OTL/OCL means “Output Transformer-Less” and “Output Capacitor Less”. In an OTL/OCL preamplifier, there is no coupling device between the preamplifier and the power amplifier, that is, the preamplifier’s final output tubes are directly connected to the power amplifier. Normally, an Output Capacitor or Output Transformer for separating AC music signal from the DC operating potential; if this is not done, the latter will destroy the power amplifier or loudspeakers.
But these two types of coupling devices are effectively obstacles to signal transmission that add their own character (color), increase distortion, and consume small signals according to physical efficiency theory. In addition, they limit signal dynamics.
Because of all these adverse effects, OTL/OCL has been considered the best solution for amplifiers in order to maintain signal purity.
* Removing these two coupling devices from the signal path, gives the best results.
* No coloration is added to the musical signal.
* Extremely detailed expression, natural harmonics and subtle musical decay are achieved.
* There is the lowest distortion possible due to the absence of coupling parts.
* The widest musical dynamics are attained.
* Some circuit experts might worry about DC potential in the music signal, but there is no need to worry. Allnic uses a “floating power supply circuit” which prevents the creation of any DC potential in the first place.
Remote Controlled 61-step ‘Constant Impedance’ Attenuator
Mr. Park has completed development of the world’s first 61-step, constant impedance, “bridged” type attenuator. Allnic’s new attenuator is now the most sophisticated on the market, and we believe, without a doubt, also the absolute best sounding. With fixed impedance and no (± 0db) channel unbalance at any volume level, the new attenuator will astound users with its elevation of the fidelity and purity of any system in which it is used.
This revolutionary and currently unique, oil clutched, motorized attenuator will be standard equipment on the L-8000 preamplifier and L-10000 OTL/OCL preamplifier.
LCR Type RIAA Equalization
RIAA equalization is a specification for the correct playback of vinyl records, established by the Recording Industry Association of America. The purpose of the equalization is to permit longer playback times and improve sound quality. The necessity for this equalization process arises from mechanical difficulties inherent in record production. In order to prevent the cutting needle from over-cutting into the next record groove in the bass, as a record is cut, some bass frequencies are attenuated. In the treble region, in order for high frequency sounds not to be masked by the noise inherent in moving a stylus over and through a modulated vinyl surface, some treble frequencies are boosted. With the application of the correct filtering techniques on playback, the result is a
flat frequency response with better signal to noise ratios.
There are four de-emphasis methods that can be applied at playback:
A. Active filters (Negative feedback types): Different quantities of negative feedback are applied, with deeper feedback to the high frequencies and shallower to the low frequencies. The benefits of this method are improved signal to noise ratios, low cost and consistent operation. Some of the shortfalls are looser bass reproduction and possibly a pinched and compressed high frequency playback due to excess feedback ratios.
B. Passive filters (CR type): The frequencies are filtered to fit the RIAA specification by varying the amount of attenuation at different frequencies through a complex capacitor-resistor network. This technique results in no voltage overload, purer reproduction (because there is no feedback), and more accurate RIAA compensation. However, there are problems because the system provides no gain, and insertion loss and impedance matching issues arise.
C. Hybrid filters (use of both CR and negative feedback types): In this method, both types of filters applied separately; an active filter is applied to the low frequencies and a passive filter to the high frequencies. Unfortunately, both the advantages and disadvantages of each of these two types of filters, already discussed, affect the playback system at the same time.
D. LCR filters, which are used in the Allnic’s H-7000V : Two pieces of a linear reactor (a kind of choke coil) comprise the main part of these filters, assisted by precise CR filters, in order to lower impedances and insertion loss. In vacuum tube circuits, active and passive filters usually are operated on one hundred plus kilo ohms of impedance. An LCR RIAA filter’s impedance is a constant 600 ohms. Furthermore, an LCR RIAA filter’s series resistance is less than 13 ohms (as a comparative, some famous ones are 31 ohms). The lower the impedance, the more dynamic is the sound reproduction, with better bass response and speed. But LCR RIAA units have drawbacks as well. These drawbacks are high cost and the difficulty of impedance matching; the latter has been the primary hindrance to the commercialization of this superb method in the construction of phono stage amplifiers. However, Allnic Audio manufactures a high quality LCR RIAA unit and has developed a 600 ohms impedance matching method.
Cutter Head Type MC Cartridge
Every LP record master is engraved using an LP cutting lathe’s cutter head. The Allnic’s all moving coil (MC) cartridges are designed to reproduce music via a mechanism that emulates the LP cutting lathe’s cutter head, of course, however, with a diamond stylus that tracks the record grooves’ faces, rather than with a diamond chisel for cutting the grooves into the vinyl.
Please refer to Figure 1, illustrating two types of MC cartridge in comparison to a cutting head.
Also, Allnic’s MC cartridges have two separate hollow polycarbonate bobbins, as opposed to one bobbin designed as an iron square or cross-block. Please refer to Figure 2. Iron is about nine times heavier than poly carbonate, so a conventional iron bobbin reacts with far less agility to the musical grooves of a vinyl record than one made of hollow polycarbonate.
As a cantilever moves along the vinyl’s grooves, it needs a pivot. Conventional MC cartridges’ coils are located near the pivot because of their heavy moving mass. Because of its lighter moving mass, relative to conventional MC cartridges, the Allnic MC cartridge’s coils are nearer to the diamond stylus. The result for the Allnic MC cartridge is increased coil vibration capability and, therefore, more detailed audio reproduction. Please refer to Figure 3. In addition, the Allnic MC cartridge cantilever’s length meets the same specification as for a cutting head.
Powerful Driving Circuitry
Allnic believes in the importance of using high-quality, low noise and powerful driving circuitry in all its amplifying devices. Therefore, for example, in the M-3000 mk2, we employ the E282F tube (E55L for M-5000) in triode mode as the second stage driver tube, with a load of about 6 k ohms, and using 20 mA of current.
The listener can easily hear and even “feel” the differences between this design and other, more conventional, ones. Please imagine, as you listen to the M-3000 mk2, its sound compared to the sound of an amplifier with conventional 12AU7 or 12BH7’s used as drivers, with a load of about 47 k ohm, and using 2 to 3 mA of current.
Soft Start Circuitry
Allnic uses soft start circuitry that, after sufficient warm-up only, provides the high voltage supply to the plate of each tube. This protective design results in prolonged tube life and fewer and less frequent issues with tube performance.
New Vacuum Tube Damping Technology
Allnic Audio’s patented “Absorb GEL tube damper” technology prevents harmful vibrations from reaching the signal / gain tubes and, therefore, prevents micro-phonic noise propagation in the tubes. The Allnic Audio Absorb Gel damper technology effectively solves a problem that plagues most tube amplification systems.
Provided other tube components do not introduce micro-phonic noise into your system, with the Absorb Gel damping system, you will enjoy a degree of transparent sound that will surprise and please you.
Permalloy Output Transformer
Allnic uses very large permalloy (Nickel/FeSi) core output transformers. This provides for higher inductance with fewer windings than other designs can provide and results in the great benefit of an extremely wide range of output frequencies.
Line Output Transformer Coupling
In tube amp circuitry, there are two coupling methods; one is capacitor coupling and the other is transformer coupling. Capacitor coupling is the traditional, low cost method. It is somewhat stable but transfers only voltage, not wattage (i.e., not real energy).
With transformer coupling, about 90% of real wattage is transferred (there is still a transformer loss of about 10% of wattage–voltage is not affected). Transformer coupling is superior to capacitor coupling. However, all the advantages of transformer coupling depend on the quality of the transformer and on the choice of tubes.
Allnic Audio manufactures its own transformers and uses what it views to be the best core material, permalloy. Allnic Audio’s unprecedented, wide (16Hz ~ 75kHz,-3db), low distortional, and ultra-flexible(up to 20kHz square wave response) output transformer helps Allnic Audio to realize the ideal transformer coupled amplifier. Of course, gain tubes are also carefully selected for three critical factors for function with the permalloy output transformers : high gm, low internal resistance and high mu.
Beautiful 20kHz Square Wave Response
We can show you how beautifully a 20kHz square wave response is reproduced.
Full Engagement Output Transformers
Conventional output transformers use pre-set secondary windings to accommodate 4, 8 and 16 ohm loudspeaker loads. However, these conventional transformers utilize only one secondary winding at a time, while the other secondary windings remain “idle”.
This approach has two adverse effects. First, the output transformers are not working at their maximum efficiency, reducing their output relative to their potential.
Second, the “idle” windings are not actually “idle”; they are subject to parasitic oscillations, producing their own “signal”. This undesirable electrical information is additive to the transformer’s output, distorting the amplified signal going to the loudspeaker.
Allnic’s “Full Engagement” transformers address these issues by having 4 independent, secondary windings which are always fully connected, never “idled”. This means that all secondary windings are always connected to your loudspeakers, regardless of which output switch position.