L75 tonearm rewiring and headshell modifications

[Devo]

I also have been thinking about if it isn't possible to bend the arm tube (like you bend a brakeline or a copper waterpipe) in the wright angle so you can use a normal straight headshell.

Just a thought

[rightspeed]

The new headshell looks a bit short indeed. If you can´t achieve correct overhang etc., you coud try to extend your headshell by placing a small plate to which the cartridge would be attached. You could then adjust the VTA at the tonarm base.

However, it could fit the geometry for smaller records (10-inch, 7-inch). Not sure about that, just a thought.

Also, I would think that bending a tonearm is a rather difficult thing to do, especially on the sturdy, chromed Lenco armtube.

Pierre

[tsip]

Thanks Pierre. Bending the armtube is not in the scope of this exercise which is finding a simple way of altering a non original headshell for a rewired arm that had the connector removed.
As mentioned the black angled headshell seems to have an effective length of 215mm so I can play with a protractor to see what may come out of it. Interestingly the straight SME type headshell has an effective length of 225mm which again makes it possible to test. I am intending to use an AT-95 headshell. At the moment I am testing with AT300P which might have the cantilever placed further than non P mount cartridges.
Anyway the only way i guess is to measure and test.

[ecco]

One possible solution is to build adapter between the Lenco original tonearm and SME headshell. Something like this 3D print I made:



When using that angled SME headshell the geometry might be quite near the original layout?

Unfortunately, the pin connections between the two types are not the same, so it is not possible (or at least rather difficult) to connect these two connectors directly together.
This solution only works when you have drilled those inner parts out of both.

[tsip]

Nice work ecco! I have removed the pin on my arm and will rewire straight through. The headshell fits nicely without an adaptor so I am happy with that part of the experiment. I need to play around with a protractor to test geometry. I have another angled headshell to test  and will report back

[tsip]

An update on a couple of really interesting stuff.
I have measured the black angled headshell and it will not work. The effective length of the tonearm (at the edge of the headshell) is 217.3 at 25 degrees offset, which would probably not work even if we extend by 8-9mm to assume that stylus tip may extend the cartridge at the outer slot of the headshell. We need at least 227-228 effective length for optimum results and be able to achieve 22-23 degrees offset. (the straight test SME type headshell has effective length of 228.3mm but no way to past few degrees in offset.)

As I am now invested in this experiment, I also took the plunge and bought a fairly cheap AT-HS4 headshell which is still in production and readily available. This is an excellent quality angled headshell. AT indicates stylus to tip distance of headshell at 51.2mm (with cartridge sloted in the middle of the run) which i confirmed with measurements. The Lenco tonearm from pivot to edge of headshell connector measures 170mm, which means the AT-HS4 gives an effective length of 221.2. Much better. If we assume that stylus tip can extend another 8-9mm from outer slot of the headshell then we can ensure proper alignment. So this will be the headshell that i will test.

Another interesting idea is the rubber washers that SME type headshells sport at the connection with the tonearm have 1mm thickness. So a couple of these can extend the effective length by 2mm. See the attached pictures. Same would be true for appropriate diameter metal washers or of any type of washer. The advantage in this application is that 2x1mm spacers align exactly the pin hole of the SME type headshell to the pin hole of Lenco tonearm, which makes it ideal for a screw or pin to go in to secure the bond! I would probably put a slightest touch of cyanoacrylate glue as locktite in addition to the screw.

The question is: would the rubber washers at this position provide any useful damping or would it be preferable to have metal or other stiff material washers?

Attaching some pics as they are far better than words. Thanks for any additional advice.

[Chopsaw]

That’s a nice headshell and I like what you’ve done so far. I don’t think the rubber washer will be of any consequence. It does look good in position though and adds some contrast so if it were me I’d leave it in. I’m not keen on the self tapping screw though. A short grub screw in the hole just to gently lock the headshell in place would be sufficient.

[tsip]

Thanks Chopsaw for the encouragement. Regarding the rubber washers I researched their use and for SME type fit these are there to mainly ensure the collar doesnt get overtightened. Therefore in my application rubber has no real use, and as you pointed out, there are no material gains in terms of damping. However in my application they do extend the effective length which is great. Therefore after a brief research I found a seller on ebay that sells replacement washers made out of 6/6 nylon instead of rubber, which is exactly what i need, a rigid and light material (that also looks cool as you noted).
Regarding the grub screw you are right, that would be ideal but unfortunately I dont have the tools to create a nice tap. I therefore used the no2 self tapping screw and it worked great. I also added a small piece of stiff packing foam to direct the tonearm cables away from the threads of the screw.

I removed the collar nut,  and did a "dry" fit  of everything and I am very pleased with the result. In terms of weight, there is a reduction of 8.25gr over the original setup, which is substantial. In terms of effective length I measure around 228.2mm with an AT VM95C at the furthest edge of the run. I will finalise my measurements in the next few days and insert the cable and should be good to go.

[Chopsaw]

Nice

[Devo]

Looks really good with the AT headshell

[Wout]

Agreed! Nice work. 
I wouldn't worry too much about the original alignment parameters of the L75 tonearm, they are a bit odd.

[tsip]

Thanks Wout and Dennis.
Wout, this thread has been my bible so far as it has been confusing figuring things out from published specs.  Good thing is that AT, in typical japanese style, has everything well documented regarding the headshell and cartridge including measurements so I can largely rely on these to solve for part of the equation.

[Pockets]

Has it gained 8.25g or lost it?

[tsip]

lost it comparing to the original shell and connector. I edited to make it clearer, thanks Mike

[tsip]

A brief update. I have now had time to do some better measurements. The GL75 spindle to pivot is 210.95 so pretty closed to published specs. The tonearm effective length with the VM95 at its furthest is 226.5-227mm and the stock offset angle of the headshell seems to be 22 degrees.
This allows for pretty good alignment possibilities and I am very happy with the result. I haven't listened to it yet as its now time to do work on motor and plinth.

The result of this endeavour is a rewired tonearm, with a modern headshell, half the price of the Thakker/Analogis and better manufactured with less connections to the phono cable, and a reduced weight of 8.25gr over stock headshell. The trade-offs are tight effective length threshold and irreversible modification to the tonearm with the removal of the headshell locking collar.


Not sure if any moderator would want to change the title to what has essentially been retrofitting an SME type headshell on stock Lenco arm. If there is interest I can post a few pictures of the process as a guide.