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Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Sunday, March 26, 2023

Beogram 4000: Installation of Newly Designed Beolover RIAA Pre-Amplifier Board

In the past I had a few inquiries for an internal RIAA pre-amplifier board for the Beogram 4000. So when the recent re-design of the Beolover RIAA pre-amplifier for DC motor Beogram 4002 and Beogram 4004 finally came together, I decided to adapt the circuit for the Beogram 4000. 

The owner of the Beogram 4000 that re-visited my bench last week for a little warranty issue decided to let me install the new board in his unit.

This post shows how I installed it. For measurement data, please, check out my post about the characterization of the 4002/4 version, which has the exact same circuit.

This show the board in its current form:

It is still a prototype board and has a couple features that will be removed for the final version. I was not sure how I would power the amplifier in the 4000 since it is set up differently compared to the later 4002/4. I ended up connecting to the 24V rail. The amplifier section of the board is not affected by this, and so this version is already suitable for regular use. 

The 4000 is still fully wired with directly soldered harnesses. This means the board needs to be soldered into place in the 4000. In the 4002/4 the board is simple plug and play due to their more modern design with wire-to-board connectors. Due to the 'permanent' soldered installation I gave this board two switches, with which one can route the output signal through the amplifier, or bypass it in case a traditional Phono amplifier input will be used.

Anyway, let's do the installation! Exciting!:

This shows the output terminal of the Beogram 4000 with the red switch that I installed last year to enable connecting signal and system grounds if there is a hum issue.

Here a detail-photo of the terminal:
The first step was to remove the output cable and the switch from the terminal:
Then I removed the screws that bolt the terminal to the enclosure bottom:
The Beolover RIAA board simply screws on top of the terminal 'bar'. The mounting holes are slots, i.e. the board can be pushed up to the wire terminals for directly soldering it to the contact pads on the board:
The next step is to solder the terminals to the matching board pads:
Then the output cable can be soldered to the output terminals of the RIAA board. They are spaced exactly like the terminal pads, i.e. the output wiring does not need to be modified, and it can directly be soldered in place:
The last step is to connect the red power wire to the 24 rail of the Beogram. A convenient spot is on the main board, where the 24V rail comes in on another red wire.

The strange 6-diode contraption in the back is the Beolover's approach to replacing the Wien oscillator light bulb with a diode based Automatic Gain Control for easy oscillator startup....but that is an entirely different story...;-)

The final step is to pull the output cable a bit further out of the enclosure in the back since the RIAA board pushes the wire terminals a few cm towards the back of the enclosure.

And that is it. This Beogram 4000 can now directly be connected to any modern receiver without Phono input.

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