Practical construction

The mechanical construction of the preamplifier is comparable to that of the power amplifier. The housing is about the same, only the heat sinks are missing. In the front of the housing the power supply and the controller are mounted above each other. To the right you can see the controll amplifier. At the right back side of the housing you can see the channel selection PCBs, to the left three conectors. On the picture below the backside of the housing is shown. The right connector is the 230V power output, the middle one the 230V input. Next to that is the RS232-connector.

Front panel

The picture above shows the front panel. As you can imagine, the power button is used to switch the preamp on and off. The LED next to the button shows the standby-state of the amplifier or by blinking the reception of commands from the remote control. In the middle of the front panel is the graphic LC-display. On the right half of the panel are the controls of the preamp. The main element is the large turning knob, which is connected to a rotary encoder. It is also possible to press the knob to control some special functions. With the pushbuttons Menu and Enter the user can select from several menus on the display.

Mechanical contruction

The front panel was milled by Schaeffer Apparatebau. From their homepage you can download the Front panel designer. This program allows you to design a front panel and to send those data to a CNC milling machine. The files I created can be downloaded here. The pictures show the front and back side of the front panel.

The pushbuttons are connected to the front panel with small hinges (from a cigar box, 1). To prevent the pushbuttons from falling out of the panel, I glued small pieces of PCB material behind them (2), so they can only flap inwards. For the actual pushbuttons I made some small PCBs, which are screwed behind the panel. Since I didn't want any holes in the front panel to mount the PCBs, I glued small metal pieces to the back of the front panel (3), in which the screws are mounted (4). For mounting the PCB with the rotary encoder, I used the same technique (5). Additionally there is a lead-through for the axis between them (6).

Result

Below you can see the result of this mounting technique. "Keyboard 3" is the PCB with the rotary encoder, next to it is the PCB with the two pushbuttons ("Keyboard 2"). Additionally on this PCB is the connector for connecting the front panel with the controller. To the right you see the counting of the LC-display, which is the same as for the PCBs with the pushbuttons. The bottom picture shows the PCB with the power-pushbutton and the standy-LED ("Keyboard 3").

A few more pictures

Input selection

Control amplifier with switching noises suppressor mounted on top

On top is the mainboard with the microcontroller board, below that is the power supply.