SL-1200 DC Power Supply DIY

[Co&]

Sideband at 1.050Khz is ex the Hi Fi News record.
Cardas 1Khz is OK.

That's probably why it's only at one side...

[Ianmac]

@ Dimmie
Test record was High Fi Sound stereo Test Record HFS69, Side 2 Test 1. All I have for info is the cover rear.
@ Coen,
Yes Im rusty using FFT I should have noticed that !

[Ianmac]

Tried ARTA but no better.
I dont think Im making much progress in obtaining meaningfull measurements. There are too many variables associated with using a record as a reference tone source and low end sampling scopes
The answer I want is probably available via one of the servo error signals inside or on pin on the AN6680.
I still havent been able to get hold of a Platter at a reasonable price. I could machine out the centre to give me the motor only and allow free scoping of the electronics with the platter running.
I will probably just have to content myself with my ears for now.

The big consolation is that my Deck is now very very good.
It hasnt cost me a lot of money to get there.

...... Im still using the std arm with my own silicon arm damper...... Do I now look at some mods to the techie arm ?

[dimkasta]

Gogo rewire it. Single wire run from cart to rca is a nice improvement. Especially with some nice thin teflon/silver wire. I have even removed the pins from the headshell so that I ran the wire in a single piece. I just cannot change headshells easily, but who cares

BTW, I had done some measurements some time ago through the power entry hole. The probes can easily get in through there.
I just had to tape them down to keep them from obstructing the platter rotation.

[Khom]

Tried ARTA but no better.

Try Spectrum Lab http://www.qsl.net/dl4yhf/spectra1.html (free). I did make some measurements and looks like it can be useful. I will upload several spectra catched from FG in nearest time.

[Ianmac]

Thanks will down load a copy ASAP

[dimkasta]

Where are you guys measuring? At pin 24 of 6680?

[Khom]

So, promized pictures captured at the pin 23 AN6680 - i.e. FG signal amplified by Q203 and internal 6680 amplifier-filter*. I used Spectrum Lab, two small windows "Components" and "Configuration" will show how to obtain spectrum.

First one - platter 'as is' with my resin mat, second and third screenshots captured with added mass on platter (400 and 850 g, I used 2 and 4 old bearings from my mini-lathe). All measured data are with power upgrades described above.

Main interested peaks are:
50.5 Hz (note: it's NOT mains 50 Hz). Main peak width is wery important thing, but it depends on FG coil and disk magnet and I'm afraid it can't give us useful information.
55 Hz (i.e. 50.5+4.5) - sideband 4.5 Hz, motor torque signal (3 phase, 12 stator coils and 16 rotor magnet poles @33 rpm)
64 Hz (50.5+3*4.5) - 3rd harmonic of 4.5 Hz.

Using this signal we can see changes in sidebands amplitude even when resin mat removed or attached.

* Note: signal after internal 6680 amplifier has some distortion (components at 101 Hz etc.), but we can watch it in real time. Will be better to take signal after Q203, amplify it and use.

[dimkasta]

I found some time and tried to measure the FG signal.
Unfortunately, the parts are not in a position that allows the probe to fit without obstructing the platter.
I eventually managed to get a measurement (using some jumpers) between R119 and R220.
I got a steady 50Hz (20ms) signal which is good in general, but the signal was dirty and I do not know how much of the dirt was because of the jumpers. The noise appeared pretty random.
I tried applying some digital high pass filters to locate any harmonics or peaks, but I could not see any.

Tomorrow I will try to solder some permanent test points and retry.

[Khom]

I forgot one more peak between 4.5 and 13.5 Hz: approx. 6.7 Hz.