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jmcilkley · 4th May 2021, 9:08 am

Thanks for the advice so far. When I say that the frequency oscillation is at about 4Hz that is not the amount by which it changes but the up and down of the frequency oscillates at 4Hz (approx) - like a 4Hz vibrato!
I was hoping to work out the rotation speed of the capstan to see if this 4Hz warble is related to that.
The flywheel is not too tight and has been cleaned with ipa, so I don't think that is the problem. I'm still thinking it is a capstan problem as the warble is so constant. The tape speed is 1 7/8 in/s which is 47.624 mm/s. So the capstan circumference would be 47.624 divided by the number of times the capstan rotates in 1 second and the diameter would be 47.624 divided by pi divided by the rotations.sec (=15.157 per revs/s). To match the warble of about 4Hz the capstan would have to rotate 4 times a second which would make the capstan diameter 15.157 divided by 4 = 3.79mm.
Clearly the capstan is smaller than this - using a mm rule it looks about 2mm. So it seems it is not in time with the capstan itself. Unless an eccentricity makes 2 cycles in 1 rotation which would give a diameter of 3.79/2=1.9mm which looks about right.
Any mathematicians out there to check my working?

4th May 2021, 9:08 am	#6
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Cassette capstan speed. Thanks for the advice so far. When I say that the frequency oscillation is at about 4Hz that is not the amount by which it changes but the up and down of the frequency oscillates at 4Hz (approx) - like a 4Hz vibrato! I was hoping to work out the rotation speed of the capstan to see if this 4Hz warble is related to that. The flywheel is not too tight and has been cleaned with ipa, so I don't think that is the problem. I'm still thinking it is a capstan problem as the warble is so constant. The tape speed is 1 7/8 in/s which is 47.624 mm/s. So the capstan circumference would be 47.624 divided by the number of times the capstan rotates in 1 second and the diameter would be 47.624 divided by pi divided by the rotations.sec (=15.157 per revs/s). To match the warble of about 4Hz the capstan would have to rotate 4 times a second which would make the capstan diameter 15.157 divided by 4 = 3.79mm. Clearly the capstan is smaller than this - using a mm rule it looks about 2mm. So it seems it is not in time with the capstan itself. Unless an eccentricity makes 2 cycles in 1 rotation which would give a diameter of 3.79/2=1.9mm which looks about right. Any mathematicians out there to check my working?