Rebuilt lenco gl75

[IslandPink]

Ooh ....
Sounds unlikely to be the platter.
What's going on in that mysterious headshell ? - I'd go investigating for anything loose betwen the stylus and the arm-wand.

[cressy]

we are all ok there, nothing loose, it does it in a certain frequency band. with the balance and rider weights in place the counterweight stub vibrates around like you wouldnt believe. flick the end of the rider weight stub and it vibrates for ages. the counterweight stub is decoupled using a high tensile wire so is a resonant structure rather than a damped structure. having had a chat with my dad, i reckon its this coupled with the cart compliance and the fact that the new v blocks are solid and not rubber thats setting up a resonance in the arm which is causing this wierd distortion.

[Cressy Snr]

The crappy counterweight tension wire resonant system needs to be disabled, to stop the counterweight doing its own thing and wagglng the cartridge about. Failure to do this will wreck both cartridge and records eventually. Unfortunately this is not as easy as it may sound. This problem explains why not many Lenco restorers keep the stock arm. If the counterweight and stub have any sag then the tension wire system is fooked and the arm is scrap.

I reckon it is possible to fix this by sawing off the counterweight stub and drilling out the brass inserts and tension wire, then fitting a tube within the tube and Aralditing the stub back to the arm tube. Another possibility would be to wrap thin waxed twine into the concentric gap where the arm tube meets the stub. That should short circuit the internal tension wire and also prevent the counterweight swinging about.

This page gives a list of arms that fit the Lenco hole without having to hack the top plate about.

http://www.hifi-studio.de/hifi-klassike ... .html#arms

[cressy]

OK, I'm slightly shocked.
I genuinely thought there was a problem with the way I'd put the arm back together, but no.
Picked up some waxed twine, wrapped it into the gap, not even a full wrap, just sort of stuck it in there so it was held in by the pressure of the counterweight pulling down.
No distortion.
If this is a mod, how the hell does anyone put up with the way it sounded before?
It was hideous. If this is a case of 'they all do that sir' unless you short out the decoupling then I can see why nobody gives the bog stock lenco arm the time of day.

[IslandPink]

That system does seem to have died out , for some reason

There must have been a few duff ideas along the way, particularly back then . I'm not actually too impressed with the way SME did their counterweight ( decoupled with rubber bushings internally ) on the 3009 and 3012 to be honest. At least it sounds 'mellow' ; but you lose a lot of midrange tone, when compared to a Schick arm, or a Mayware, or some of the modern arms like the Origin Live.

[cressy]

At least the SME system was a damped system, that I suppose starts to lose some clarity as it wears and the bushes start to go. With the lenco system, when the piano wire stretches, the tail wags the dog, adding a large amount of distortion as the arse end of the arm is doing whatever it wants in reaction to what the cart is doing at the other end. To make matters worse, you have a lump of weight on one end of the counterweight stub in the form of the counterweight, and another on the end of the rider weight shaft. These are unequal weights at unequal distances from the point where it is pivoting, setting up a pendulum effect that's constantly trying to snap back into line, but cant. A bloody awful piece of design in hindsight. But a design of its time and hindsight is a wonderful thing..
You could actually see the entire assembly going crackers at the slightest input.
I've honestly never heard anything quite like it
Perhaps I could turn a solid arm wand..........

[cressy]

OK so now we have resoldered all the joints in the arm wires and heatshrunk them rather than the tape lash up I had to give it a test, I also changed the armtube earth ground point from the back of the left phono socket ground to the back of the IEC inlet and changed the arm ground lead to a much more flexible one, I felt it wasn't flexible enough. Also cleaned up the headshell leads and crimped them a little to better fit the cart pins. It could do with some better ones but they'll do for now.
I did the waxed string mod properly and tied it off , all you can see is the black knot in the string above the gap.
Set it up again with an ADC qlm30 mk3.

It sounds actually really rather nice, comparisons with the modded lenco and the awesomeness that is the jbe are a little unfair as they have the origin live arm and the mc10 on them, ( i swap the complete arm and cart over ) but its more laid back in its presentation more so than the jbe in particular, the bass is good if a little thick for my tastes, treble a little recessed, bit I could quite happily live with it day in and day out. A change of cart would probably pay dividends. Wish you were here sounded really good, I had been using it to see if there was wow on the long steady tone on crazy diamond, mainly as the drive system has been completely rebuilt. There was none.

So the answer to the question no one asked, is a standard lenco worth a bothering with ......
Of course it is!
Providing the awful counterweight stub design is circumvented. And its put in a decent plinth rather than a sprung one
Think I'll put my sl15 mc cart in it.