DIY power supply for Technics SL1200/1210

[jonners]

The KAB external power supply for the Technics provides a regulated 34V DC that goes to the internal diode bridge. The deck's own regulator on the main circuit board drops that down to 21V. I decided to make a regulated 21V supply and bypass the internal reg completely.
I downloaded the circuit diagrams from the Technics forum at Vinyl Engine, and saw that it would be possible, by cutting a wire link, to attach the new supply without having to remove the circuit board. (Referring to the page showing the Drive Control PCB, I cut the vertical link near the top of the board, just left of the word 'Technics', and connected the 21V DC to the lower part of that wire. The earthing point is at the bottom corner of the board. The page from the manual shows the underside of the board, but of course when you remove the platter and the plastic cover you will be looking down at the board from above.
Connecting the new supply in this way disables the strobe light and the cueing light. I've never had much use for either of them, so that was fine by me. If you want to keep them, it's not too difficult to find a different way of connecting it up. (See below - Post no.10). My way of connecting also in effect eliminated a supply bypass cap C3, so I attached another one.
My first impressions are positive. Not a dramatic difference, but more spacious and with a quieter background.

John

[Marco]

Interesting, John. Can we see some pictures of your work?

Marco.

[jonners]

Interesting, John. Can we see some pictures of your work?

Marco.

Sorry, haven't got a working camera at present.

John

[Marco]

That's a shame, John. Perhaps you know someone who does? The D.I.Y threads tend to work best when there are accompanying pictures which show work completed or in progress.

Interesting that you thought the external PSU didn't make a dramatic difference. Adding the KAB one to a 1210 in my experience (and others) certainly does - it quite simply transforms the deck and moves its performance to another level

Marco.

[jonners]

Marco - My listening impressions are at an early stage - and I must say I find that sort of thing difficult unless I can do side by side comparisons. It would be possible to create of way of switching between the two supplies but I don't think I can be bothered - too busy listening.

Regarding the possibility of pictures, I think that it's really preferable anyway for people to understand what they are doing, rather than follow a 'soldering by numbers' guide. After all, this project involves mains voltages and I wouldn't like anyone to frazzle themselves as a result of attempting to copy what I did.

Anyway, the wire link that I snipped can just be seen on the first picture in this sticky:http://theartofsound.net/forum/showthread.php?t=1020 It's on the side of the board that is nearest the back of the deck, near a white connector. The earth point can be seen in the next picture, at the corner of the board, below AC terminals 1 and 2.
John

[jonners]

As the new PS settles down my impressions are that the sound is improving further. I'm using the standard, unmodified Technics arm, by the way, with a Sumiko headshell and Denon DL110. Standard rubber mat, no other mods.

John

[muffinman]

genuine congrats to you jonners. I wish I had the brains/balls to take a soldering iron and a set of snips to my kit in the search for improvement. Alas I don't. The saving grace for me is that you have started to notice a real improvement with a psu. My ps1200 should clear customs soon and I'm glad to hear it wasn't £2mil wasted

[jonners]

Thanks, Muffinman. I've just heard that the Barking Audiophile Tax has been revoked so your final bill will be considerably less than £2m. Give the new supply a bit of time to settle in and I think you will be well pleased.

John

[jonners]

I see that Sound Hi Fi have recently posted details of their SL1200 power supply on their website. Interesting to see that they are critical of the internal regulator in the deck, and their approach is also to bypass it completely: http://www.soundhifi.com/sl1200/SL1200%20PSU.htm

John

[dmckean]

I see that Sound Hi Fi have recently posted details of their SL1200 power supply on their website. Interesting to see that they are critical of the internal regulator in the deck, and their approach is also to bypass it completely: http://www.soundhifi.com/sl1200/SL1200%20PSU.htm

John

Impressive.