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AD2-QC Kit

Assembly instructions and additional information

( German Version: Bausatz AD2-QC)

Content

A few Words in Advance

The AD2-QC kit (analog/digital converter, 2 channels, quad speed) is equipped with RCA inputs and outputs as well as an optical output for normal use. A modification of the AD2-QC is the AD2-QP, which is intended more for professional use and is equipped exclusively with XLR connectors for the inputs and the output. Both are functionally identical.

The kit is supplied complete with all the necessary components. The circuit board is equipped with all SMDs and tested on a special test station. A housing with front and rear panel is currently planned, but there is no sample yet.

I attach great importance not only to the technical properties of my developments, but also to a good appearance. With this in mind, I have also made a few comments in this description as to when and where, if I were to produce such a kit or a device myself, I would also make its "inner workings" visually appealing with a little more effort.

Final Assembly

The photo shows all parts of the ADC2-QC kit except for the housing.

The Parts to be Populated are:

• The socket for the 12 V connection, the optical transmitter (PLT133) and the three cinch sockets are soldered in the area of the rear panel. It should be noted that these 5 components are fully seated on the circuit board.
• The switch for the input level: It can be used in two positions: Slightly closer to or further away from the front panel. This is intended for knobs that can be placed at different distances from the axis of the switch. For the button supplied, the switch should be inserted closer to the front panel. The switch is inserted without a union nut.
  → The switch does not need to be inserted if the ADC is to be operated with a fixed setting for the input level:
• No further action is required for +15 dBu
• For the frequently required 2 V_rms setting, the connections marked 2 V_RMS on the circuit board can be made.
• For +12 dBu and 1 V_rms, corresponding connections can also be made on the PCB.
• For other fixed settings, resistors R2.4 and R3.4 can be fitted, see Other input levels with switch set to +15 dBu.
  
• The switch for the sample rate is inserted.
  → The switch does not need to be inserted if the ADC is only to be operated at 48 kHz / professional.
  
• The LEDs for the operating voltage indicator (green) and overload indicator (2 x red):
  They are plugged into the holder so that the longer legs (the anode connections) are closer to the front panel after angling, see photo.
• Do not forget: If, as in most cases, the grounds of the two RCA inputs are to be connected to the housing and the rest of the electronics, close the solder bridge J32 on the top of the PCB with a small drop of solder. The solder bridge is also labeled RCA GND.
  
• Do not forget: If, as in most cases, no changeover switch is provided for several inputs:
• Either close the 4 solder jumpers on the underside of the PCB with a small drop of solder each, or:
  
• Insert a 16-pin header for ST2 and provide 4 with jumpers (pins 3-4, 5-6, 13-14 and 15-16).
Further information on the options available with the 16-pin header can be found below.

The AD2-QC is now basically ready for operation and can be tested.

Housing

The housing will look similar to the housing of the AD2-QP shown in the following photo, but is approx. 40 mm shorter and only 30 mm high. The back of course looks completely different.

The assembly of the housing should be self-explanatory, but I would like to give a few hints:

Two mounting blocks ("mounting brackets") are screwed to the back of the circuit board with one M2.5x6 mm pan-head screw each, not yet fully tightened.

The lower housing shell is screwed to the back plate with 2 M3x10 mm pan-head screws.

The module is inserted into the lower rail of the lower housing shell and fastened to the back plate with 2 M2.5x6 mm pan-head screws via the mounting blocks. The other two screws under the PCB can now also be tightened.

The front panel is fitted and also screwed to the lower housing shell using 2 M3x10 mm countersunk head screws. Attention: Make sure that the 3 LED holders protrude into the openings provided before screwing them in!

The upper housing shell can be fitted and screwed in place with 4 M3x10 mm pan-head screws.

Finally, 4 housing feet should be glued under the housing if necessary.

Final Inspection

A simple function test should suffice as a final test. Some further information can be found in the article AD2-QC.

Settings

Sample Rate

The following settings can be made with the SAMPLE RATE switch:

The 12 sample rates, whose digital audio signal is referred to as "Professional Format", are selected in position 0 - C. Position 0 corresponds to the situation where the sample rate switch is not fitted. The sample rate is then set to 48 kHz.

Positions D, E and F are referred to as "consumer format", in which only 32 kHz, 44.1 kHz and 48 kHz can be selected. In consumer mode, the category code of the ADC is "General" (00hex) and copyright is not claimed.

Input Level

With the INPUT LEVEL switch the input level U_IN for 100% FS ("Full Scale") can be set to 4 levels:

• +15 dBu (~4.36 V_rms)
• +12 dBu (~3.08 V_rms)
• 2 V_rms (~+8.2 dBu)
• 1 V_rms (~+2.2 dBu)

Options

Other Input Levels with Switch set to +15 dBu

For the +15 dBu switch position, the input level U_IN for 100% FS can be set to a value between approx. 100 mV_rms and +15 dBu. Two additional THT resistors R_Gain can be inserted in the slots provided for this purpose:

            2 * U_IN
  R_Gain = ------------ kΩ
          4.36V - U_IN

The front panel label +15 dBu is then of course no longer correct. In principle, settings for even lower input levels than 100 mV_rms (i.e. approx. 47 Ω) also work, but this is not recommended.

Input Selector

The 16-pin pin header ST2 provides everything you need to switch between the RCA inputs on the board and external inputs, e.g. balanced XLR inputs.

Variable Gain

Furthermore, switches or potentiometers (preferably neg. logarithmic) can be connected via ST2 to set the gain or the 100% FS input level. The 4-stage switch "Input Level" (SW2) is then not installed or set to +15 dBu.

The input level U_IN results from the variable resistance and a fixed series resistor of 47 Ω as follows:

        4.36 * (R_Gain + 0.047kΩ)
  U_IN = ------------------------ V
             2.047kΩ + R_Gain

With R_Gain in kΩ. The minimum achievable input level with R_Gain = 0 is therefore approx. 100 mV.

Preamplifier

A balanced supply voltage is also available on ST2, e.g. for microphone preamps or RIAA equalizers.

AES/EBU Output

An XLR connection for an AES3 or AES/EBU output can be connected via ST4.4 and also operated simultaneously with the S/PDIF and Toslink output.

USB Interface

A USB interface is planned as a plug-on module for the AD2-QC, but is not yet available. The area for the interface attached to the circuit board with 3 spacer pins and the position of the pin header for the connections between the interface and ADC can be seen in the photos. The functions of the interface and the behavior correspond to those of the DA2USB. To avoid ground loops (or other interference due to equalizing currents), the USB connection is galvanically isolated from the ADC ground.

Technical Data and Measured Values

The measured values for the audio signals practically correspond to those of the AD24QS, as is to be expected due to the similar technology.

The measured values listed above are from a sample device and cannot be guaranteed.

Finally here: The circuit diagram of the AD2-QC.

Contents of the AD2-QC kit

How to Order...

... and the price list can be found on page AD/DA24QS_Order.