Sony PS-6750 - tonearm twisted.

[Gromit]

The tonearm on my 6750 appears to be slightly skew in its mounting. That's to say that it's impossible to get the arm anywhere near parallel to the record - try it set parallel and the VTA is way off, I mean seriously way off. I'm wondering if it was like this from brand new as there are no grub screws holding the arm pipe into the bearing housing - if it was held in with screws I'd have no problem re-setting it (as I did on a PL71 once). The arm can't be bent either as being CF it's stiff. Put the arm into its rest position, look at it from the side you can see the headshell end bending dowards - the only way it would do this is if the armtube isn't set correctly. From the front you can see that it's as though the arm's been twisted anti-clockwise ie the 'outer' bend of the tube is pointing up - this puts the headshell in a downward attitude. I've tried gently twisting the armtube to where it should be, but there's no way it's going to budge and of course I don't want to force it.

The cartridge azimuth is spot on (ie the headshell collar's slot is perfectly vertical) and whilst the VTA is perhaps a little hot, it all sounds fine. It's just that to get the headshell platform 100% neutral in terms of VTA, it means having the arm set very low.

Think this might be a job for J7.

Question is, does anyone else's 6750 display this? Bit of a long shot I appreciate as the deck's quite rare. Thanks all. :)

[hermit]

There's a copy of the service manual on Vinyl Engine. The manual has an exploded view of the arm which may be helpful. My deck doesn't have a similar problem as far as I can remember. It's away being recapped just now (-:

[Gromit]

Thanks Paul - I've actually got the service manual, and it's a useful thing to have of course, but it doesn't say a lot about the tonearm except how to remove/re-fit it.

Clearly Sony thought it better to glue the armtube in place rather than use a slightly more conventional grubscrew set-up (a la Tecchy/Pioneer PL71 etc). It's the same at the headshell collet end - glued in place (or an extremely tight interference-fit). I'm just wondering if there's a sonic penalty being paid due to the fact that the arm has to sit very tail-down to achieve correct VTA at the cartridge end. It certainly sounds very good, nonetheless.

Will be interested to hear how your Sony sounds/performs when it's been re-capped. Been considering having mine done - who's working on yours?

[hermit]

Richard, have a look at the exploded diagram of the arm at the end of the manual :) I'm not expecting my deck to sound any different when it comes back. I'm hoping that the recap will sort out a slight speed stability issue that has developed. It's inaudible but visible against the strobe. I'm getting the work done at a local hifi repair store.

[Gromit]

Had a look at the diagram Paul - the lateral weight is held in by a tiny locking nut but it doesn't actually have any effect on the armtube itself. I was hoping it might double up as a locking nut/screw for the armtube but sadly not. I removed it anyway, and gave the armtube a careful but firm tweak, resulting in slight movement, but really it's not going anywhere without some serious force being applied. My mechanical sympathy makes me reluctant to force things. :)

If I could get the arm removed I'd send it up to Johnnie7 for him to take a look at.

[Johnnie7]

is it possible the arm was bumped in transit etc?
hard to image it would come out the factory not straight

[Gromit]

Hi John - not sure if it's suffered any damage, but I dare say it's always a possibility. Saying that, there's no evidence of any impact and the geometry is spot-on using the gauge. The arm tube is so stiff in its mounting (ie where it goes into the bearing housing) it would take one hell of a knock to twist it - a knock which would most likely show up with damage elsewhere.

[Ammonite Audio]

What you really need is another PL-71!

[DSJR]

Sony and Technics weren't above making slight errors in their day - the two SL1500's I've had in recent years both suffered rattly tonearm bearings, which was easy to sort with a Dual bearing setting tool (the pins on the Dual outer tool fitted the external slots perfectly).

The headshell socket is probably where the important setting for vertical azimuth should be (as viewed from the front of a cartridge). If the pipe is slightly twisted, I don't think that's an issue if the headshell socket can be swivelled and locked in place. Is VTA adjustable in the arm pillar, or do the vertical pivots not line up with the offset headshell angle (causing the azimuth to vary depending on pivot height)?

I'll see if VE have the manual and take a gander...


P.S. Just done this and the horizontal arm bearings are not in the same angle as the headshell offset - a design anomaly IMO as it would have cost nothing to have corrected it I feel, as the S bend could have been adjusted to suit at least. This means as you've said that the bearing height is critical to the vertical azimuth of the cartridge (as viewed from the front). Looks like you set the pivot height to get the arm as level as possible and adjust/swivel the headshell socket to get the headshell level at the front.

P.P.S. No problem in having the arm set slightly too low at the back, as so many styli it seems, even now, offer too deep a rake angle IMO...

[Gromit]

Thanks Dave - that's useful info. :)

Yes, the arm does have adjustable height, quite nicely engineered as there's a spring within the pillar which forces the whole assembly up when the VTA screw is released. Setting height is therefore really easy - release the screw, and push down on the arm pillar until correct height is achieved.

The OEM Sony headshell is adjustable for azimuth and overhang, cartridge being bolted into fixed-position screw holes.

The deck still sounds pretty darn good though. :)