THE ONE WAY WAY
There is always parallel development in the audio arts....better speakers create better electronics which create better speakers...and the cycle continues....not quite...because there are classics that have never been topped
There is one area of speaker development that is an important sub-revolution within the current directly heated triode revolution and it is one those gizmologically imperatives like mustard and hot-dogs...one way drivers and ultra-low powered directly heated triodes. I see the clear connection between this trend and the popularity of electrostatic and OTLs. The current revival of interest in the Quad 57 is a reflection of your desire for a virgin aural matrix....one of pristine purity. We are searching here for purity, clarity, an unblemished subatomic harmonic intimacy. It is the kind of feeling we get when we encounter an angel at our local hi fi hangout.
This type of intimacy is intoxicating because it takes us beyond the multiple voices in every multi-driver system. Even when these one driver speakers systems are operating in an non-optimal way they are powerful teachers who are reminding us of how much work we still need to do with passive crossover design.
But their most intoxicating feature is their magnetic horsepower to weight ration. These drivers are like putting a V-8 into a VW beetle. This class of driver is usual above 95 db efficient, and many approach 105 db. And all have extremely favorable/uniform impedance, meaning high, so that single ended output transformers are happiest. In short they reveal the nascent beauty of single-ended triodes in terms of their harmonic delicacy and transient response that normal monkey coffins cant approach. These micro-speakers are trying to be headphones in a box in terms of immediacy and clarity.
Of course I am now talking about the Lowther driver which is becoming more well known and the one way Fostex driver, which is very popular in Europe and Japan but still unknown here
With these drivers 8 watts is much too much horsepower, and you can drive these speakers to their limits with probably no more than 1 watt, which means you can design an amplifier for ultimate refinement.
My experience with these drivers is limited but it doesnt take more than a few minutes of listening to get their virtues and their challenges, and I want to put them in two categories: (1) amplifiers (2) cabinets. All of these challenges arises out of the unique aural personality of these drivers which arises because they are basically the size of midrange driver, which are asked to do the job of a full range system. Even when you put these mighty midgets into a horn cabinet they can not produce authentic bass response...and that shouldnt be a problem, and (2) they require a non normal single-ended triode amplifier.
There is an essential paradox here: the outstanding virtue of these drivers is their midrange clarity, but when used with a quasi-horn cabinet the larger box and the universal horn coloration infects the midrange robbing of its ultimate clarity. Anyone who tells you that their horn has no coloration, and is not storing energy deserves a gift of new batteries for their hearing aid. But again...you pays your price and you take your choice...there are no free rides in the audio arts.
This means that the speaker cabinet requires the utmost skill in tuning its resonances which all speaker cabinets have....it is a matter of getting them just right for your system which includes you, your room and your amplifier and cables. The Lowther/Fostex journey is NOT SET EM UP AND FORGET EM. This is more like building your custom hot rod motor, and that means you must experiment with various speaker cabinet tuning techniques, which I think is great fun.
Cabinet manipulation is how you deal with the unique personality of the lower register of Lowther/Fostex.
To deal with these speakers unique upper register harmonic requires that you use a non normal single ended triode amplifier, and this is an area that needs more exploration. The conventional wisdom is that a 2A3 amp is better than a 300B, and some assert that a 45 is even better. With the Lowther/Fostex speakers there is a papery distortion in the upper harmonics, which to my ears sounds like it is around 3 kilohertz there about. I dont know anyone who has designed a passive notch filter to smooth this out, or anyone who has yet built this type of filter into their input circuit, but this quirk must be addressed or you will grow to hate these marvelous speakers.
The resonate character of your output transformer is also very important, and in Japan the Lowthers are very popular because they are used with the best quality OPTs. These speakers demand the best output transformers. I also think that using a input/driver circuit that is RC coupled is an advantage because you can use the coupling caps to flavor your amplifier to suit your speaker. The luscious warm ripe aroma of oil caps should be considered. I also suggest that aluminum electrolytic caps in the power supply are off limits and you should use as much oil capacitors before and after your choke and be sure to use and experiment with different brands of TUBE RECTIFIERs.
What I find so wonderful about the Lowthers is that you can order them with either the Alnico or neodymium magnets. There are connoisseurs for each...but both are vastly superior to the ferrite magnets in your normal monkey coffin.
A GIZMOLOGICAL OPPORTUNITY:
These drivers would be much more popular if they didnt demand the construction of a complex horn cabinet, which means that they would need a bass driver to compliment them. Such a driver does not now exist and would have to have a complimentary horsepower to weight ratio to match, and it would be expensive. Let me suggest the following gizmological opportunity: an eight or ten inch driver with a paper cone that is designed to produce 600Hz down, and has either Alnico or neodymium magnets and is designed to compliment the full range driver.
The proper way to use this driver is by using a simple first order filter built into the input circuit of the amplifier that is driving the full range driver. This would be a very small capacitor and resistor, thereby preserving the integrity of the no-passive crossover design. A separate single-ended amplifier would be needed for our new woofer, and the OPT for this amplifier could be maximized for its limited lower frequency operating range by having higher inductance, and it should have some variable feedback adjustment.
I know there is great interest in this ONE WAY REVOLUTION so any info you have would be valuable to all of those who surf the Triode Guild.
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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