A quick visual guide to externalising PSU from your Technics SL 1200

[OneyedK]

Should be perfect

[Qwin]

[UV101]

I'd go even bigger....... It's the main reservoir smoothing cap.

My external psu rectifies and smooths with 2 x 10,000uF before the supply hits my internal low noise reg.

If you move the transformer external, you can either put additional caps in the psu or utilise the space where the transformer was inside the techie.

[Qwin]

Ian - There isn't much room on the main PCB, 1000uf is probably as big as will fit there.

I have cut off the transformer well, so not a lot of space internaly.

Where would you fit additional Caps into the circuit of my externalized Standard PSU?

[UV101]

From a circuit point of view, it need to sit on the across the + and gnd rail after the diodes that rectify the AC.

In my case I use a 3 pin regulator to give me the 21v like this diagram.
I rectify the ac (D1-4) in the external psu and I smooth the ripple (c4 in the attached example) with 2 x 10,000uf also in the external case. The very small value cap (C1 in the example) should be as close to the regulator as possible as it is the low value that shunts noise to ground.

http://www.tasel.net/images/Adjustab...it-Diagram.gif

It's fairly simple in my case, the external psu contains an updated toroidal transformer, hexfred diodes, and the large value caps. The output of the psu connects to the input to the replacement regulator inside the techie and the output of the reg connects to the same spot that the original regulator circuit output.

This internal C1 cap we are talking about is no longer in circuit.

The job of the smoothing cap or reservoir is to fill out the dips in the rectified rail. Large current gulps can cause the rail to sag in the dips if there is not sufficient energy stored. On a scope, you'd see the waveform with dips on a DMV you'd just see a volt drop.

http://pfnicholls.com/electronics/psu_smoothed.png

Check this page out.....it's really useful

http://pfnicholls.com/electronics/power_supply.html

[Qwin]

I ended up getting a "Unicon" 1000uf 63V cap to replace the 470uf 50V on the Techie board. Got this from Maplins, the one I was going to get from Farnell would have been fine but they have a minimum order of £20.

Its getting harder and harder for the hobyist to buy parts in this country.
RS and Farnell have minimum order qty's on many parts that you can order as single items from places like Mouser in the States. The last order of parts I made up had only 8 items with qty's of 2 or 4 of each, it was CONSIDERABLY cheaper to get it all from Mouser (including shipping) than either RS or Farnell due to their min qty's (I didn't wan't 50) and Maplins didn't stock most of the parts.

eBay can be of use, but so many of the people advertising don't give a complete specification for the item. eg I was after some uninsulated crimp on spade connectors (Faston etc), three of the four people advertising did not say what cable diameter the crimps in question were designed for. I bought from the chap that gave that information because it matched the light duty (thin) wire I was using.

Sorry for the Rant I've just finished ordering parts for my deck mods and had to use seven different suppliers to complete.

[Frankyc2003]

Check this page out.....it's really useful

http://pfnicholls.com/electronics/power_supply.html

+1

This really helped me understand the 4 stages of a power supply!

[Qwin]

Must say a big thank you to Francois for this illustrated guide.
It set me up for my own version:





This is part of my TT project to be found here: http://theartofsound.net/forum/showthread.php?t=23257

[Frankyc2003]

Wow! That looks seriously good!
I am delighted to see that my modest attempt inspired you.
But I have to say your TT is a thing of beauty!
Would love to hear what it sounds like!

[MartinT]

I'd go even bigger....... It's the main reservoir smoothing cap.

Just one word of caution: if/when you use an external regulator, say one of the Paul Hynes modules, you don't want a big reservoir in that position as the reservoir/smoothing/regulation will be in the external unit. Replace the 470uF with the best quality cap you can find, but don't make it a larger value.