New Technics SP10 motor controller specification

[brianco]

Originally Posted by Steerpike

I just finished etching the PCB. Better not drill it now, it's 1:45am and the neighbours would complain!

You are really motoring now!!! Well done Steerpike!

[Shaun]

Nice going! You seem to have used the copper space very efficiently.

Gotta love that Tango, huh? Gees that brings back memories...

[Steerpike]

PC board is finallly drilled!
I've been correcting/matching-up all the component part numbers on the PC board overlay & circuit diagram, and creating a parts list.
I'm short on some components, so I'll have to go shopping early next week before I can fill the board & test it.

[Steerpike]

This is now as 'final' as the theoretical circuitry gets; (though practical tests might show up faults that require modifications)
sp10pwm2.gif
Above pic is linked from my page4 in case you want the accompanying text. Certain component values are still not show - tests and calculations required to determine them.

[Steerpike]

Dang! I was soldering in IC sockets & pondering the wanderings of electrons and I discovered an oversight:
C16 has a DC offset on it = the RMS value of the phase pickup coil voltage, and I neglected to remove it anywhere.

In a way, it's being there can simplify things, since it eliminates the need for the 4053 analogue switch having a negative supply reference (Vee), and the op-amps then get a larger supply voltage.
The DC can then be removed by making R51 a capacitor/resistor series combination.
The TTL level shift circuit voltages change very slighty too (0v instead of -7)

[LewM]

It seems I stayed away for just the right amount of time. This is very exciting to me, too. Will this controller work for a MkIII as well? If not, will there be a way of altering the electronics to run the MkIII? And, Steerpark, how do you plan to disseminate this work? As a kit, for example? Thanks in any case for your work.

[Steerpike]

Originally Posted by LewM

Will this controller work for a MkIII as well? If not, will there be a way of altering the electronics to run the MkIII?

As far as I can tell from the paperwork I have on the MkIII, my circuit ought to work - a few passive component changes to accommodate the much heavier platter. I have not actually studied 'numbers' so I won't promise it will yet - I'll have to look at the service data for the MkIII.
The main problem - if there is going to be one - would be the current drawn by the MkIII motor at startup. The L165 chips can handle quite a heavy current briefly, so I don't expect it will bother them, unless you did something like forcibly back-cue the platter while it was trying to run.

There is ALWAYS a way to alter electronics to do something you want

... how do you plan to disseminate this work? As a kit, for example?

For now, my plan is to put it all on my web-page, circuit diagrams, pcb artwork, etc.
I had not really planned a kit, but depending on how much demand there is, I could possibly do that. And I have NO idea what people would expect to pay. My aim was to get an SP10 going for absolute minimum cost (a kind of 'show it can be done' experiment') since the motor cost me almost nothing, but if I bought all the components (rather than using from my accumulated store) it would add up.
Another main aim was to use universally available parts, that anyone, anywhere in the world could easily get - so a kit wouldn't really give you anything you could get from your favourite components dealer.

One friend was concerned that someone might lift the information off the web and use it commercially - i.e., THEY make up a kit and sell it. But one thing that really bugs me about 'public' projects in magazines & on the web is where they withold one critical component, like the eprom code that you then have to buy from them.

Progress so far:
Page 6 # testing

[Cobra2]

MkIII has a different motor, (last I looked, is reminded me about the SP-15-motor)

Arne K

[Steerpike]

I've found two Japanese web sites that seem to use the Kaneta circuit on an SP10 and an SL1200 motor:

Google Translate

Google Translate

These are translation-routed URLs. I have a little difficulty understanding the translated version!

[Steerpike]

Originally Posted by Steerpike

The DC can then be removed by making R51 a capacitor/resistor series combination.

^^^ What a load of rubbish!
I had a momentary lapse of reason. Putting any DC blocking element in the drive path will prevent the motor from self starting, no matter how long the time constant. It needs static DC voltages corresponding to the 3 phases to exist even when stationary, as if the 3-phase AC were frozen in time.

A workaround is to add a DC offset to the rectifier. But the offset is determined by the amplitude of the exciter oscillator, if that drifts, a DC error will result. So the offset is derived by rectifying the oscillator output, and feeding an adjustable portion of that back into the rectifier's otherwise unused non-inverting input.

Correction principle shown in the attachment.

Looking at the Kaneta circuit, I see no such DC correction. I think he just ignores the DC offset and lets it persist throughout.