Beogram 4002 (Type 5504): Installation of Newly Adapted Beolover RIAA Pre-Amp

After recently redesigning the Beolover internal RIAA pre-amplifier for DC-motor Beogram 4002/4 turntables, and adapting the circuit for the Beogram 4000, it was finally time for the next chapter in this design process: Adaptation of the circuit for the AC motor Beogram 4002.

The owner of the 4002 (5504) that I just restored asked me to install the RIAA and so his Beogram will be the first AC-motor 4002 featuring a Beolover RIAA!

This shows the new board:

The input jack of the board connects to a replicated Beogram style plug via a multi-lead wiring harness. The output jack on the right matches the plug that is on the output cable of this type Beogram.

Due to the large footprint of the output jack, I decided to give this design bypass switches instead of the two completely separate signal paths via separate input and output jacks that I chose for the DC motor board. The switches allow connecting the Beogram to a standard Phono input without re-installing the original output board.

A look at the backside of the board reveals a separate grounding wire that allows connecting the board ground to the chassis of the turntable. This has shown in my experiments to help if there are any 50Hz hum issues (but in some cases it also causes hum, so this is something to be tried out in your particular setup):

Here is a look at the board next to the original board that I restored when I finished this turntable:

For installation of the Beolover RIAA board, all that is required is unplugging the board

and replacing it with the Beolover RIAA board:

The only difference is that the ground wire needs to be bolted to the 'cable clamp' bolt:

This shows the board after bolting the keypad back in:

It is designed that the control features are accessible with the keypad cluster installed. This allows setting the gain and switch between RIAA and non-amplified operational modes.