Beogram 4000/4002/4004: Test of New Custom Manufactured Beolover Carriage Motor

Sometimes carriage motors in Beogram 4000, 4002 and 4004 can be pretty noisy. Most likely their bearings are also in need of an oil infusion under vacuum, like the DC platter motors. Unfortunately, both the original Faulhaber and Maxon motors cannot be opened easily. So the remedy until now was a drop of oil on the shaft and hoping that this would do the trick for some time. After all these motors run much less than the platter motors.

But I always thought this was a less-than-Beolovely solution. Therefore, during the last couple years I tried out a variety of small motors with similar footprint but had to find out that all standard motors were way too noisy and vibration generating. Only after I sent one of the original motors to the supplier of the motors that I use in the Beolover SyncDrive for evaluation it became clear that the carriage motors used in the Beogram 400x are something special:

They are so called "coreless DC motors". Such motors have a rotor constructed as a hollow, self-supporting coil, often in a basket or honeycomb pattern, which eliminates the need for an iron core. This results in reduced mass, reduced eddy currents, lower inertia, and smoother torque/lower vibrations. The result is a motor that runs much more quietly and draws less current compared to normal motors with iron cores for the same performance (but that also has a significantly higher price - you get what you pay for!...;-). The quietness is crucial for driving the carriage since the slightest vibrations on the floating chassis can translate into sound audible in the speakers since they directly couple into the pickup. During my trials of standard motors the carriage drive was quite audible while listening to music at moderate volumes.

My supplier was able to design a modern coreless replacement that has a torque and voltage that is close to the original motors. I had a few samples manufactured and recently received them.

Here is a picture of the new Beolover carriage motor fitted with a custom pulley::

These motors are now available at the Beolover store.

The motor is easily mounted in the original motor enclosure using two EPDM rubber O-rings that help dampen any vibrations the motor may emit and also align it with the enclosure:

Since the new motor is a bit shorter than the original Maxon and Faulhaber motors, the leads can be fed though the cutout in the bottom of the enclosure:

This makes for a nice and clean installation:

It is a good idea to replace the original usually wobbly plastic pulley on the carriage spindle with a new precision machined Beolover aluminum pulley when exchanging the motor.

I performed some measurements that compare an original Maxon motor in one of my Beogram 4002s with the new motors. These oscilloscope traces show the voltage at the motor terminals while playing a record. The first curve corresponds to the original motor:

And the second one to the new Beolover motor:

The oscilloscope settings were the same for both measurements. We see that the new motor responds at a lower voltage, which corresponds to a smaller deflection of the tonearm necessary to get the motor to move. This is most likely a result of the lower friction inside the motor due to its fresh bearings that provide optimal lubrication. The consequence is that after implantation of the new motor the tracking feedback may need to be adjusted slightly to get the specified sensitivity. If a Beolover Tracking Sensor LED Light Source has been already installed in the tracking sensor, this can be achieved by simply reducing the light intensity of the LED slightly by adjusting the built in trimmer.

An important factor in motor replacements is the current draw under identical operational conditions. The H-bridge on the main board already struggles a bit with the current consumption of the original carriage motors, which is evident in the occasional need to replace the power transistors, especially those providing the current for the travel direction towards the home position (>>). So I definitely did not want replacements that would draw more current than the originals.

These are my measurement results for the two motors:

The only difference between the two columns is that the original motor was replaced with a new one. All other parameters like the <, > speed trimmers were kept the same.

It is clear that the new motors draw considerably less current in the same setting. Their performance however is very similar to the original motors as can be seen from the time it takes to complete a full platter sweep. This was done with an empty platter and measuring the time it takes between pressing Start and the moment the deck shuts off after the carriage came home again. The original motor did it in 18.0 seconds while the new motor was slightly faster at 17.5 sec. It should be noted that these absolute numbers will be somewhat different in every Beogram due to friction variations caused by adjustments and lubricants etc...But it is clear that the new motors will result in much less heat load in the H-bridge.

Another happy aspect of the new motors is that during these tests it became apparent that the new motors run noticeably quieter than the original ones. Which may have to do with their more modern design, but also with their fresh bearings and better lubrication.

In summary, it appears that the Beolover carriage motors are an easily installed cure for noisy original motors.