Couch potatoes are right....relax, take it easy. Take it as it comes. Stop fussing and bothering with circuits...just enjoy the music.

But some men are blessed and cursed with highly developed dog DNA, which makes them, in many ways, just like dogs...which brings me to the most fundamental question of why we keep on searching for more subtle and mysterious forms of musical ecstasy? The answer is the same reason why dogs lick themselves....because they can.

Because this sports is all about the search for mystery we must fully embrace the mysterious dimensions of the audio arts, and in the current genre of ultra DIY there is nothing more delicious that the recapitulation in a modern format of the oldest; let me repeat, the oldest forms of circuit topologies; those which take us back to a time when there was a radio on the living room table and a big lead acid battery underneath it.

My father told me stories about the men who went from door to door with their battery filled horse drawn carriages exchanging batteries, and at a time when a hot dog and a coke and French fries cost 5 cents, battery charging was expensive...radios were a luxury item, tubes cost a fortune, and the radio was only used for a short time each night to save the DC juice.

When you look at those primal tube circuits what you see are input transformers, plate chokes, interstage transformers, single-ended output transformers, and parallel feed output transformers...all surrounding and connected to a two stage amplifier with both tubes being directly heated triodes, because there was nothing else. All of these iron elements were used either because, there was no other way to get the gain and drive voltage, or, to save money. The idea of wasting a few milliamps of DC current with a plate resistor made no sense...and a plate choke, because it was more efficient and didn’t waste current made sense.

Because we love to dance in the dialectical paradox of the audio arts we are once again deep into these primal topologies, but not because we want to save money...because today the opposite is true...DC power and tubes are relatively cheap and "iron" is expensive.

The reason this is such an exciting time in the thermionic arts is that there is a community of ego secure men who are prepared to open themselves to circuit notions that have become the mainstream. The searcher, searches and that means everything is worthy of our investigation and experimentation..


After reading Nobu Shishido’s article in Glass Audio in which he published his schematic of his interstage transformer coupled SET amp, I began to correspond with him, and then we started to talk regularly on the phone, and then shortly three of his WAVAC amplifiers arrived in the a very big shipping container, and I had a chance to live with them for about six months. This was my first experience with the unique aural matrix of interstage transformers, and their unique aroma was apparent on the Tannoy Westminster Royals. In my articles about them I first coined the expression HARMONIC WHOLEOSITY...and the quality is indescribable, and the differences obvious when compared to other topologies. There is an organic unity to the sound that is lost when the interstage transformer is absent.

Let me quote Nobu here from his second Glass Audio article:

Now, to be honest, I do not why IT (interstage coupling) offers better sound, nor do I know why a high value resistance, in the order of several kilo ohms, in the signal path tends to deteriorate sonic quality. Here our oriental culture differs from western in that we Orientals are less eager in analyzing "why it works" than finding out "what works and what not": a culture rooted on empirical study rather than analytical study. A good example is Chinese medicine which works but does not lend itself to western "scientific" analysis. SE amps would not have been accepted if one had insisted on "scientific" explanations. It is not, however, that we do not want to know "why".


Years latter I once again had the good fortune of living with the Sun Audio push/pull 300B amplifiers which used the Tamura transformer phase splitter, and again I remark that there was an organic unity that is absent in 300B push/pull amplifiers that use conventional tube phase splitters.....and around that time we started to see two American companies, Wavelength and Cary Audio create amplifiers that used interstage transformers.....

Along comes the Internet and we notice that all over the world, because we are connected, we are learning from our bros’ experiments and what are we hearing?...."Try plate chokes, interstage transformers and input will love they way they sound"...and because we trust our tribal brothers we start to experiment...and soon there are many "transformerwindermeisters" all over the world making a new generation of the ancient iron elements, and that is way cool, because we have so many options.



For three weeks surrounded the new year I immersed myself into deep experimentation with single-ended topology, experimenting with different combination of tubes and tuning, tuning, tuning, tuning.....and listening, listening, listening....beyond the beyond...

Now that I have returned to using the Marchand tube crossover I am able to more deeply explore the very subtle aspects of our beloved input driver circuits, and what follows is a works in progress because, as you know, for a pilgrim on the path experimentation never ceases.


This is also a clear example of how the Internet is expanding our imagination. I think I can trace the beginning of this virus all the way back five years to my encounters with Nobu Shishido..... but it is the most recent Internet encounters with Jac Vanderwalle (Germany) of AVVT who turned me on to the new AV8 tube (the first DHT designed specifically as a driver/voltage amp tube) who then turned me on to which is Mattijs de Vries website (Holland), which illustrated, with schematics the newest concept for single-ended circuits...and it was, again, the circuit topology used by very first amplifiers at the primal roots of the audio arts, from radio days: an input transformer feeding a directly heated triode, with an interstage transformer driving a directly heated triode connected to a single-ended OPT.


Anyone who roller skates on the edge is aware that for a number of years there has been growing interest in the use of input transformers, plate chokes and interstage transformers, which have totally disappeared from mainstream audio orthodoxy, because they are so "old fashioned". On the other hand line level input and output transformers are an essential aspect in pro audio!

In 1994 Nobu Shishido’s interstage coupled 300 SET circuit was published in Glass Audio, and at about the same time Sound Practices started to illustrate the modern versions of these classic "iron" ideas. Flipping through Cositruire, the Italian audio magazine, also illustrate the growing interest in this primal circuit notion. And while more and more are experimenting with the use of plate chokes, input trannies and interstage transformers there has been little communication to you about the effects these devices have on your aural matrix, and that is my challenge here.

Of course this is a difficult challenge, because to once again I return to Nobu’s is very difficult to describe in words what are the apparent benefits of these devices...and they may even be un-measurable...and if they are measurable, the correlation’s between their performance and perceived sound effect is elusive.

CAVEAT EMPTOR AGAIN: What I will describe is true for my audio system, and I can not assure you that you will experience the same in your system...but none of what I am describing is subtle....there is a major change in my aural matrix, in terms of my most important musical value..harmonic whole-osity and dynamics. Also remember that I use independent tube regulated power supplies on all of the voltage rails of my amplifiers, excepts the filaments which have solid state regulation. My input circuits and outputs have their own independent supplies so there is no interstage-interaction.



THE 6SN7: There are better tubes in some regards (much lower output impedance), but this tube is extremely popular for a good has great readily available in two hundred different NOS vintage varieties, and is very easy to work with, and I had about twenty in my inventory.

I decided to start with a very simple direct coupled configuration eliminating the coupling cap between the two 6SN7 stages. I built four identical laptop SETs, because this gave me the basis of comparing any modification I made to the "basic" configuration.

By itself I can highly recommend this configuration. It is simple. It works very well; is clear, dynamic and if nothing else existed on this earth I could live with this circuit, and it had no problems driving any of the wide range of DHT output tubes I used. All of the cathode bias caps were bypassed with small oil caps, and I used four identical RCA circa 1960 tubes.

There are many other tubes to experiment with, and the laptop design concept is perfectly suited for this process because building a completely new amplifier takes about one hour and so very little money.

And there are some very exotic tubes...... from the Western Electric triodes to directly heated triodes that are worth exploring...but for now I chose the most common, and easily implemented. I have these exotics and will report my results as they occur.

My initial experiments (remember I bi-amplifier with a tube crossover) lead me to use an .1 mfd oil coupling cap on the dedicated woofer amplifiers and a .083 oil cap on the tweeter amp. All of the parts used to build this input circuit can be purchased for under a few dollars....except for the coupling caps which I already have a large assortment. THIS BECAME THE "STANDARD" CIRCUIT FOR WHICH I JUDGED ANY FURTHER MODIFICATIONS.

The good news first: There is a reason that the world’s "transformerwindermesiters" are now deep into input trannies, plate chokes and interstage transformers, where only a couple of years ago the only place you could purchase them was in Japan. Your demand for more ecstatic tonal whole-osity means that your hard earned dollars are being spent to create greater musical mystery in your living room, and when properly used all of these devices will take you down the path to a far away place deep in your musical soul. They work. They do their job, and this, once again, is the eternal paradox of the audio arts....want to go forward? Go back!

Let’s trace the transmigration of this advanced thermionic coolosity:

FACT: Japanese audiomaniacs also study on the potty, and what they study are those amazing Japanese tube reference books that have schematics of literally every tube amplifier ever manufactured in America beginning with the first....and what do they see being manufactured in the 1920s... just two directly heated triodes, input trannies, plate chokes and interstage transformers, because, during the good old days, that was the only way to design a tube amplifier...there was no other way....and if you have the fire, the intellectual curiosity, and live in a culture that admires the beauty of the past, which is eternal, you get out your soldering iron and start to explore.

So it makes perfect sense that Japan and Italy ( I call Italy the Japan of Europe, in terms of art) were leading the way to this advanced "iron" aesthetic.

Before we continue, the bad news: The only bad news is cost. Assume, for one minute, that your input tube can cost you anywhere from $20 to $135 (AV 8 (new) or Western Electric 417 (NOS) are selling for $135), you are faced with an additional cost for input trannies, plate chokes and interstage transformers which can add from $300 to $700 to the cost of two channels. Of course you can use just the plate choke or interstage transformers and save money, but, no matter what path you choose, as you can see, this become an expensive exploration. Remember all of this "iron" was originally developed to save a couple of pennies.

There are a growing number of manufacturers in America now using interstage transformers and plate chokes: Wavelength. Doc Bottlehead, and Cary Audio. The question is, "Are they worth the expense?". The good news is YES but...if you want to sway to their beauty you have to pays. So sorry. The advantage here is that none of these parts will ever wear out, and they are very easy to install and use. They are worth the cost.


I want you to start thinking of yourself as a gourmet cook. We are about to cook up an input circuit, and in the same way there are literally thousands of different ways of creating recipes by combining the same basic ingredients, we can do the same gourmet blending in creating our input stage....and we can with the same basic "components and electrical forces" create literally thousands of "right" recipes. Try and get into this notion so you can begin to imagine your creative possibilities. Nothing I am going to explain is technical.....all that I am doing is creating a thermionic aesethetic meta-structure for you to consider.

Here is the challenge facing us...How do we take the teeny beensy little audio signal that is entering the input stage and create enough gain, in a linear way, with sufficient drive to properly drive the grid of the output tube? Do we create gain with tubes, or transformers? Do we use capacitors as coupling devices between the various tube stages, direct coupling or magnetic coupling? What is the proper way to load the input stage and driver stage? Do we use one stage or two stages?

The above questions keep our Japanese audiomaniac brothers very busy at the audio coffee houses of Tokyo...and these are the profound speculations you are engaged in.

TUBES: think of the hundreds of different tubes that can be used for input/driver tubes. There are single triode, dual triodes, all indirectly heated. There are pentodes, and combinations of triodes and pentodes in one tube. And then there are the new breed of directly heated triodes driver tubes.

The gourmet cooking begins the minute you pick the tube you want to use...for what ever reason......and now let’s get down and have fun.....

We can literally surround this tube with different forms of "iron element" with (1) input transformer, (2) plate chokes, (3) grid choke (this is new) and (4) interstage transformer. Every inny and outy of this tube is connected to some form of transformer/choke. It is possible to use all, or use some combination, or just one of these "iron" elements. The iron element is really nothing more than an analogy for an electrical force that will interact with the tube and transform its ways that are still mysterious to us...though very apparent, and well known technically. These electrical forces: resistance, inductance, capacitance, reactance, and magnetics, can be used in many different ways at different positions of the tube, the grid, plate and cathode, and this is exactly like what a gourmet chef does with his basic "iron elements" ingredient.

For example: There is a school that follows this path:

A single medium gain indirectly heated triode with a 1:2 step up IT, interstage transformer, to get the drive voltage needed for the output tube. Here "magnetic" coupling takes the place of a capacitor.

Others, like myself like the combination of plate choke and 1:1 interstage transformer, but I am in the process of exploring others.

An acquaintance Jim Dowdy has eliminated all plate resistors and is on the way to removing all grid resistors and has replaced them with chokes... swears by an input tranny connected to a plate loaded AV8...and loves the Magnequest Para-Feed interstage transformer

Some swear by using an input transformer for gain and then using a medium mu triode/capacitor coupled to the output tube.....

As you can see the blending possibilities are endless, and every time you change the "iron" blend, with exactly the same tube there is an immediate and obvious change in your aural matrix.

Or....think of yourself as a "iron juggler", which you know is a very high archetype, and you are juggling all of the electrical interactions in your input stage by what kind of "iron element" you put where....and that is the joy of using different electrical forces to tune your harmonic to a higher tune.


As you know when you get really high on the path all of life tastes like a perfectly barbecued steak...that is made from harmonics and it smell, tastes and sounds exactly the way it should...and this is all about tonal wholeosity, which is the easiest and the most difficult thing to achieve. There are no guides, and there are no measuring devices that can be used. None of this matters of course, because we (not those deaf guys over there) have ears that were specifically developed to detect subtle harmonics, because that was the key to our survival during four millions years of sitting, huddled in darkness and not wanting to get eaten by a Saber Tooth Cat.

What is the meaning of musical intelligence? Survival, and that is why TONE is so central to humans musical sensibilities, and why it is the primary consideration in the creation of any audio system.

All of the manipulations and experimenting that I am suggesting "around" your input stage is that you can discover what tune of tone gets you off. This our way of tuning our input stage, the way we tune our musical instruments, and our cars and motorcycles.

Because tone is the most important consideration in ever audio system, it is the very attribute which is weakest, and that is because every audio system is a "chaos" system. There is absolutely no way that anyone can buy a combination of audio equipment and plug it all in, and together and expect it to sound right. It can’t, and if you passively accept that state of tune, then email me and I will send you, free of charge, new batteries for your hearing aid.

The reason that I am so excited by this sort of "iron" play is not that I am inherently in love with input trannies, plate chokes and interstage transformers...NO...I am in love with having even more tuning choices and options....we all now have more freedom of expression, and nothing is more important to me, and you, and our fellow freedom loving audiomaniacs all over the world.

Before I continue I would like to ask you all to re-consider the one mile fire-walk I suggested as a way of making contact with your inner warrior. This is a good idea because what I am about to reveal could really cause a major eye twitch.

Like everything else in audio, the gizmo is endowed with the spirit of the creator. That’s right, each and every "transformermeister" have their own unique style. You could order a transformer with the same specified electrical value from the worlds best transformer winders and each would have a completely different personality, and that is a good thing.

These different personalities becomes another multiplier in our equation, and a way to keep busy for the next 100 years. Why not have an amplifier that has one brands of OPT, a different brand interstage transformer, and plate chokes made by someone else? Who wrote the rules?

Only you know how to cook perfectly to your taste, and it is evolving and restless and wanting more and more of what it loves best...surprise opening breaks through the clouds and there before you is a new fertile valley that you never knew existed, and it is just down the path........


I remind you that, five years ago, I was the first to report on Nobu Shishido’s WAVAC amplifiers, all of which used his interstage transformer coupling, and SUN audio’s 300B push/pull which used a transformer phase splitter. In both of these cases I noticed a similar, (if it is possible to make the comparison between push/pull and single-ended) quality, and this is when I started to use the expression HARMONIC WHOLE-OSITY. Compare the taste of skim milk, which obviously tastes like milk, to farm fresh, thick with cream milk..right out of the bucket....I think that describes the harmonic advantage of using "iron elements" properly.

It is very difficult to talk about harmonic whole-osity in America because so many entrenched elements are antithetical to this aesethetic. Complicated speaker/interconnect wires, complicated high powered amplifiers, digital audio, and ferrite magnet speakers are absolutely the worst combination for producing tonal whole-osity, and this is the dominant mode in America.

Here is what I hear: the quality of voices become fuller, richer, more resonant..... what I mean is that the emotional impact of voices is expanded whereby their tone become filled with juice of the human spirit....more vocal authenticity. This higher state of tonal authority is also very apparent in the tone of all instruments, which also become more three dimensional.



I notice this characteristic both in the WAVAC and Sun extremely tight bottom end that has a very uniform wave front, which means that the way the bass moves through the room and impacts our body is much improved, and that includes an improvement in transient response and clarity.

The reason I created the expression, "Putting the bullwhip back into the bass", is because that is the impression I had.....of a bullwhip type snapping transient response that I never experienced before in single-ended amplifiers...even with regulated power supplies. I can no longer say that single-ended amplifiers do not have optimal bass response. The secret to a more uniform low end energy patterns is plate chokes and interstage transformers, and regulated power supplies.

Here is a warning: use the wrong interstatge transformer and you are going to give up the best of the your bottom end....and you may loose that top end sparkle. At the moment I am not using a IT on my tweeter amps, just on my woofer amps...

There is an alchemy of the sublime with both the plate choke and interstage transformer because the delicate becomes more delicate and the dynamic becomes more dynamic and tone is taken to a new higher place wholeness. What this simply means is that the input driver stage is freer to do what tubes do best when they are surrounded by the right electrical forces delivered to the scene by various "iron" elements.

It would be irresponsible to avoid this issue...all of my voltage rails are tube regulated which is NOT NORMAL in amplifiers that have plate chokes and interstage transformers... with the voltage rail for the input tube/plate choke/interstage transformer completely independent from the output stage power supply. I am certain this is making a big contribution to the outstanding performance I am achieving and confirms what I experienced when I installed a completely separate regulated power supplies to the Sun’s amp input and output stage. This translates to a much higher resolving power and a rock solidarity of presentation no matter how loud my system is playing. This is so easy to implement I do not know why more of you don’t try it.

All of this fancy iron fandangling has taken King Tone to his richest, most authentic level I have ever achieved, and I aint no slouch in this department...and this process is just beginning.

I will shortly be embarking on my experiments with the AV8 as a driver tube which will be used in various configurations of plate chokes and interstage transformers...and there are other tubes.

At the moment I have limited my exploration to Lundahl and Magnequest plate chokes and interstage transformers, and will shortly have Bertolucci plate chokes.....more thrills, chills and spills are on the way, including another one of my history making reports.....

GRID CHOKES....Mike Le Fevre has created GRID chokes, and this is a new thing that could be very compelling.....