Passive/Active

I see a lot of guys going through rounds of speakers, amps, preamps, dacs in the quest for the perfect sound. Or at least the sound they could finally be happy with.

But the sound they wanted could have been in front of them all the time.

The fact is, there is no perfect sound, we all hear, and seek different audio nirvana.

What I consider important to sound quality, you may dismiss in favour of some other aspect, and that is perfectly correct, audio is personally subjective.

There are many ways to voice a loudspeaker, from monitor quality, accurate frequency speakers for studio use to romanticly flavored midrange accentuated ear pleasers.

But no speaker will sound exactly as the designer intended in every room, or system.

There are so many variables that affect the sound,  that a speaker can sound vastly different from room to room,  and system to system.

One way to get closer to the sound that suits you is to actively drive the speakers individual drivers , thus providing some adjustment to tonal balance, with other important advantages.

I'll describe a couple of my own passive/active systems to explain.

Btw passive /active means the original passive crossovers are retained but split so they can be driven by a set of amps. So a two way speaker would have 4 amplifier channels, and a 3 way would have 6 channels.

Fully active means no passive crossover and crossover done by electronics, either digital or analogue.  This can give even more control over the sound, at some compromise.

I have an old set of AR-LST speakers , a legendary speakier that has a reputation for excellent sound, but difficult to drive and match to an amplifier.
It is a 3 way speaker, but with 9 drivers per speaker, and a rather complicated crossover.
In stock form it needs a very capable amp with lots of power , yet high quality as it is very revealing.
I could never get it to sound quite like I wanted, so decided to run it actively, to see if  I could manipulate the sound into shape.
I had to modify the crossover so that an amplifier could be connected to each of the bass, midrange and treble sections.

While I was there I replaced some of the older electrolytic caps for more reliable and accurate polyprop caps.

3 sets of amplifier connectors, split crossover sections.

Now that the load to each amp was now only a single section rather than the complete crossover,  it is much easier to drive, and I can even use low power tube amps for the mid and treble sections,  giving a much nicer and realistic sound.

But the real advantage is that now I can adjust the levels of each amp and the balance of the overall tone of the speaker.
It takes some time, and persistence, but there will come a result of each amps level adjustment that will result in the perfect combination of room and speaker , and your own taste, that will be very pleasing.

You will find that there is much more distinction between the bass ,mid and treble. They will have more entity and seperation, more openness,  you will simply hear more as you now have  amplifiers operating with specific and achievable functions.

I think this is one of the most rewarding ways to achieve good sound, you are actually making major changes to the speaker/room/taste equation, rather than wasting money on cables, equipment,  or another set of speakers.

You need a good preamp that can easily drive 3 sets of amps, a Supratek of course.

Digital or analogue active crossovers give even more control over the sound, with the ability to do room EQ , crossover frequencies and slopes. But apart for bass applications I'm not a fan of fully active systems, they always sound compromised to me, although maybe essential with a really difficult room/speaker.

Many speakers these days have jumpers on the crossover connections , especially 2 way speakers , so that they can be bi-amped, but it seems few take advantage of this excellent opportunity to customise the sound to your own ears.

Ive been building the Dual Cabernet preamp, with this specific purpose in mind, for years now, but sadly few seem to see the obvious advantages.

My Acoustat 2+2 electrostatic speakers have two panels per speaker , one bass and one treble.

Each panel is driven by a very high power amp, which stats need, so 2 amps for each channel.

I use a Dual Cabernet preamp which has a level control for the second preamp section , which is used for the bass amp.
The master volume control adjusts the overall volume and the level control for second preamp section adjusts the bass panel amplifier level.
The Acoustat is very sensitive to this adjustment and even fine adjustments can make a big difference to the tone and overall quality of sound.

Its hard to site a 7'10" tall speaker that needs to be a fair distance from rear wall, and this precise form of level control is very useful.

But any speaker that can be bi-amped will immediatly be transformed by using the Dual Cabernet and an extra set of amps.

I'd suggest you could spend a pile of money to get an expensive new pair of speakers , that still wont get you where you want to be, when going to bi or triamping will give you exactly what you want.

NOS 6SN7 Tubes

The 6SN7 and its derivatives 6H8C, ECC33, CV1988, CV181, VT-231, 5692 are excellent tubes and eagerly sought by tube enthusiasts after the "best" sound.

I've been buying 6SN7's for more than 30 years and have hundreds of them, with examples of all of the above.

So what is my personal preference , what is the Holy Grail of 6SN7's?

Well maybe surprisingly I'm not that keen on old NOS tubes, mostly because most of them are not NEW OLD STOCK.

The only way you can be sure that a tube from the period 1930- 1980 is a genuine NOS tube is if it comes in a sealed box that has not been opened .

Anything you buy from ebay is suspect, even genuine tube sellers really have no way of knowing if a tube has ever been used or not, or how many hours, and under what sort of operating conditions a tube has been used.

They like to assert quality by using a tube tester and give some vague measurement that really doesn't mean anything.

Quite often the tube tester is more than 50 years old and long past its use by date.

The only way to tell if a NOS tube will give optimum service is to actually measure it in the circuit it is being used in.

Gain and channel balance can be checked and if its a highly sophisticated circuit like the Supratek, the operating parameters can be adjusted for perfect performance. On the proviso that the tubes were in excellent condition to start with.

New production tubes aren't that exciting, the current Sovtek and Chinese 6SN7's aren't bad, but they aren't quite as good as the tubes made when cost cutting wasn't more important than quality.

The tubes I use in my preamps are Russian military NOS tubes with OTK certification.
I buy them in boxes of hundred , never used and they have what I value the most, near identical parameters and performance. They are constant and I know they will work as they are intended to.
You get the occasional bad one, but it would be less than 1 in a 100. And they are all checked in circuit to ensure the preamp has identical performance in each channel.

This is very important for phase response and resultant sound-staging.

Ever wondered where the imaging and sound-staging went with that pair of warm sounding NOS 6SN7 you bought off ebay?

Most likely the tubes are operating quite differently from each other and there is a mis-match between channels.

NOS 6SN7, particulary the early ones from 1930 on are usually microphonic, sometimes quite badly .

Some of the 6SN7 derivatives like the CV181 and the ECC33 aren't  really 6SN7s. They have different plate resistances and will give quite different electrical voltages in a circuit designed for 6SN7's.

This can result in different operating points and distortion figures , which might sound "warmer" or "romantic" .

Nothing wrong with that if it is pleasing to the ear, but it is not what the preamp was designed for.

So playing around with NOS 6SN7's can be a minefield, sometimes you'll get a blast you like, sometimes your shooting yourself in the foot.

Lyrics

Howard got it- Jane Siberry's "At the Beginning of Time"

An otherworldly , spiritual artist that really got to me a long time ago.
Not so much into her now, and I do wish her splendid works were better recorded, but I do still very much like this song.

Here's the complete song, I've never been much into classical poetry , but this is nice.

Tomorrow I'll talk about the NOS 6SN7 tubes I'm sending Howard.

At the beginning of time
Before there were waves
We'd sit in our boats
We'd float there all day

And there weren't any waves
'cause there wasn't any wind
'cause there wasn't any sun
We were waiting for the world to begin

We were waiting in the darkness

Each in our own boat
Each in our own thoughts
Sometimes you could hear people
Talking amongst themselves but...
(someone had a boat with wheels and I said
You're a bit early but I know how you feel)
But mostly it was just silence

And the silence only broken by
The absence of the clinking of the masts
And every now and then a bird would not fly by
And someone would look up and say
What wasn't that ?

We were waiting in the darkness

And one night (or was it day?)
I was awoken from a dream
I was dreaming of someplace like I'd never been
And I heard someone say
Someone's fallen in and they can't swim
So I leaned out and I pulled them in
And he was holding his head
And it was huge and shaped like a fish
And he slid down to the crook of the keel
And when I was sure he'd fallen asleep
I fell back to my reverie

We were waiting waiting waiting
Waiting in the darkness

And you know what I miss most about that time?
It was the quality of blackness
It was soft somehow
In the absence of fear
You could take it into your mouth
And send it out through your teeth
My dear

But the silence...
Oh, if I could go back to those times
I'd take that silence there
I'd take it into myself and bring it back to you
And this is what I'd say

Waiting in the darkness

At the beginning of time
Before there were waves
We'd sit in our boats
We'd float there all day
(or was it night?)

And there weren't any waves
'cause there wasn't any wind
'cause there wasn't any sun
We were waiting for the world to begin

We were waiting for the world to begin

Now?

No.

Songwriters: JANE SIBERRY

At The Beginning Of Time lyrics © Universal Music Publishing ARE YOU UP TO DATE WITH THE MOST AMAZI

And now for something completely different....

First person to name the song and Artist from these lyrics gets a pair of NOS 6SN7 tubes from my stash .
Email me at supra@supratek.com.au if you know the answer.


"And the silence was only broken by
The absence of the clinking of the masts
And every now and then a bird would not fly by
And someone would look up and say - what wasn't that?"

Preamp Gain

All the Supratek preamps have high , greater then 20dB, gain.
There's a pretty simple reason for this, it simply sounds very much more dynamic and realistic than a low gain preamp.
The 6SN7 triode tube is a dual triode, it has two separate sections, independent of each other, except for the heater.
In the Supratek preamps the two sections are cascaded, the first section is the input, the second section is the output.
This results in more gain than a single section, although the total gain is reduced by a step down output transformer, and the circuit design.
I've never heard a single section with the dynamics and ease of a cadcaded design.
The high gain can be a nuisance with many of todays power amps, as they often have high gain themselves,  a power amp should just convert gain into current , but too many power amps are designed more as integrated amps than dedicated power amps.
This is usually so they can be used directly with a CD player , and no preamp, just about the worst sound quality you can get.
So with a high gain power amp and a high gain power amp,  there will be a lot of gain, with the volume control at 9 o'clock or less.
There may also be a problem with noise as with such high gain the noise floor will be amplified.
I still would rather put up with a bit of noise (which you wont hear when the music is playing anyway) than listen to the dull and boring sound of a low gain preamp.
Obviously the best way is with a high gain preamp and a power amp with reasonable gain structure,  avoid those high gain power amps,  which are just integrated amps anyway!
Recent models of the Cortese preamp have  a gain control to fine tune the gain if necessary. It is switchable and can be completely switched out of circuit , but handy if you do need to use a high gain power amp.

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.