Lenco L75 rumble : Help (video)

[duroon]

Hello,
when I rise the volume (a little) then comes the rumble
If I push the top plate (in the corner) the rumble desappear
How can I better the situation without working too much ?
Thank you

Here is the Video :

[da-jack]

Hi Duroon,

I could be wrong - but to me this sounds much more like hum than 'rumble'.
Does the hum only stop when you press down top-plate or is it enough to just touch it to make it stop?
If so, you should double-check if the earth-wiring of your tonearm and top-plate is ok.

Good luck!
Dan

[bush baby]

Hi, It might be useful to know the history. Have you moved the tt recently or dismantled it? Has the rumble always been there or did it suddenly appear? Etc.......
I agree it is worth checking the earth condition.
For a rough solution you could always stick a suitable weight in the corner assuming you don't have to press too hard.
Also I would check the idler - is it clean, is it in good shape, try experimenting with the tension spring.
Good  luck.

[duroon]

there is also a bit of "uhm" due to imperfect ground (when the plate is stopped)
But when it's ON (playing) (cartridge on LP ..)
There is NOT the rumble in the beginning of the video (cartridge is not yet on the LP)
The top plate has vibrations, I can feel them, touching with my hand
there is a kind of resonance, vibration, and rumble (I do not know how to call this)
perhaps the platter should be more isolated ? (the springs are not working correctly ?)
perhaps the turntable sounds better without springs ?

[da-jack]

The Lenco does sound better directly mounted to a heavy plinth... BUT:
If everything runs as it should, it is also a very fine sounding deck in it's original state!

Since you're writing that you can feel the vibrations on the top-plate, I would guess your motor is not running as quietly as it should.
Have you checked out the 'Lenco Guides' section of this forum regards the cleaning and lubing of the motor, bearing, etc?
If not, you should go through these servicing procedures, it's all very well documented and an easy job to do.

Best,
Dan

[duroon]

Thank you for answer da-jack,
you're right, there are many things to check

.. I add : to hear better sound of the video you have to use headphone

[OsteSpiser]

 Ummmm - feed-back "howl" ? Are the speakers close to the turntable?

Hum or rumble would be constant in level relative to the music, feed-back increases as you increase volume.

-kristian

[duroon]

Correct OsteSpiser, the speakers are close to the turntable  (unfortunately, that's the situation ...)

Hum or rumble would be constant in level relative to the music, feed-back increases as you increase volume.
it is true !!

[mucko]

Sounds like mechanical noise to me. Have you removed the transit screws? Pressing the chassis like that might change the geometry underneath and disengage a light contact.

[h-j-hill]

Well, it is not mains hum, nor a harmonic of mains hum.  The frequency of the oscillation is 82 Hz.



I suspect that feedback from the loudspeakers is causing the Lenco top-plate to oscillate vertically on the springs. 
When you touch the top-plate, you dampen that oscillation.

I'd go further and suggest that you have a problem with one of the 'room modes' - the air along the length, width
and height axes of the room behaves like air columns in an organ pipe.  Is the turntable and/or the loudspeakers
near a wall or the floor?  Is your room about 4.2 metre long?

[duroon]

The room is 4,23 metres long !!  

The turntable should be restored : old idler wheel produces noise, old top-plate's springs ... (better spings or top-plate fixed on the plinth ??)

Using cubes in "Expanded Polyethylene Foam" from packing  ("A" in photo 2) I have eliminated completely vibrations and feedback, (see photo 1)  the sound was nonetheless undefined
I have used then 3 wall door bumpers ("B") the sound has bettered but I haven't obtained isolating, and I have feedback if I rise the volume, much more than at the volume that I usually listen .. maybe is better than nothing and better than before (photo 3 and 4)
The Clamp betters the sound a little but is boring using it everytime, for the feedback problem I didn't hear improvement (photo 5)

photo 1 :


photo 2


photo 3


photo 4 :


photo 5 :


Best Regards

[Andr039]

Could you remove the lid? 
best,

[mucko]

I shall try again. Have you removed the transit screws?? They lock the motor for transport. They are under the platter - normally with a dab of red paint. They might seem to be clear but the geometry changes when you fit the platter. Take them out altogether to be safe.

[duroon]

with or without lid is the same (for feedback)
the strange thing is that approaching the speaker the feedback increases

[duroon]

here is the situation :