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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

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

Tuesday, January 16, 2024

Beogram 4000: A New Arrival from Massachusetts

It is always a happy moment when a customer comes back for more! In this case I restored a Beogram 4000 for a client in Massachusetts in early 2023, and now I received a second 4000 from him. I guess one cannot have too many Beograms!...;-).

This Beogram 4000 arrived safely packaged in a Beolover box. It also came with an exciting present for the Beolover!! (Thank you very much!):

This lovely 180g re-issue of one of the greatest Jazz records of all time, Bill Evans Trio: "Waltz for Debby", which was recorded live in 1961 at the Village Vanguard, will be perfect for celebrating the completed restoration of this Beogram 4000!

I inspected the cosmetic condition. The aluminum surfaces are in pretty good shape!:
The plinth corners are also still pretty sharp and have only minor flaws:
I removed the platter and the panels for a look 'below deck':
The unit seems in pretty much original condition. The usual stress-fracture is developing in the carriage pulley:
Happily, the red position indicator is still intact:
I plugged it in and pressed start: The strobe light for the RPM adjustment came alive with a health orange glow:
Beautiful! The deck also found the LP setdown point and the solenoid activated. All good signs!
This should be a straight forward restoration. Stay tuned!

Thursday, January 11, 2024

Redesign of the BeoloverRPM Device: Precisely Measure and Log the Platter RPM

I recently decided to redesign my BeoloverRPM device, which I started developing in 2015 for the detection of intermittent RPM variations mainly of DC platter motors. I thought after ~8 years it could use a little update in terms of ergonomics and performance. The original device was based on an Atmega 328P processor (aka 'Arduino') and this limited the performance a bit. I recently got into using the much more advanced ESP32 platform. This enabled a few new tricks due to the much higher speed.

The new BeoloverRPM can be placed on the aluminum panels for a quick and convenient RPM check

but it can also be configured for frame mounting when working on a Beogram:
This was achieved by a design where the frame adapters can be removed from the main device:
The BeoloverRPM comes with two frame adapters that have different spacing between the 'legs' that straddle the enclosure wall. B&O used slightly different enclosure designs with varying wall thickness.

Another significant update is that the BeoloverRPM now has two data acquisition modes:
The modes can be selected via buttons on the device. The 'slow' mode performs similar to the previous designs. It shows the RPM and min/max values on the display, and sends a RPM snapshot to the serial port every 10s (faster if the RPM changes quickly).
The 'fast' mode is new: It graphs all datapoints as they come in whenever a rib passes under the sensor. The display shows a rolling snapshot of the last 64 datapoints. The data is also sent out via the serial port. Here is an example measured on a Beogram 4004:
The main graph shows the data output from about 60 platter rotations. The graph shows a repeating pattern modulated by a sinusoidal envelope. Closer inspection yielded that the pattern repeats every 24 points, i.e. everytime the platter makes a full turn (there are 24 ribs on the platter). This can be explained by minute changes of the rib spacing (it varies by about 0.1%).
The sinusoidal modulation is a result of the feedback based RPM control of the DC platter motors of the later Beogram 4002 and 4004. Feedback control always results in an oscillation of the actual value around the set point. And that is what we see here. The analog feedback mechanism used by the later Beograms is based on time constants defined by capacitors and resistors, and this results in sinusoidal RPM variations.
Fascinating stuff!...;-).

I made a short video about the new BeoloverRPM. Enjoy!

Thursday, January 4, 2024

Beogram 4004 (5526): Installation of a New Hood and Aluminum Trim

This post is a follow up to the main restoration summary of a Beogram 4004 that I recently posted here. Due to a shipping mishap I had to wait for another hood to arrive from the Beoparts-store in Denmark. The first one  came chipped:

Unfortunately, the Beoparts-store seems to enjoy saving on packaging, and so a minor whacking of the package on its way through automatic sorting machines or while being bounced around in speeding delivery vans can cause significant damage. This shows the damage to the carton at the location of the above chip:
These fairly delicate hoods come in a single cardboard wrapper 
with barely enough space on the inside for a double bubblewrap layer around the hood.
Definitely not enough cushioning. Luckily, the Beoparts-store does not make a fuss about such damages and they replace for free. Though I really wonder if this is very efficient compared to double boxing them outright. Charge a few $$ more for the additional packaging and save everybody some time?

Anyway, the replacement recently made it in good shape, and so I set out to repaint the corroded hinge. This happens fairly often with Beogram hood hinges. Two pictures of the damage:
I took the hinge assembly apart to get the main part ready for spray painting:

Normally, pretty decent results can be achieved by sanding the corroded areas with an orbital sander followed by spray painting with a satin enamel. This is the result of my efforts:
Not perfect, but definitely much nicer than the corrosion!
This shows the hood replacement and the reproduction aluminum strip:
And here after everything was put together:
This concludes the restoration of this Beogram 4004, and it will soon be time to send it on to its owner.