On the power of the SL1200

[Mike_New]

The fellow who I am working with on the conversion of a SL1200 to a cutting lathe, is now in Europe and will be flying to Australia to work with me on the fitting of the cutting head and my Base Plate and Bearing in mid May.
However I have an interesting question which maybe only the experienced SL devotees can answer:

The German engineer who is supplying all the high tech cutting-head gear, where he has spent a week in training; says that the SL1200MK2 provides more power/torque that the other models. And therefore is better for use in a cutting lathe application.

As far as I know the same motor-drive IC is used across the range of models and the coil assembly and drive magnet are the same.

Does anyone know if there is any truth in what he says??

[MartinT]

I thought the basic motor drive circuit uses the same drive IC in all the variants, but I might be wrong.

[The Grand Wazoo]

This is just what prospective Techo-jockeys need - another variant of the '301 Grease Bearing Legend' to drive prices up.

[Marco]

Lol...

That's a new one on me. I'll ask a man who'll know, though, and report back :)

Marco.

[Sonority]

This is just what prospective Techo-jockeys need - another variant of the '301 Grease Bearing Legend' to drive prices up.

Evilbay has them in all prices at present, bits from pence to a new boxed 1210 for £1500.00
Talk about taking the mick.

[Mike_New]

Lol...

That's a new one on me. I'll ask a man who'll know, though, and report back :)

Marco.

Thanks Marco, this also took me by surprise, the one thing that could be a variable is the output voltage of the regulator, if this was 1/2volt or more above the stated 21V then perhaps this could account for the extra torque.

[Marco]

No worries, Mike. The response from the chap in question:


Hi Marco,

All the motor boards are identical in all models MK2, 3, 5.

First, I suspect the comment is comparing an original 1200 with a Mk2.

The original 1200 had poorer control of torque.

The advent of the frequency generator in the MK2 gave much better control under load. And that would of course apply to all following models as well.

I don’t think voltage is the issue with torque. It is a question of control under load. I think I have seen mods to the control circuits that can improve control under heavy loads, but at what expense I don’t know.

Also, I think the SP-25 was rated as having higher torque, but I could be wrong. The SP-25 has the same parts as a 1200 MK2.
I would have to check into that further to give a definitive answer.

Torque is of little consequence in our applications. It takes a very loud groove modulation to demand more torque from the free running level.

I once put a scope on the control signal that drives the motor. And under most music, there is no added control whatsoever, the motor just runs free. The third 300 hz track on the hifi news test record for example will have the motor requesting more torque to hold speed. But that is a very loud track.

This is also influenced by tracking force. The heavier the force, the more drag the stylus placed on the groove.

My tests were done at 1.5 grams.


For me, the bit in bold would appear to nail it :)

Marco.

[Lodgesound]

All good for normal record playback however the tracking pressure of a cutting head is a lot greater than that of a replay stylus and tonearm.

Cutting lathes have extremely high torque motors for this reason - there was a company called Kingston who made a cutting head attachment for an SL-1210 - I believe it was a mere £7000 and was plagued with speed stability issues.

The turntable in your former avatar Marco - SL 1000 was it? - had an extremely high torque motor that is WAY more powerful than that of a 1210 - just try holding it by hand and pressing start.

[Mike_New]

You are correct the cutting pressure on this particular unit is I believe about 35gm
(as opposed to 1.5gms) which will cause some drag on the platter and hence the motor, however the German system seems to work fine for most direct recordings.