OTLs and Quad
- Hits: 4375
The history of this amp's circuit starts twenty five years ago when Julius Futterman, understanding the limitations of the output transformers. patented an Output Transformerless design. The clarity of the sound has been unsurpassed to this day and a cadre of serious music listeners has remained steadfast to the genius of Julius Futterman. The man was the embodiment of integrity in the audio world and working in his small shop pursued his calling in furthering the art of music reproduction. Had this inventor lived in Japan. the government would have decreed him a national treasure and allowed him to live his last years on a national pension. As it was, he doggedly pursued the creation of honest amplifiers without recourse to the coarser aspects of business such as fads, hype, or cosmetics. His dedication to perfection is typified by the hand wiring of power transformers and personally checking the accuracy of each piece in the unit. Is it any wonder that his amplifiers have worked continuously over a generation without displacement of "so-called" higher technology.
Before his death, Julius sold the rights to his OTL circuit to Harvey Rosenberg of New York Audio Laboratory, Inc. Harvey recruited Ted Hammond, a genius of tube circuits in his own right, to refine the Futterman circuit. Brian Clarke was enlisted to create a computer model of the Futterman circuit to bring this "Classic" circuit to modern electrical standards. This cooperative team has refined virtually every aspect of the original Futterman circuit, including the input circuit, screen regulator, power supplies, bias and feedback networks. The amount of effort this team has put into power supply design is evidenced in the special low impedance power transformers that are used in these amplifiers.
Attention to parts quality necessitated use of "red" Wima and photo flash caps. The mechanical layout is bulky in size and depth but with a small fan in each chassis the amp's critical parts, resistors, etc., never exceeded room temperature. The conservative construction and rating are indicative of the intent of the designers to build a product for continuous long term use of a generation or longer.
Although we are describing one amp model, there exists a family of OTL amps; some specialized for particular drivers. The OTL 2 for instance is a 25 watt triode midrange and tweeter amp which is highly prized by the Japanese for exotic tweeters and horn tweeters in triamp systems. The OTL 3Q is a model custom built for the old Quads and Quad 63. (One pair of output tubes removed from each amp plus external capacitor box to roll off the base @ 100HZ). And in the future there will be a Futterman amp for all electrostatic head phones including the Stax models. The OTL 3 is a doubled mono amp and equally capable of driving cones and electrostatics.
We have placed the OTL on a variety of speakers and on each occasion have been confounded for proper verbal description. How do you describe an UTTERLY TRANSPARENT sound? Any description becomes in essence a listening of other amp's colorations. For instance, small chamber pieces, vocal & instrumental, are rendered with a "you are there" realism-such as the delightful Monteverdi madrigal "Tirsie Clori" (Book Seven) on Harmonia Mundi 1068, as sopranos and tenors trade off lines playfully. Or the left channel violin exchange with the right channel violas (2 bass viols centre stage) opening the Andante movement to the Brahms's Sextet, Harmonia Mundi 1073.
Try as hard as you can to focus the mind on the Futterman and you can't hear its sins. You can hear the faults of the preamp cartridge and speakers but not the amp. The sound superceeds "laterally open" to project a "frame-less picture" of the stage performance. In fact, the Quad/ OTLs can occasionally transcend the best available audio (from say 400 to 4,000 HZ) into a hackle raising "live in your living room'' performance! Just try listening, for example, to the female vocalist on Tiden Bara Gar, Opus 3 79-00. Here is a physical presence, a focused resolution, matched only by the latest Bob Fulton big Premier system (which includes a "time aligned" crossover network plus direct coupled preamplifier). Hear as well the ambient sounds splashing off side walls and rear sound-stage. In line with the picture analogy one observer speculated that the picture contained subtle pastel tints as well as oil pigments. The highs are superbly defined without edge or hardness, and are as extended (more so) than any other amp known to us. Amplitudes of sound level glide steplessly and seamlessly through a gradient to the highest levels. Bass response was surprisingly good, if not in Quicksilver's class. Many other amps sound FORCED and unnatural in side-by-side comparison. Coupled to a phase aligned and phase coherent speaker, the imaging capabilities are well nigh perfect. We cannot offer scientific proof to its superiority but are content to bear yet another testimonial. Every serious audiophile should get the opportunity just once to audition the Quad/OTL system.
Be forewarned that the amp is considerably load sensitive. Any speaker impedance lower than 6 ohms reduces power to the speaker. At 8 ohms the amp produces 75 watts and at 16 ohms, 125 watts. The audiophile must choose a high definition, high impedance speaker. On typical cone speakers with low impedances in the bass frequencies, the amp invariably becomes bass deficient and soft. Bass reproduction is closely allied to the damping factor a speaker needs, and the damping factor of 60 of a Futterman is an excellent compromise. On the other hand, it is the ideal amp for the old Quad's, Quad 63's, Acoustats, and other low coloration speakers. It is estimated that fully 90% of the Futtermans in the field drive Quad's, and this combination of ancient designs is startingly correct. Audio has not progressed as far as our hopes would have it. Do not listen to false prophets. Harvey Rosenberg, Ted Hammond, and the guiding principles of Julius Futterman are leading us.
AUDIOGRAM. P.O. Box 27406, St. Louis, MO 63141, 1983