2 questions for the knowledgeable

[Linnik]

GROUNDING

1. How the case of a NAC is really grounded to the mains ground? Or is it? Where exactly is the grounding connection and how is it led to NAC case? (old question, I know but once again pals, please!)

TWO SECONDARIES

2. I have my temporary DIY CAP which applies a transformer from a Linn LK1. This toroid is giving out three wires. Two lives and one zero. Between zero and a live you can take out 18 V. Between the two lives you can have 36 V.

Now I had problems when I made it last winter. I tried to use both lives and then put the zero between the main caps. But this resulted by very high voltages, around 50V after rectification it was. Got some gunning from the reg tants few times..

Then I finally cured it by using only the other live and the zero and bridged them to two rectifiers etc. Works.

Now, when I am starting to build dedicated ground wiring from NAC to the CAP I am thinking again: If I would take the other secondary in use and kept the rectifiers and the main caps separate, as well as all the regulators and wiring.

But no! Then my mind says, the problem will arise later...
In the NAC and the voltage will throttle high again in some place.
Would it? Now I have regs in the CAP and second regs in the NAC. The other rail is for the buffer amps and the other for gain amps.

Will the secondaries get against each other somewhere in the preamp and will the voltage run high? Still, my sense says the regs will limit the voltage in any case. As it cannot run high in the DIY CAP before the first regs, it just cannot happen later anymore. Or can it???

I would like to have your word for this before I start all over rewiring the CAP and separating the grounds for the main caps there etc.

I can, of course, just keep using only the other secondary and still make dedicated ground wires from between the caps. But naturally separate secondaries would be better, if possible to use.

Thanks!

Oz

P.S. Boys, I made a new cable from 5x1,5 mm2 rubber mains cable. And DID SOLDER four of those leads to 5 PIN DIN!!! And did it clean! The cleanest 5 pin DIN I have ever done. Thanks to Les and his e-book. I am an elite solderer now!!!

 

[Andrew L Weekes]

How the case of a NAC is really grounded to the mains ground? Or is it? Where exactly is the grounding connection and how is it led to NAC case? (old question, I know but once again pals, please!)

Via the CD player 0V connection or the Turntable. If these items don't connect signal 0V to mains earth then the NAC isn't earthed.

What rectifier / PSU setup do you have presently, from the selection here ?

Andy.

 

[Linnik]

Thanks Andy!

(I have never got into your site's specific reg pages... for some reason? Tried many times)

1. I am using a Naim CDX now with 5 pin to 5 pin cabling to NAC so propably the mains grounding is in use then. My LP12 assembly does not serve grounding this time. Will check the mains ground by meter/wire.

2. None of those. I do have two full bridge rects side by side and connected parallel now from the one live and zero. From minuses to between the caps and from pluses to the plus ends of the caps.

Oz

 

[Linnik]

My thinking get into knots with the transformer output of the 18V LK1 t-former.

Is it that it is actually giving out 36 V with a center tap?
And taking out from other end and ct you will get 18V.

So perhaps I CANNOT at all take out 2 times 18V.

If I try so, it will finally make the ct referring on DC as plus to the other 18V and minus to the other rail. And connecting that to the center grounding finally mixes things up and start offering 36Vplus rect liftup, so. around 50 V out ??

So propably the way I have done now is the only way to use it: taped blind the other output end of the secondary and using only the other and and ct.

Oz

 

[prowla]

Everything attached to the mains should have any metal surface grounded. I think this is a safety requirement.
There's a difference between signal ground and safety ground.
Looking at DIN plugs, it looks like the circular surround connects to the case. Is that right?
Now, a preamp isn't connected to the mains, so what's the requirement for grounding?

 

[Patrick Dixon]

Now, a preamp isn't connected to the mains, so what's the requirement for grounding?

None really - providing that the case is not likely to get attached to a mains voltage under fault conditions.

In general, I would have though it would be preferable to earth any metal case, since it would be safer and better from a emc PTV. However, if you don't have a mains cable attached to the equipment, you can only earth it by secondary means - which is what Naim do.

 

['Ed]

Originally posted by Linnik
Is it that it is actually giving out 36 V with a center tap?
And taking out from other end and ct you will get 18V.

It sounds like that is the case.

So perhaps I CANNOT at all take out 2 times 18V.

Again true, unfortunately.
The only way you could get two positive voltages out would be to have separate half-recification from each 18v secondary - that is a single doide out from each & ct as 0V. You wouldn't get the full 18V though, & current performance would also be poor.

So propably the way I have done now is the only way to use it: taped blind the other output end of the secondary and using only the other and and ct.

There is another way - just use the centre-tapped secondary the way Naim do - a rectifer diode from each secondary feeding the same +ve & ct as 0V.
You will still only have one voltage there, but you lose a diode from the bridge which should give better performance (& slightly more volts).

I've never heared of parallel rectifiers on the same secondary, by the way - I'm not sure how well this would actually work! It might be best to just have one rectifier/cap & then parallel 2 regulators from this setup. Not ideal, but you only have the one secondary.

 

[Linnik]

Thanks very much Ed!

Well, now I do have two dedicated full bridges for the 2 rails, two caps with minuses binded together and both minuses coming there. The pluses on each + sides. Then pluses going to rail dedicated regs and minus going to both regs but separately from the mid of the caps a minus lead going to the socket for the NAC lead.

Now, even this is a temporary PSU for me, I think I will re-build the rect with fast recoveries or Schottkies, change the caps from 10 k to 15 or 22 k, the mid ones being Kendeils, so perhaps them..

And arrange two dedicated ground wires to the socket and then connect with my new cable with dedicated ground wires from NAC and also connect another ground wire to the NAC end DIN socket from the center grounding tap.

Your idea to rectify by one diode from each end of secondary sounds very interesting as it would lift the voltage somewhat and that is the weak point of this PSU. The voltage is a bit too low for feeding double regs and still yielding about 24 V for the NAC. Well, no problem in having 22 V either as I have passed the delay circuitry but anyway the higher the better they say.

So I might go to some experiments. I do not have clue now which way the diodes should be but I have to check some schemas in the net... Perhaps I will get the idea..

Then I might solder two schottkies directly to the cap's + tag as horns and (for both caps separately) and then bring parallelly both ends of the secondary to the diodes.

This PSU is actually for my DIY prefix and it is housed into a Naim shoebox case together with a DIY geddon. But the better I will make it now the better it will later serve the prefix, too. I just have to build dedicated ground wires to the prefix also before I will give it back to it's use from feeding NAC.

Thanks to all!

Oz

 

['Ed]

Originally posted by Linnik
...Your idea to rectify by one diode from each end of secondary sounds very interesting...

Not my idea at all! The first place I saw it explained was the Avondale site - where you will find the schematic.