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View Full Version : Modified SL1200 VTA Mechanism to fit alternative Tone Arms



Mike_New
08-05-2010, 02:41
For those of you who have been wishing for a decent VTA adjustment on your replacement arms on the SL1200MKx. I have decided to offer a service to modify the existing SL1200 VTA adjusting mechanism to accommodate the different arms that may be chosen for the SL1200.

I have made this decision following a large degree of interest from those people using my new bearing, and who have expressed interest in proceeding with a changeover.

As can be clearly seen from the first image, the existing adjusting ring is retained; as are all the threaded components. The centre mark is exactly 214mm from the spindle centre and is the distance required for the popular Jelco arm. The scribed arc represents a distance of 222mm and is the distance required for the Rega 250 arm.
You will note that I have not shown any mounting holes for the outer retaining ring. The provision of these and the cutout to clear the Platter may need to be at the option of the customer as I have noted that there are a number of fixing hole arrangements used on the various SL1200 models.

As can bee seen from this arc there is more distance available for longer arms. However allowance must be made for the locking nut underneath, which in the case of the Rega is a whopping big nut which is 37mm across corners, for a column diameter of 23mm. The Jelco has a column of 30mm but the outer diameter of the retaining boss (which is clamped to the top of the brass insert by three screws) is 57mm. This will conflict with the location of the VTA clamp lever, unless the boss is relieved in this area to clear the lever.
Alternatively a replacement boss could be supplied for those people using a Jelco arm.+

The blue marking represents the boundary of the locating and locking pin mechanism underneath the centre ring (see the second image) and cannot be infringed on.
On this second image you can see that the locating pin and locking cam are located into a solid brass block, once again, as with my bearings, this provides for a rigid mechanism.
You will note the four socket bolts, these clamp the outer ring onto the new adapter plate, which now locates into the arm well and allows the modified VTA to sit further down below the surface of the plinth. In fact if you look carefully, you will see that the threaded outer ring held by these bolts is in fact the original top plate, now machined down to a minimum diameter and fitted onto the adapter plate.

The original locating pin and locking mechanism are used, as these fit well with my modifications and so there is no sense in changing them!!

I believe that this approach for the SL1200 models is the better path than trying to re-engineer a VTA device from scratch, which entails some complex threading which will result in a stiff or sticking mechanism if it is not carried out to very fine standards. The design flexibility of which is constrained by the small space in which the assembly must fit. I have made use of the existing three finely threaded rings, and have therefore retained the smooth operation of the device, especially when well coated with a good silicon grease or Vaseline. The VTA assembly and the direct motor drive are the two great features of the SL1200 model in my judgment.

Now we come to the difficult bit!! Because I am modifying an existing VTA assembly, I obviously require one to modify!! So potential users have two options, they can send their VTA assemblies to me for modification or they can procure a second unit on Ebay for a few dollars and send it to me. This way they can then either retain the replaced VTA/arm or sell it on Ebay to someone else who maybe wants to do the same thing!

I make no claims to any radical improvements in sonics or massive increases in sound depth for this mod. It only serves as a convenient means of varying the VTA on the fly! on replacement arms that do not provide any convenient means to do so, and that would be most of them I believe.
I have not mentioned any price for this service, as Dave in the UK may possibly want to work with me on this.

Finally a word of advice, do not try to do this yourself unless you are a very competent fitter/machinist, the sections are very thin and can be instantly destroyed if you are not very careful!!

Gdg
08-05-2010, 12:24
Mike, is this spare part enough to get the job done:
http://cgi.ebay.it/Technics-Parts-Turntable-Tone-Arm-Base-Assembly-Black-/140399527040?cmd=ViewItem&pt=DJ_Gear_Lighting&hash=item20b076c480

or you need the outer piece, too?

EDIT: Yes, of course you need the VTA locker, too...

Mike_New
09-05-2010, 06:27
What you are looking at in both images, is the modified complete VTA assembly which consists virtually of the complete unit minus the arm. I remove the arm from the top part and then cut off the rest, then machine out the inner part to take the brass insert.
the outer dished black part which normally fits into the plinth is machined down to fit the new fixing plate.
The part shown on Ebay is ideal except that it does not include the outer part which is internally threaded and into which the assembly shown on Ebay fits.

Mike

Jason P
09-05-2010, 14:19
Can you PM me a cost for this Mike - ballpark if arm dependant?

Jason