Tangential tonearm for turntable

pjrebordao

Senior Member
During the early 80's, tangential tonearms were all the rage, mostly for top of the range models. At the time, I admired their sophistication but I was clueless at how they worked. Nowadays, thanks to the web, few secrets remain. I decided to try building one, based on the workings of the Denon Linatrack.

In it, the cartridge was suspended from a very short arm that could rotate horizontally from a carriage assembly that would move linearly along the record radius.
While following the record groove, the needle would pull the arm from its straightahead position, an optical switch would detect the motion and command a small motor to pull the carriage assembly along using a wire guide, thus restoring perpendicularity of arm and cartridge. So, even a small tracking error leads to an immediate correction.

My tonearm follows the same principle, although with a different mechanical layout. Here, the carriage is attached to a toothed rubber belt pulled by a stepper. A photodarlington is used to detect the cartridge movement and 2 micro-switches signal the limits of the carriage travel along a linear guide. User input is provided by a 4-way joystick, and the following features are supported: Auto-stop at the end of play, Auto start for LP's and Singles, Auto-Repeat, Up/Down, Linear movement and finally Stop.

Due to the number of I/O lines needed, I opted for a 28X1 controller. The extra lines also allowed me to control the stepper using halfstepping, providing a bit of a smoother action from the stepper.

The tonearm works incredibly well and reliably. Only a very muffled sound can be heard on quieter parts, when the arm assembly moves. Guess that driving the stepper using microstepping would take care of that. That's a more complex circuit maybe for the future.
 

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slurp

Senior Member
It's a small world... I'm sure I've just seen this "rapid prototype" arm on the shapeways forum :D

Nice to hear more of the project.

regards,
colin
 
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