PCB design and high voltages

[GainFreak]

Hi,

I need some help designing a PCB for a tube amp. I would like to know how high voltages relate to traces width and thickness and spacing between them?
Can you point to a standard, application note or calculator for this?
Thanks.

[BackwardsBoB]

Google "high voltage" trace clearance and you can become an expert, which is a good idea if you're doing a board for a tube amp.

[R.G.]

... you can become an expert, which is a good idea if you're doing a board for a tube amp.

Amen, Brother!

Tube amp PCB layout is not for the beginner, unless they have very deep pockets indeed.

[GainFreak]

Actually I'm not a beginner - I have several tube amp layouts that work without any problems so far. I just wanted to make sure they comply with the standard.

[BackwardsBoB]

I didn't mean to blow you off. I have a similar problem. It took me a few tries on Google to get good links, but the search I recommended will point you to standards and calculators.

If you've already done a few boards, you know it's all in the details.

[Steve Conner]

http://www.ce-mag.com/ce-mag.com/arc...uctSafety.html

enjoy

FWIW, one of my favourite things about tube amps is that they don't require PCBs. I do PCB layout in my day job, in fact I just finished a 6-layer mixed-signal motherboard with 350 SMT parts and am sick of the things.

[raiken]

I do PCB layout in my day job, in fact I just finished a 6-layer mixed-signal motherboard with 350 SMT parts and am sick of the things.

I love doing PCB layouts, I find them very therapeutic after a month or more of schematic or software design. I just finished a very dense 10-layer 5/5 one with via-in-pad footprints for a 484-pin BGA and 256-pin BGA. I had to use 0402 bypass caps in between the via pads on the back side of the BGAs for decoupling. The board fab house didn't do a fill and level on the in-pad vias, so the stuffing house was complaining about the reflow, but the boards seem to work so far...

Randall Aiken

[R.G.]

Actually I'm not a beginner - I have several tube amp layouts that work without any problems so far. I just wanted to make sure they comply with the standard.

If by that you mean safety standards... good luck!

I just recently fought this battle and mostly won it. But it's an issue of far more than PCBs.

You're going to want IEC600650, that being the one which relates to musical gear among other things (like refrigerators and other appliances... )

A copy of that will set you back between $200 and $400. No, they are not given away free. The standards organizations sell them like novels.

A safety standard does NOT tell you what to do to be safe. It tells you if you don't do at least this much you are definitely not safe. While that may sound like sopistry, it's an important legal distinction. You cannot and will not get the information you need to pass safety certification (e.g. CSA, CE, CCC, etc) on an internet forum.

If you have to meet a standard (in the USA, you do not; you can be sued even if you do: in Canada, you must meet standard; in the EU, you must meet the standard but are not shielded from lawsuits by it; in... in... - it's almost like there's a different law in each country, isn't it?) then you need a quick education. I recommend reading "Practical Guide to the Low Voltage Directive" by Gregg Kervill and "Electrical Product Safety" by Tzimenakis and Holland to start with, buying a copy of the standard, and then hiring a local certification engineer to review if not actually collaborate.

And remember - it's not me, or you, or anyone on this forum you have to convince you did the right thing.

It's the judge and jury.

[Steve Conner]

Randall, sounds like fun We actually bought a single board computer module in to avoid having to deal with BGAs. I figured that we could always redesign it all on one board if it got popular.

The flipside of RG's argument is that, since standards don't protect you from litigation, there's no point in bothering about them. As long as your product doesn't kill anyone or set fire to anything with insurance, I'd bet nobody would even notice a complete absence of safety approvals

Better still, sell it as a kit, and in court you can argue that it was badly assembled.

[R.G.]

The flipside of RG's argument is that, since standards don't protect you from litigation, there's no point in bothering about them. As long as your product doesn't kill anyone or set fire to anything with insurance, I'd bet nobody would even notice a complete absence of safety approvals

In the USA, yes, that works. In the EU, since the testing labs are no longer paid by the government, the game works like this: selling equipment without a "CE" mark is forbidden by civil law, with big fines. Putting a fraudulent "CE" mark on equipment that is clearly non-compliant is a criminal offense in most EU countries. if the testing lab receives a "complaint" of non-labeled equipment, they do a formal test. If that test reveals that the equipment is non-compliant, they are authorized to charge the full price for the formal testing to the manufacturer or seller, as well as most likely being the place that gets the business for re-testing after repairs. So the testing labs have become bounty hunters. They can drum up business by just hunting down non-compliance. In the EU, you **will** get noticed if you have no CE mark on new equipment.

The water is murkier for kits. I didn't look into that. I suspect that one had better be in a position to prove that the kit, assembled to the letter of the instructions and including likely mistakes would pass CE muster. It's hard to argue that a PCB with too-small spacings would get better when assembled. In any case, if it's not CE labeled, the person who builds it may not legally sell it to someone else, and perhaps not even give it away. I'm not an EU lawyer, I just read safety standards and associated literature for several months solid. That is NOT enough. +

[GainFreak]

FWIW, one of my favorite things about tube amps is that they don't require PCBs.

Depends on the amp. If you have 3 channels + couple of effects built in + uCU for switching not using a PCB is possible but is a real nightmare.

In the USA, yes, that works. In the EU, since the testing labs are no longer paid by the government, the game works like this: selling equipment without a "CE" mark is forbidden by civil law, with big fines. Putting a fraudulent "CE" mark on equipment that is clearly non-compliant is a criminal offense in most EU countries. if the testing lab receives a "complaint" of non-labeled equipment, they do a formal test. If that test reveals that the equipment is non-compliant, they are authorized to charge the full price for the formal testing to the manufacturer or seller, as well as most likely being the place that gets the business for re-testing after repairs. So the testing labs have become bounty hunters. They can drum up business by just hunting down non-compliance. In the EU, you **will** get noticed if you have no CE mark on new equipment.

The water is murkier for kits. I didn't look into that. I suspect that one had better be in a position to prove that the kit, assembled to the letter of the instructions and including likely mistakes would pass CE muster. It's hard to argue that a PCB with too-small spacings would get better when assembled. In any case, if it's not CE labeled, the person who builds it may not legally sell it to someone else, and perhaps not even give it away. I'm not an EU lawyer, I just read safety standards and associated literature for several months solid. That is NOT enough. +

If this is the case we're all screwed.
Then what about a private person selling a DIY effect/amp on eBay?

[Steve Conner]

Well, all you really need to do is make sure that your equipment would comply with the CE mark if a lab ever tested it, and keep a low profile. You have to try really hard to make a tube amp fail an EMC test (though if you wanted to, putting a uC in it would be a good place to start!) so it's basically just safety.

There are grey areas: for instance, if I bought someone else's homebrew amp on Ebay, am I right to expect a CE mark? If I got tired of one of my homebrew amps and sold it to a friend, and it malfunctioned and burnt their house down, would their insurance company sue me for the damages because it wasn't CE marked? Could they tell from the remains whether the CE mark was fake? If I left the country, would the loss adjusters come after me? And so on.

I personally don't sell any of my homebrew equipment that plugs into a wall socket, for this and similar reasons. I come across similar dilemmas all the time at work, but since I work for a limited liability company, it's not so much of a worry.

[raiken]

You have to try really hard to make a tube amp fail an EMC test (though if you wanted to, putting a uC in it would be a good place to start!) so it's basically just safety.

Unfortunately, a uC or DSP is necessary if you want to implement MIDI switching or digital reverb/effects...!

Speaking of DSP, has anyone here ever played around with the Freescale Symphony DSP chips? I like the idea that they are using a free Eclipse-based toolset for the IDE...AD and TI charge a small fortune for their development software.

[raiken]

So the testing labs have become bounty hunters. They can drum up business by just hunting down non-compliance. In the EU, you **will** get noticed if you have no CE mark on new equipment.

And just wait until the RoHS non-compliance fines start rolling in....

[raiken]

Randall, sounds like fun We actually bought a single board computer module in to avoid having to deal with BGAs.

Unfortunately, it looks like everything is going to either BGA or those tiny QFN leadless packages like most switching regulators come in nowadays. It makes hand-assembly nearly impossible, even for prototypes.