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.