EMT 930

EMT 930 is a turntable with an idler wheel. Built as the „smaller brother“ of the legendary EMT 927 it is still a very demanded unit.

A chassis made of bakelite and coloured with „Hammerschlaglack“ rests on a metal frame. A synchronous motor with three phases moves a heavy platter by means of an idler wheel. Upon the heavy platter rests a light weight auxiliary platter which can be stopped. When the brake is released the continuously rotating main platter runs the auxiliary platter very fast with the standard speed. The motor rotates synchronous with the mains frequency and was either built for 50c/s or 60c/s. Also the strobo light is locked with the mains frequency and shines through the holes in the auxiliary platter to indicate the speed. The speed can be fine tuned by means of a felt brake below the main platter. Also like the motor the auxiliary turntable must be used with the mains frequency it was designed for. For using the 930 with another mains frequency please follow this instructions.

A direct coupled lift raises or loweres the tone arm. Until the tone arm EMT 929 was introduced the first units EMT 930 have been equipped with tone arms made by Ortofon.

The very first units had been pure mono units and have been equipped with the tube driven equalizer amplifier EMT 139 which was later replaced by a stereo version. Here and there the mono units are still available while the EMT 139st is a very rare unit. Attention: For using a tube unit the according supply voltages for tube and anode potential must be available.
The successor was the equalizer amplifier EMT 155 (available in mono and stereo) which in same cases was customized with 47kohms input for magnetic pick-up’s. To simulate a current at the anode potential a resistor was built-in. The high voltage was not longer needed for the EMT 155, but in older EMT 930 it was used to drive the stroboscope lamp.
Only the equalizer amplifier EMT 153 did not longer offer the possibility to switch to several equalization curves.

The bearing sleeve and the axle of the main platter are adopted to each other and can’t be replaced as single units. A good bearing will show about 180 seconds until the platter stays when used without felt fine tuning brake and started with 78 rpm. Replacing the oil depends first of all on the usage of the machine. But also a unit which is only seldom switched on should be serviced after 3-4 years. As far as your unit is not equipped with the rather old bearing (without cover with thread) it is not too difficult to replace the oil and clean the bearing. Please take care that also the motor, the felt of the fine tuning brake, and the felt of the idler are supplied with some oil. You can order the appropriate oil in packages of 50ccm (will reach for about 2 fillings) and 500ccm.

EMT 930 motor alignment

The motor of the EMT 930 is supplied by the mains transformer. So the motor gets always the right voltage, independent of the mains voltage. Although it runs with three phases it is connected only to one coil of the transformer. By means of a capacitor and a resistor an artificial phase is generated.

The needed capacity (about 1.75µF) was measured in the factory with a special measuring unit. Then the capacity was adjusted as close as possible by some small capacitors in parallel. So the hum of the motor is minized.

Over the years the capacitor’s capacity is drifting away and you may hear an annoing hum. At the same time you may recognize an increasing motor temperature and you may feel the motor vibrating.

For an alignment is needed:
Millivoltmeter, oscilloscope, soldering iron

How to align?
ATTENTION, YOUR ARE WORKING AT HIGH VOLTAGE!!!
DON’T CHANGE THE ADJUSTABLE RESISTOR!!!

In case of a safety cage at the motor you need to remove it to get access to the capacitor.
Connect the voltmeter and/or oscilloscope to the equalizer’s output.
Place the needle into an empty groove and try to get the mains switch in a position between the left most and the middle (not marked and normally not stopping there). In this position the motor should be switched on but the platter is not rotating. Depending on the sensitivity the hum will now be visible on the oscilloscope/voltmeter.

It will normally be ok to add small capacitors to the large one to minimize the hum. But it is also possible that the capacity is already too large and you may not achieve a better value.
In this case the large capacitor needs to be replaced. Please order the complete alignment set (9 930 902 which contains also the large capacitor). Then replace the large capacitor and add small ones in parallel until the hum shows a minimum value.
Don’t forget to mount the safety cage again and enjoy a hum free EMT 930.

EMT 930 with a different mains frequency

The motor of the EMT 930 was built for a certain mains frequency, thus terminating the number of revolutions and the platter speed. This is either 50cps or 60cps.

Therefore an EMT 930 made for 50cps but connected to 60cps will run too fast and vice versa (60cps unit connected to 50cps).

With the correct mains frequency the small holes in the auxiliary platter above the stroboscope bulb will show whether the platter rotates too slow, too fast or with correct speed. With the fine tuning brake the correct speed can be adjusted. The stroboscope divisions of the auxiliary platter are of course fix and valid only for one mains frequency (50cps or 60cps).

Even if the platter runs with the correct speed a wrong platter will show a wrong velocity.

How to adopt an EMT 930 to another mains frequency?

1. The best and most correct way is the replacement of the motor and the auxiliary platter:
Motor for EMT 930 50 Hz: 7 930 006
Motor for EMT 930 60 Hz: 7 930 012
Auxiliary platter 50 Hz: 7 930 237
Auxiliary platter 60 Hz: 7 930 398

2. Another way is to supply the turntable not directly with the mains voltage. On the market you will find a lot of frequency converters.
Although it would be technically correct the combination of a sine wave oscillator, power amplifier and reverse used mains transformer can’t be recommend as one would work with hazardous voltages which may cause personal injuries.

3. Resourceful people may also offer different solutions like modifying the motor axle. These ways don’t lead always to useful results and will cause trouble in case of a repair. Also the motor is used in a frequency range where it was not made for.

It is clearly recommended one of the first two methods. But it is not recommended to adjust the exact speed by means of an artificial mains frequency and to avoid the fine tuning brake. Each deviation of the nominal frequency (50cps or 60cps) leads to a misalignment of the auxiliary phase thus causing hum and warmth.