New Technics SP10 motor controller specification

[Steerpike]

Those who've scrutinised my PC-board layout very closely, will see that I've changed the design slightly from the circuit which I posted a while back. Now LM317T and LM337T ICs on both supplies:
(i) the are better performing chips than the 78- and 79- fixed regulators.
(ii) I'm still not exactly certain what voltages I want. With the 317/337 chips the voltage can be set anywhere just by specifying 1 or 2 resistors, rather than swapping the IC itself.

[Steerpike]

I'm getting close to finishing up the printed circuit layout for the board which will contain these circuit blocks:

• the 3-phase power stage,
• the exciter oscillator,
• the 3-phase AM phase detector,
• the tacho preamp & wave shaper.

As always, when the board gets close to finished, squeezing in the last few components and tracks becomes annoyingly tricky. A few more days ought to suffice. I hope!

[Steerpike]

Not absolutely complete - a few traces still to place - but this is pretty much the above post in visual form.
poa.gif

[Steerpike]

I have updated the power supply web schematic / circuit-diagram to match the one I used for the PCB layout. This is its 'final' form, unless things go unexpectedly later on.
sp10psu.gif

[Steerpike]

Here is now the entire drive circuit (schematic), excluding the PLL section, which will plug into the socket on the bottom left of the diagram:
drivepc.gif

This is the schematic that matches the printed circuit board artwork (except the component reference don't match up yet)
poa.gif

With this board, the motor will be able to be run - although not with quartz accuracy.

[Steerpike]

In a private message I was asked:

but what does signal name "NFZB" stand for and who generates this signal?

I think I used those letters to stand for "Negative Feedback / Zero Balance".
It is the feedback signal derived from the motor's star-point, filtered and buffered.

If there is any asymmetry in the motor armature windings (due to physical tolerances of construction) this signal compensates for that by adjusting the drive so the star point is always at zero volts. In a perfect motor the star point would always be at zero volts and need no external connection.
With star-point feedback, the torque is more uniform within a single rotation. It's not strictly necessary, but it takes some of the burden off the servo system to have as linear-as-possible motor.

[ckniker]

Thanks for the explanation.

So, how does one adjust the NFZB signal? I see the potentiometer for the adjustment in your schematic but am unclear on how I'd go about setting it.

Sorry to be so dense but am I to adjust until "NFZB" and "Star" are at equal potential (voltage)?

Since one leg of the pot is connected to ground, it's pointless to adjust to 0V in reference to ground.


p.s. The schematic names the signal as "NZFB". I assume this is a transposed typo.

[Steerpike]

Originally Posted by ckniker

So, how does one adjust the NFZB signal? I see the potentiometer for the adjustment in your schematic but am unclear on how I'd go about setting it.

Sorry to be so dense but am I to adjust until "NFZB" and "Star" are at equal potential (voltage)?

Since one leg of the pot is connected to ground, it's pointless to adjust to 0V in reference to ground.

THEORETICALLY - since I have not finished building it yet:

The pot would be adjusted by putting an oscilloscope on the motor's star point, (referenced to power supply ground, 0V) and adjusting for minimum (or zero hopefully) amplitude. A centre-zero moving coil meter would also work.

The NFZB signal will be an asymmetrical sum of 3 sinewaves. By addng more feedback, they ought to be supressed. I have no idea what the variation among the production run of motors was, hence the adjustment rather than just puttting in values based on my particular motor.

p.s. The schematic names the signal as "NZFB". I assume this is a transposed typo.

Probably done late at night! I can't exactly remember what I invented the acronym to stand for. Maybe it was Negative Zero-point Feedback. It's all the same signal though. That actually sounds better than my previous guess :-)

[Steerpike]

What joy! The drive PCB layout is finished. Just needs proofreading & a little neatening up.

[24valveman]

Well done Steerpike. What would diyAudio be without people of your vision. Thanks.
Andy