Meandering Pitch, Where’s The Problem?

As I’ve mentioned in other posts, I’ve been modifying a Thorens TD 160 MK1. It is and will remain a dedicated mono table. Currently, I’m using the original TP 16 MK1 tonearm with an AT 33 mono cartridge. I will eventually replace the TP 16 with an Origin Live tonearm and EMT mono cartridge. I still however like playing records while in it’s current state. What I’ve experienced with a number of classical records is pitch instability. Primarily when playing piano recordings. There are certain passages that are a problem and I’m not exactly sure the cause. My cartridge is aligned using Baerwald. I understand that with some records, especially very old mono vinyl, that the pressings could be off but if that were the case, then the entire album would be an issue. I do need a new belt but I’ve still had this issue with a brand new Thorens or Origin Live belt. Just wondering what others think and if there’s an antidote? Thanks!


If the belt is more than 5 years old that's the first thing I would try.  Cheap and it never hurts to have a new belt ....  

AC synchronized motor deck, I’d look at the belt drive system.

Remove and reinstall the outer platter inverted along with the mat and a record stacked on top to accurately load the TD-160’s suspension. Turn on the platter rotation and view the belt’s action on the drive pulley - I believe you’ll see it hunting along the taper causing the pitch deviation.

Dave @ Vinyl Nirvana knows Thorens belts.

@boothroyd Thanks Dave. You've been helpful the many times I've posted. I can do as you suggest but I fail to understand 'I believe you’ll see it hunting along the taper causing the pitch deviation.' Would you please clarify?

The drive pulley has a large 45 rpm diameter surface that tapers to a smaller 33 rpm diameter surface where the drive belt is meant to ride on. A drive belt with the wrong tension can have difficulty staying on the proper area where it will occasionally move vertically along the drive pulley where it bumps into the taper area which alters speed.

Again, Dave will be familiar with this 👍

On my off-Centre records, the pitch instability seems to get worse as the stylus gets to the innermost groove area. Does yours do the same? If it is an off-centre pressing, you will see the cartridge meander back and forth.

I imagine many of your mono recordings are old - or perhaps they were cut during the stereo era on an old lathe and it had speed problems? That would bake the wow and flutter into the vinyl.

I imagine you have checked the motor, and the condition of the pulley and belts?