Music Hall mmf-7 spins faster

It is indeed in the right groove, Eddaytona: the smaller one (and the larger one, as indicated, when I am using the Speed Box II).

Where is "as indicated" indicated?

The Speed Box appears to output 16 volts ac (VAC), while the MMF-7 appears to come with a 12 VAC wallwart power supply. I note that the ratio of 16 to 12 just happens to be approximately the same ratio as 45 rpm to 33.3 rpm. However the recommendation to use the larger pulley diameter with the Speed Box, for 33.3 rpm, would seem to make sense only if the motor speed were inversely proportional to supply voltage, which seems nonsensical. .

I don't know what kind of motor the MMF-7 has -- whether it is synchronous to the power line frequency, and what the sensitivity of its speed to line voltage is. But very conceivably it is different from the motors used in the Pro-Ject turntables for which the Speed Box is intended.

I would therefore do three things:

1)Try using the Speed Box while the belt is placed on the smaller rim of the pulley.

2)Try the 12 volt ac power supply from your friend's turntable.

3)Use a multimeter, set to measure ac volts, to measure the voltage provided by the power supply that came with your turntable, and compare it to what your friend's power supply puts out. Since you will probably have to disconnect the power supply from the motor to make that measurement, keep in mind that the voltage figures to be higher than it would be with the motor connected and running. Which is why I suggest comparing the readings of the two power supplies.

Re bearing oil, see page 14 of the manual for the 7.1, which I assume is similar to the 7 in that regard.

Regards,
-- Al

Lrmellon -- Are you reading the 18 volts while the motor is connected and running (in which case it is probably much too high), or when the motor is not connected to the power adapter or is not running (in which case it might be ok, and the best way to tell is to compare the measurement with your friend's table, under the same conditions)?

Re your second question, I have no knowledge of what might be inside the motor assembly, but my guess would be "no."

Regards,
-- Al

Just grasping at straws here, but have you at any point taken your complete turntable to another location, such as your friend's house, and tried it there? Although it would seem unlikely, perhaps there is something grossly wrong with your ac power, either the frequency being too high, or unusually large amounts of harmonic distortion. If, as I suspect, the turntable's rotational speed is synchronized to the power line frequency, perhaps that could be the explanation.

Also, you've undoubtedly checked this, but just to be sure, could there be an accumulation of some sort of detritus around the rim of the small pulley, that would in effect increase its diameter?

Regards,
-- Al

My feeling is that pursuing a variac-type device is not worthwhile at this point. Although I'm not familiar with this particular design, I would expect the design of any turntable to be essentially insensitive to ac line voltage variations, within a reasonable range (although it quite likely is sensitive to ac frequency); you've measured that the voltage is perfectly reasonable; you've tried a voltage regulator; you've tried the turntable at another location; and you've tried two alternative ac power supplies (your friend's, and the Speedbox).

Another thought is that in my (extensive) experience as an electrical engineer, often when a problem is particularly baffling, and making all kinds of substitutions does not help, it turns out that there are two problems simultaneously present. Such as one of the substitute parts having a similar problem to the original. I don't know what that might mean here, but it's something to think about while you wait for the next motor to arrive.

Regards,
-- Al

Wow! Seems counter-intuitive, though, that a loose fit between the rod and the pulley would result in too fast a speed. Too slow a speed, or an erratic speed, certainly would be understandable. In any event, glad it's solved!

Regards,
-- Al