New Technics SP10 motor controller specification

[Steerpike]

Originally posted by Steerpike
Kbe = 17.99 v/rad/sec

Well that's wrong! It should be 0.506
(But I can partly blame Quattro Pro - their linear regression help gives X and Y data the wrong way round)

[Steerpike]

Page 3 has some additional new theory and simulation plots.

[Steerpike]

Two rather interesting articles I found on phase detectors - if anyone is thrilled by such arcane reading material:

Kikkert, C.J., Two novel phase trequency detectors. 2006. James Cook University, Queensland Au

Gillig, S.F., Linearised three state phase detector. 1990. Motorola, Schaumburg Ill.

I want to get some suitable ICs next week & do some experimenting with circuits as described in these articles.

[rich121]

Shawn started this thread over a year ago..he posted 2 times..then I answered, as I also have dreamed of being able to build an updated/seperate controller and power supply for both of my SP-10's.
The 3rd poster was Steerpike, which again, was over a year ago..all type of talk since about building updated controllers/power supplies with XYZ functions...

only problem, one problem..

it seems this is just talk.

I am limited in what I can offer, I am an electrician, I do have soldering skills and can put together a project..
but, I can't design one, or this would have been done long ago.

Question:
Is this just talk and banter, or is this actually going somewhere?

I have posted so many times because right when everyone gets their collective hopes up, this place dies...then, I make a similiar post, and then Steerpike, and/or others post eventually stating that projects are near finished..... blah blah blah...

I just want to know..as I find myself checking this thread less and less..

Am I wasting my time??????

Rick

[Shaun]

Hi Rich

Steerpike has done some substantial groundwork, but it seems this is the kind of project that just takes a while to get done. I personally have no reason to rush, given the current financial state of affairs and the fact that I have an SL-1200 as a stand-in until the SP10 project is done.

Although I am capable of designing the controller myself, I just don't have the time or experience to make it a feasible effort. So I'm glad for Steerpike's initiative. His approach is correct, and he has done stuff I simply would not have done, that is, developing a mathematical model.

Even I have been rather slow. I promised to send Steerpike an SP10 chassis but, until now, the furthest I've got is to package it. At least now it is sitting in my lounge, and I'll probably send it off this week sometime.

[Steerpike]

Hi Shaun & others
I'm looking forward to getting this piece of hardware, and seeing if & how my mechanical tests using the old Garrard 301 platter-with-extra-weights differ or match up! So thank you very much for that offer!

One thing I now know better is that using a low DC supply to the motor will affect the startup time. Dynamics ought not to be affected once it is at running speed. Originally I anticipated using around +/-9V to the motor, but I think I'll up that to +/-15V. Not that it really matters for Hi-Fi use - fast starts are important only to brodcasters.

I now have my Pres-'n'-peel, so I can start putting together a PCB for the power amplifier stage. That is a necessity before I can do some experiments on the actual PLL circuit.

I have been wanting to write a software model for the ASM (algorithmic state machine) type of PLL - the one on my web page that uses a shift register.

Sadly projects like this have to wait for leisure time.

[Steerpike]

I've also been investigation other types of oscillator for the motor's phase pickup exciter winding - the 50kHz one. The original used a Hartley oscillator with a custom inductor - so it would be silly to copy it, since specific inductors are tricky to source.

My first tests were using a Wien bridge - which works very well, but I'm not sure that it is a particularly "easy" oscillator to use, since gain stabilisation is quirky.

I'm looking at a few phase-shift oscillators, and the curiously named Bubba oscillator (from a technical aspect, this one is sexy).

Low (i.e., much below 1%) distortion here I think is not important at all, but if anyone thinks differently, do please tell me why.

[rich121]

Would this also work with 60 hz power?

Thanks,

Rick

[Dave Cawley]

.
Great thread! 1% distortion is undoubtedly OK and I think short term stability might be important?

However I'm a fan of filtering square waves to get a sine wave, either with an op-amp LPF or this caught my eye http://www.maxim-ic.com/appnotes.cfm/an_pk/1999 a clock oscillator can be as little as $1, a divider and a filter.

Ditch IC1, Q1 and IC2 and use a 4040 or 4060 divided with an external crystal clock oscillator into some sort of LPF ?

A bit complex but technically elegant?

Regards

Dave

[Steerpike]

Originally posted by rich121
Would this also work with 60 hz power?

Yes, this whole thing runs on -18/0/+18 DC, more or less. Actual voltages not yet specified, but it will be symmetrical DC supplies, somewhere between 15v and 24v. So you can use batteries if you like!

I learned not so long ago that "45" rpm discs in the USA are cut at a different speed to European 45's, neiher of which are spot on 45.00 RPM. I will try to incorporate these two speeds into the system as well. (this all due to the use of synchronous motors in cutting lathes, and reduction gearing based on integer division)

Originally posted by Dave Cawley
Ditch IC1, Q1 and IC2 and use a 4040 or 4060 divided with an external crystal clock oscillator into some sort of LPF ?

The oscillator I am considering above isn't a timing reference, so no need for acccuracy. It is the means of exciting the variable reluctance pickups in the motor. This ultrasonic carrier is modulated by the changing reluctance of the rotor. The pickup coil signal is then AM demodulated, to derive three phase reference signals of around 5 Hz. The 50kHz is therefore removed completely before the signal is 'used'.

My concern about distortion is that with distorted waves, you get RF harmonics, which may heterodyne with other signals in the system, and then those may leak into the audio.

HOWEVER, I like your reference for OTHER reasons, thank you. It would be a great starting point for generating 50Hz or 60Hz signals to drive AC synchronous turntables, or tape decks. (my Revox G36 springs to mind!) Low frequency sine waves there would be a boon (horrible word!) there, where hormonics would cause the motor to ring objectionably.
Tweak that circuit to make a quadrature oscillator, and you can dispense with any phase shift capacitors the motor previously required.