User manual

AMP2-DA Instruction and Service Manual P/N 821505 Rev-B Section 3: Technical Information

AES/EBU Input D/A Converter Module PCB Circuit Description (919117)

There are four primary and three ancillary sections comprising the 719117 AES/EBU digital to analog converter:

1) Input source selection.

2) audio data extraction.

3) Digital to analog conversion.

4) Analog buffer / output amplifiers.

5) Power suppy, Reset, and Error indication.

Input Source Selection (IC13)

Each of the two selectable signal inputs are transformer-coupled to the inputs of a one-of-two active buffer/switch (IC13). The output

of this switch is applied to the receiver stage of the AES receiver/unframer.

Audio Data Extraction (IC11)

"Header" and ancillary data are removed from the recovered input datastream, yielding a datastream having only alternating left/right

channel audio data, which is output on pin 26 of IC11.

Digital to Analog Conversion (IC10)

The "pure" audio datastream, along with a data clock and a channel ID (left/right) clock, are applied to a 20 bit two channel D to A

converter (IC10), where the datastream is converted into left and right analog outputs.

Analog buffer (IC4) / Output Amplifiers (IC8, IC9)

Buffer/amps provide balanced left and right channel outputs as well as single ended outputs. Gain calibration, the analog level, which

corresponds to a given digital value, is settable via a DIP switch. The default factory setting is 20 dB below "full code" (digital zero)

to equal +4 dbu (0.775V). The other three settings possible are for -18 dBfs = 0 dBu, -20 dBfs = 0 dBu, and -20 dBfs = +8 dBu. See

page 16 for DIP switch location and settings.

Power Supply

The 24V rail internal to the rest of the unit is converted to +5V for digital portions of the 919117 PCB by switching regulator IC12.

Error Indication

The AES status LED is a bicolor LED (Red/Green). It is green as long as a valid digital data strean is being received. The 8412 receiver

is capable of indicating two types of error conditions: 1) Faulty data; data identified by the sending device (possibly invalid), and 2)

Faulty reception; errors in reception of data or no data stream at all.

Level Generator (919126) and LED Driver (919110) PCB Circuit Descriptions

Level Generator Boards (919126)

All signals are input to discrete level generator PC boards. Each level generator PC boards responsibility is to process tasks such as

Digital Signal Processing (DSP), frequency response, integration time, and VU or PPM “dot” display mode. The ADSP-2115 chip on

the each Level Generator board handles the entire processing function. During the assembly of an AMP2 Digital unit, software is

programmed and loaded to a socket chip for a specific unit in-house.

A standard factory calibration of "0" indication when input level is +4 dBV is set for the calibration level unless specified differently

by the end user. A bank of DIP switch sections is located at the rear of Level Generator boards, which can be accessed through the top

cover. A combination of DIP switch settings can be used to apply display mode (VU, PPM) and level meter gain.

LED Driver Boards (919110)

All the digital information processed from the Level Generator PC boards are transfered to the LED driver boards through either a 10-

pin color coded cable. LED Driver Boards accept fixed-length word serially, and latch the outputs for the bargraph segments

corresponding to those bits in the received word, which are set high.

Brightness of the bargraph displays can be adjusted to a desired setting by adjusting the trimpot located on the front panel. All bargraph

displays are simultaneously adjusted with this one trimpot.