I have a Garrard 401 that I cannot get to hold a steady speed. Even after 30 minutes warm-up, the speed will vary +/- 0.01 RPM on each rotation. I am measuring with an accurate tachometer that does not average.
The main bearing has been cleaned and polished, and oiled properly. The platter rotates smoothly and rundown is over 30 seconds. The motor has been disassembled and the bearings replaced. It spins freely.
I know that these tables do have some inconsistency but it seems that this one is too variable.
The only thing I can think of is that there might be some problem with the motor windings. I will appreciate any suggestions. Thank you.
The main bearing has been cleaned and polished, and oiled properly. The platter rotates smoothly and rundown is over 30 seconds. The motor has been disassembled and the bearings replaced. It spins freely.
I know that these tables do have some inconsistency but it seems that this one is too variable.
The only thing I can think of is that there might be some problem with the motor windings. I will appreciate any suggestions. Thank you.
That is one part in 3333, or 0.03% which is excellent. Variance once per revolution of the platter
would be mechanical (not electrical), such as platter balance, etc.
would be mechanical (not electrical), such as platter balance, etc.
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The manual says wow < 0.08%rms, which means yours is performing just fine. The obvious cause of an error
like this is wear of the idler, leading to slight eccentricity - a spare idler wheel could be tried to see if it changes
performance. Slight eccentricity of the platter might be involved too, not easily fixed. What is the accuracy of
the tachometer too?
like this is wear of the idler, leading to slight eccentricity - a spare idler wheel could be tried to see if it changes
performance. Slight eccentricity of the platter might be involved too, not easily fixed. What is the accuracy of
the tachometer too?
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Thanks to each of you for your excellent thoughts. I'll try to answer them.
No, I can't really hear the problem when playing albums. However, I've restored about 40 turntables, including a couple 401s, and this performance is notably worse than any other. Trying to fix/improve it is a DIY quest for better performance.
It does make sense that it could be something mechanical. I will go back through all the mechanicals again today.
The idler wheel is new (Audio Silente). The motor bearings are new. I've tried removing the eddy brake system and that doesn't make a difference.
I am already using a motor control system. The one I'm using is based on the SG4 driving a class D amp which steps up through a transformer. The design is proven and allows fine tuning of the frequency and the voltage sent to the motor.
I don't know the specific accuracy of the tachometer (from thread here on DIYAudio). It's based on Arduino and uses a Phoenix sensor. I've validated it's results to a phoenix Engineering Roadrunner. The RR averages the response but I've diabled that feature on my other tachometer.
The tachometer reads speed only once per revolution, so I don't know what the variation might be during any given revolution. I do have the Feickert Adjust + as well as a Kenwood Wow & Flutter meter so I will give that a try today.
Thanks again.
No, I can't really hear the problem when playing albums. However, I've restored about 40 turntables, including a couple 401s, and this performance is notably worse than any other. Trying to fix/improve it is a DIY quest for better performance.
It does make sense that it could be something mechanical. I will go back through all the mechanicals again today.
The idler wheel is new (Audio Silente). The motor bearings are new. I've tried removing the eddy brake system and that doesn't make a difference.
I am already using a motor control system. The one I'm using is based on the SG4 driving a class D amp which steps up through a transformer. The design is proven and allows fine tuning of the frequency and the voltage sent to the motor.
I don't know the specific accuracy of the tachometer (from thread here on DIYAudio). It's based on Arduino and uses a Phoenix sensor. I've validated it's results to a phoenix Engineering Roadrunner. The RR averages the response but I've diabled that feature on my other tachometer.
The tachometer reads speed only once per revolution, so I don't know what the variation might be during any given revolution. I do have the Feickert Adjust + as well as a Kenwood Wow & Flutter meter so I will give that a try today.
Thanks again.
I am using a very similar solution for measuring rpm and find it a bit optimistic to trust for a single revolution measurement. Not quite sure what exactly is to blame but if you really want accuracy consider using multiple sensors and not just a single one.
I agree completely. I have used this tach with multiple sensors (4) but not on this table. Of course it's critical to get all sensors evenly spaced around the platter or false readings result.
This tach also has the option to average. I have used that function and the speed still varies more with the 401 than with other tables I've worked on (idler and belt).
Could the addition of an electronic motor speed control that monitors platter speed be the cause of the issue? The Garrard motor is designed to work against the eddy brake ie there is meant to be some resistance in the drive system. Could the two speed control systems be incompatible?
Not really. What is called a "controller" here is merely an accurate frequency, low distortion ac source, so not substantially electrically different from the mains. Of course, there is also a step-up transformer, so driving impedance is higher than using the mains.
Does that higher impedence present a problem?
By the way, I've tried with eddy brake removed and it doesn't seem to make a difference.
I don't think the higher impedance makes any difference. Only mentioned it because it is the only electrically meaningful way your setup is different from stock.
It must be easy to repeat the measurements while feeding the motor straight from the mains.
It must be easy to repeat the measurements while feeding the motor straight from the mains.