By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Sunday, December 24, 2017
Beogram 4000: Final Adjustments, Some Odds and Ends and a Test Drive with Cal Tjader
After exchanging the black painted plinth with a teak plinth from a Beogram 4002, it was time to do the final adjustments and give this beautiful Beogram 4000 a first test drive. After adjusting the platter height, tilt and alignment with the surrounding aluminum panels, I adjusted the arm lowering limit to ensure that the needle will miss the black ribs on the platter should there ever be a malfunction in the platter detection mechanism. The limit needs to be adjusted that the needle misses the lower parts of the ribs by about 1 mm:
The next step was to adjust the tracking sensor feedback that the arm would track parallel to the sensor arm:
Then came the motor waveform adjustment. Essentially, the trimmers need to be adjusted until a nice sinusoidal is achieved at the highest possible amplitude. An oscilloscope is helpful, but in absence of one it is possible to adjust the motor simply by listening to it. Increase the amplitude until it starts getting noisy, and then reduce it until the noise goes away. This is the measured waveform:
While I still had it open, I also installed a grounding switch that allows connecting signal and system grounds. This can be helpful for hum reduction, especially if RCA cables are used like in this Beogram (RCA does not carry the system ground, that is why there is usually a separate wire to connect the system grounds of amplifier and turntable when RCAs are fitted). This is how the output terminals looked like before implantation of the switch:
And after installing the switch:
Then I installed a nut on the screw that holds the counter weight of the arm in place. Originally, this screw is only held in place with a flimsy retaining washer allowing it to move a bit:
I took the retaining washer out and replaced it with a M3 nut and a washer:
This allows fixing the calibration in place in a more permanent way, which is a necessity if it is to survive the shipping process intact. Now it was time to calibrate the tracking weight:
This is done best with a digital gauge since they are very accurate and do not cost much money anymore. One last thing: One of the mounting bolts for the hood had a 'custom fashioned' spring that did not work very well. I replaced it with a new one to ensure trouble free hood installation:
And then it was finally time to give this lovely Beogram 4000 its first post-restoration spin!
I selected a recently obtained record by Cal Tjader from 1971, simply called "Tjader". His output from the 70s usually earns less raving reviews than what he did earlier, but I really like this record. Especially the tune "What Are You Doing The Rest Of Your Life" (one of my big questions, too!...;-) is a very nice and smooth tune. Here is an impression of Cal together with the Beogram:
A lovely combination! I will now play this Beogram a bit longer and then it will be time for it to travel back to Germany!