Thump Once Per Revolution

Thump Once Per Revolution

Postby Dorian » Sat Jan 06, 2018 1:17 pm

Hi guys

Experienced an odd issue last night, listening on headphones. Put on a new album and started getting a low frequency thump once per revolution. Experienced it on two different albums. Thump got worse as I increased the volume, even though listening on headphones, so I don't think it's acoustic feedback.

If you take a look at this video and watch closely, you'll see that there does appear to be a bump in the record once per revolution. I imagine that is very normal though, as no record is perfectly flat.

I checked that platter is level, VTF and anti-skate are good, and that nothing is physically impairing the movement of the platter or tonearm.

I then tried listening through speakers. As I turned the volume up, one of my power tubes cut out on the Integrated amp and then all sound cut out. I turned the amp off, waited a few minutes and turned it back on, and now it's fine playing through speakers, although I do see my woofers pumping a lot. Haven't gone back to try headphones again yet.

Any idea what the issue was? Tube going bad and not handling the low frequency thump once per revolution caused by the bump in the record?

Thanks.
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Re: Thump Once Per Revolution

Postby Brf » Sat Jan 06, 2018 1:38 pm

Does it happen only with that particular album? If so, there’s the problem.
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Re: Thump Once Per Revolution

Postby Dorian » Sat Jan 06, 2018 1:49 pm

Brf wrote:Does it happen only with that particular album? If so, there’s the problem.

No, multiple albums. But not every album.
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Re: Thump Once Per Revolution

Postby Stringreen » Sat Jan 06, 2018 2:39 pm

it sounds like the arm and cartridge aren't happy together....though Soundsmith carts and VPI arms usually do work well together. Do you see the arm shaking before the mistracking occurs?.....just looked at your video again and see the arm shaking....Call Soundsmith for a suggestion. (he might want to take a look at the cartridge)
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Re: Thump Once Per Revolution

Postby WntrMute » Sat Jan 06, 2018 2:50 pm

That looks like a warp that would cause a thump to me. I have heard a thump from warps just like that one myself. If you look closely, you can almost see the transmission of vibration into the cantilever! What happens if you let it play for a while? Most warps like that get less pronounced towards the center of the record. Since you hear it through the headphones, can't you look at it as you are hearing it? Another thought would be to mark the warp with a chalk mark of a small piece of tape on the side and then see if the thump occurs simultaneously as the warp passes under the stylus.
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Re: Thump Once Per Revolution

Postby Stringreen » Sat Jan 06, 2018 3:24 pm

Your arm/cartridge should negotiate most every warp.....something is amiss
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Re: Thump Once Per Revolution

Postby Dorian » Sat Jan 06, 2018 4:03 pm

There’s no doubt that the record does have a warp, but many do and never seen this behavior before even with this same record. It’s weird because now the same record is playing fine after the tube fritzed and I reset the amp. I’m leaning towards a tube problem.
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Re: Thump Once Per Revolution

Postby Brf » Sat Jan 06, 2018 6:42 pm

Your headphone output will be independent of your speaker output i.e. different circuit. Tubes either fade gracefully or quit. Since the thump is measured, it is more likely table, arm, cartridge related. The first thing I would do is re-lube the bearing, then check the vtf.
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Re: Thump Once Per Revolution

Postby Stringreen » Sat Jan 06, 2018 8:16 pm

Cartridge suspensions are designed to negotiate warps..... I would be suspicious of what you are experiencing.
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Re: Thump Once Per Revolution

Postby Lewisranchmike » Sun Jan 07, 2018 10:30 pm

I had a somewhat similiar issue. Just give a quick check to see it the anti skate thread is not binding on something. I my instance the knot at the end of antiskate thread was getting caught. Just one possible thing to look out for possibly

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