Beogram 4004 Type 5526: RIAA preamp board hiccup and fix on Beogram 4004 Turntable #1 from Dallas

In the last post of the Beogram 4004 Turntable #1 from Dallas I installed Beolover's custom RIAA preamplifier board he designed for the Beogram 4002 turntable.

I left off in that post with the Beogram 4004 ready to check that the original functionality of the modified output board still worked. In other words, the normal mode where the phono cable is connected to an amplifier that provides the RIAA preamp.

That test worked perfectly so it was on to try out the new RIAA preamp mode of the Beogram 4004.
I switched the two connectors from the original module 8 connectors P8 and P9 to the two connectors on the Beolover RIAA preamp board.

Now I would be able to connect the Beogram phono cable to an amplifier's auxiliary, tape or CD source input connectors and listen to the Beogram.

I was surprised when I tried that and the Beogram 4004 would not respond to any of the control panel buttons.

Thinking about it for a few moments I realized that while the Beogram output board on the Beogram 4002 and 4004 have the same P8 and P9 connectors, the BG4004 has an extra connector and circuitry for its remote control capability with a Beomaster 2400.

Here is a diagram of the Beogram 4004 output board and its additional remote control circuit.

The part of the diagram below the dashed red line is the phono output (with muting relay) that does not involve the remote control. The Beolover RIAA preamp board uses those two connectors to perform its function. Switching the P8 and P9 connectors between the original module 8 output board and the RIAA preamp board allows switching between the original, no RIAA output and the RIAA amplified output from the Beogram.

With the additional remote control support circuitry in the Beogram 4004 some of the P8 inputs are needed in the remote control circuit and work with the Beogram control panel via the additional P10 connector on the output board.

When I move the P8 and P9 connectors from the original output board to the RIAA preamp board the original output board loses its 30V, 21V and system ground wiring. Those are not only necessary for the remote control circuit but also for the control panel switches in the Beogram 4004.

That is the reason the Beogram 4004 acts dead when the P8 and P9 are configured for RIAA preamp mode.

The fix turned out to be simple. When the P8 connector is moved from the original board to the Beolover RIAA preamp I must have jumper wires keep those key pins (30V, 21V and system ground) between the boards connected.

Here is a diagram of the output board with the RIAA preamp board after the jumpers were added.

I retested the Beogram 4004 with the Beolover RIAA preamp board again by connecting it to the Tape 1 input DIN jack on my Beomaster 6000.

It works awesome!

This is a great mod for a Beogram 4002/4004 turntable. With this modification all of the record play bases are covered. In a vintage audio system where the amplifiers were designed with specific phono inputs you can use the Beogram with the output connectors in their original position. When you need to connect to a modern amplifier that has no phono record play support you can set the Beogram to use the RIAA board.

I will definitely want to do this same mod on one of my own Beogram 4002 or 4004 turntables.
Time to put this cabinet back together and get the Beogram ready for delivery to its owner.

Beogram 4004 Type 5526: Last minute mod on the Beogram 4004 Turntable #1 from Dallas

The Beogram 4004 turntable number one (of two) from Texas was ready to return home to its owner when a special modification was requested. The owner has a modern integrated Bang & Olufsen system from the late nineties (Beocenter 2500) that is now the intended receiver for this Beogram. That presents a problem because the modern systems do not come with a built-in RIAA preamplifier which is required to prepare raw phono cartridge signals for amplification. The resurgence in the popularity of vinyl records has meant a whole bunch of amplifier systems out there without support for phonographs.

There are quite a few third party solutions of course. Those involve a small RIAA preamplifier box between the turntable and the modern amplifier. That works quite nicely but there is a better way when it comes to a Beogram 4002 or 4004 turntable.

Beolover has designed and built a custom Beogram 4002/4004 RIAA amplifier board that connects right into the Beogram (on the existing output board).

The beauty of this design is two-fold.

1. The modification is internal to the Beogram so it doesn't require an external box and additional cables. The original phono cable is used as-is.

2. The modification retains the original connections so the Beogram can still be used with amplifiers that have their own RIAA preamplifier.

The installation of the Beolover RIAA preamp is quite easy.  Here is the sequence.

In most cases the installation is just to remove the phono output muting relay and solder in the custom RIAA preamp board. For this case I also had to remove the grounding option switch I had installed earlier in the project.

The grounding option is not necessary when using the RIAA preamp connectors. If the owner wants to change the receiving amplifier for this Beogram later, to one that has an RIAA preamp, then the grounding option is still nice to have.  The switch I had installed before would be in the way so it has been replaced with a simple two-pin jumper between signal ground and system ground.

Here is the Beogram 4004 output board with the new RIAA preamp mod re-installed.
This picture shows the board connected up for use as the original Beogram....without any RIAA preamplifier.  I want to test that the original functionality works first.  Then I will switch it to use the Beolover RIAA preamp connectors and test the Beogram in that configuration.

If any other Beogram 4002/4004 owners would like to try this preamplifier for their Beogram just contact Beolover at beolover@gmail.com.