Building high-end 'tables cheap at Home Despot II

In the original thread there was considerable conversation about hum that originates if the arm/cartridge crosses over the the motor. I think I am experiencing this.

I (finally) took the time to experiment with this low frequency hum from my VPI/giant Lenco/Decca (Grado now, as the Decca had to be sent off for repair).

It is coming from the cartridge interacting with the motor - either the electrical/magnetic field or amplifying the motor noise. When I de-couple the arm from the table, the low frequency hum remains audible, growing especially loud when the cart passes near the motor. Move the cartridge 6-8" away from the motor, and the hum disappears. I tried various grounding wires from the chassis and arm, and none of these made any difference. It's gotta be from the motor.

I don't think I can reset the arm - and when I move it to another corner, the hum remains about the same. The base is at the corner where the motor is, but the arm doesn't really cross over the motor directly. It seems to be more about how close the cartridge is to the motor than anything else. I have been using a grounded plug with this motor, but I doubt that's the cause. But maybe, as I am using the same motor from an earlier version but changed the cord, adding the ground. I suspect I have to somehow shield the motor better, but can't imagine how. Maybe something beneath the platter?

Any suggestions? Many thanks, and happy Thanksgiving. Btw, this baby still is magnificent, hum or no hum (it's not that loud, not nearly as annoying as, say, a ground hum).

Ccryder,
Why not try disconnecting the ground from the motor plug, or better yet, switch it out to a 2 prong plug. It may be an easy fix, well worth a try.
Of all the Lencos I have, not one has 3 prongs.
Good Luck and keep us posted.

Hi Mike: to make Direct Coupling a success the wood-screws must be tightened just so, just like tuning an instrument. So I use several wood-screws and I do indeed use lock-washers (or rubber-sided washers) to go between the head of the screw and the Lenco top-plate. I tighten until the washer is snug and solid with no sign of movement (and solid enough that if I try to move it with a screwdriver it can't be moved), and no further. I also use bolts in the original bolt-holes as Lenco intended. Also, I have Direct Coupled Lencos both with and without nitrile rubber as a shim (there seems to be some variation in the height of the top-plate), and have found absolutely NO sonic or musical penalty, recipients of either of these types of rebuilt Lencos have been universally gobsmacked, and I use both myself and am myself gobsmacked (thank you Dr. Lenco!) at the speed, detail, high, lows, midrange, power, bass and incredible dynamics, in either iteration!!

Hi Chuck: the Decca is a hummy cartridge (like the Grados), no doubt about it. The hum you're experiencing is the Decca picking up the motor's electro-magnetic field. So far, the only way to wipe this type of hum out is to follow Mario's recipe of two sheets of mu-metal glued to the platter. Click on Mario's system to see how it is done. In my own system the Decca also hums (like the Grado), but at such a low level that it is inaudible when playing music and I am not motivated to do the mu-metal mod. Also, I'm used to this sort of thing, being a fan of both Grados and Deccas (both of which hum on most turntables to some extent), and so it simply doesn't bother me (like tube fans used to some level of tube roar). You could try grounding the Lenco motor itself and see what happens, and as usual try grounding the 'table and not the arm, vice versa, both together, motor alone, all together, and so on until you achieve the best level of silence, every system responds differently to these combinations.

Over here I took my Mr. Red (copyright Mike Green ;-)) on the Great Travelling Lenco Road Show to Toronto, where a manufacturer and distributor of high-end audio goodies heard it, and he and his associates were blown away (it turned into a mega session with hours of music, no one could tear themselves away), and now there's a good chance the Lenco will be used to more effectively demonstrate their wares at an upcoming audio show, and in their shop. I won't report further until things are certain, but at least the prospect is pretty exciting news!! In order to make the demonstration more effectively, I used a $200 cheapie high-output MC to show what it can do with one hand tied behind its back, my beloved Satin M-117 with removable stylus, mounted on my Morch UP-4. Vive la Idler-Wheel!!!

Oregon & Jean: thanks both. I will try both ideas and let you know. The power of this thread is so formidable that when I was fooling around yesterday (with my wife's help listening) she was the one that said "you should post the problem on your favorite thread."

Ladies and gentlemen, for my wife to reach this opinion, well let's just say we've penetrated well down into the masses!

Thanks Jean, I'll tell you where to send the royalties :)

Mike