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Reply with quote  #16 

I very much appreciate the sound quality in TS products based on many listening hours of T16 amps in my own and friend's system, and also based on experiences as a Masterpiece preamp owner. It is the best sounding preamp I have had in terms of openness, tightness, frequency extension, depth, imaging, micro and macro dynamics etc. you name it. It has served me flawlessly over a year now.

As a music lover the sound quality is the decisive factor if a component stays in my system, meaning sound quality with my sources and speakers. But as an engineer I also need to believe in the technical solutions including long term reliability in and as of part of the system. Amplifier design is about sound quality, versatility, reliability and cost. All designs are compromises vs. these dimensions and deep discussions can be had where aim at and which solutions are right, wrong or between those vs. intended use. Tubes and tube amps have been around for decades, so there must be lots of cumulative knowledge on good design practices with respect to sound quality and reliability.

I believe OTL is the way to go in my bi-amped system (class D in bass and tubes above that). I do not yet own OTLs, but I am looking around, and as said, I have enough listening experience on them to believe in their merits. But even with OTLs, especially when using parallel tubes, I would welcome cathode resistors to balance currents between parallel paths. I am glad when biasing has some sort of feedback to control against ageing and thermal effects. I also like when the current rush in output tubes is controlled during switch-on as well as the output fluctuations staying small. Output protection is a must in OTLs. Delay circuits and relays welcomed. There are reasons for these, but as with everything, these can be over-done or speculated if so is done. On the other hand there must be reasoning if good design practises are not followed and resulting limitations must be understood.

Interesting collection of information from tube manufacturer's view-point:
Reply with quote  #17 
AnntiR here is the problem. Yes there is a massive body of knowledge to build an old fashioned PP tube amp and some really old info for single ended. And many of the designers out there use that info. That is why in many cases their designs look and sound like amps of the 50's and 60's. In fact look at the schematics and you may have trouble telling them apart. If you saw the schematic for Bruces Beast  you would understand how far advanced they are compared to those old amps. His power supply is very, very quiet. [My speakers are 99db/1 Watt] The driver section brings out detail that most amps do not and the OTL output keeps the integrity of the sound. I also know that Bruce builds safety features in the power stage to protect the speaker by using fuses and resistors in critical locations. He also uses a veristor to control the initial rush of power at turn on. A couple of years ago I heard the best sounding transistor amp of my life. It was a very highly modified amp. To make it sound that good required this small amp. to increase in price by 10 fold It went from 2,500 to $25,000. The man that designed the mods was one of the top modifiers in the transistor world known for thinking outside the box.
But here is the question. How many of us could afford to put that much money into an Amp.? By the way Bruces Beast is still the best amp. I have ever heard and for a lot less.
Kelvin Tyler
Reply with quote  #18 
I am in complete agreement with many of the sentiments expressed in Sailor's last post. In no way can I claim to be a 'newbie' as I have lived and breathed electronics for most of my professional life.
Until about a year ago my only experience with the OTL audio field was within the area of headphone amplifiers. Then, out of curiosity, I picked up a copy of 'Tubes and Circuits' and was immediately intrigued. I decided to build the SOB amp described there and was captivated by the results that it gave with quite modest speakers. My practiced eye recognized sound engineering in this design and this amp still gives me much enjoyment. I have had no stability problems of any kind with this design. No DC offset drift or shorting tubes.
At first I was a bit sceptical about the 300B SE. What's this? Four 300B tubes for one watt? Then, as I have previously mentioned, and having some 300B tubes not doing much, I built my DC version of this amp. I then understood what all the fuss was about; outstanding sonics. The performance of this design quickly dismissed all my initial reservations.
I have closely studied several of BR's designs with a critical eye and what do I find? Always sound engineering principles, thoughtfully applied, often with great ingenuity and innovation. Apparently simple circuits usually contain subtle features. For me, he has squeezed just about as much performance as is possible out of these designs, consistent with economic constraints. Of course, all engineering involves compromises, but, to my mind, Bruce has made the right calls. At the end of the day, performance and listening pleasure is what counts. Don't get me wrong. I think experimentation is very important and I have been inspired to do much myself, often with pleasing results. It's just that I feel that Bruce has not left much scope for major improvements and we are likely to run into a 'diminishing returns' scenario quite quickly.
I am no hero worshiper.  I simply try to speak as I find. I don't think you will find any better value than with TS products. No 'snake-oil' and no odour of 'horse manure'.
I am sitting here looking at a load of Edcor and Hammond transformers weighing many pounds, and even a stereo 211 design I built a while back with its 1200V power supply and thinking, 'What can I do with these...?'. Great fun this DIY audio!
Reply with quote  #19 
The sign of good engineering is re-use of components or parts of the circuit. You see same chokes, electrolutic caps, transformers, chassis etc. in very different Transcendent amps. The T16 and SE-OTL even shared same output stage pcbs. The original SE 300B used small bunch of ordinary stock components which fitted together like a glove for outstanding sound.

Compare it with e.g. chinese gear - each component of same brand is completely different (probably also sonically) - they don't know what they are doing and only shoot blindly...
Eric C.
Reply with quote  #20 
I have a dumb question: if someone can understand Bruce's circuit & build a TS amp from scratch, then in theory he can steal Bruce's idea/circuit and make exact same product to sell (in other countries?). How to prevent this situation to happen?
Bruce Rozenblit
Reply with quote  #21 
They already are.  
Kelvin Tyler
Reply with quote  #22 
It now seems appropriate to report further on my experiences with the 300B pp amplifier I constructed late last year. I have to say at the outset that my enjoyment of the sound quality of this amp goes from strength to strength. It is a truly wonderful sounding amplifier for all types of music I am able to try. Most of my listening has been with My Fostex full-range speaker setup with no sub-woofer. I wanted to get an unalloyed impression of the amps capabilities.
It so happens that, by chance, I have very recently built the kit of the latest version of the TS SE-OTL amp. This has enabled me to make some very interesting direct comparisons between the two, very different amps of similar power outputs.
From the word go, the SE was clearly very fine sounding, with a clarity and openness so characteristic of the genre. I had then before me two excellent, yet distinctly different sounding amplifiers. Which did I prefer? Excellent as the SE is, my choice is with the 300B pp. I just do not wish to switch this amp off, it is so captivating and with 'punch' to spare. Absolutely no listener fatigue, just beautiful 300B sound.
For sheer bang-for-buck I have to say the SE-OTL is hard to beat. I built the kit for a relative who asked me to make him 'something like yours' which he seemed to like very much. I said I would, but only if he bought the TS kit, as the actual design was not officially published as far as I knew. Personally, I will never attempt to clone an unpublished TS product for any third party. I always say, 'Buy the kit'. Bruce has been so open with so many of his designs in his several publications, that the least we owe him is not to act as rip-off merchants.
Last words (for now!). 300B pp - not to be missed! SE-OTL - fantastic bargain.

Bruce Rozenblit
Reply with quote  #23 
Thanks, for your input Kelvin.  The SE OTL is called the Mini Beast. I used to make an amp called the SE OTL which the Mini Beast has replaced.
Reply with quote  #24 

Does your 300B PP have the same magic in the midrange where it sounds like the performer is in the room with you as does your 300B DC OTL SE's?
Kelvin Tyler
Reply with quote  #25 
In general, the sound of the 300B PP and my take of the 300B DC SE are quite similar. Both give a good sense of presence with the extra power of the PP giving noticeably more dynamism. With my Fostex FE166en single driver speakers the mid-range is pleasantly strong. The higher registers are quite markedly 'beamed', so orientation of the speakers is important and can, indeed, act as an effective 'tone' control. My musical taste precludes excessive, thumping bass, but I do like it to be sharply defined. The 300B PP gives that.
I can hardly claim that my modest, space limited, speaker set-up is in any way optimum, but others do comment on the pleasant integration of the music it provides.
Personally, I am more than happy with the performance of the 300B PP. I would be very interested to hear the opinions of other folk who have constructed this amplifier.
Reply with quote  #26 
Thanks Kelvin,

 I too  would be very interested to hear the opinions of other folk who have constructed this amplifier.  It would seem that  since this 300B PP amp came out over 6 months ago someone else would have built it would have a comment.

 It has always been strange to me that this forum has such few comments regarding the best components designed  at any affordable price.

I would love to here from someone that built the 300B DC or AC version comparing it on Horn speakers. 


Reply with quote  #27 
What plate voltage and current are the 300Bs set at?  How long will they last?
Kelvin Tyler
Reply with quote  #28 
Paul. The 300B plate voltage is 315V and the idle current set at near 60mA. The resulting plate dissipation at idle is therefore about 19W which is less than half the maximum allowed for this tube. I would thus expect tube life to be very good.
Reply with quote  #29 
Than you for your response.  I have never seen a directly heated triode used in in a push pull OTL except for here. Are the 300Bs direct coupled to the speakers or capacitor coupled?  

Kelvin Tyler
Reply with quote  #30 
Bruce is an extremely innovative designer and his OTL circuits are constantly evolving. The coupling to the speakers is direct, but there is good protection against any possible speaker damage.

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