The Programmable Padnet for the AMPEX ATR-100 was designed by AUDICON DESIGN LABORATORIES in cooperation with Flux Magnetics. It is intended to make the recording technician's life much easier by automating the ATR-100 equalization alignment procedures and more.

A complete single-speed two or four channel equalization alignment can be performed in about three minutes. A fully operational (4-channel, 4-speed) ATR-100 can be aligned in under thirty minutes.

A complete set of alignments can be performed through its simple user interface of three pushbuttons and 18 indicator lights, or a plethora of functionality can be opened through its RS-232 communications interface with an IBM-compatible personal computer and MS Windows compatible software. With an external computer, equalization settings can be saved and recalled, allowing the operator to recall instantly equalization settings unique to a given tape or head stack.

The Programmable Padnet is plug compatible with the original ATR-100 padnet after a single jumper wire to supply power has been added to the audio board. The quality and integrity of the original analog channel is preserved, as the signal path is virtually identical to that of the original ATR-100 padnet.

• Supports All Four Speeds
• Fully Automatic or Manual Operation
• Built-In Frequency Generator
• Built-In Level Measurement
• True 3rd Harmonic Measurement for Bias Adjustment
• Uses Only the Highest Quality Components

The AMPEX ATR-100 analog tape recorder, designed and manufactured by AMPEX Corporation until the mid 1980's, is still considered to be one of the standards in audio tape recording. Even though significant advances have been made in digital recording technology in recent years, analog recorders such as the ATR-100 are still considered by many recording engineers and artists to possess superior sonic performance.

While some analog tape recorders may be considered superior to their digital counterparts in sonic quality, the digital machines are more convenient to use in some respects. By their nature, digital machines are relatively insensitive to slight variations in tape or head performance. As long as they meet certain minimum performance standards, different makes or batches of tape may be interchanged without affecting the sonic behavior of the machine. Similar variations in tape characteristics would result in noticeable changes in the sonic characteristics of an analog machine. This would require that corresponding adjustments be made to the record and reproduce channels in order to preserve sonic consistency from machine to machine.

While digital machines require factory service personnel to perform head or scanner replacements, analog machines such as the ATR-100 often have their head stacks replaced by studio technicians. Heads vary in their electromagnetic characteristics. It is virtually impossible to make two head stacks that perform identically. Performance characteristics also change as the head stacks wear. Such changes in head performance require that corresponding changes be made in the record and reproduce channels to preserve sonic consistency.

In the case of the ATR-100, changes in the channel characteristics, or equalization, are made through adjustments to the padnet circuit board of each channel. The architecture of the ATR-100 separates channel equalization from the main audio board and localizes these adjustments on the padnet board. The padnet board plugs into the audio board via an edge connector, and presents rows of potentiometers along its edge to the operator. These potentiometers look like rectangular blue bricks with tiny screws on one end. The operator accesses these screws for adjustment through holes in the aluminum extrusion mounted on the edge of the padnet board. The aluminum extrusion provides labeling information and also serves as a handle for inserting and extracting the audio/padnet board assembly from the electronics bay. The original ATR-100 padnet comes in two-speed and four-speed versions. The Programmable Padnet replaces both of these boards, and handles all four speeds.

In the case of the ATR-100, an experienced studio technician provided with the appropriate test equipment may typically perform a complete set of channel equalization adjustments for two channels and one speed in about half an hour. These adjustments would include record and reproduce equalization, record bias level and azimuth. The ATR-100 is capable of operating at four tape speeds and four channels. That would suggest a total alignment time of about four hours for a fully operational machine. That also assumes that all goes well during the procedure and that Murphy's Law does not result in human error, such as the technician inadvertently placing the screwdriver in the wrong hole and adjusting the wrong potentiometer. Since the Programmable Padnet performs these functions in a fraction of the time and with higher reliability, it will quickly pay for itself in saved time and frustration. The ability to save these equalization settings on an external computer means that each tape or head stack can have their own custom settings instantly recalled.

Hardware

Comparison of Major Functions and Hardware

The Programmable Padnet signal path is essentially the same as that of the original padnet. The potentiometers have been replaced by digitally controlled potentiometers, or digipots. Test equipment has been replaced by an onboard Digitally Synthesized Oscillator (DSO), specialized filters and a microprocessor with analog signal measurement capability. FET’s (Field Effect Transistor), DIP switches and jumpers have been replaced by high-performance monolithic analog FET switches with a very low "ON" impedance. All signal-path capacitors use an NPO/COG Class I dielectric, which has superior thermal stability and extremely low dielectric loss. The original padnet is fabricated on a double-sided printed circuit board utilizing through-hole technology. The Programmable Padnet is fabricated on a six-layer printed circuit board utilizing surface-mount technology. By their nature, surface-mount components possess less parasitic capacitance and inductance than their through-hole counterparts.

Microprocessor Function

An onboard microprocessor has complete control over all adjustments. The microprocessor can function autonomously, or in conjunction with an IBM-compatible personal computer running MS Windows 95/98. When not performing alignments or measurements, the microprocessor shuts off its clock and enters a sleep mode. This is so that during studio record and reproduce sessions, no digital activity is present which may radiate noise components into the signal. If there is any communication with the microprocessor through the pushbuttons or RS-232 interface, or if the tape speed is changed, the clock will re-start and the microprocessor will resume active operation. After completing its assigned task, the microprocessor again goes back to sleep. Onboard software and board settings are saved in non-volatile memory located inside the microprocessor.

Front Panel

The Programmable PADNET's front panel consists of three banks of status LEDs, three pushbuttons (UP, DOWN, and SELECT), and two communication jacks. Using the three buttons, the user can step through each adjustment, making changes manually or letting the board auto adjust. This can be done on a board by board basis, or one board can be placed in Master mode, causing the remaining boards to track manual adjustments or make auto adjustments simultaneously.

Software Support for Both PC and Macintosh

For more advanced control, the Programmable PADNET connects to a PC or Mac using an RS-232 link. The following screenshots represent some of the features available in the software. Click on a screenshot (taken from the PC version of the software) to enlarge it. Use your browser's back button to return to this page.

The Standard Adjustments window allows the user to easily load, save, copy, or adjust all of the common controls. Input and Output level bars provide instant feedback while making adjustments. Auto Adjust buttons are provided for all major controls.

The Nonstandard Adjustments window provides unprecedented control over the equalization components used for each tape speed.

The Frequency Generator window controls the extremely accurate, on-board sine-wave generator. Presets are provided for all of the standard frequencies, but the user can enter any frequency from a few Hz to 100 KHz. Reference tones for Mastering can be sequenced and generated with ease.

The Full Auto window allows for easy alignment in record time. Choose the channels you want to adjust, the reference and work tape types, and press the Start button. For the reproduce side, the Programmable PADNET listens for the tones on the reference tape and makes the appropriate adjustments automatically. For record side adjustments, the onboard frequency generator automatically generates the correct frequencies.

The tabbed Options window allows you to change the frequencies used for auto record adjustments and the frequency ranges used to trigger auto reproduce adjustments.

The Network Analyzer window allows you to sweep the frequency generator or one of the board controls while plotting playback level, allowing you to easily see changes in the equalization. Plots can be saved and used for later reference.

The Level Meter allows you to measure reproduce level, record level, 3rd harmonic distortion during bias adjustment, relative phase during azimuth adjustment, and master bias level. Approximate signal frequency is also reported for easy identification of reference tape tones.

For easier azimuth adjustment, an analog meter representing the summation of all channels is also provided. When the sum is maximized, the head azimuth is correct.

The Block Diagram displays a low-level representation of the board. Click on switches to open and close them, or click and drag a potentiometer to change its value. Changes to hardware settings are always reflected in the Block Diagram so you can always see exactly what the hardware is doing.