Beogram 4002 (5513): Replacing the Incandescent Light Bulbs in the RPM Indicators with LEDs

After rebuilding the main PCB of the Beogram 4002 (5513) that I am rebuilding right now it was time to replace the incandescent light bulbs that provide the backlight for the RPM trimmer scales with LEDs. I like to do this to achieve better long term stability since LEDs have a much longer life expectancy than standard light bulbs. This picture shows the small circuit boards that I designed for the SMD LEDs. They are direct drop-in replacements for the bulbs:

These assemblies are available to other enthusiasts. This video shows how to install the LED boards.

This photo shows the RPM trimmer panel from the back with the original bulbs installed:

This shows the bulb covers removed:

and after installation of the LED boards:

And with covers back on:

On to repairing the keypad and rebuilding PCB #8 that sits underneath.

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!

Beogram 4002 (5513): Replacing the Electrolytic Capacitors, RPM Relay and Trimmers on the Main PCB

After rebuilding the DC motor of this Beogram 4002 (5513), it was time to do the main PCB. I like to replace all electrolytic capacitors with high quality Japanese origin 105C grade capacitors. The Tantalum capacitors have a tendency to die a fiery death when they short circuit, and so it is a great idea to extract and replace them with modern capacitors before they get to be 'spectacular'. Here is an impression of the original board:

the red and blue parts are the capacitors that need to be replaced. This shows the DC motor control section in detail:

I recently designed a replacement part for the original Siemens relay based on a modern Japanese fully encapsulated SMD relay. I just received professionally manufactured boards made by a major PCB house. Here is an impression how these beauties (at least in the eyes of an engineer...;-) look now:

This shows the 25 turn 5k  trimmers prepared for installation:

And everything installed:

This shows the trimmers from solder side of the PCB. Their adjustment screws protrude through the original openings allowing RPM trimming while the turntable is running:

I improved the original design in that the trimmers are oriented in a way to correlate increasing RPM with a CW adjustment of the trimmer, which is more intuitive. Beolove lives in details!

After this I exchanged the capacitors and this is the end result:

The final step was to replace the original reservoir capacitor

with a new one. It sits in a 3D printed adapter to make it fit precisely into the compartment on the bottom of the enclosure and into the original holding clamp:

Beolovely! After this I calibrated the RPM with my BeoloverRPM device, and this is where the 25 turn trimmers shine. They allow a very precise adjustment, much more so than the original single turn pots.

Beogram 4002 (5513): Restoring the DC Motor

After I rebuilt the arm lowering and tracking mechanisms of the Beogram 4002 (5513) that I am restoring right now, it was time to get into the electronic parts. I decided to first look into the motor. This Beogram showed a perfect RPM stability, so there was no immediate need for rebuilding the motor, but I think a full restoration should include the motor to ensure longterm stability of the restoration and full day-to-day usability of the unit. So here we go:

This shows the motor extracted from the enclosure:

Then I took the motor out from the noise shield:

and took it apart. 

Then it was time to lubricate the sleeve bearings, clean the commutator and the brushes and put it back together. After installation I did another 24 hrs test, and the result was essentially the same as before. So it is all good in the motor department! On to exchanging the electrolytic capacitors and updating the RPM trimmers and relay!

Beogram 4000: A New Arrival and a First Look

A Beogram 4000 arrived recently for a restoration from Norway. I just took it out of the box and had a first look. Everything went well on the shipping end due to an excellent packing job using the original styrofoam inserts but a new box. The only thing that happened was that two of the control pads came loose, but the tape and foam inside the hood kept them from going anywhere and so no further damage occurred. Another demonstration how crucial it is to directly tape them down with non-residue tape to the aluminum panel above them.

Luckily this is an easy fix. Overall this Beogram is in great cosmetic condition:

A deep clean of the aluminum panels will make them shine again like new. The hood has the usual deep scratches:

This can be fixed with a nice 3 hr polishing workout in my garage...;-).

The plinth is in exceptional condition. It has very nice corners:

and only a few small dents.

Under the hood everything is pretty original:

No obvious signs of 'human creativity' albeit the carriage spindle bearing is bent preventing the spindle from turning:

Also the pulley is gone. I hope I'll find it lodged under the control pad or somewhere else, but for now cannot find it. But usually they are cracked anyway and one of Nick's nice aluminum pulleys will look great in there for sure.

There are another two key items that are in nice condition in this 4000: The lovely red position indicator appears to be intact

and the strobe light is working:

When I started it the AC motor came on without making noises, a testament to its quality Swiss design. However the tracking system did not work and also the OFF button is ineffective. But these are small issues that can be fixed for sure.

More critical is the damaged MMC20 mount in the original tonearm. In fact this 4000 came with a 4002 arm installed that also has a damaged mount:

One of the contact terminals is pushed back a bit...the original arm came taped to the aluminum panel and it has the unfortunately all too often observed broken off plastic tab and the flex PCB is dangling freely:

Luckly, it appears that my recently developed MMC20 mount replacement part is performing well in Sonavor's Beogram 4000 that he recently rebuilt, and I am getting more confident that this part may be indeed ready for prime time. This Beogram may be the second one to receive it!

Another issue is the right hood hinge, where a screw is currently replacing the steel pin that belongs in there:

I really wonder why people do such things to their 4000s!

In summary, however, I think this Beogram 4000 is a great starting point for a full restoration. At this point I do not see any show stoppers to get this beauty back to a near-new condition and functionality.

Beogram 4002 (5513): Rebuilding the Arm Lowering Mechanism and Linear Tracking System

I started working on the next Beogram 4002 (5513) that I recently received for a restoration. I first rebuilt the arm lowering and tracking mechanisms. They usually need attention due to hardened lubricants and misadjusted tracking sensors. This shows the solenoid-damper set-up before I took it apart:

Here is an impression of the disassembled mechanism for cleaning and lubrication:

  

This video shows how to rebuild the tone arm mechanism in detail. Next I focused on the linkage that connects the damper with the tonearm. It often moves with difficulty due to hardened lubricants:

The photo above shows the back of the arms. The two screws at the bottom right behind the solenoid (yellow) hold the sensor arm in place. I removed these screws and took the sensor arm out for disassembly:

This shows the linkage removed:

This video shows how to get to the damper to arm linkage and re-lubricate it. After putting everything back together I aligned the arms to be perpendicular to the keypad and parallel to each other:

Then it was time to replace the tracking sensor light bulb with my custom designed LED assembly. I always do that since the original bulb assemblies are not available anymore, and the LED based replacement has the potential to last for a very long time, ensuring trouble free operation down the road. This shows the original set-up:

and after replacing the old bulb housing with my replacement part. 

The blue square is a trimmer potentiometer that allows the adjustment of the intensity of the inherent LED. This makes the fine tuning of the tracking response much more straight forward than with the mechanical excenter alone.

Then it was time for Sam River and my dented MMC20EN cartridge from ebay to do the tracking sensor sensitivity adjustment. There is a video that shows the tracking sensor adjustment procedure in detail.

This photo shows the adjustment of the potentiometer after the coarse mechanical adjustment was accomplished:

On to the next task!

Beogram 4002 (5513): Rebuilding the Output Board and Adding a Grounding Switch

I also rebuilt the output board of the Beogram 4002 that I am restoring right now while I had the keypad out for cleaning the contacts. The output relay is a frequent source of low or no volume on one or both channels and so it is a great idea to replace it with a modern Japanese made encapsulated relay, which will last for decades. This shows the output board in its original configuration:

The old Siemens relay was replaced with this custom designed SMD relay assembly:

This assembly directly fits into the solder points of the original relay. It is available to other enthusiasts. Just send me an email. Here is an impression of the rebuilt board:

I also replaced the time delay capacitor for the relay with a 105C grade Japanese type. The switch that sits in front of the output jack can connect signal and system grounds if necessary for hum suppression. This can be helpful, especially if RCA plugs are configured and there is no separate grounding pin on the amplifier.