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
Dfc1b742 2146 4dcb bc58 f88d04cbafe0daveyonthecoast
I would try to fix the warp.

There used to be devices to fix warps. One remedy used to be to gently heat the vinyl between two sheets of glass in an oven. (Done carefully!)

I have a ring clamp on my VPI turntable which is heavy enough to flatten most warps.

Question: If this thump did not occur before your move, what has changed? Did you change any of your tonearm settings, like stylus pressure? Is the turntable support still level?
I suggest the back of your cartridge is hitting the vinyl .....a ring clamp would add height to the edge and probably make it worse. I suggest you raise the back end of your arm.... the result might even be better sound.
Turntables are tricky things to get set up optimally.

Warped records are always a problem, but more so with some setups than others.

Others might correct me, but if you hear the thump noise frequently regularly even with just modestly warping in the records, I'd suspect initially its most likely some combination of the tonearm having trouble tracking the record through the warp combined with a table system resonance occurring in the frequency range where the thump noise occurs.

All tables have resonant frequencies, but they can be tweaked in various ways using different combinations of tonearms of various mass and associated carts. There is info in agon forums and other sources on how to address these things.

Also, in general, higher mass tonearm/cart combos tend to have more difficulty in general trqacking through warped records due to the higher mass and associated inertia.

Its hard to recommend a specific solution to this problem, but at least these are the things I would say are worth researching and giving some consideration to to help remedy the problem.
As Stringreen says, the arm needs lifting at the pillar as either the rear of the cartridge is riding on the warp or the warp is catching your tonearm (you don't mention what tonearm you're using). A tapered tonearm like the SME IV/V series can be hit by a warp if the warp is bad enough or the tonearm is too low.
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.
Dear Friends
Thanks for all the feed back
When I mention that I have moved house, I can have the volume up a bit, thats when I noticed the "thump", om slightey warp LPs, as it has been very hot and humid down here, I have reset VTA etc!!
I was thinking, maybe the cartridge(Garrot Bros new P770 approx 200 hours), before many years ago I was running a Well
Tempered labs clasic,at high volumes, but becaused a long time ago I fogot the MC carridge?
I/m not sure do you all think. may be a promblem with the cartridge(suspension)?
Regards
David
Dear Friends
Thanks for all the feed back
When I mention that I have moved house, I can have the volume up a bit, thats when I noticed the "thump", om slightey warp LPs, as it has been very hot and humid down here, I have reset VTA etc!!
I was thinking, maybe the cartridge(Garrot Bros new P770 approx 200 hours), before many years ago I was running a Well
Tempered labs clasic,at high volumes, but becaused a long time ago I fogot the MC carridge?
I/m not sure do you all think. may be a promblem with the cartridge(suspension)?
Regards
David
Daveyonthecoast (Threads | Answers | This Thread)
It is possible for a cartridge suspension to fail spontaneously after some period of use.

I don't know much about the Garrot Bros P770, but have you looked to see if the cartridge sinks too close to the vinyl?

I assume you would notice if the cartridge body were actually hitting the record, but a faulty suspension could result in poor tracking ability and cause the thump you are hearing even without the cartridge hitting the vinyl.

Do you have another cartridge to try?
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....