[steinba]

I'd like to use one single enclosure for my PPAv2 and STEPS psu.

How far apart will the cards have to be to avoid interference/noise?

Should I shield the cards from eachother with a metal plate? (Copper?)

How do I cope with the different "grounds"?

Will it suffice to use a power LED and switch on the PSU end only?

And lastly: Any enclosure recommendations?

 

[Francis_Vaughan]

Quote:

Originally Posted by steinba How far apart will the cards have to be to avoid interference/noise?

As far as you can. You are almost entirely worried about magnetic field. It is complex, but as a first approximation you are looking at 1/(distance squared) for reduction of effect - once you get out of the near field of the transformer. But in truth I have a STEPS in a case that spends most of its life almost touching the PPA's case. There is no discernible hum or interference. Opposite sides a conventional sized HiFi case is more than adequate for all but the most obsessive. Then you do separates anyway.

Quote:

Should I shield the cards from eachother with a metal plate? (Copper?)

Little point. There may be the tiniest bit of radiated hash from the PS, but the pretty careful design of the STEPS makes this very low. You can't shield the magnetic field except with Mu Metal. This is painful, and usually not needed. Distance is your friend.

Quote:

How do I cope with the different "grounds"?

Complex, in a way. There is no ground on the STEPS, except for the power ground (earth) connection to the Y cap. This goes straight to the IEC plug. There MUST be a chassis ground, that is a separate connection from the chassis, directly to the ground connection on the IEC plug. Don't let anyone dissuade you from this. Connect the signal ground in one place only to the case. For a conventional PPA build this is the connection to a bolt on the back of the ALPS volume control. This works well. Ensure you use insulated input and output connectors.

Quote:

Will it suffice to use a power LED and switch on the PSU end only?

Depends how many LEDs you would like on the front. But yes.

Quote:

And lastly: Any enclosure recommendations?

Zillions. Have a look at the sticky thread at the top with pics of builds. There are lots of PPAs - mostly in Hammond cases - but this isn't what you want, but quite a few other ideas. The Parmetals cases seem to have a good following. But there are as many possibilities as your imagination and patience will take you. (Wallet can take a beating too.)

 

[steinba]

Thanks! Very informative.

 

[n_maher]

This is a PPA in a Parmetals case.

It's as quiet as can be, no AC hum to be sure. I find that careful routing of wires and proper grounding make the biggest difference with respect to a noisy amp. And I'd have to disagree with Francis on the issues of the chassis ground. While it is certainly safer to have the AC power grounded it complicates things a bit so it is a matter of personal risk to decide whether or not it's ok for your setup. I'm not trying to tell you not to do it, just to research it for yourself and decide what works best for you.

My 2¢,

Nate

 

[skyskraper]

problems with mains earth? ive never run into them. i've encountered problems when it's NOT connected on some bits of kit, but never with. they're not wired hugely differently from a non mains earthed, just tie the chassis to ground (many advocate a ground loop breaker). check out amb's mmm site and click "wiring and ground" it's got plenty of good info and examples.

for something like a step's + ppa, i don't think you'd run in to many problems if you're sensible. as in keep the mains connections as far away as possible from the input connections, don't go crisscrossing input signals with mains connections, etc,etc. just keep all the wiring and connections as short as possible, and you should be alright putting it all in the same case, even if the boards are butted against each other. just find something that's convenient and has the looks you like

 

[Francis_Vaughan]

At some point I am going to get really over the top on this. But I'm not kidding here. Never ever build a metal cased mains powered device without properly grounding the case.

Sure, you can argue that it is all about your personal assessment of risk, until your 3 year old child is electrocuted, or you advise another member of this forum that it doesn't really matter, and maybe only notice a year later that they don't seem to be posting here anymore.

The entire integrity of the safety of a ungrounded case may rest on nothing more than the quality of a solder joint of a first time DIY builder's efforts. Or a loose nut that can get jammed under a PC board, one that just happens to carry the main input traces. And so on.

All you need do is get your signal grounding right. Ground cheater plugs, ground lifting, or just plain omission of safety grounds are all potentially lethal situations.

 

[skyskraper]

word. its law down under for a reason

 

[steinba]

So... I have the STEPS, Crossfeed and PPA all built, and a Par-metal enclosure on the way.

When I screw the board mounted alps pot to the metal front panel, do I still have to ground the pot like this?

...Or should I ground the board to the case as well instead?

 

[KWS]

Take a look.
I can't feel any interference/noise from the PSU.

 

[n_maher]

Quote:

Originally Posted by steinba /img/forum/go_quote.gif So... I have the STEPS, Crossfeed and PPA all built, and a Par-metal enclosure on the way. When I screw the board mounted alps pot to the metal front panel, do I still have to ground the pot like this? ...Or should I ground the board to the case as well instead?

It sort of depends on how you intend to deal with the AC mains ground. I'd experiment and see how it goes. And holy heck, I can't believe that you're coming back to this after 4 years.

 

[MisterX]

http://www.amb.org/audio/mmm/gnd3.png

 

[steinba]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif It sort of depends on how you intend to deal with the AC mains ground. I'd experiment and see how it goes. And holy heck, I can't believe that you're coming back to this after 4 years.

I've never really stopped. I've just been moving forward really, really slow. I'm like lava!

Anyhow: The amp is tested and works great with no apparent problems whatsoever (knock on wood). I'm just waiting for the case now, as I said. Thanks everybody.

 

[steinba]

Quote:

 And holy heck, I can't believe that you're coming back to this after 4 years.

Guess what! After yet another year and a half, it's done.
 

 

[tangent]

Not too shabby, lava-boy. 

 

[steinba]

Thanks. I'm pretty satisfied. It looks a little home made, but hey... It is!
 
Now what am I going to do the next five years?