Beogram 8000 (5613): Installation of Redesigned Internal Beolover RIAA Pre-Amplifier

I recently redesigned my internal RIAA pre-amplifier for the Beogram 8000 and 8002 to feature a set of dip switches that allow choosing between amplified and non-amplified signal routing. That makes it possible to switch the pre-amp off if an equipped Beogram is moved from an amplifier without RIAA to an amplifier with a phono input. 

My previous design required removing the pre-amp board to accomplish this, and I thought this needed to change. All my other RIAA designs have this capability. The RIAA circuit is unchanged in this latest iteration, i.e. my previous in-situ measurements apply. Read here about my distortion and frequency response measurements on this design.

This shows the new board:

The main change from previous versions is the addition of a 6-position dip switch:

The above picture shows the switches set to 'RIAA'. Flipping all six returns the Beogram to its non-amplified configuration, and it could be plugged into any standard phono input.

In the following, I will discuss how to install the board. It connects directly to the solder points at the end of the ribbon cable that connects to the carriage. I usually mark the right channel with a black marker so I don't get confused when it is time to solder the wires to the RIAA board outputs:

For clarity, here is a snippet from the service manual showing the terminals of the ribbon cable:

The terminals at the bottom are the left and right outputs.

The first step was unsoldering the right and left output wiring and cleaning the solder pads with a desolder gun:

After removal of the mounting screw at the end of the ribbon cable assembly, I bolted the RIAA board in using the same screw and positioned it to overlap with the four solder pads of the output cables. Then I put a small amount of solder into each of the 'connection vias' of the board to make the connections between the RIAA inputs and the ribbon cable terminals:

The next step was to connect the L and R wires to the respective output terminals of the RIAA board:

I replaced the original woven insulation of the shield braids with modern shrink tubing (black) for a cleaner look.

The final part of the installation was connecting the RIAA board to its power supply.

Unfortunately, there is no power connected at the end of the ribbon cable, i.e. a separate wire needs to be installed to the 15V regulator. I connected a wire to the "15V" solder pad of the RIAA:

Note that the 15V label corresponds to the minimum voltage the RIAA needs for proper functioning. The maximum voltage allowed is 36V for this design. The next step is routing the wire to the voltage regulator PCB next to the front rod of the carriage. I recommend routing the wire along with the other wires beneath the subplatter. The critical routing points are labeled yellow in the photo below:

By feeding the wire under the plastic clips that hold the other wiring in place, it reliably avoids chafing with the sub platter. This shows the first of the clips (counted from the RIAA board):

And this the second when the wire emerges from underneath the subplatter:

This is how these two spots look with the subplatter installed:

The wire terminates at the input terminal of the TIP32 (0TR1) voltage regulator of the 15V rail. This terminal connects directly to the rectifier and main capacitor of the 15V rail and usually carries about 23V. I soldered the wire to the terminal, and this concluded the installation of the RIAA board!:

And then it was time to enjoy this redesigned RIAA pre-amp! I plugged the Beogram into the tape input of my amplifier and put on one of my favorite records, "Very Tall" by the Oscar Peterson Trio with Milt Jackson. This record was released in 1962 on Verve Records. I appear to have a re-issue from 1982 (UMV 2026).

Beolovely! This Beogram is now ready to be used with pretty much any modern amplifier or 'device' that still has a wired line-in!