HJFP2

Last update 10/8/07

ASSEMBLY INSTRUCTIONS FOR THE HJFP2 AND HVTP2 MICPRE STEP ATTENUATORS

The pictures below show the assembly procedure for the step attenuators. The procedure for both kits is the same, only the resistance values in the tables are different (refer to the appropriate table for your kit). The kits will include 2 x 23 position Military grade rotary switches, all 1% resistors (22 individual values per switch), and mounting hardware.

1. Using an ohm meter, sort the resistors out in the order shown in the 2 most left columns in the table below, Rn / OHMS.

2. Begin with R1, install it into the terminals shown, do not solder the GND terminal yet.

3. Install R2, and solder the terminal where R1 and R2 join, leaving the other end of R2 unsoldered. Make certain the terminal is filled with solder, but avoid overheating the switch.

4. Install R3, and solder the terminal where R2 and R3 join, this time leaving the other end of R3 unsoldered.

Continue this procedure all the way through R22, leaving the end of R22 which is by itself on the input unsoldered.

6. Along the way you can check your work by measuring the resistance from the RETURN/OUTPUT to GND. These values are given in the "R, RET TO GND" column for each step. As you add resistors, the total resistance is the sum of all the resistors in the divider. Basically they are all connected in series. Switch position #1 is fully CCW or off. Position 23 is fully CW or maximum volume. Completely test the resistance at each step before installing into the micpre.

7. Follow the instructions for the HVTP2/HJFP2 kit for installing the pot, but instead you will install your attenuators. Make certain you do not mix up the "SND" (send), and "RET" wires, refer to the pcb layout and text on the back of the pcb. If you have already installed pots, remove them from the front panel, and carefully remove the wires, and re attach them to the attenuator. If the wire gets over heated or damaged, use some of the spair provided in your kit (1' of the three most common colors).

8. Put the flat spacer washer (or one of the two nuts if yours comes with 2) on the rotary switch shaft, and slide the switch into the front panel, with the counter rotation tab in the small hole. If needed, bend the tab outward so it goes into the hole, otherwise the switch may come loose. Install the lock washer and nut on the outside of the front panel, onto the switch and tighten. Install the knob onto the shaft

9. ADDITIONAL TEST: If you have a function generator, you can test the attenuator has the correct output. In general this is not necessary if you followed the test in step #6. Put a 10Vrms 1KHz test tone into the SEND/INPUT, measure AC volts rms on the output and compare to the voltages in the far right column of the table.