6SN7 NOS

An interesting article about the origins of the 6SN7 .

I dont agree with some of the comments , but some good info here, especially the historical content.

Double click to expand page.

FAQ -DHT PREAMP

What happened to the Directly Heated Triode preamps you were building ?

Yes I built DHT preamps for quite a long time , I built the first commercially available 300B preamp, and built quite a few different models, using different DHT tubes over the years. 45, PX4, 33, 101D, 4P1L and a bunch of obscure tubes.

I still very much like the lush, slightly warmer sound of DHT , and I still have a DHT preamp in one of my systems.

In the right system, or to cater to a certain subjective taste they can be very enjoyable, and I will still custom build them if required.

Its a bit of a shame that the best DHT preamp tubes are NOS from the 1930-50 period, I really like the 71A, 10/10Y/801A , but buying them now is a bit of a lottery as to what you will get.

And DHT tubes, because the filament is in the signal path,  are usually very microphonic. Some are worse than others, the 300B isn't too bad , the 4P1L can be quite "ringy".

It doesn't particulary worry me, I even think a little microphonics can be a good thing, but it drives most audiophiles crazy, as they think that something is "wrong" with the tube.

All the time I was building DHT tubes , around 10+ years, I still had 6SN7 preamps, and continued to work on them .

The octal 6SN7 tube was designed for applications such as preamps, and is maybe the ultimate preamp tube.

Everyone uses 12AX7,12AU7, 12AT7 etc, but these tubes were designed for TV purposes and to my ears aren't a patch on the 6SN7 and its Russian equivalent the 6H8C.

The 6SN7, in the right circuit, which lowers the output impedance to an optimum level , without any side effect degradation , is just about perfect in every way.

Its accurate, has a big soundstage and sounds natural and full of ease. Clean  solid bass and lots of air.

Most other tubes sound closed in, strained and brittle in comparism.

A couple of years ago I found a combination of componentry and circuit which gave the 6SN7 preamp a performance that I thought gave all the advantages of DHT without any disadvantages.

Its since been fine-tuned and is my number 1 product .

Tomorrow I'll talk about different 6SN7 tubes and the pitfalls and advantages of NOS.

That's not a tube, THIS is a tube!

Apologies to Crocodile Dundee.

211 on the left V1505/212E on the right.

I built quite a lot of SE amps 20 years ago, the V1505 is the most impressive tube , sounds pretty good too, like a giant 300B.

Tube Sound

Here's an interesting article about tube sound,

https://en.wikipedia.org/wiki/Tube_sound

6SN7 Preamp specs

Someone asked for specs of 6SN7 preamp,  specs don't really tell you how a preamp will sound, but here they are, in approx order of importance:
Output Impedance 1300 ohms.
Gain 0-26 dB adjustable.
Tube Compliment 6SN7  linestage 5881 5AR4 power supply
6688 6H23 phono preamp.
Power supply 300VA transformer, CLCRC shunt regulated
Copper chassis chrome plated
Remote volume
Lundahl, Magnequest amphorous input and output transformers

What Makes a good Tube Preamp- Pt3 Power Supply

A tube power amp can get away with a good solid power supply (PS) that consists of a big transformer , rectifier and a simple capacitor /inductor/capacitor bank.
If its big enough and of sufficient quality thats all that's really needed.

A preamp though is a different story- its a gain device and if the PS isn't clean, fast and powerful the good (the signal) will get amplified along with the bad (noise and distortion) .

A really good PS for a preamp will have 0.0mV of noise at the voltage output of the PS feeding into the loads of the triode tubes used for gain.

So for example, a Supratek will have 300V DC at the loads and will measure 0.0mV AC with no signal.

There's not many preamps that can achieve this and it takes an evolved and sophisticated design to do this competently and reliably.

Personally , I dont really take a PS for a preamp seriously unless it is regulated.

This means the voltage will always remain constant no matter what the mains voltage is or regardless of the demands of the circuit to produce distortionless amplification.

There's simple and more sophisticated ways of doing regulation, a good solid state regulator can be made with a handful of transistors and components, but being a died in the wool tube guy, I prefer a tube based regulator.

These come in either series or shunt versions, series is simpler.

Tube shunt regulators bleed off a portion of current to earth to maintain a constant current through the preamp circuitry, and from a sonic perspective are superior to series regs.

I've been using shunt regulators in my preamps forever, and they are a big determinant in the sonic signature of the Supratek preamps.

They provide a "blackness" around the amplified signal, with zero noise and distortion.

There's no strain with complex or dynamics passages as the voltage to the circuit is always constant and uninterrupted.

In contrast, an unregulated PS will "sag" with the demands of voltage peaks.

Component choices are also a big factor in performance. Once again, you will hear me say how detrimental electrolytic capacitors are to audio quality, and how so many audio devices these days are filled with them.  Its not uncommon for a modern preamplifier to have 50 or more electros in them, with a maximum lifetime of 10,000 hours.

There are 2 electro caps in a Supratek linestage, one for the tube heaters, and one for the remote volume.

Polyprop caps are much better, or even better again, minimal or no cap designs simplify design, performance and reliability.

There is no substitute for transformer size, you can definitely have too small a transformer, but its hard to go too big!

The Supratek preamps have a seperate power supply chassis simply because the PS is too big to fit in one chassis, and there are advantages in getting the transformer and inductors away from the circuitry.

I also use 1.2mm copper chassis for both preamp and PS, its expensive but if you live with a copper chassis for a while you will hear that a steel chassis does have a "sound" that is less neutral than copper.  It's almost intangible , but it's there.

There's a good reason the hyper expensive Japanese AudioNote gear is copper chassis based.

Power supply on the left. The middle tube is rectifier, the outside tubes are the shunt regulator tubes.

60 Year old tube amp that kicks arse.

Ok lets get away from the technical stuff for a day and do some reminicising.
A very long time ago I found a pair of Altec-Lansing 604B coxial speakers in a big cabinets on the side of the road.
Turns out they were from the Australian Broadcasting Commission radio station, and in the back of each cabinet was an industrial looking tube amp.

This was back in the day when tube amps were being phased out, solid state was becoming dominant and tubes hadn't had the renaissance they enjoyed a decade later.
But you could still buy replacement tubes in the local electrical shop and I'd heard old guys tales that these old fashioned tube amps actually sounded pretty good.
A new 5Y4G rectifier got it going again , and goddam the 604B and amps sure sounded different to the English amps and speakers we were listening to back then.
The tube amp was an Australian made Trimax A52 , a push pull EL34 design with a 6AU6 input tube and 12AT7 driver.
These were built on commission to the ABC , Trimax was mostly a transformer winding company , who had a very clever and enterprising design dept.
They produced quite a varied range of professional gear for the ABC, including some interesting preamps  and mixers.
The A52 was loosely based on the Mullard 5-20 EL34 amp. It put about nearly 30 watts with only a minimal amount of feedback, achievable because of the very high quality of the output transformers.

Its a very elegant design, straight out of the Golden Era of tube design. A fantastic output transformer, that would take the very best winders to match today.
Only one electrolytic capacitor in the entire amp, and that was probably installed later in its life.
Todays electronic components have hundreds of electrolytic capacitors , mostly used because they are very economical- the paper in oil caps used back in the 50's and 60's were much costlier, and can be as good as new 60 years later!
The pair of EL34 tubes put out a solid 30 watts,  but its not stressed or working hard to achieve this, so it will keep working reliably year after year.

I dont have the original pair I found 40 years ago, but i do have another 2 sets of amps I bought about 5 years ago.
I have a lot of respect for these amplifiers, they are of a good solid, timeless design, have incredible reliability that comes from over engineering of components,  and sound excellent.
There are very few audio devices that can maintain this sort of integrity and quality over a 60 year period.
It may be as ugly as sin, but underneath that exterior is a real beauty.
The Trimax A52 inspires me in my own preamp building, my preamps are very over engineered, with massive power supplies, and a reluctance to use those damn electrolytic capacitors with their limited life.
Suprateks built 25 years ago are still working reliably  and I'm even more focused on the latest models being super reliable and long lifed.
This is what makes a classic in the vein of the old tube Marantz , Luxman products. They are simply built to last, something that is sadly not a priority these days.
I was using my Trimax's in an active/passive configuration with my Supraxox field coil speakers, but the Supravox are going back to France for a re-cone and i now have the Trimax's on my AR-LST speakers.

These are another high quality, over engineered product from long ago, a fantastic speaker that was very revolutionary when introduced. It has 9 drivers per speaker, a 10 " bass driver, 4 mid range and 4 tweeters per speaker, kind of like a big Bose .
Despite receiving much praise, the LST's never really took off as they came out at the end of the tube era and they needed high power solid state to work well.
They were just ahead of their time, the high power Crown solid state amps they were partnered with were quite horrible sounding amps.
Ive split the crossovers on mine so the three bass, midrange and tweeter sections can be each driven by a separate amplifier, with the Trimaxs driving the mid range and tweeters.
This relieves the need for a really high power amp and the 30 watt Trimaxs are adequate for mid and treble, with a high power SS amp on bass.
I've installed level controls on each amp, so tone can be adjusted to suit. Of course a powerful preamp that can drive 3 sets of amps is also required.
LST stands for laboratory standard transducer and that is pretty much what they are, monitor standard with the ability to colour  the tone if required.
There's a real satisfaction using products you know are well designed , engineered and constructed to perform at the highest level, and last a lifetime .
The Trimax was probably the highlight of the Australian audio manufacturing of its era, and I feel privelged to own them.

What makes a good tube preamp- Pt2 The Circuit

In todays marketing focused world there's a lot of hype - especially about hyper quality components- exotic capacitors , resistors etc .

But the determinant factor in quality sound reproduction is simply the requirement for a high quality electronic design (or circuit)

Super duper capacitors and resistors wont turn a pig of a circuit into something that sounds wonderful.

A really competent design with bog standard , nothing-fancy parts will rock the socks off a poor design that someone has stuffed with $1000 of hyper parts.

The trick is to use the most advanced, up to date and state of the art design and then carefully choose the componentry to achieve the desired sound signature.

Its a matter of synergy and the experience of knowing what works best in situation.

I've never been a big fan of electrolytic capacitors, but most audio devices have hundreds of them in them.

Eliminating them is difficult and expensive, but the result is very worthwhile, as it results in a superior phase performance, which means more 3D imaging and more expansive sound-staging.

My Supratek preamps have typically no more than 3 or 4 electro caps , and used only where absolutely necessary.

The painfully common direct coupled/cathode follower design is the stalwart of preamplifier design and is employed in the vast majority of low cost preamps on the market.

Cheap to make with 12AU7 or 12AT7 tubes , and with reasonable performance , there must be many thousands of these preamps built over the years.

Its a great way for designers who wish to produce a tube preamp without too much thought or development- its a proven design with just enough "tube" sound to classify as a tube preamp.

These designs are really hangovers from the 1950's , state of the art tube design has well and truly moved on from there , but surprisingly few modern designers deviate much from the tried and true.

More innovative and developed designs use a hybrid mix of tube and solid state components, and even iron chokes and transformers in the mix,  with sophisticated power supplies to give highly accurate frequency response , the ability to drive any amplifier and superior phase performance to give realistic imaging and sound-staging.

Tommorow- power supplies.

What makes a good tube preamp? PT1 - Output Z

What makes a good tube preamp?

There's quite a few tube preamps available from the cheapest Chinese import to the exotic and expensive, so what makes a tube preamp good?

The most important feature is low output impedance ie the ability to drive loads. A power amplifiers load (input impedance) will vary from typically 5000 ohms (solid state) to 100,000 ohms(tube) and its generally recognised that a ratio of 1:10 is suitable, ie the preamp will have an output impedance 1/10 of the input impedance.

So if a tube preamp is going to sucessfully drive a solid state power amp with an input impedance of 5000 ohms it should have an output impedance of around 500 ohms.

This is just about worst case- 5000 ohms input is quite low, but not uncommon.

What happens if a preamp's output impedance (Z) is too high?

The preamp will not be able to transfer its frequency response in a linear fashion, it will be inaccurate and "sloppy' sounding.

This can happen when an unsuitable high resistance tube is used in a circuit that does not do any "shifting" from high to low output Z.


Tubes like the 12AX7, 6SL7 are often used in simple, minimal preamps but their high resistances require circuits such as the cathode follower to be used , which lower the output Z.

Unfortunately there's a price to pay , as 100% feedback is employed in this circuit, which does introduce a bit of haziness and veiling.

Without the cathode feedback, the high resistance tubes sound slow, warm and so "romantic" they will put you to sleep pronto.

Another way to lower Z is to use a "transformer" a step down device which can drop the ratio by a chosen amount,  for example a 4P1L triode tube has a resistance of 1000 ohms, if we use a 4:1 ratio step-down we will end up with a  Z of 250 ohms, which is low for a tube preamp, and lower than you will ever need!

Transformers vary tremendously in quality , and they must be carefully matched to each tube and application. Transformers don't work well with high resistance tubes and even with well matched tubes, its quite an art to build a really competent and high performance transformer.

I use the 6SN7 tube in my preamps , with a special circuit and Lundahl or Magnequest output transformers the preamps have an output Z of 1300 ohms , nice and low .

So output Z is important for a preamp in order to control a power amp with accurate frequency response and drive.

Tomorrow I'll talk about something else that's important.

Sophisticated and Elegant Tube Preamplifier .

Custom Cortese

I've built half a dozen of the new 6SN7 preamps now , and I'm over the moon at how well they are turning out.

I've been building preamps for nearly 40 years and to hear an old recording, that I thought I knew every last detail and nuance of,  to sound like I'd never heard it before, with a freshness and amazing retrieval of detail and vividness , makes it almost impossible to believe I'm hearing the same recording!

I thought I knew the old Beatles records very well, but I had no idea that so much musical info was there that I'd never heard that way before- a presentation that is like listening to a completely different recording.

What this preamp does so well is the 3D thing, it lets you hear way into the music, the depth and width of the soundstage seems to be much magnified , it sounds less like a recording and simply more lifelike, digital is less digital, and vinyl is more vinyl!

Supratek preamps have always had a reputation for that, but now there is a new standard.

To get such a big step up in sonic gains with a new design is unusual- preamplifier design usually results in little steps over a long timeframe to achieve a remarkable design, which in essence is what I've done when one considers that I've been playing around with the 6SN7 tube for so many years.

What happened over the last couple of years was a very rewarding coming together of a lot of synergy, lots of knowledge and experience that resulted in a mix of design elements being put together , that went KABOOM and resulted in something special.

Not that there was , or is , anything deficient with any of the previous Supratek designs, they are all very highly thought of world class preamps.

And I think there may be some who still prefer the warmer, delicious sound of a Supratek DHT preamp, with its slight emphasis of tone and perhaps a touch of veiling.


But I'm finding the new 6SN7 preamp to be perfect in just about every way, its a magical looking-glass into the heart of the music , its exciting, AND soothing and so damn musical , yet is also so very accurate and transparent- theres no tube shortfall or compromises, its an exciting state of the art design that I'm going to find a real challenge to improve.

I'd like to go into some detail of the design and component elements of this preamp- I don't usually get too technical , but I would like to shed some light on the numerous elements that go together to make this such an extraordinary and incredible value preamplifier.

Everything starts with the power transformer and a big 165VA  transformer that is the size normally used in a power amplifier provides plenty of electrical energy comfortably and reliably.

A tube rectifier provides DC voltage into a CLCR filter , designed specifically for use with the tube rectifier (I've lost count of the number of tube preamps I see with inappropriate filter design. Tube rectifiers cannot use the same values as a solid state design, but the wrong component values that suit solid state are all too common)

Electrolytic capacitors are not used in the High Tension voltage supply,  electros have limited life, and a thinner , less satisfying sound.  They are used extensively in commercial products because they are cheap, and polyprop/oil caps are too bulky to fit in a one chassis design.

The DC voltage is then fed into a tube shunt regulator- one for each channel. I've been using tube shunts for over 20 years and they are part of the reason for the Supratek sound- they keep the voltage of the preamp tubes constant no matter what the current draw is , and help with the definition and "blackness" around all dimensions of the music.

The power supply also contains a solid state rectifier for the tubes heaters- very over-engineered and mounted on a large heatsink for reliabilty.

This is attached internally to the chassis of the power supply, made of 1.2mm copper plate which is an excellent heat transfer .

copper chasis before polishing and plating

Copper plate is also used for the preamp chassis, it has a different sound than the steel chassis's used in virtually all other preamps, its not a sound instantly recognisable, but is a softer , less harsh sound over long term listening.

On to the preamp circuitry.

The first tube preamp I built 40 years ago was a phono stage that used 12AX7 and 12AU7 tubes, which are still very common these days and the first choice today for commercial tube manufacturers - they are readily available and cheap.

They were also designed to be used in televisions.

The 6SL7 and 6SN7 tubes were the lower distortion predecesors of the 12**7 tubes and came from audio applications, but back in the 1970's they were largely unused , and for a decade or so until they came back into vogue , one could buy really nice NOS 6SN7's for peanuts.

The first 6SN7 preamp I built I fell in love with the sound - lush , inviting and so much better than the newer , modern tubes which sound strained and distorted in comparism.

Simple circuits - plate resistor loading , capacitor outputs , highish output impedance that demanded an easy load, preferably a tube amp.

Over the next 40 years I tried just about every possible combination of tube/circuitry/components till I have finally arrived at todays 6SN7 circuit.

Both triode sections of the 6SN7 (It's a double triode with two seperate triode gain sections with a common heater) are cascaded, ie the line inputs are connected to the first section ,  which is then connected to the second gain stage section, which becomes the output stage. It's not quite as simple as that as there are some design tricks I'm not going to divulge , but that's a basic description.
This results in a high gain circuit, which to my ears always sounds more dynamic and flowing than a low gain circuit, and there are ways to make the gain useable and useful.

6SN7 double triode 

Both sections are plate loaded with solid state constant current sources, (CCS) which have been refined over many years to be as transperent and musically coherent as passive devices without the limitations.

The cathodes of both sections also use constant current sources, but in this case its to avoid the use of capacitor/resistor bias devices.

CR filters must introduce phase anomalies , and this affects the imaging and sound-staging of the preamp. By eliminating the CR filters common to almost all other preamps , the Supratek preamp gains a tremendous advantage in realism that preamps with CR filters always degrade.

The CCS's used in the cathodes are discrete solid state devices, mounted on a small PCB with the plate CCS devices.

Traditionalists could argue that passive loading use transformers or steel/nickel/wire chokes sound more "tube like" . I did use metal/wire chokes  and transformers for these purposes for quite a few years, but I was always aware of the severe limitations the resonances and frequency anomalies of the devices brings to the sound when using them for plate or cathode loading.

I like a preamp to sound beguiling and interesting, but there's no reason it cant be accurate and technically proficient as well.

However, there is a place for transformers and chokes in a well designed preamp , as long as they are very well made and used accordingly.

I use Lundahl and Magnequest input and output transformers and  grid chokes - these are expensive , high quality products that are the result of many years experience with transformer winding techniques.


The use of transformers for the output stage has two distinct advantages.  Its a step down transformer which transforms the high gain of the circuit into a lower gain , and also lowers the output impedance
of the circuit.  This 6SN7 circuit has an output impedance of around 1500 ohms, which will drive any solid state or tube amp.

It also has a centre tapped winding which allows the use of balanced or unbalanced output switching.

This is by far the best way to achieve a balanced output. We can use a Single Ended Class A circuit throughout the preamp and then get a perfectly symmetrical fully balanced or unbalanced output signal.

(I'm sorry but if you think an all balanced preamp, with double the components working in push pull sounds better, then you need to get new speakers. 😊  (but not as critical with balanced power amps which have their uses)

People like to talk about the use of super expensive and exotic capacitors. I do use very high quality caps in my preamps, but the overall determination to the sound is the correct value of a high quality cap, rather than some exotic all-talk device designed to make money.

Using high quality film capacitors rather than electrolytic caps has far more effect than replacing a capable film cap for an exotic one.

My line stages have no electrolytic caps , and the phono stages have only a couple of Elna Silmics electro caps in them.

The result of this circuit design, high quality components and dedicated handmade craftsmanship is a preamp that is sophisticated and elegant.

It is technologically state of the art design , but is also an instrument of music - its purpose is to convey the music in as pure a form as it can.

It will startle you and calm you, it will enchant and beguile you.

It is the result of my dedication to the art of the tube preamplifier over a very long period and a lot of hard work, combined with a lot of joy taken from the amazing and heart lifting world of music.

               Custom Cortese. Power supply on left with tube shunt regulators and tube rectifier.

New Design and Preamp.

New Supratek design and preamp!!!

There hasn't been a" new" Supratek preamp for quite some time.

The DHT models have been the mainstay of the product range for a long time, starting with the 101D, 300B/45/PX4, and lately the 4P1L versions.
I also did some custom preamps with the rare 71A and 801A tubes
.
A long time ago (30 years!) Supratek preamps were based around the the 6SN7 tube, a triode which could arguably be called the perfect preamplifier tube
.
Despite gravitating towards the DHT tube's I continued to have had a very soft spot for this tube, and have always had a 6SN7 preamp in my arsenal , and continued through the years to build 6SN7 preamps, alongside the DHT preamps, for those who wanted them.

There is nothing really new in preamp design, we have better components to use, we can mix tube technology with solid state design, but in essence all the claims for "new" designs are just variations on a theme.

Breakthroughs in sound quality now come from finding the right combinations of all the available design and component choices. Its a little like alchemy , find the right synergy of all the combinations and you might make gold!
I couldn't say how many 6SN7 circuits I have built over the years. In conjunction with my friend Kevin Covi's design and simulation skill , and my own design and building experience, I'd say it would possibly be over a hundred circuits.

It's hard to build a bad 6SN7 circuit, it's a very good tube with a lovely sound .In its most basic preamp configuration, it has high-ish output impedance , which restricts drive ability, and can give a tone which some call "tube or valve" sound.

The Supratek preamps have always used designs which give low output impedance , and with the in-built power supply regulators, can drive most power amplifiers, even multiples of amps in active systems.

Supratek preamps are always designed to be very accurate, fast and clean. Even the DHT preamps , while having the DHT sense of musicality were always accurate.

Many tube preamps these days are designed with conventional, 1950's style circuits that are are more tone control than accurate preamp.

This last year I've put together a 6SN7 preamp that achieves every goal I've wanted - its very accurate, has lots of drive , is amazingly transperant and as resolving as anyone could wish for.

It truly is a window into the music , so many times I've sat down to listen for a little while, and a complete album later gratified to hear and enjoy it as if for the first time.

It has the musical tone of a DHT preamp, with the resolution and accuarcy of the very best , and very expensive, solid state preamplifier.

I built this pre using all of my experience and knowledge of 6SN7 tubes, design technique and component choice.

It uses very high tech solid state anode loading, Magnequset and Lundahl transformers and chokes.

With the Supratek immense power supply , copper chassis, tube regulators and all the tricks o f 30 years of  preamplifier construction, I have built a preamplifier that is simply the best I have heard.

Somehow it seems to make the very best DHT preamp sound a little veiled and un-exciting.

Now sound quality is very subjective and some will still prefer the sound of a well designed DHT preamp, but the compromises of DHT- microphonics, noise levels do not exist in this new 6SN7 design.

I have half a dozen preamps, both 6SN7 based and DHT , and whilst I enjoy all of them, I find it very hard to listen the DHT preamps now.

No mistake, the DHT preamps are excellent preamps of the highest sound quality. The new 6SN7 design is simply better.

I addition to 6SN7 tubes, this pre can use Russian 6H8C , CV181, and with a convertor base the 6F8G/VT99 tubes.

As of the 1st July 2017 Supratek will be returning to full time production of preamps, and I expect to be building mostly the 6SN7 preamp.

The preamp pictured is a Dual Cabernet . It has the new 6SN7 circuit ( in this case CV181 tubes at back) and a 6H8C/6H30 circuit, both independent but working off a master volume. Useful for bi-amplifying, or active application.

Also available as Single Cabernet- just the 6SN7 circuit.

Also the Cortese- 6SN7 circuit with tube phono stage.

300B Dual Cabernet

Just finished this 300B Dual Cabernet, and very happy with this one. I haven't built a 300B preamp for quite a while, and incorporating some new design ideas and the features of the "dual" preamp with the iconic 300B tube turned out very nice indeed.

I don't think many people "get" the concept of the DUAL CABERNET so I've copied some of the text from user manual that explains further. Its from the 4P1L manual but also applies to 300B or any DHT tube used.

"The Dual Cabernet has two separate line stages, one utilising a Directly Heated Triode tube – the 4P1L , and the other line stage utilises a two stage tube design , using one half of the dual triode 6H8C/6SN7 and a 6N6/6H30. These two tubes are Indirectly Heated Triodes, which means they have a separate heater , rather than the directly heated filament of the DHT tubes.

Both stages can be used independently , or together. The gain of the 4P1L has two settings, and the gain of the 6N6 circuit can be set with it’s own adjustable level control.

Overall gain is set by the master volume control on front panel.

Both circuits, the DHT and the IDHT are state of the art designs, with high bandwidth, very accurate frequency response, and excellent drive ability.

The 4P1L has all the attributes of DHT tubes, a sense of “tube euphonics” , some microphonics (not a bad thing) and a pleasing, elegant musicality.

This stage also has the option of switching in the other half of the 6H8C/6SN7 triode, which will give higher gain, useful for using with low sensitivity amplifiers, or very low efficiency speakers.  You may find a greater sense of dynamics when this driver stage is switched in, depending on your system and requirements.

The Dual Cabernet’s 4P1L line-stage has a switchable output to choose either transformer or direct output. The transformer output, with switch towards rear has lower gain and because of it’s lower output impedance more drive, handy when driving multiple amplifiers , or a difficult load.

The 6H8C/6N6 circuit is simply one of the most technically advanced tube circuits available. It has very high bandwidth, extremely low distortion, very low output impedance, which enables it to drive any amplifier. It is a “state of the art” design using some of the best audio tubes ever produced.

With both of these circuits you have the very best of both the DHT and IDHT worlds, with this preamplifier you are sure to be able to find a combination that finds the perfect synergy for your system and tastes.

One way to use this dual preamp is with bi-ampable speakers, with separate connetions for bass and mid/treble.

The 4P1L linestage would be connected to the amplifier driving mid/treble and the 6N6 linestage connected to amplifier driving bass. Or the opposite, depending on your requirements, taste etc.

The 6N6 level control can then be set to give the best balance of bass and mid/treble to get exactly the tone preferred for your room and system."

The 6SN7/6H30 IDHT line-stage  alone would cost far more than the total cost of a DUAL CABERNET if purchased from a mass produced high-end audio company, but with the DUAL you get a world class DHT line-stage as well, and a preamp that is custom hand made , tested , tuned and run for at least 3 days before sent to owner.

There's nothing else like it in uniqueness and sound quality in this world.

6SN7/6H8C/6F8G

I've been using the double triode 6SN7 tube for as long as I can remember, I have a collection of about 500 NOS 6SN7's , about the same of the single triode version the 6J5.
The older NOS tubes sound damn nice , but they are frequently microphonic, and although I don't think that is necessarily a bad thing, with a high gain preamp that can be a problem.

NOS 6SN7's 

For at least 10 years I've been using the Russian 6H8C version of the 6SN7, it is a well manufactured, sturdy version that sounds very good, and is not too microphonic.

Russian 6H8C

Another earlier version of the 6SN7, made around the 1930's is the 6F8G. This has a top cap for one of the grids, which is a bit inconvenient as a hole has to be made in the chassis for the top cap connection.  Although it uses the same octal socket as 6SN7, the pin connections are quite different.
But its a fine sounding tube, and I built a few preamps and power amps that used it.
I built one power amp with 6F8G and 807 , both using top caps which gives an "antique" look.
Recently there have been some convertors available on Ebay which allows one to use the 6F8G in place of 6SN7 without any re-wiring of circuit.
One of my Russian customers asked if it was worthwhile, so I bought a pair to give it a try.
They look kind of stupid, but there is something about the 1930's period tube sound  that is very nice, it's different rather than better, but it is a enjoyable alternative , and the 6F8G tubes are relatively inexpensive, or they were when I last bought some many years ago.
A fun experiment for those of you with 6SN7/6H8C preamps.

801A/10/10Y DHT Preamp

One of the oldest DHT tubes is the 10 , with near identical substitutes the 10Y and 801A.
Although not rare, it is sometimes difficult to get good NOS matched pairs.

It's perhaps one of the finest DHT tubes to use in a preamp, it has a lovely tone and very balanced sound.

I've built a few 10 preamps for myself over the years, but never sold one as I was worried about tube replacement.

I've just finished building this "copper finish" preamp (all the Supratek preamps have copper chassis which is usually chrome-plated or powder-coated).

It was built to be used at an upcoming hi-fi show, but I've decided to use a production preamp with more available tube (4P1L or 300B) instead.

The 801A is conservatively run and they last 10's of thousands of hours, I'm still using the same tubes in the first 801A preamp I built around 10 years ago.

This is a DUAL CABERNET preamp with two line stages. The 6SN7/801A is the DHT output and it also has a 6SN7/6H30 line stage with volume control to be used in active systems, for example driving the bass amplifier , while the DHT section drives the mid/treble amplifier.
Or either stage can be used on their own. The 6SN7 driver stage can also be switched out when a low gain preamp is required.

The 6SN7/6H30 stage is a wide bandwidth , state of the art
design with outstanding technical specifications, which also sounds excellent.

The 6SN7/801A linestage has all of the Supratek DHT qualities , reinforced by the use of  perhaps the best DHT preamp tube ever made.

The finest components have been used- Mundorf capacitors, Magnequest output transformer etc.

Speakers

In the last post I talked about finding a speaker that will give maximum enjoyment and satisfaction.

I believe it is vitally important to consider the speaker the most important component in any system, it is vital to get this component suited exactly to your taste.

There should be absolutely no doubt that it provides the sound you enjoy, you should have no qualms about it at all.  It should be a 10/10 , and something you could live with over a very long term.

Forget about the dac of the month, find the speaker that speaks to you and everything else will fall into place.

I've had many speakers over 40 years and here follows a description of the 3 speakers I simply could not live without ( ok I could choose one above the others, but I dont have to!)

AR-LST


LST stands for Laboratory Sound Transducer and Acoustic Research meant this design to be a genuine studio monitor.

Released in 1972 its very hard to find a pair in good condition now, But despite their age,they can surpass the best of modern speakers in accuracy and musicality.

With 9 drivers per side- a 10" bass, 4 tweeters and 4 midranges they  throw a large and realistic soundstage. Almost ribbon like tonality,but with very much increased dynamics .

They require some modfication to crossover bring them up to modern standards . I replaced the electrolytic caps with polys and removed a tone shifting network consisting of a stepped transformer and large electrolytic cap.

I also separated the 3 crossover sections so they could be individually actively driven. This requires 3 amps per side but is required if speaker is to be driven by tubes, as the total load is quite difficult .

This also provides the ability to adjust levels of bass,midrange and treble independently so as to adjust tone to suit room and taste.

Back in 1972 there were very few high current amps available that were able to drive the high current requirements of the AR-LST.

I used the speakers for quite a few years with 6 tube amps and was very happy with sound.

But recently I used a modern solid state amp capable of 1000 watts into 1 ohm , with bass, mid and treble paralleled and was very pleased with sound.

Of course a state of the art tube preamp is necessary to get a nice synergy with all that power.
Because this power amp has high gain, I'm using my DHT preamp switched to low gain/high drive.

The midrange of the LST is very good, but probably so because of the excellent integration of the bass and treble units, its a complete sound proficient in all areas.


Supravox 215/ Eminence Alpha/Raal ribbon tweeter. Open Baffle

I've only had this speaker system for a short time time but I can see me living with it for an extended time.
I've already described it in previous posts so will just give a short summation.

Field Coil Drivers are different, The Raal ribbon tweeter is different . Open baffle with the Eminence Alpha 15" drivers is different.

All up this is a great speaker that sounds different (surprise) from anything else. It seems to have the best of everything , with very few vices. Maybe the bass isn't as deep as it could be, but it is so tuneful and articulate .

The music comes out with real ease and vitality , very expansive sound-stage with every instrument clearly audible at its particular level ,and clearly defined.

The drivers aren't cheap , but this is an affordable speaker that anybody would be impressed with.

Its particularly demanding of preamps, nothing but the best for this speaker as it demonstrates the very best (and worst) of all.

I'm using a DHT preamp with 3 outputs and low output impedance in order to be able to drive all 3 outputs.

It works very well with an all tube system , a mix of Single Ended and Push Pull amps and responds very favourably to digital EQ/room correction . (that will get the traditional tube die-hards up in arms!)

Accoustat 2+2

Another old design from the 80's. I've had numerous  electrostatic speakers over the years- Quad, Crown, Martin Logan, Nakamichi (Whise), SoundKing) but the one that overawes them in size and sound is the Acoustat 2+2

Electrostatics are famed for their detail and crystalline highs, but the 2+2 has the most majestic tone of all stats. It isn't bright , as most stats can be, but has a very natural tone that most resembles real ,
voices and instruments better than any other speaker I've heard.

It does low bass and although not as "heavy" as a bass driver it is nicely articulated. I use a pair of subs but crossed in low at 50Hz, so they mostly are contributing little to the sound.

Voices, brass instruments are so natural sounding ,its the closest thing to being at a real show!

They do beam,so its a one man show,but in the optimum seating position the soundstage is huge and wide, as you would expect from a speaker this size
.
Like all stats they only really gel with a very powerful set of amplifiers, I'm using two pair of 1000W into 1 ohm solid state amplifiers
'
The designers got this one right and they dont require much modification to surpass any modern day stat.
I did split the crossovers so I could bi-amp, rebuilt the high voltage section with up to date stronger components and did a mild jump in HT joule capacity.

These mods enabled me to use my Supratek Dual Cabernet preamp. The 2+2's have 2 step up transformers and using one of the preamps outputs to drive the amp for speakers bass/mid transformer and the other preamp output to drive the amp for speakers treble transformer , I'm able to make fine adjustments to the speakers blend of bass/mid and treble.

Every speaker/room benefits from the ability to do these adjustments and is the perfect example of how the Dual Cabernet can be utilised.

If I had to choose the 2+2's would be my preferred speaker, and I'm presently building a dedicated (large) listening room to suit them.

There are many other speakers that can make fine music, the trick is to find the the one that suits the way you enjoy your music, and what really sounds like music to you.

Its obvious from my choice of speakers that I like big sound-stages, wide and deep imaging , and speakers that disappear.

Others will value tone or frequency response, it's all subjective but important to find what sounds like the real thing to your ears.

Get the speaker right, then the preamp, power amp/s and finally the sources and everything will fall into place.

Photos above used for illustration only- not my speakers. Photos coming.

Finally-Beautiful Digital Sound 2

My Finally Beautiful Digital Sound post from March 2014 created a lot of interest and still gets quite a few visits.

These days I'm often asked what I'm using for digital in 2016 and I'm pleased to say I'm still using the "old" Philips TDA1541 R2R dac chip.

I still haven't heard a modern dac chip that gives the same ease and musicality - the new delta sigma chips  are much better than the earlier ones, but still don't quite give that overall fatique free listening experience the olde R2R dac chips like the 1541, PCM1702, 1704 etc.

I'm using state of the art FIFO buffering and USB to I2S direct into the 1541. This enables play of hi-res up to 384Khz . So its a combination of the old and new digital process's.

I also use a no-usb approach , which is also FIFO based ,  and I2S direct . IMO this sounds even more natural and organic than the USB approach, although the difference is not startling, just again a more relaxing, emotive and musical sound.

Over the last few years DSD has gained some traction in the audiophile world. Every new dac seems to be DSD capable , and I've spent a fair bit of time playing around with DSD dacs and DSD implementation.

Make no mistake, DSD can sound very good .

But at its essence , any method, whether its the PCM  derivatives - MP3, FLac, AIFF, etc or DSD, SACD, DXD etc are only as good as the original recording .

A good sounding DSD , just like PCM , requires a very good recording technique and equipment , if its a poor recording being DSD wont "fix" it or sound any better.

A very well recorded MP3 file will sound far better than any mediocre DSD recording .

Another method gaining some popularity is up-sampling  PCM to DSD 512 or higher. Again, this can sound very good, but is also dependent on the quality of the original recording .
And this method requires heavy computer power and an almost obsessive dedication to going to all the trouble of doing this.
I did it for a while, but then came to realize I was missing the basis of why I enjoy fooling around with all this- the enjoyment and satisfaction of listening to music.

And it all comes down to the quality of the original recording, so isn't it just as meaningful to concentrate on what really makes a difference rather than concentrating on the small differences between playback methods, whether PCM or DSD etc.

I think its vitally important to get a speaker and system that really appeals and talks to you.
It should be so good that you would consider it a lifetime choice if needed .
Speakers and preamps count far, far, more in your system than any dac, and have so much more effect to give you the music that you want to listen to.

Get the basics of your system right, find the speaker you can listen to, and enjoy all day long.

When you have that right you will enjoy listening to music and not fretting about whether your missing out on the latest dac of the month.

Eminence Alpha/ Supravox 215-EC/RAAL 70-20XR Pt 3

I used Dirac Live with calibrated mic to measure the 215/Eminence combination and this is the result.
It looks a bit bumpy, but this isn't actually too bad. It's a result of speaker and room.

The Eminence bass level is higher than the Supravox , but I've deliberately set it like this .
I also tried moving the bass crossover frequency up higher, but sonically it sounds best like this.

You can see the 215 rolls off from about 5Khz, it doesn't sound as bad as it looks, indeed I didn't think it needed a tweeter, till I heard one in place.

The orange line is the target for correction , and Dirac does a pretty good job of getting very close to the target.  It cant compensate for the roll-off above 5Khz , but it follows the target to there.

But it does show that for true full range a tweeter is needed. The problem is finding a high efficiency tweeter to match the Supravox.

I've used ribbon tweeters before, with limited success, they can be  thin and metallic sounding , however I've heard very good things about the RAAL ribbon tweeters, some claiming they sound unlike any other ribbon.

I ordered a pair of the 70-20XR from Russel Story at Stones Sound Studio and installed them alongside the Supravox.

Well,  the claims were valid, these are the best sounding ribbons I've heard and match the 215's wonderfully well.  They have quite amazing dynamics , seem completely unhindered and play as though they have much higher efficiency then their 92dB.
Detail is all there, but not in a metallic or tizzy way, its just open and realistic.

They don't sound as though a tweeter has been added, they combine effortlessly with the 215 to give a truly full range , organic and exciting sound.

I simply used a 3.6uF capacitor as passive crossover for the ribbon, and will experiment further with different values and adding an inductor.

Here is measurement of the complete 3 way of Eminence, Supravox and RAAL. Dont forget, this is speaker and room.  A bit of juggling of levels and and the bass's DEQX EQ would get this even better, but I'm going to rely on Dirac to sort it out at this stage.

And here is the corrected response.

And here is the impulse- impressive!

I've had mixed results with Dirac, it doesn't always suit all types of speaker/room correction, sometimes the correction is worse than the problem, but here it has done a superb job with the Eminence/Supravox/RAAL combination.

Building this system is not in-expensive, but frankly I doubt you could get the same exciting , realistic and satisfying sound for  many multiples of the cost.

I've heard very expensive (>$20K)box speakers that cant do what this combination does.

Defined, tonally correct bass, the dynamic vividity of high efficiency near full range field coil , and the ribbon tweeter that sounds like it's not there, yet everything is so correct and beautiful.

And that is the perception of live , real music.

Next is to do a bit of fine tuning and put the drivers onto a nice furniture grade baffle.