TABLE OF CONTENTS

SPECIFICATIONS...............................SECTION 1

VACUUM TUBE PLACEMENT DIAGRAM...SECTION 2

GENERAL..........................................SECTION 3

CIRCUIT DESCRIPTION.......................SECTION 4

FRONT PANEL CONTROL
& INDICATION..................................SECTION 5

REAR PANEL INTERFACE......................SECTION 6

WARRANTY INFORMATION...................SECTION 7

SPECIFICATIONS

Power Requirements............................105 130 VAC (210 240
VAC)

Input Protocol.....................................SPDIF, AES/EBU, (Optical,
I2S, and 13W3 available)

Data Bus............................................24 Bit

DACs.................................................24 Bit

Sample Rate.......................................16 kHz to 96 kHz (192 kHz
in double speed mode)

OverSampling....................................64 to 256 Fs

Frequency Response.............................4 Hz to 22.5 kHz +0, .25 dB

Dynamic Range....................................104 dB

Signal to Noise Ratio.............................104 dB 4 Hz to 22.1 kHz

Digital Silence.......................................-102dB unweighted

Distortion (THD + IM) ............................ < 0.02% full scale, full
bandwidth

Output impedance...................................225 ohms

Output level ..............................................+12 dbm

Model 34 MXL Digital Audio Processor

GENERAL INFORMATION

I. The Model 34 MXL Vacuum Tube Digital Processor has been designed and tested to provide the highest quality in sound achievable in digital and analog devices. Many years of research by one of the industry's most notable designers has resulted in a product that is superior to higher priced equivalents.

II. The I2S bus is used internally because of its open architecture, and is capable of operating at double speed (up to 200 K samples per second!). Unlike other systems, it can accommodate the entire 24 bit word. It is also compatible with 24 bit CD and DVD Audio.

III. Assembled, with every single part matched by hand and approved by a single team of engineers and technicians, it has conformed to our highest standard, passing every evaluation applied to it. The Model 34 MXL will continue to achieve peak performance for many years to come!

Circuit Description

The circuitry of this equipment is comprised of elements that are both proprietary and under public domain and utilizing software that is proprietary and the property of AUDIO LOGIC Co. .

A synoptic description of the architecture of this device, detailing the mechanics that produce the high resolution results follows:

Input Preamplifiers

There are 3 separate preamplifiers individually engineered to receive a specific signal sent by the Digital Sources (CD Transport, DAT, DSR, etc.,). Each exhibits a calibrated input impedance for both SPDIF and AES/EBU transmission standards via appropriate connectors. The optional optical Amplifiers are loaded and calibrated internally for TTL interface characteristics. Input Circuitry is designed to "latch up" on any unused inputs, preventing random input noise which could feed back to the power supply and cause random jitter and digital noise.

Logic Control

A single, passive Programmable Logic Device (PLD), performs all the logic functions and incidental housekeeping. Its high speed, low noise operation and immunity to outside interference (i.e., RFI or ESD), make it the preferred choice over an active device. The PLD controls bus operations for the conversion circuits and incidental functions (such as Front Panel Indication and Internal Mute Processing). Timing of the PLD is structured mathematically, making the device "invisible" to the digital signals through which it passes. Contents of this component is unique and proprietary, programmed by Audio Logic and cannot be read or reprogrammed. The Digital bus structure is of open architecture type , capable of 24 bit operation at double speed mode (192K), accommodating all CD, DAT and DVD formats. The 34MXL also utilizes a unique microcontroller containing specifically designed high level code which enables it to perform silently. After detecting the input status and analyzing the signal format the controller configures the system to accommodate the signal, reports its status on the internal bus and then turns itself off. This process preserves the excellent low \noise performance of the 24MXL

PLEASE NOTE ; Software upgrades will be available to original owners when future digital audio formats evolve.

Clock Extractor

The circuit that regenerates the primary system clock of the source, and, provides the primary system clock for all other signals is called the "clock extractor". The system used in the Model 34 MXL is Sixth generation and is rapidly becoming accepted as the best. Sonically speaking, it is the most important part of the digital circuit. A poorly designed or improperly working clock extractor will cause the jitter that degrades the final output. The function of this circuit is so important that it warrants further expansion at this time. A digital audio source, such as a CD transport, is under the control of a primary high frequency crystal oscillator. The critical timing of all other digital clocks in the transport, and the data they control, is derived from this oscillator. It is called the "system clock". The processor also is a link in the digital audio chain and therefore must eventually come under the control of the primary system clock. The system clock, internal to the processor is merely there for "idling" when no signal is connected. The problem is that the system clock from the transport is not sent to the processor via the standard digital audio interface formats. It is instead "implied" by the lower frequency clock that is sent down the wire or fiber (often called the "bit clock"" or "data clock"). The processor must then recreate an exact replica of the transport system clock for its own use. The challenge is not in the recreating of the frequency, but rather in knowing if the lower clock signal has been corrupted by an extraneous source (such as transmission line problems, power supply problems, motor problems, etc.). Essentially, the clock extracting circuitry must make a "long term" analysis of the bit clock signal, and regard the results of this analysis as being senior to any short term anomaly that is most likely an error. The result is that any jitter from the transport isessentailly ignored. In electronic circuits a second is long term. In a worst case scenario, it will take the Audio Logic Model 34 MXL less than 1/4 of a second to analyze the validity of the derived clock signal from the digital source. This does not mean that optimal results are achieved in a quarter second. You will notice optimal timing characteristics after about 30 minutes of operation.

PROTOCOL CONVERTER

The protocol converter processes the serial form of the transmitted data and outputs it onto the I2S parallel bus. Once the system clock has been correctly established, this process is a relatively simple one using internal shift registers.

ERROR CORRECTION

Error correction in the Model 34 MXL has been intentionally minimized. There is no limit to the amount of error correction one can perform on an audio signal, either digital or analog. The question is, when is the corrected result no longer the actual signal The answer is that as soon as any correction is made. With digital, it is necessary to provide for some error correction, yet important to minimize the effect. It is better to realize that there is something wrong in the system than simply to listen to the"masked" results of extensive error correction. In the 34MXL error correction has been reduced to 400 samples (about 10 ms), after which the unit will mute, and the digital status indicator will show an error. It is rare that even this minimal amount of error correction is necessary. Most times it is the result of a bad disk or malfunctioning transport.

FIR FILTER

The Finite Impulse Response filter is similar to those used in most high quality digital converters. It prevents the actual DAC from receiving any erroneous signals that it cannot handle.

DATA CONVERTER

In all, there are four channels of data conversion, which are combined in the interstage transformers to provide the derived stereo signal. The data converter utilizes DELTA/SIGMA conversion techniques for the lower order bits, and the more common "LADDER DAC" circuitry for the upper order bits. This approach takes advantage of the better qualities of both systems. The DELTA/SIGMA DAC delivers the deep inner detail you will hear, while the LADDER DAC delivers the authority and power needed to reproduce the lower mid and low frequency material. AKM chip sets used for all conversion.

Laser trimming is employed to achieve the accuracy required. Before actual conversion to analog, the digital audio data is subjected to a 32x oversampling linear interpolator/dither processor and then a 2x oversampling sample and hold circuit. An additional bit position is added to accommodate the dither signal rather than have it "steal" a position from the sample word size.

POST CONVERTER FILTER

The Model 34MXL uses a differential conversion method allowing the post filtering to be kept to a minimum and virtually eliminating the phase distortion which is usually associated with this type of filter. This is the primary reason for choosing the differential approach. Periodic images produced by other types of converters are simply cancelled out by the interstage transformers, rather than by "heavy" filters that can produce phase distortion. The mathematical model of the analog post filters is proprietary.

ANALOG SECTION

As dependant as all digital devices are on solid state circuitry, once the analog signal has been retrieved, the value of a correctly designed analog section cannot be overstated. The Model 34MXL uses two independent differential interstage transformers of our own design. The transformers provide the differential amplification function formerly provided by a vacuum tube circuit . The primaries are direct coupled to the output of the dual differential DACs. The secondaries are coupled to the control grids of the cathode follower output stage. The operating point of the tubes has been selected for optimal linearity and long tube life. Due to the differential configuration, no analog filtering is required. The audio signal is routed to the output connectors through large high quality coupling capacitors and the highest grade OFC wire. Isolated and regulated filament power supplies preserve the low noise operation of the output stage. Printed board and point to point wiring methods are both used to their individual advantages.

A word about audio interstage transformers. The marrying of solid state and vacuum tube circuitry is the perfect scenario for the use of interstagetransformers. The low impedance output of the DAC devices and the high impedance characteristics of the vacuum tube allow for high-gain amplification via magnetics. The magnetic transfer characteristics of the transformers far out perform that of the vacuum tube. The result is Lower distortion figures and a more natural rendition .

POWER SUPPLY

The internal power supply is the commercial version of our laboratory supply. In all, there are three separate transformers used. This is the only way to achieve the low noise, distortion, and dynamic characteristics exhibited by the Model 34 MXL. The high voltage B+ section utilizes a larger than necessary (approx. 15x) shielded transformer allowing for passive regulation. The filament supply is series regulated and isolated from all other sections of the power supply. The digital supply for the control circuitry is series regulated, with two stages of regulation providing for low impedance operation and ample heat distribution. Although heat is not a concern with the power supply, some ventilation room should be provided. The analog voltage for the quad DACs is totally isolated and is in three stages, insuring the low level linearity and low intermodulation distortion characteristics of both DACs are preserved.

FRONT PANEL CONTROL AND INDICATION

INPUT SELECTION

The Model 34MXL's front panel is marked by a simple array of
pushbuttons. When activated, the unit will scan all the input ports and lock on to the first valid signal. After that, other inputs can be selected. All the inputs, except for the auxiliary input, are software compatible with the SPDIF and professional AES/EBU standard. The three pin XLR connector is hardware compatible with the AES/EBU transmission standard. The optional ATT ODL50 optical input is hardware compatible with ODL50 transmitters, and all optical transmitters operating between 810 nm and 850 nm. The auxiliary input is undedicated and can be configured (as an option) for any nonstandard protocol, such as I2S or 13W3.

POLARITY SELECT

This button corrects for absolute polarity error in the digital domain. In the event that the digital material you are reviewing was inverted in the mastering process, setting this switch will correct phase. There is no need to correct for a phase inversion of the actual digital signal sent by a transport or DAT. The input receiver in the Model 34 MXL is very sophisticated, and will detect this error and automatically correct for it. All bit periods will be perceived as occurring on the rising edge of the input signal. The Model 34 MXL will indicate a lock condition by illuminating the internal blue LEDs.

REAR PANEL INTERFACE

ANALOG SECTION

The line output connections indicate the left and the right channel, RCA connector compatible. True balanced outputs via male XLR connectors are available as an option.

DIGITAL SECTION

The Coaxial Input connector is RCA compatible. The AES/EBU connector is XLR compatible. The (optional) Optical connector is ODL50 compatible, requiring a male ST connector. We recommend glass optical fiber. Single mode optical fiber will function perfectly with the ODL50 receiver, provided it has been manufactured to the strictest tolerances. NOTE: I2S and I3W3 (all levels) are available as options.

IMPORTANT SAFEGUARDS

WARNING! To reduce risk of fire, electrical shock or injury:

Do not insert any object into holes or openings of this unit. Never spill liquid of any kind on this unit. Do not place this unit on an unstable cart, stand or table. The product may fall, causing serious damage to the equipment.

Use only as described in this manual. The internal power supply included with the Model 34 MXL is extremely powerful and constitutes a high voltage hazard if not properly handled. The unit must be in the STANDBY position for at least l0 minutes before disconnecting it and opening the chassis.

All Audio Processors are guaranteed to be free from defects, (excluding vacuum tubes) for a period of three (3) years from the date of purchase, from an authorized Audio Logic Dealer. This warranty does not cover misuse by the user or any unapproved or unregistered modifications. We will warranty modified units provided the modification is registered and approved.

This warranty is fully transferable.

Audio Logic Co.
Westport, Connecticut
USA

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