SL-1200 DC Power Supply DIY

[dimkasta]

I finally received the parts I was missing. My board is almost ready once again. I'll do some more testing tomorrow and hopefully have a functional turntable again

I was wondering about another thing for a while now. Since it makes such a big difference powering IC302 with a proper reg instead of a zener, could there be some merit replacing the old chip with a modern CD4011 ?
I remember reading somewhere that it made a difference.

[dimkasta]

Found it
https://www.vinylengine.com/turntabl...ic.php?t=36482

[Co&]

If you don't use the speedcontrol, you can remove the 4011 and short pin 2 and 3 on the 6680.

Anyway that's what I did a couple of years ago.
I cannot remember being impressed bij this mod. The FG amp regulation is much more important. I put mine on 8.7V.

Oh, I lost the 4011 chip and ordered a new more modern one when restoring the deck last summer. It is in there now with the zener and the CCS (se my previous post). Sounds fine to me. I have a LM431 and resistors ready to replace the zener though.

regards, Coen

[dimkasta]

Does that mean we can get rid of AN6682 as well?

Damn it would be nice to have the datasheets...

[Co&]

yep.

I removed that one too. Theory was that unused components can and will disturb the circuit and power supply.

the schematic is straightforward. The 4011 is a complicated way to operate the "reset" button of the speed control. Though I think the output buffering may be beneficial.

[dimkasta]

Cool

Yes I like removing all "unnecessary" parts as well.

I was just not sure if AN6682 still provided the base speed since it seems connected directly to the speed control through the FI pins.
It's lazier if someone else has already done the deeper homework

So one less regulator too
And replacing that zener made a big difference... Just proving that "unnecessary" stuff can be bad I suppose

[Co&]

Some more details:

I've put a dip14 socket into the 4011 position to remove it later w/o soldering, should have done that for the 6682 as well. I'd go first with removing the 6682 and leave the 4011 in place or "upgrade" it to a 21st century version. Like I said the buffering the logic provides may be beneficial, not sure though.

[dimkasta]

By the way, removing 6682 we practically lose pitch calibration. Did you notice any speed issues after removing it? Or the chips are spot on coming from the factory and the calibration was just to care for the pitch fading controls?

And yes I am adding some sockets as well (AN6680 for now). Although I do not like the extra parasitics, they are rather handy.

[Ianmac]

So far I have had no luck in getting data sheets on the dedicated chips
There must be some out there !

I have now modded 3 decks using LT series regulators
all going well.

[dimkasta]

Like I said the buffering the logic provides may be beneficial, not sure though.

From the logic diagram, the FO pin of 6680 appears buffered already