New Technics SP10 motor controller specification

[Dave Cawley]

I understand that, but this is a simple and elegant solution that won't take up much time or money!

Regards

Dave

[Steerpike]

I've put 'generic' circuits of the two phase shift oscillators on my PAGE 4
just to illustrate the basic layout. As they are, these will not drive the SP10 motor exciter winding with anything like the power it requires.

Both simple and easy, a single dual opamp or a single quad op amp.

[Steerpike]

A change to the BLOCK DIAGRAM .

Not an improvement, just a fixup of a rather stupid error.

[Steerpike]

Trials of other oscillators (phase shift types) are not giving results as good as the Wein Bridge; distortion is relatively high, unless gain is trimmed - which defeats the purpose of using this design.

Looks like the Wein Bridge is going to be the one used, as I originally fantasized..

[Steerpike]

Another circuit diagram added.
The 3-phase phase-pickup-coil AM detector, and 3-phase PWM modulator.
About 3/4 of the way down PAGE 4.

(One or 2 small circuit errors, that I only noticed after uploading - nothing that affects operational principles)

[bulgin]

Hi Fellas

I've been following this fascinating thread as I'm totally new to DD technology. I have recently acquired my first dd turntable - a Micro MR-711 circa 1974. I have no speed or speed instability problems and would like to know (if you have the time), if there would be any major differences between the SP10 family of dd systems and that of my oldtimer Micro?

I got some translated blurb from Audio Database regarding the Micro's drive system"

"The direct-drive scheme using the DC servo motor by an electronic-circuitry control system is adopted as a drive system. The meter scheme of electronic circuitry adoption is adopted as 1/3 or 45rpm velocity checking. The zero point adjustment on this meter is proofread so that it may be in agreement with a constant-speed degree rotation of a motor using a frequency counter, and it is pursuing the accuracy more. Moreover, 33.3 speed control organisation in which 3 or 45rpm became independent, respectively is carried, and +-6% of fine tune is possible to a convention velocity".

What do you think of all this? Does the Technics system have any relevance here?

bulgin

[Shaun]

Ah, Wein bridge... built one a long time ago. From what I recall, The Art of Electronics said that the GBW (gain-bandwidth product) of the op amp must be at least 20x the oscillator frequency. I also seem to remember that the signal gain within the oscillator had to be exactly x3. That particular application also required a constant amplitude, and I had to include a FET-based constant voltage amplifier... memories...

[bulgin]

Isn't it Wien bridge?

bulgin

[Shaun]

Originally posted by bulgin
Isn't it Wien bridge?

Ja, but "wine" sounds better...

[Steerpike]

Hi Bulgin

Could you prease transrate that into Engrish.
I'll take a look for technical information on that motor & post soon.

Shaun:

Yes, the WIEN bridge osc needs a gain of precisely 3x, no more no less. Which in real life is impossible to achieve. Hence the need for some sort of automatic gain compensation system - Ge diodes, thermistor, or a filament lamp.

In theory, the phase shift osc shouldn't make more demands on the GBP, because it uses two amplifiers, not one. And a gain of just over 4 is the theoretical minimum. Still, it tends to clip much more severely than the Wien. And the quadrature osc, with gain compensation added, becomes unreliable and reluctant to always start.

I used to call it a 'Vine' bridge, but a friend at university always referred to it as 'Ween' - somehow it unfortunately rubbed off on me, and with it a tendency to spell it wrong; that and the fact that the Austrian version of Vienna is Wein. Internet references seem to use both, interchangeably - more proof not to cite the www as a reliable source!