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Thump noise on the lead in on warped LPs

Hello friends
I have a Mitchell Tecodeck, with a upgraded Garrot Bros P77 cartridge.
I have moved appartments, which means I can turn up the volume a bit, but not that much!!
I have had a bit of a promble, a lot of my mint LP,s were purchased with shwink plastic, and a lot comes with a slight warp(Which I guess is normal)
I have played all above with no prombles, but now seem to have a "Thump" on the lead in track, when the cartridge,arrive to the top, but when the cartridge drops down from a very slight warp, it makes a Thump??, untill, half way thought 1st track, where it settles down
Hopimg some can help
Regards
David
128x128daveyonthecoast

Showing 2 responses by moonglum

moonglum
619 posts
 
Hello Davey...
I agree the likeliest explanation is the cart could be "bottoming" on the warp.
Also agree tapered SMEs and warps do not mix well.

If you are using a technodec then chances are you are using a Technoarm(?) I'm not sure these come with ready VTA adjustment. (Perhaps owners will advise?)

If this be the case you have options :

1. Shim the arm at the base.
2. An easier, less stressful fix is if the Technodec uses a 5mm mat you could try a thinner one e.g. Ringmat with Latex underlay (4mm), bare Ringmat (3mm) or the 3mm Achromat?

Kind regards...

PS : You may have to increase the VTF after any of these moves.
moonglum
619 posts
 
Dear Davey,
Your comment about rising temperatures could be significant.
Each 5 degree C temperature change could be equivalent to 1mm of VTA. This is how much you should be looking to compensate for once it swings away from the ideal 21-22C.

If I'm not in error, each 4mm of VTA is equivalent to a 1 degree change of angle(9" arm).
4mm VTA change needs approx 0.25g VTF compensation.

If the cart is indeed "bottoming", it doesn't surprise me that it normalises halfway through the first track. If you were having serious suspension problems I'd expect you to get less specific instances of record contact.

Hope this helps.
Kind regards....
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