Tube Legend Bob Carver

I've always respected legendary amplifier designer Bob Carver- he's been around for years, he has designed classic amp after classic amp, both in tube and solid state.
He's upset a few people over the years as he is a little too honest and forthright in the BS loaded world of audio. My kind of guy!
Years ago he had a big kerfuffle with Stereophile magazine when he claimed he could replicate the sound of any amp , regardless of price, in a relatively inexpensive SS amp.
They weren't able to prove him wrong and they held a grudge against him for a long time.
Bob retired but now he's back with a return to his true passion- high power tube amplifiers.
Dick Olsher's review tells it all, nice to read a review written intelligently for a change, by someone who understands how tube amps work.
There's far too many "reviewers" around now who dont have a clue about the technical aspects of amplifier design and how they interact with speakers and other equipment .
One peculiar problem of the internet is that people dont do an "apprenticeship" now- they absorb all the opinions from the forums and web pages , but dont actually do any hard studying or actually get their hands dirty - its all accumulated opinion rather than knowledge and it is sad thing.
I remember in my late 20's having tube audio design books brought up from the bowels of the State Library and the excitement of finding something new and enlightening, in the quest for knowledge.
Anyway, Dick's review of Bob's amp is excellent and highly recommended as a template for aspiring reviewers.
There's  nothing  new in Bob's design , but he sure has been innovative in bringing some interesting concepts together in this amp.
High plate voltage, pentode operation, negative and positive (current) feedback and the "dc restorer" which controls bias operation at high power.
It's expensive at over $7000 but if I was going to buy a tube amp for myself , this is what I would have.
I'm a little thrilled and a little proud to say that we've been using some of these concepts in the Monduese and Malbec amps for many years now-  positive feedback is a big advantage to speaker control , and the bias control we use enables maximum power output with zero crossover distortion. Although I use pentode amps in one of my systems we have persisted with Ultra-linear operation and that has kept maximum power done to around 100 watts, however inspired by Bob I'm going to build some high plate voltage, high power pentode connected amps soon.
Enjoy the music review:
http://www.enjoythemusic.com/superioraudio/equipment/0512/bob_carver_cherry_180_tube_monoblock_amplifier.htm

                                                   Mondeuse power amp 100watt mononbloc

LowR bias preamps

I've been building preamps for over 30 years, my first preamp was a phono stage using 12AX7 and 12AU7 tubes in a SRPP configuration.
It's a little frightening that this is still considered state of the art by many manufacturers , and while it is certainly a good sounding circuit, a little imagination can definitely improve the sound by a large margin.
Over the 30 years there have been some constants that I've adhered too, as they majorly contribute to the sound I enjoy. Direct coupling, 6SN7 tubes, tube shunt regulation , silver plated solid core wire, polypropylene or oil caps in place of electrolytic caps whenever possible, "bird's nest" wiring (direct, non capacitive), copper chassis , transformer outputs, are some of the design criteria I've followed for many years. I believe Supratek was the first manufacturer to use DHT as preamp tubes in a commercial sense, the 300B, 45, PX4, 101D were all used in the Supratek range, but I also built preamps using other DHT tubes-the 801/10 series, 26, 30, 33, and the fabulous 71A were all used at some stage, but the preamp tube that has stood the test of time and is probably the most uncompromising of all is the 6SN7.
The Directly Heated Triode tubes are maybe better sound, certainly more fashionable, and definitely harder to work with as it takes a lot of engineering to get them quiet enough for high gain preamp use.
My favorite DHT for preamp use is the low gain 71A used in conjunction with a 6SN7(or 26) as input tube. Transformer coupled it has lots of drive, lots of gain (=dynamics) and suits all amplifiers and types of music.
Unfortunately they stopped making 71A's 70 years ago and they are becoming very hard to find in new condition now.
I have enough to last my lifetime , but not enough for preamp production . The 101D is in current production and with some fine tuning also sounds very good.
It may have been discovered many years ago, there's nothing really "new" in tube design, but a form of tube current setting (bias) was presented in 2004 that is unique and different in concept from the usual forms of setting current-cathode resistors, negative grid voltage,etc.
 LowR bias uses a seperate power supply to set the current thought the tube and enables very low resistance values and no capacitor bypassing.
Capacitors are "bad" and minimizing them is always useful, but eliminating them in the bias circuit has very favorable advantages, particularly in regards to phase response behavior . Bass is one area  where improvement is noticeable but the overall performance is enhanced. There were a few technical problems to overcome , but the gains were so significant I started to use LowR in my preamps around 2009 , after Kevin Covi brought it to my attention and we evolved the design to fit in with the anode follower 6SN7 design we were playing around with then.
The first thing I noticed about the 6SN7 circuit with the LowR bias was the similarity of the sound to my DHT preamps, indeed in some systems I even preferred the sound of 6SN7 LowR to the conventional 71A preamp.
At the price we can build the lowR 6SN7 preamp I believe it is probably the best performing preamp in the world.
Of course we incorporated the LowR concept into the DHT preamps, and after quite a lot of experimenting, and some really wild circuits that were very intriguing and interesting to build, we settled upon a DHT preamp design that I believe is unique and unlike anything else available at the moment. The bass performance is extraordinary, 3D imaging is startling, and it brings any system to life.
There is increasing talk about the role of analog preamps disappearing, I think this is rubbish, and anyone who hears a great tube preamp in a digital system will instantly recognise it as an absolute neccesity.

                                                                6SN7-71A preamp

Tannoy 15" Gold Monitors and Malbec PP amps.

                                 Tannoy 15" Gold Monitor with JBL active subwoofers


Although the last post finished on my preference for accuracy in a stereo system , this post is about one of my systems that although designed to be as accurate as possible , does tend to lean a little way towards musical rather than absolute "master tape" accuracy.
Some less experienced audiophiles listening to my main system, can find it too analytical for their own taste, which usually tends towards the "beautiful" sound they consider "correct" . Some even find the sound of absolute accuracy a little harsh , this is usually reflective of the recording, rather than the system, as the very detailed and analytical sound of an accurate system quickly reveals any flaws in the recording technique.
For myself, I must have system that is capable of revealing the very finest recordings, rather than a system that makes everything sound "nice".
One of the advantages of using the DEQX digital crossover is the ability to have 3 different settings, this makes it possible to have one absolute setting and another two settings for less than perfect recordings, all available by remote control.
If I had to live with only one system this would be it, however the fact is most recordings are not well done and songs have to be chosen for their recording quality to sound good on this system.
With the best recordings, nothing else sounds as good, but 80% of recordings are less than optimal.
What to do when one just wants to put some music on and not listen critically?  Fortunately I'm able to have 4 systems, and as I build preamps and power amps its convenient to listen to new designs on a variety of speakers.
All of my speakers are designated as studio monitors, and reasonably accurate with a  load tolerant amplifier.
The exception is my pair of Tannoy 15" Gold Monitor speakers- these were designed back in the early part of the 20th century, and while they were classified as monitors then, these days the requirement for accuracy is much tighter and the coloration of the big 15" co-axial speaker does not classify it as a studio monitor .
The main advantage of the big Tannoy is its ability to fill a room with sound. Mine are used in a big room, in an open plan house and they have a remarkable knack of filling the whole house with clear concise music.
Quite a lot of the Tannoy coloration comes from the conventional cabinet design, they are mostly used in big , heavy boxes, and deliberately tuned to fill in the lower midrange with some cabinet "sound".
With a compression driver and crossover at 1000hz this is normally a good thing.
In truth a Tannoy Gold will sound good in just about anything, but with my penchant for accuracy I wanted to see if I could get it accurate without taking the soul out of the sound.
Straight away I decided to use a subwoofer as I believe it is too much of a compromise trying to get sub bass from a co-axial , and relieving the Tannoy cabinet of sub bass duties let's us concentrate on getting cabinet effects to a minimum .
I use a 100 litre cabinet constructed of two layers of heavy MDF , but more importantly inside the cabinet is a large cardboard tube a little larger than the driver, and about 30 mm thick. This is attached to both the front and back of cabinet so driver is actually in a round , very rigid sub-cabinet. This takes out any form of cabinet coloration, and The Tannoy is heard as it really sounds, with out the usual cabinet effects.
The tube is filled with very dense Belguim foam which helps to give a surprisingly good bass response which sounds clear, tight and articulate down to 50Hz.
I was quite surprised by this, usually the big Tannoys go into big 200+ litre enclosures, but the bass in this unconventional 100 litre cabinet is just about perfect to mate with the JBL active subwoofers which are switched to 50Hz crossover @ 24dB. The subs contribute very little to the music and only really come into play with genuine sub-bass.
Crossovers are standard passive Tannoy, I might investigate them one day, but they sound fine as they are.
The sound of these speakers is pretty much was I was hoping for- they are reasonably accurate, maybe not studio monitor but quite close, are still very musical, without that excessive "cabinet" sound the big Tannoys sometimes have.
They fill the room with sound, and are very enjoyable to listen to over long periods.
I tried many amplifiers and really think that tube amps are a must for Tannoys. They also will work quite well with low powered amps, but do struggle if louder volume levels are required. Around 30 watts seems to be minimum and I found that one of my lower powered push pull 50 watt Malbec amps, using rare 7027 pentode output tubes (similar to 6CA7, the USA version of EL34) , 6SN7 driver stage, octal 6H30 screen regulation, a tiny bit of negative feedback, and just a bit more of positive feedback, gave the sound I was looking for, for me, preferable to the sound of much more expensive and over-engineered SE amps.

                                                        JBL SLR4312SP active subwoofer