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Old 11th May 2013, 01:14 AM   #11
gootee is offline gootee  United States
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You could also order a small stack of double and single sided FR4 PCB blanks, maybe 4x6 inches each, and experiment as you read. A high-speed rotary tool (like a Dremel) can remove narrow areas/lines of copper, to make planes and traces very quickly. And the toner transfer method can get a PCB pattern from computer to copper in about an hour, or a bit less after you are experienced.

I think that you will find that a single-sided PCB is the MOST-challenging PCB design environment of all, because it makes everything so difficult to get working really well. And routing traces on them is also a pain, just by itself.

I guess that if you want to DIY your PCBs, which is a great way to go for a lot of circuits, it might be best to use THIN two-sided boards, and leave either the entire bottom or top layer for ground plane. (But I still like my idea of stacking several thin boards, to get more than two layers. I need to make some time to try designing a sample layout that way.)

Do you have an oscilloscope (and proper probes with proper high-frequency accessories, e.g. shorter ground leads, and maybe even special two-prong tips with both signal and ground just a few mm apart, for example)? Those can be extremely handy, especially if the scope goes to 100-200 MHz or more. Used oscilloscopes can be extremely cheap. Even brand new ones (e.g. Rigol, from China, starting at about $329) are not bad and are extremely economical, now.

(Personally, I'd also really love to have an HP 3577A network analyzer, which covers from 5 Hz to over 200 MHz (Yes, they go down to 5 Hz.). But unfortunately those are NOT cheap, even used and quite old. I was about to buy one, anyway, WITH the optional s-parameter test set, about a month ago, but then suddenly found a pair of like-new Magnepan MG-3.6/R speakers for under $2000 and bought those instead. )
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Old 12th May 2013, 01:07 PM   #12
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Hi Gootee,
I've been etching pcbs as I go on various projects using the toner transfer method. I've mostly completed a small cnc router, with the intent that I can whip up a layout in eagle and then output code to cut it for me. Hopefully once thats working properly I'll have a workflow that allows time efficient experimentation.

I actually really enjoy the circuit layout side of the designing process. It intrigues me like a complex puzzle that actually has no perfect solution but can be tweaked to be 'best' in a number of different ways. I'm really happy putting hours into what I hope is a good design - although explaining why I think it's an enjoyable challenge is harder I guess I'm looking for the 'rules' that guide this part of the process to the best possible result given the constraints.

In a perfect world I'd just build multiple iterations of whatever I'm trying to build and compare empirically as to the improvements, but cost and time prevents this being a viable way forward for most projects. Hence me looking to develop a theoretical background on which to base design decisions on.

In terms of testing finished builds, I've a few older oscopes around - the best of is a 50MHz unit which appears to only have one working channel. Standard probes and ARTA on a pc for testing amp distortion into dummy loads. The sort of equipment you're talking about is beyond my needs, and sadly beyond my understanding as yet

Last edited by aspringv; 12th May 2013 at 01:09 PM. Reason: spelling
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Old 12th May 2013, 02:14 PM   #13
marce is online now marce  United Kingdom
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Quote:
In a perfect world I'd just build multiple iterations of whatever I'm trying to build and compare empirically as to the improvements, but cost and time prevents this being a viable way forward for most projects. Hence me looking to develop a theoretical background on which to base design decisions on
With CAD you can try different iterations on screen, and depending on the software, the type of design can simulate the layout. Mainly for high speed, but with analogue you can use spice and as long as your layout parasitics are not excessive will get a result very similar to your spice sim.
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Old 13th May 2013, 12:56 AM   #14
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Short tracks kept as thick as possible is a good start.

I fell flat on my face with a audio mixer pcb when there was hum everywhere getting into the audio stream.
After some investigation it came from the power supply.
I had simply mixed the audio and power supply grounds willy nilly.
When I completely separated the grounds and joined them once at the edge connector all the hum disappeared.

I have applied this method to all sorts of audio even valve circuits and had some great results. There is nothing worse than listening to hum and noise between tracks.
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Old 14th May 2013, 10:07 AM   #15
peufeu is offline peufeu  France
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This is excellent reading (but complex).

Design Techniques for EMC
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Old 14th May 2013, 11:37 PM   #17
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Especially marce but others too. Please keep it simple.

I also want to design my first audio PCB but the links overload from all of you is too much for a beginner DIYer . If I have to read all those books and all those papers, understand all of it then perhaps in the end I should open a shop and start doing it professionally .

There are some confusions even over the basic concepts. I am still unable to understand the ground plan for a DAC. Two separate ground planes (digital & analog) attached only at one point under a specific pin of DAC, one ground plane with segregated portions, ........I have read arguments for both and some other techniques. For example, here Grounding of Mixes Signal Systems Henry Otto favors single segregated ground plane but then I see many experienced members using and advising two ground planes? What is the final consensus?

Can we please have a mutually agreed upon list of 25 Do's and 25 Don'ts (with diagrams, pictures) for audio PCB from experts which if any member follows will make the project at least 75% perfect?
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Old 15th May 2013, 01:14 AM   #18
qusp is offline qusp  Australia
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EMC is not simple, there is no way to make it simple...

there is no consensus for mixed signal layout, it depends a great deal on the specific design, your ability and budget. if youve already found Henry Ott (not Otto), then thats a very good start, read all you can on his site.

Last edited by qusp; 15th May 2013 at 01:16 AM.
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Old 15th May 2013, 01:33 AM   #19
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Quote:
Originally Posted by new2hifi View Post
There are some confusions even over the basic concepts. I am still unable to understand the ground plan for a DAC. Two separate ground planes (digital & analog) attached only at one point under a specific pin of DAC, one ground plane with segregated portions, .......
You'll never reach consensus on that because DAC chips themselves differ. I prefer to use cheap 8-pin DACs in my designs where there's no separate analog and digital ground connection - just to give one example.

Quote:
Can we please have a mutually agreed upon list of 25 Do's and 25 Don'ts (with diagrams, pictures) for audio PCB from experts which if any member follows will make the project at least 75% perfect?
You'll first need to say what 'perfect' means to you. Perfect sound (forever!) or the best possible measurements? Even a simple 'Do' will attract detractors - let's try one for starters : 'Do establish separate signal (quiet) and power (noisy) ground connections'
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Old 15th May 2013, 06:50 AM   #20
marce is online now marce  United Kingdom
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Single ground plane with some segregation, and creative splitting, or two ground joined at one point, or three with a power ground.
I am very busy at the moment doing PCB's day and evening, but I am in the process of putting some basic notes together. The stuff I have posted is what I post on a couple of engineering forums for people who ask about PCB design, I consider them the basics.
There are no simple do's and donts for PCB layout, each design is different start your design and I will try and help (and its for free on here)
(Audio layout is analogue layout, using a DAC means you will have some digital layout.
As to PCB experts, you have me as a regular contributor, and I am a PCB expert.
I will contribute more later...
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