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-   -   Improving a turntable (motor controller circuit) ;) (https://www.diyaudio.com/forums/analogue-source/42461-improving-turntable-motor-controller-circuit.html)

ogeronimo 2nd April 2006 07:26 AM

milteo
 
Ive a Lenco L830 DD turntable and the IC AN620 is burned. The motor and the 3 phase controller is the same of Seks technics.
Anybody know any circuit for replace the original speed controller?

thanks!!

soundnut 30th July 2008 06:52 AM

any luck
 
I know this is along time ago for the reply. Any luck with the sl-2000 Technics turntable? I just bought a used one for $53 usd. to replace my Dual 1219. The 1219 gets honors for being a real piece of crap. All mechanical...the speed switch is stuck, the speed is very slow, the anti-skating and weight balance all failed by just letting the unit not being used in 8 years. The sl-2000 works perfect. I will do some of your suggestions. Such as clean and put in new oil bearing oil. Change pots to 5 or 10 turn. Replace all electrolytics. And beef up the power supply with bigger electrolytics and maybe more if possible I have not opened the unit yet...just got it today.
Mitchell

analog_sa 30th July 2008 09:35 AM

Re: any luck
 
Quote:

Originally posted by soundnut
The 1219 gets honors for being a real piece of crap.


It's probably pretty trivial to fix all that's wrong with the Dual. I bet it will beat the pants out of that Technics sonically.

sek 30th July 2008 10:56 AM

I second that, although I don't know this particular Dual model. ;)


Quote:

Any luck with the sl-2000 Technics turntable?
Not really. I have to admit that the conditions were difficult to start with. The platter was excentric, the arm bearings were loose, the power suppy was crappy and the acrylic cover was damaged beyond repair. :(

I had stripped the motor assembly from the chassis and experimented with the combination of motor and platter. They could benefit from a hefty laboratory supply (with regulated 18V). My attempt would have been to replace the 33/45 switch and pitch control unit with something more convenient (button switch, single potentiometer) and the stroboscope with LEDs for a sharper image.

But then I got hold of an SL-1710MK2! :devilr:

There's no way back.

I currently use an SL-1200MK2 that I refurbished and repainted (white chassis, white LED illumination, improved power supply, renewed pitch assembly, recabled tonearm, etc.).

Don't get me wrong, I don't dislike the SL-2000 parts for what they are, it's just impossible to improve them beyond what they are capable of - at least not without spending more than for a used MK2.

Cheers,
Sebastian.

PS: I like to keep the SL-2000 parts in the drawer, though. We share the same year of birth. :) So in case you have any questions, don't hesitate.

Steerpike 30th July 2008 11:03 AM

We are working on something similar here:

"New Technics SP10 motor controller specification"
http://www.diyaudio.com/forums/showt...hreadid=121934

Sek, your shematic shows no frequency reference (quartz crystal) so it will not be as accurate as designs like the SP10. (probably because they want pitch control, and pitch control with PLL is (was) not an easy or cheap circuit)

The motor also appears to have no true tacho coil - only the three phase detection windings. These CAN be used for tacho purposes as well, but are not very accurate (from the SP10 motor measuremnts I did, only about 6 pulses per revolution, as compared to 190 for the true tacho pickup). For PLL control you will need that sort of accuracy (190 pulses per rev). You could always add a photo-detector on the rim of the motor, and stick on a laser printed band of stripes for it to read.

To answer some of your questions, I'm guessing the following:
D1-D3 are germanium signal diodes, to demodulate the AM signal from the phase detector.
The white wire at S2 is likely the excitation voltage for the phase detection coils - probably at around 50kHz.
R10/R5 etc. MAY be the lead/lag compensation for the servo loop.

I imagine you could certainly increase the current drive to the motor. - after all, it' only the impulse current to get it up to speed, its normal runing current will be unchanged. It has a long thermal time constant and won't suffer badly from a higher start current.

sek 30th July 2008 11:43 AM

Hi Steerpike,

I'm not the one who wants to improve it (anymore). ;)

I'm aware of the things you mention since I dissected a SL-1710MK2 and a couple of SL-1200/1210MK2 for comparison. The SL-2000 incorporates the technology that has also been used in the SL-1200 series (without MK2): no frequency generator, no crystal reference.

Oh, and I recognized your thread and followed it from the beginning. ;)

In other forums, I discussed the option of retrofitting the motor assembly with a frequency generator coil (i.e. from a superseded MK2 series player or a DIY one) and a reference generator circuit. But the amount of work is similar to your approach of a redesign...


Quote:

D1-D3 are germanium signal diodes, to demodulate the AM signal from the phase detector. The white wire at S2 is likely the excitation voltage for the phase detection coils - probably at around 50kHz. R10/R5 etc. MAY be the lead/lag compensation for the servo loop.
Thanks for your description.

It's even more severe: I made a mishap in my circuit description and accidentally took the drive coil connections for the position detector connections and vice versa. It's the other way 'round. :rolleyes:

The circuit can be improved as you mention - by increasing drive current and adjusting the lead/lag network in the feedback loop to the servo. Measured frequency is lower than 50kHz, btw...

But as the controller IC is not documented anywhere, the risk of increasing the current through the IC is too high for me. At least, it incorporates a metal plate for mounting a heat sink. External driver transistors are a possible solution, but too complicated to fit into the original housing...

Cheers,
Sebastian.

soundnut 30th July 2008 12:39 PM

Heres what I am going to do. I will upgrade the power supply. It is 18 volts. I will use a LM7818 T220 chip instead of the existing supply. The LM 7818 can supply 1 amp constant and 2.2 amps peak (sounds good). Will use existing heatsink. However I will need a bigger transformer, I will try and find one that just fits inside. I need one that is 24vac (thats what I measured, 20-22 volts is ok too). Capacitor after the bridge rectifier will be 700 t0 1200uf. Capacitor at output of regulator will be 330-500uf. The bridge rectifier will be changed to 1 amp.

This is a little overkill since fuse for existing power supply is 350ma, I might change fuse to 500ma if I get a bigger transformer only if fuse blows once in a while. Existing power supply has only one capacitor at 330 uf. Using a LM7818 is better than using discrete componets. Existing transformer looks like it is 6 watts, hope to replace it with a 10 watt. In reality I need a beefed up power supply that will supply 1/2 amp instantly:).

soundnut 30th July 2008 12:39 PM

Oh I will also change the speed pots if I can find ones that will fit and hopefully get 5 turn ones or 10 turn ones but 10 turns ones are overkill.

Steerpike 10th September 2008 01:59 AM

Is anyone still watching this thread?
A couple of weeks ago I got an wrecked Marantz TT, that upon disassembly proved to contain a Technics motor - not *quite* the same as the SL2000, but *very* similar. I'm still trying to figure out which Technics it comes from - the motor ID is PM2330009, with the ubiquitous AN620 IC in it. And no FG!

So I might look into upgrading this motor too - but the SP10 one comes first.

sek 10th September 2008 09:58 PM

You could try to take some pictures from the stator and rotor assemblies, as well as the bearing and of course the circuit board. ;)

Cheers,
Sebastian.


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