SL-1200 DC Power Supply DIY

[6L6]

Use the stock transformer in the time being.

Return the one you have, get one with 22 or 24 volt secondaries. (Or just use the stock one... The toroid will do a much better job of coupling all the high frequency hash and crap on the AC lines into your circuit. That's actually bad. An EI transformer is not as good at those frequencies, which in this case is better.) My $0.02

Remember that the DC voltage you have after full-wave rectification is 1.4X your AC voltage, minus the diode losses, in this case -2V as a full wave bridge has 2 diodes in series. (and you lose about 1 volt per diode.)

So 22 * 1.4 = 30.8
30.8 - 2 = 28.8

That's close enough.

Now when you have a big capacitor bank like that, and not hooked up to a load, the voltage will build and read high. That's normal.



EDIT - What is the voltage rating of your small film caps?

[6L6]

Another thing - drill some holes in the sides and top of the ABS case - it gets warmer than I would have guessed- I am going to do that to mine immediately.

[Frankyc2003]

That is a sensible thing to do.
I shall proceed with the stock transformer.

I did notice the heat, so I will ventilate the case too...

Cheers

[Frankyc2003]

Now, onto another problem...

here is the stock traffo.
In 6L6 example, being a US deck, there is no switch between 120VAC and 240 VAC obviously,
but as you can see here, the primary are split to accomodate either or.



Which way is the right way round?
Instinct and colour coding would indicate BROWN live, BLUE return, and BLACK and WHITE connected together...

But I am curious to see if anyone has the correct answer.

Pretty please

Ta

[Firebottle]

Didn't you make any notes Francois when you took it apart

I wouldn't necessarily assume that the 240 goes to brown and blue without confirmation.
The brown and black being together and exiting from the bottom of the trannie 'looks' like the mains input, but....

Do you have a multimeter that you could measure the resistances with?
The primary on this size of trannie is going to measure in the 10s of ohms on a meter, with the secondary only an ohm or two.

If you find two windings that are very close in resistance, say 40 ohm, then that would probably be 2 off 120V primaries.

I can't say anything more certain as I haven't played with one of these. I'm sure someone will come up with the correct sequence.

It's gtreat having a ply isn't it

Alan

[Frankyc2003]

Aha Cheers Alan, Yes I did try to get some notes, but it all happens inside the 120/240 switch. And unless I crack it open, i won't see the way its connected... And I'd rather keep things intact in case I want to revert!



I might have a lead on vinyl engine...

[Frankyc2003]

Ok, so it might have taken another cup of strong coffe to get there but...

tadaahhh!



OK, so very important note.

If you intend to do 6L6 upgrade and mod, and that you live in a country with 220 / 240 VAC mains supplied to your wall plug, please be advised that you will need to wire the primary of the stock Technics transformer accordingly.

BROWN - Live (from your mains cable and plug)
WHITE - BLACK (connected together and properly insulated from the rest of the circuit)
BLUE - Return (from your mains cable and plug)

This way the transformer is stepping down the 220 / 240 VAC of your domestic to 30 VAC, which is what is specified in the service manual of the Technics.

Reference documentation is available here.

http://www.vinylengine.com/library/t.../sl-1210.shtml
(please be advised that you need to register to be able to download and read docs)

One final word of advice as usual, LIVE MAINS ELECTRICITY ISN'T A TOY, AND CAN HARM YOU AND OTHERS AND YOUR PRECIOUS EQUIPEMENT, SO PLEASE MAKE SURE YOU HAVE TAKEN ALL SAFETY PRECAUTIONS BEFORE ATTEMPTING ANY OF THESE MODIFICATIONS!

Otherwise have fun!

[6L6]

Looking great so far!

I wish you success! Please continue to take lots of photos.

[Frankyc2003]

There we go!

All done, according to specifications!







And it must be the fact that the bridge rectifier is gone from the main PCB but, yes it does sound better than just taking the PSU outside in an external housing (see my earlier post)...

Sound wise, the stage is more defined in width and depth, there is more space between instruments. And Bass overall has gained definition and authority.

SO MASSIVE THANKS TO JIM FOR PROTOTYPING THIS!
CHEAP AND EFFICIENT UPGRADE!

All in all I did spend around 35 GBP for everything.

PS. to finish in style, a free (free P&P too) vinyl to anyone able to spot the mistake I made in wiring the double post rocker switch...

[6L6]

Fantastic!!! I'm very flattered that you did this mod so quickly on the heels of mine. There are now 2 of us with such a cool thing.

The performance increase is startling, isn't it? And it has little to do with how much this costs, although the value for money is completely off the charts.

I hope others are inspired to do the same, I'm sure they will be as pleased with the results.

Re: AC switch - other than it looks to be in upside down, I don't really see much wrong... unless you are not allowed to switch both the Hot and the Neutral in the UK...

And it must be the fact that the bridge rectifier is gone from the main PCB...

No question that there is benefit in that.

I don't think that's the only thing - as there is an awful lot of filtering before the regulator that wasn't there before. (I've seen power amps with less capacitance) The CRCRC filter in the outboard box is rather significant, especially using 10ohm resistors, but there is another stage of RC filtering made by the umbilical and the electrolytic cap on the PCB. So the incoming DC to the regulator is much, much more filtered than it has seen before, relieving it (the regulator) of some work, making it's output smoother.

I'm looking forward to removing the 70's-era discrete regulator and replacing it with a higher performance regulator and then a modern high-performance discrete.