SNEAK PREVIEW: THE 300B KARMA SUTRA TEST PROCEDURE
As you will soon discover, when you read the exciting fall issue of Positive Feedback, I am embarking on a intimate examination of the different sensual pleasures derived from many different brands of 300Bs : the 300B harem. Because of my obligation to you, as Guildmeister of the Triode Guild, I am describing my test procedure for audio intellectuals which may be one of the most intensive investigation of this directly heated triode eroticism. By the end of October my full erotic conclusions, which may be very neurotic, will be ready, and I hope they dont drive you psychotic....we cant be sure because triodmaniacs are, by their nature, unstable.
TUBES TESTED: Sovtek, Svetlana, KR, Western Electric, JJ/Tesla, Golden Dragon, Valve Arts.
(1) Single-ended /transformer output stage: I have now configured my own custom amps so that there is a separate adjustable tube regulated power supply for the output and input/driver stage, so I can dial in exactly the ideal voltage for each output tube. While the Magnequest FS 30 output transformer is designed for 60-75 ma of bias current it is easy to hear when a tube is at its optimal point as I adjust the voltage. This may be shocking to you but, in the same way you adjust the tracking angle of your cartridge and hear exactly when it is optimal, so it is with a 300B and its output transformer. A difference of ten or twenty volts is apparent. At one particular voltage the sound locks in, and it is not subtle.
This is the only fair test of these tubes because some tubes sound best at anywhere from 350 volts to 450 volts. Of course having adjustable independent tube regulated power supplies for the output and input stage is a significant sonic advantage because it enhances the image stability, creates a much more refined presentation, brings tonal quality to another level, and most importantly, it releases the tubes do to their dynamic best. It confounds me that this notion...independent regulated power supplies for both the input and output stage (so that they are completely isolated from each other), which is as old as the hills, still alludes mainstream triodemaniacs. If only a few of our leading triode savants would try this experiment they would realize what a shocking advancement this is in the single-ended performance. I will tell you in advance that when going back to a tube rectified power supply many of the sublime differences in these tubes are masked, especially their dynamics.
Can I be more subtle and poetic in explaining this point? Think of a regulated power supply as making love without a condom, and using a tube rectifier or solid state rectifier and no regulation as making love with a workmens rubber glove on. Did you understand that pure guy analogy?
These amplifiers have no electrolytic capacitors, because they are tonal arsenic, and only use oil caps, or polypropylene in the power supply. I use pre-1960s 6SN7 input tubes in my classic RC front end.
(2) Push-Pull/transformer output stage: In the fall issue of PF you will read my extensive review of the Sun Audio of Japans very deluxe and refined push/pull 300B which uses a transformer phase splitter. This 20 watt amplifier, which uses all Tamura transformers, is one of the most refined push/pull amplifiers I have ever heard, and I love it. Hello out there...300B push/pull is being completely ignored in America, and at this level of refinement it is a exciting new form of eroticism.
For this test I have modified the Suns ( soldered four wires...big deal) so that I can attach my independent adjustable tube regulators to the input and output stage so I can hear, again, optimized operation of the different brands of 300Bs. The advantage of a push/pull amplifier, of this quality, is that it has more coherent top to bottom dynamics and is lower in overall distortion than a single-ended circuit. While this amplifier doesnt have the glorious midrange of single-ended circuits, but it does have a more coherent bottom end and a very uniform wavefront dynamic that I wish single-ended amplifiers had. The Sun amps dont have the normal discombobularity of those whopper pentode push/pull amplifiers because they uses a Tamura transformer phase splitter. I am extremely impressed by this amplifier and it offers a completely different, and fascinating vision of 300Bs aptitudes, which is important in any 300B evaluation. Thats right boys and girls push/pull 300Bs are way cool, and give us another insight into the aptitudes of this tube that single-ended circuits can reveal.
(1) Mr., Normal Gifted Listener SET Amp: I am using Solo Electronics $1,750 stereo 300B single-ended amplifier because it is very normal and is very affordable. There is nothing adjustable on this amplifier (it is completely stock) and the question is..... does it reveal the big differences in the different brands of 300Bs? This is the nitty gritty of this test...at what level of amplifier quality does the differences in tubes become significant, or does it really make sense to buy $300 tubes for a $1,750 amplifier?
(3) David Bernings 300 B SET ZOTL: This is the most transparent and fastest five watt amplifier in the world because there are no capacitors or inductors from input to output. There is nothing better at revealing the nascent nature of each 300B brand. This is the amp camp for frequency extremes, transient response and horizon like wideness and midrange whole-osity... but ...the amp has been permanently set at one voltage for Western Electric 300Bs, which may not optimal for other tubes. This is, again, the worlds only direct coupled front input to output single-ended amplifier where there is nothing between the output tube and driver. This amplifier also has a minus 120 db noise floor, which is completely quiet spooky, and has fully regulated power supplies. There is a paradox implicit here: this is still a hand made amplifier...maybe ten or twenty have been made so far, and that means my conclusions about tubes with this amplifier are not yet relevant for the masses...but....consider this ZOTL circuit the ultimate astronomic telescope into deep directly heated triode space....and you, the readers of PF deserve this level of seriousness.
TANNOY WESTMINSTER ROYALS: I am using these speakers, which I finally moved into my home (with the aid of a hydraulic lift and four moving men), with both the Marchand tube crossover and custom made passive crossovers.
In critical testing like this it is absolutely essential to eliminate the passive crossover fog that is inherent in all dynamic speakers. Let me say this more forcefully....in evaluating amplifiers, to know their true nature, they must be experienced directly connected to the driver...without the impediments of the passive crossover. This is the only time you are listening to the amplifier and not a bunch of inductors and capacitors. This means that I have to use a separate amplifier on the woofer and tweeters, and because I do not have four of each amplifier I have connected two of the same amplifier to one speaker and listen in mono, and then I try two of the same amplifiers only on the woofers and then only on the tweeters. This is a valuable procedure because it gives me a much better sense of how each brand of tube does below and above 1 KHZ, and thereby permits me to get a better sense of their individual strengths and weaknesses. Is it possible that there are ideal 300B woofer and 300B tweeter tubes? Am I developing a new optimal 300B strategy? Does a bear shit in the woods after eating a pizza with pepperoni?
It would be absurd NOT to test these tubes with a passive crossover because, you the gifted listeners of America, have not yet made the ultimate commitment to triode knowledge and still use passive crossovers....so I have also constructed my own hot rod passive crossovers so that all of the series inductors..the inductors that a signal passes through are AlphaCore Silver foil inductors and all of the parallel inductors are AlphaCore copper foil inductors. The capacitor in series with the tweeter, which makes up the 6db/first order filter is made up of a blend four different brands of polystyrene and polypropylene capacitors that I have blended for optimal tone and transparency. The capacitors used in the 12 db woofer network are Hovland Music caps. After years of experimenting with passive crossovers I have concluded, as you know, that while it is impossible for a speaker manufacturer to put ultra-high quality parts in their crossovers because of cost, that doesnt mean that we cant upgrade them...it is very easy.
But let me be clear about this...I loose, you loose about 30% of the glorious directly heated triode bliss when using passive crossovers.
The Tannoys with their Alcomax magnets and 100db efficiency present a single problem for me...I cant make the amplifiers clip in my home without having the police come to my door, and cause ear damage. I speculate that I am always listening to these tubes in their optimal operating region of below one watt. On the other hand there is no other speaker that will reveal the dynamic character of different brands of 300Bs and their tonal refinement and complexity. Let me assure you that I can not think of any other speaker, other than the Sunlight Engineering 308, that can reveal the vast differences between these different brands.
B&W CDE1: These are $1100 a pair mini-monitors that I use to determine how the significant difference in these tubes translate into a relatively normal speaker.
SUNLIGHT ENGINEERING 308 NOT: I am in the process of designing new cabinets for these 55 pound drivers that are worthy of them, which is not an easy task. I am considering some of the secret construction techniques that King Tut used to build his pyramids, and other eccentric monumental notions, that will shock and delight you all, and be applicable to your own speaker building projects.
All cabling, interconnects including wiring within the passive crossovers is AlphaCore silver foil.
PREAMP: I use the new Marchand passive stepped attenuator preamp because... there is nothing in it to distort the aural matrix. With this unit the signal is passing through two resistors before it enters the Marchand tube crossover.
MARCHAND TUBE CROSSOVER: My articles about this unit tell the story. The only modification I have made to this unit is to change the stock coupling caps to polystyrene units.
SOURCE MATERIAL: I use original master DAT tapes and master CDRs produced at Ambient recording studio as the ultimate pure digital input. I am sorry I cant get the Ampex tube tape recorder in my home. I do not have my vinyl system set up in my living room now, but hope to rekindle my VINYLMANIA soon.
ACCESSORIES: These are absolutely essential for any critical evaluation, and I don't understand why other audio critics don't list theirs: Jasmine incense, slivers of mango, peeled grapes, hot coconut oil, masseuse, cigars, silk kimono, candles, whips, chains, handcuffs, Vibrapods, VansEvers AC line cords, red M&Ms, round toothpicks, and Godiva Truffles.
CAVEAT EMPTOR: All reviewing of audio equipment to a great extent is completely absurd, because it is all about perception, emotion and imagination. While there is a world wide consensus about the erotic possibilities of 300Bs, it should be obvious that what turns one man on, puts another to sleep.
IN SUMMARY: I am a totally freaked out 300B maniac just doing my job...shredding the perimeter of triode knowledge, testing the different 300B brands in four different types of amplifiers as a way of determining the deep and subtle nature of their differences. I am listening to these amplifiers with their output stages directly connected to the speakers drivers and with passive crossovers, and using digital master tapes and CDRs as a source material.
If anyone has any suggestions on how to make this test procedure more revealing let me know....I love learning new erotic tricks.
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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