higher order distortion than other types of tubes, and good indirectly heated octals like the 6SN7 and 6V6 are reasonable regarding distortion in the higher harmonics. When I rebuilt a ton of vintage tube gear I instantly could hear that pieces using small signal tubes, particularly the 12au7 were not very good. If you see a 12au7 in a piece of gear other than a tuner, go buy something else. I always preferred amps with octal tubes as drivers. Anyway, to keep upper harmonic distortion down we choose a great DHT, the 300b for the output tube. Traditional feedback approaches can keep higher order distortion down, but phase split circuits and the usual coupling methods, and the feedback itself rob the amp of clarity. Push pull amps have lower levels of distortion. Class A is the way to go. If you can build an amp with no feedback at all and solve all the problems it will sound cleaner and clearer. The driver stage has to be able to really push a 300b. There are numerous forms of coupling, but interstage transformers (if really well made and designed for the circuit) solve a lot of problems. Recovery around clipping is really important for the driver stage and the transformer coupling aids that considerably over traditional RC coupling. LC coupling sounds very good for an input stage where an interstage transformer would have to deal with the higher impedance of the input tube. Power supply topology and design is critical and the output stage should be isolated from the input and driver stages. Of course the quality of the output transformers is a key as well as the power transformer, which should have good regulation. I am sure I am leaving some things out, but those are some key points of the design.

@lynn_olson 

I did check catalog of one European manufacturer for SE to PP interstage transformers. Within the limited offerings, it does seem that a tube with low Rp is needed in the SE stage - if not a DHT, ones like 6EM7 (the half with 750ohms Rp) may work. The gain will be less, but can still work with an active preamp. 

Ultimately, I agree that it all depends on the design goal - I wonder whether having some 2nd order harmonic would end up being a good thing for someone who prefers sound of SETs. But there is a lot factors to balance in such a design that uses SE in the first stage.

What a great thread!  Reminds me of the early 2000’s when I was on here more often.  I love how charles1dad said it back a ways so I’d like to repeat it, hope he doesn’t mind: “If a thread topic generates quality insight, information and perspectives from genuinely knowledgeable and earnest contributors then this is what happens.”

In January 2021 I bought from Don Sachs a Valhalla integrated amp.  I couldn’t be happier with the sound of my system.  After years in the “pursuit” I have felt no desire to change anything.   The Spatial Audio X3 speakers have a lot to do with what I love about my system now.

Don mentioned in an email last month that he was working on some 300B monos for the Seattle show.  Immediately I was interested and have been looking forward to hearing them in the Spatial room since I’ll be there.  Although much of the technical info in this thread is over my heard it is fascinating to read.  I’ve gained so much further insight into Don’s expertise, learned about Lynn Olson and how the two have worked together with their combined knowledge on this amazing project.  I think anyone who has enjoyed one of Don’s masterpieces would probably feel these new amps are a must have, including me.  It’s fortunate I’m so happy with the Valhalla since the new amps might be out of reach.  Hearing them in the Spatial room could be dangerous.

Looking forward to meeting Don and Lynn and would be nice to see Clayton again this year like last.  Hope he can make it.

Jeff S.

Gig Harbor, WA

@jeff_ss 

I don’t mind.😊

I am interested in your listening impressions of this amplifier  at  the upcoming Pacific audio show.

Charles