New Technics SP10 motor controller specification

[Shaun]

I think that Steerpike's effort has superseded mine, so it is more likely to be a 2-way shoot-out. It is possible that in the future I might use some of the lessons learnt from Steerpike's circuit to implement more functionality as per my original intention. For now, I'm a bit overextended and just grateful that Steerpike is running along with it.

[Steerpike]

Will the L165s accept being driven in inverting mode?

I can see no reason why it won't; though the application notes show all motor drive circuits as non-inverting.
Most op-amps work somewhat better as inverting amps, though since it's being used as an amp with a gain of only around 1-2x, with a bandwidth of 10Hz, I never thought there was much in the way of 'performance' being asked of it.

I thought I might omit all/any preceedig buffer stages at some time in the future (to reduce complexity & component count) and then it would be nice to have the very high input impedance of the (+) input.

My original plan was a very boring push-pull stage made with TIP31/32 discretes, but the L165 just takes up less space, and makes for easier PCB design - laziness prevailed here!
I also rather liked an excuse to buy a handful of L165's - they make rather Ok audio amps too I have read - something to play with on a rainy day.
There are a few dedicated audio chips like the TDA2040 that would be drop-in substitutes for the L165. Some people may want to experiment with those.

Mark: is there a write-up or design theory of your progress so far, anywhere on the www?

[Mark Kelly]

Steerpike

Details of what I'm doing are not available for publication yet, I have to lodge some patent papers first. I'm still working through some of the implementations so I know what to include.

Re the inverting stage, because the op amp is seeing a very inductive load and you are pulling it down near to unity gain you are actually asking a hell of a lot. I've found that the inverting configuration gives better distortion performance, but that was when I was trying to find out how distortion affected motor performance so I was looking for THDs of -90 dB or so.

BTW I might have asked this before, is your 'nik a reference to Gormenghast?

Shaun

The three way shoot out was you guys, my effort and the original. I thought you were both in on this, sorry if that was a rash conclusion.

[Steerpike]

so I was looking for THDs of -90 dB or so.

I have no way of measuring something that small! I don't contest it though.
That may be barely audible if it were in the actual signal path, let alone just powering the motor.

Can we 'guess' that your SP10 drive is closely related to the electronically commutated motor article on your web page? Phase shift oscillators, etc.

Steerpike is indeed lifted from Gormenghast... and I want my throne!

[Mark Kelly]

Steerpike.

Good guess but no cigar.

I've gone away from the phase shift oscillators, too hard to get good precision and adjustability out of them at the same time (the tempco of the resistances changes with potentiometer setting).

I've gone over to the digital dark side, using OCXOs to get frequencies so precise that I have to use the ratio function in my eight digit counter to be able to see the errors (using a GPS disciplined VCXO as reference).

The distortion measurement were done by running the signal through the notch filter in my AWA distortion analyser then to the input of an HP spectrum analyser. I can reliably achieve a floor of -120dB so even -90 dB shows up pretty clearly.

I found that ultra low distortion was not the answer I thought it might be. The influence of wave shape on motor performance turns out to be very interesting indeed.

[Steerpike]

AWA

There's a name you don't often see in this country. I bought a pair of AWA valve compressor/limiters pulled out a radio station (prob. early 60s). I had high hopes of putting them into use for home-live recordings, alas another of the numerous half-fixed up audio boxes on my shelves!
The build quality is better than anything I have ever seen in any other brand.

[Mark Kelly]

The build quality is better than anything I have ever seen in any other brand.

Their chief engineer was Fritz Langford Smith. I'm pretty sure both Thiele and Small worked there at some time as well.

A mate of mine just wrote his PhD on the role of Fisk Radiola / AWV / AWA in the communications industry in Australia, he's in the process of turning it into a book.

[Steerpike]

I have nearly finished the PSU and power stage circuit board layout (5.5"x5" excl. heatsink); the power op-amp stages are now selectable - inverting or non-inverting, selected by wire links, so the world is your oyster!

The "controller" will be a second board as mentioned before;
with my current plan, I'm hoping to make it possible to implement a digitally synthesized 3-phase drive just by changing the firmware (ROM code) and a few wire links.
So (hoping!) with the same circuit board: option-1 would be analogue waveforms derived from the motor's own generator coils, option-2 would be look-up-table sine waveforms.

[honinbou]

A Japanese friend told me that Kaneda san just published a new controller for the Technics SL1100 turntable in the September issue of MJ magazine...

Sorry I have never read the magazine nor have I ever seen the cover, but guess that's perhaps one of the best alternatives for your SP10 motors.

[rich121]

I'm very curious as to your progress with the PSU and controller board? This project is so very interesting to me, I'm looking foreward to reading your next update.

Have a great weekend,

Rick

Originally posted by Steerpike
I have nearly finished the PSU and power stage circuit board layout (5.5"x5" excl. heatsink); the power op-amp stages are now selectable - inverting or non-inverting, selected by wire links, so the world is your oyster!

The "controller" will be a second board as mentioned before;
with my current plan, I'm hoping to make it possible to implement a digitally synthesized 3-phase drive just by changing the firmware (ROM code) and a few wire links.
So (hoping!) with the same circuit board: option-1 would be analogue waveforms derived from the motor's own generator coils, option-2 would be look-up-table sine waveforms.