New Technics SP10 motor controller specification

[Steerpike]

Originally Posted by brianco

It simply died. No noise, smoke, fumes, heat. New electrolytics were fitted 3 years earlier. Regs seem to be normal, Diodes all work. But voltages unstable in the 32.5 section. They swing widly, yet as I said, regs appear to test OK and caps also.

That's sort of a contradiction. If the regs are working OK, the voltage can't swing wildly. Unless the drive circuitry is drawing a phenomenal current - but something must then get hot.
Does it ever exceed 32V, or always dip below 32V?
Does the Ac voltage entering the rectifier for that section remain fairly stable - should be around 25V AC I believe?

[brianco]

Thanks Steerpike,

I have decided to wait until your units are ready.

I am sending the deck + PS etc to vantage audio who are the very good UK specialists in classic DDs. It will be handy to have an overhauled PS + motor. [I have a second SP-10 Mk11P just as it came from a BBC studio. It will be simple to add the old supply to this to compare with yours!! ]

A local tech has seen this PS and has no clue, but I think that he is more fitted to dealing with stage amps etc.

Here is Vantage Audio's site:

VANTAGEaudio reference systems® from GRP Associates

[Steerpike]

Originally Posted by Steerpike

The original circuit I posted here came direct from the Philips 1988 IC Databook but on calculating values for it earlier today, I'm pretty sure it would never work as published. My modified version is down the bottom of <<page4>>.

This has been RE-modified. I cannot get anything useful out of the Philips circuit. I abandoned it and am going with a voltage-to-current PWM setup.

[Steerpike]

Originally Posted by Steerpike

...and am going with a voltage-to-current PWM setup.

pulsegen.gif

I'm liking this circuit a lot! Varying the reference voltage (IC2 pin 3) gives a variable PWM ratio of around 7,5x. This is adequate for speed control over the entire range of 14RPM up to 100RPM. BUT, it's pushing the stability limits of the current source at the extremes. My prefered solution is to select a different value of R16 for each speed, use R4 only as a fixed reference, and drive Ic1B's pin 11 (Control Voltage) with the servo/feedback error signal. Since the CV pin modifies the reference point of the 555's internal comparators, it provides a very linear means of PWM control.

(my breadboard power supply has decided to go on the blink this weekend. The Fates must have pms)

[rich121]

Just checking if there are any updates, as I'm sure like others, I look foreward to the fruits of your work...I'm really looking forward to getting some new electronics into my SP10's...

Rick

[Steerpike]

I've got the PWM drive circuit going and generating nice variable duty cycle waves. (the dead power supply had put a delay on things, but that is now repaired).

Basically what I now have is the DD equivalent of a commutated DC motor driven from a variable voltage power supply. So it is ready for some servo control experimentation.

[Steerpike]

My under-currented Heathkit testbench supply and an overly bulky and under-voltaged computer power supply have been thus far an annoying pair with which I have been doing my testing.
I decided I needed something more convenient to do the SP10 experiments with, so I put this together with parts lying around. It's not a great supply, but it will make things from now on less frustrating!

[Steerpike]

The circuit for the phase detector and PWM generation is up:

Phase/frequency detector

I'll be doing the PCB layout for this part in the next few days. This particular phase detector layout I have not experimented with pratically before, so it will be interesting to see what sorts of results it produces!

I have left the quartz oscillator out so far. Without any pitch control, it is a very simple circuit addition - I think I'll make space for it on the PCB in that form.
Variable pitch will require the intervention of a microprocessor, which isn't yet on the cards - not until the speed control loop is working on its own.

[Steerpike]

A few minor corrections to the circuit...
clickable link to PFD circuit
The PCB layout is progressing quite fast.

[Steerpike]

The PCB layout is now done too. Slightly messy still, it needs to be checked and tidied up a bit. The clock reference (crystal) is not on this board - for testing I will use an external oscillator so I can apply continuously variable frequency.

click: image of PCB layout for PLL