Allnic/ZL Technologies L-8500 OTL/OCL

The L-8500 OTL/OCL (Output Transformer-Less/Output Capacitor-Less) is a triple gain stage, remote controlled, line-stage preamplifier, without transformers or capacitors in its single-ended signal path.

• OTL, OCL Direct Coupled preamplifier
• Two SEPP 12B4s output
• True Dual Mono design
• 41-step Silver Contact Constant Impedance attenuator

The L-8500 Preamplifier is a Direct Coupled OTL/OCL Tube Preamplifier.

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 loud speakers.

But these two types of coupling devices are effectively obstacles to 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.

*The OTL/OCL circuit is basically SEPP, “Single Ended Push Pull”, so we need a “cancellation circuit”, which adjusts the balance of signal between the upper and lower power output tubes’ input grids.

Allnic uses the most sophisticated “Active Balanced Positive and Negative Feedback Circuit”, in which a 6AN8 pentode perfectly controls all the circuit’s entire operation with extremely low distortion and the greatest speed.

Allnic Audio’s Technology

OTL/OCL Ciruitry

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. 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.

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.

Beautiful 100kHz square wave response

We can show you how beautifully a 100kHz square wave response is reproduced.

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.

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.

Analogue power tube current monitors

In order to provide constant current (bias) monitoring for the power tubes, Allnic uses a separate analogue current meter for each tube. The meters make it exceptionally easy to see the status of each tube at any time and to respond immediately to any variation in bias by use of the bias control knob for the relevant tube. The meters offer a simple, unambiguous indication of each tube’s status compared to conventional LED bias monitors.