Beogram 4002 (5513): Installation of Beolover Commander MkII Remote and Internal RIAA Pre-Amp Board

The owner of the Beogram 4002 (5513) that I am finishing up asked me to install my 4002 Commander remote control as well as my internal RIAA pre-amplifier module. The Commander allows the full control of the 4002 with an Apple remote, while the RIAA gives the Beogram a high level output that can be directly plugged into any CD/DVD/AUX input on modern amplifiers. 

This shows the RIAA board together with the mounting adapter that elevates it above the headers on the output PCB:

This shows the board installed:

It is soldered into the spot where the output relay is located. The RIAA board design includes a second output relay for the non-amplified signal path, i.e. the RIAA can taken out of the signal path by simply plugging the two plugs into the original headers. See here for more detail about the RIAA board design and use. 

This shows the Commander MkII receiver unit on the bench:

The extension to the right is the IR receiver that feeds through in between the plinth and the enclosure to the outside of the deck. The MkII version has an added auto repeat function which uses a red LED (extension to the left) to indicate the auto-repeat status (LED permanently on: One time repeat, blinking: up to 10 plays and off: no auto repeat). This LED is installed beneath the CD-4 indicator in the RPM adjustment panel. This can be seen here:

The Commander board itself just plugs into the keypad connector, while the keypad plugs into a header on the Commander. One of the four screws that hold the main PCB in place doubles to hold the Commander PCB piggybacking on top of the main PCB.

On to the final adjustments and a test drive!

Beogram 4002 (5523): Installation of 4002 Commander MkII Remote Control and Internal RIAA Preamp

I recently finished up the restoration of a Beogram 4002 (5523). My customer decided to add both the Beolover 4002 Commander MkII remote control receiver (it works together with a matched Apple remote) and the internal RIAA pre-amplifier. I developed these two upgrades a while ago. More information about their performance and installation is given on the 4002 Commander page on the blog and in this post about the development of the RIAA amp.  Both boards are available to other enthusiasts. Just send an email or use the contact form on the right. 

This shows the two boards together:

The board at the bottom of the picture is the Commander MkII remote receiver board. The MkII version comes with a repeat function, which uses the CD4 indicator on the keypad cluster as indictor. It is a plug-and-play installation. The board installs into the keyboard header on the main PCB and is bolted into place using one of the screws that holds the PCB down. 

The RIAA amplifier is soldered directly into the output relay solder points. This shows the output board as I rebuilt it with a new relay and grounding switch:

For the installation of the RIAA amp I needed to remove the relay and the switch again to make space for the board and the connectors. This shows the output PCB prepared for the installation together with the RIAA board upside down:

The red 3D printed component serves as spacer to elevate the board above the black in- and output board headers. This shows the board after installation:

The original headers are still accessible, i.e. the Beogram can easily be configured in its original way by plugging the cables into the original headers instead of the white amplifier connectors.

This shows both installed in the Beogram:

Beogram 4002 (5523): Installation of Beolover RIAA Preamp and 4002 Commander Remote Control

I recently gave a Beogram 4002 (5523) the usual 'functional restoration' treatment, which concluded with the installation of gold plated RCA plugs. My customer subsequently decided on having my just completed internal BeoloverRIAA preamplifier installed along with the 4002 Commander remote control system that allows the control of all functions with a paired Apple remote.

So this is the first 4002 that is outfitted with both the Commander and the RIAA preamp. A truly 'back to the future' Beogram!

This shows the BeoloverRIAA board before installation:

and assembled with the 3D printed support:

and installed onto the output PCB (#8):

On to the 4002 Commander. This shows the board before installation. It plugs directly into the keypad connector on the main PCB:

This shows it installed:

Here is a view of both boards:

Time to celebrate this upgraded 4002!:

I selected "Sam' Suffy" by Marc Moulin. All his 'Placebo' records (1971-74) were recently reissued by Music on Vinyl on appropriately colored vinyl. Perfect for showcasing this ahead of its time Beogram 4002!

BeoloverRIAA Preamp: First Installation of Finalized Design in Beogram 4002

I received the redesigned PCBs for my Beogram 4002 internal RIAA pre-amplifier a couple days ago. The fact that this pre-amplifier runs from the single rail Beogram-internal power supply posed some interesting design challenges that made it necessary to go through a couple of design interactions to achieve a satisfying signal-to-noise ratio. See my previous post for more details on the design process.

But now I think this design is ready for primetime. I populated one of the boards and implanted it into  a first Beogram 4002. Here are a few impressions. This shows the redesigned board with its 3D printed mounting support:

The board grew a bit in size to accommodate my improved power supply design.

This shows the mounting support on the pins of the board:

The pins fit directly into the solder points of the original output relay of the Beogram 4002. In fact, the RIAA preamp board maintains the full functionality of the non-amplified standard output of the Beogram. That is the reason that there are two relays on the board. One for the amplified output and one performing the function of the original output relay

This means the user can easily switch the deck between RIAA and standard output by simply plugging the connectors either into the amplifier board or into the original connectors on the output board (see below).

This shows the board installed on PCB 8. I had to move the grounding switch that I had initially installed to a different location underneath the original input connector:

This shows PCB 8 installed back in the Beogram 4002:

The input and output connectors are shown inserted into the amplifier board, i.e. this is the configuration for amplified output. The original non-amplified output can be configured by inserting the connectors into the original board-to-wire connectors on PCB 8:

Here an impression from the front of the deck:

After reassembling the Beogram I connected the output cable to my QA400 audio analyzer and measured signal-to-noise curves:

Nothing changed from the prototype as expected. The red curve shows the noise floor with the Beogram started and the arm down next to the platter (i.e. not touching the record). The noise floor at 1kHz is still about -100dB.  That gives the baseline for all further noise considerations. The large noise dB numbers stated for many available RIAA preamps are measured with the inputs shortened to ground, which is pretty much meaningless since the main noise source other than from the vinyl itself is the cartridge. Due to its own impedance (and the necessary 47k input resistance on the amp) the generated Johnson noise vastly exceeds the input noise of modern low-noise opamps such as the LM833 used here. 

The blue curve illustrates that the noise generated by the vinyl surface is yet another factor 3 or more higher. It was measured while playing the 'rumble track' on my Analogue Test LP. I used a good condition MMC20EN for these measurements. It is obvious that the RIAA amp performance is such that the noise while playing a record is not increased significantly. 

This beolovely performance inspired me to celebrate my latest addition to the 'Beolover parts catalog' with one of my favorite 45s of my youth (don't judge me by this!...;-), 'Dance Hall Days' by Wang Chung:

Allright, looks like this Beogram is ready to be shipped back to its owner!

BeoloverRIAA Phono Preamplifier: Further Improved Power Supply - 87 dB Noise Floor with Running DC Motor!

Inspired by Sonavor at Beoworld.org, I recently acquired a QuantAsylum QA400 audio analyzer. This neat little piece of hardware allowed me to dramatically improve my BeoloverRIAA phono preamp design.

This preamp is supposed to go right into the Beogram 4002 (551x, 552x) enclosure and be powered via the Beogram internal power supply. Basically a plug and play solution for those customers who do not have an amplifier with a phono input anymore. I also think that basically it is best to put the preamplifier as close to the cartridge as possible to avoid potential noise issues. While on paper this sounds great, the practical implementation of this concept has been quite challenging since the Beogram internal power supply is very noisy due to the DC motor induced EMF that permeates the entire system when a record is being played. My initial design resulted in a perfect RIAA deemphasis but with a quite audible noise floor. And of course that was not acceptable. I finally figured out how to quiet down the power supply sufficiently to supply a sensitive amplifier without disturbing its amplification performance. Here is an impression of the current prototype as implanted in a Beogram 4002 (5513):

And this are the curves that I measured with the QA400:

These curves were measured with the platter motor on and the QA400 directly connected to the RCA plugs of the Beogram via gold plated RCA/BNC adapters.

The green curve on top shows the original noise spectrum with my initial 'primitive' power supply based on a simple 7824 regulator connected to the 31V rail of the beogram. The spikes are mainly related to EMF coming from the motor. The highest spikes reach -30dBV, which is quite audible. Since there are many spikes one hears a 'hiss'. 

The red curve at the bottom is the corresponding curve measured after improving the power supply with a more professional setup based on a high ripple rejection regulator device from Linear Technology and a better noise control at the rail splitter (that is the big capacitor on the photo above). The spikes are basically gone and the floor is now at about -87dB. This corresponds to a  unnoticeable noise level when the output relay opens after the arm drops.

The blue curve finally shows a noise floor measurement while playing the 'rumble track' on my Analogue Test LP. It is obvious that the noise coming from the surface roughness of a (high quality) vinyl is more than 30 dB higher at the low end of the frequency spectrum, and about 10 dB (~3x) higher at the crucial 1kHz point. This means that the amplifier does not add significantly during playback of a record and that most audible noise comes from the record itself.

You may wonder why my spectra end at 12kHz at the upper end. Well, unfortunately, while the QA400 is a lovely piece of hardware, the software right now leaves a few areas of potential improvements. At this point I am not able to export spectra that are longer than 4096 points, and that means that everything above 12kHz is right now cut off in exported spectra. I am waiting for a response from their tech support how to alleviate this, but they are a bit sporadic with their attention. At any rate, the spectra were quite unspectacular at higher frequencies. Essentially they simply continue smoothly further down the dB scale following the RIAA curve as would be expected.

Comparing these curves with the specs of 4002-contemporary receivers such as the 4000/4400 or 6000 4-Ch Beomasters reveals that the BeoloverRIAA is considerably better than their discrete transistor based preamps, which have noise floors of 58-60dB for Phono and ~75dB for Tape. And this is quite obvious when I connect a 4002 directly to the phono preamp of my 6000 4-Ch for direct comparison: The BeoloverRIAA outfitted 4002 is noticeably more quiet via the Tape4 input.

So I think this design is nearing a point where it can be implemented. Stay tuned for the next PCB iteration!