"Heartbeat" sound at record end & beginning

[e093116]

I'm putting the finishing touches on an LS2 resurrection and am happy with everything that the machine does except it seems to have an excessive "heartbeat" sound that you can hear at the beginning and end of records.  I believe the noise coincides with each rotation of the record (once per revolution).

It is not a mechanical clicking or tapping sound from the mech, but rather noise that is coming through the speakers. I have two other machines in home service (LS1 and a second LS2), the other two machines are much quieter in this respect, if the noise is there at all.

The noise does vary from record to record, and I do know that all machines are slightly different and thus won't sound exactly the same, but I'm wondering if anyone is familiar with this "problem" and knows of a solution to minimize this effect? 

Maybe I just need better records?  I'd say the records are in the machine are in average condition, I have the scratch compensation in the middle position, and the needle pressure is at 3 grams for both sides.  Some of the records are not perfectly flat (you can see the tone arm oscillate up and down as the record rotates), but they all play good, the tone arm tracks nicely, and none of them skip or have other problems.

Thank you.

[Ron Rich]

Lift the ARM off the record--still there ? If so, use the Service Switch to stop the motor--still there ?

[e093116]

Lifting the arm off the record makes the noise go away.

If it makes any difference, I don't have a cover for the mech (didn't come with the machine and haven't bothered to find a replacement).  The other two machines that I have which are better in this respect do have covers.  Could this be part of the problem? 

[robnyc]

Hello "new member" What you are noticing can be caused by:

-Dried out or partially missing grommets behind the flywheel (turntable).

-Inadequate clamping by the pilot. this will often be accompanied by a flutter in the sound as the record slips slightly.

-End-to-end slop in the shaft that mounts the flywheel. There is a thrust screw at the extreme right of the mech. Do not adjust this unless you see/feel a bit of end plat in the shaft. There is a small ball bearing that may have gone missing in that screw fitting.

-Clutch member hitting one of the pins on the clutch star gear. This is rare and usually caused be someone tinkering with the clutch setups. Look at the rear of the mech while in play mode and see if the clutch member seems to be 'tapping at the the star gear. DO NOT adjust anything here unless you have the four step instructions available.

Ron probably has some more info here...he usually does.....

BTW: Does the volume fade up at the start of a record -it should as a function of the AGC squelch. I ask this because normally any turntable noise will not be heard at the beginning of a record due to the fade-up. those sorts of noises are generally only heard at the end of a record when the AGC follows the fade out of a record and brings up the gain.

What, if any, of the electronics has been serviced?

RobNYC

[Ron Rich]

Hi Rob,
Only other thing that comes to mind is the motor coupling--and how it has been installed, or if one of the "set screws" is partly sticking out and hitting the casting-- Thrust for the adjustable type turntable is, per manual, .003 to .007. IMHO that allows too much play--I adjust the screw down to .002-.005 at MAX. The .187 end ball MUST, still be round,turn freely,and MUST be properly lubricated. The non- adjustable style must also conform to the above specs. To conform, may require replacement of either/both, the ball and end plate. Ron Rich

[e093116]

Rob, Ron,

I reviewed the turntable assembly content in the manual and understand what you're getting at.

I haven't been into this part of the mech before on this machine, and knowing the as-received condition along with your comments, I'm going to start with checking the end play and the condition/lubrication of the thrust ball as recommended.

Probably won't get to this before the weekend, will report back with what I find.

Thank you for your suggestions.

Bill

[Ron Rich]

Hi Bill,
The SM is a little confusing in the statement about the washer thickness--dis-regard that, as that is an ASSEMBLY instruction, not a maintenance issue. Ron Rich

[e093116]

Managed to sneak out to the shop last night for a couple hours to finish off this job.

Wiggled the flywheel shaft and guessed that I could feel 0.010" of play. For fun, put a dial indicator on, and measured 0.013". I cleaned up the ball, re-lubricated, and adjusted to 0.003". This took care of about half of the problem.

Noticed the spring for the clamp arm was a little "sprung", with the ends obviously distorted and one coil disturbed in the center of the spring. Rather than try to tweak it, I shimmed the plate the spring attaches to on the clamp arm to "tension-ize" it a little more, shim height equal to about half of the height of the anti-rotation pin on the arm. This took care of the rest of the problem.  I'll have to see if I can find a new one the next time I need to order parts.

Then I blasted Urgent and a few other songs, enjoying the improved sound quality while I cleaned up.

Thanks again for pointing me in the right direction on this inquiry.

[Ron Rich]

Glad it's working --the spring pressures in the Seeburg mechanisms ARE critical. The "original" Seeburg, constantly inspected incoming springs, and most other "outside sourced" items, for compliance with specs. "Quality Assurance", as they called it, was very vigorous, however every once in awhile, something slipped by--probably the worst two things I am aware of were the "red tone arms" used in the SS-160 and early LS-1 models, and the main cam drive gear used in the early LS-1's. Ron Rich