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Old 16th June 2003, 07:16 AM   #11
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Where do you think that DIY amps most often fail to perform better than they could

Lack of funds for the project

Then compromises are made to
compensate.
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Old 17th June 2003, 08:56 PM   #12
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Default Re: Noisy earths

Quote:
Originally posted by walker
I have seen a few cases where the amplifier earth was disconnected from the mains earth to cure hum problems; this is of course a dangerous habit.
And some of us live in countries where we don't even have a
chance to connect the case to the mains earth since the wall
outlets usually do not have a mains earth.
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Old 17th June 2003, 09:38 PM   #13
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Default Difficult Sourcing

If the quality of parts is to be considered important (which it no doubt is) and if even the combination of said parts is critical, it seems that short of copying directly an exact design from a manufacturer, down to the part number, there could be degradation. I personally have trouble convincing myself to buy a single 'brand Y' resistor from one place and a special capacitor from another. Many of my projects are behind as I refuse to place a $3 order to anybody, and if Digikey has one part and Mouser has the other, I wait until I have enough parts to order from each prior to placing my order. My gain clone project is on hold for a 4.7uf cap, and is likely to be for a month, especially if I use an esoteric vs. Xicon. And in the end, I am never likely to hear a Gain Card or even another gain clone to compare to.

To sum up, if the results of DIY are sometimes compromised, I'd suspect the order of cause is: ignorance (which part/layout/etc is most critical), financing (spending the right money in the right places) and sourcing. After that, I bet any dedicated hobbyist could eventually beat the quality of the physical assembly.

Thanks for the chance to discuss this subject.

Sandy.
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Old 18th June 2003, 01:33 AM   #14
jcarr is offline jcarr  United States
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Rather than thinking of where you are lacking compared to commercial manufacturers, wouldn't it be more productive to carefully consider your own specific design and manufacturing environment, and come up with audio designs that utilize the resources that you presently have to the fullest extent possible without overwhelming them?

Once you are satisfied that you are extracting the most possible from your present resources, the next step would be to conduct your own assessment of the areas in which your present resources are a limitation, and then devise ways to extend beyond those limitations. For example, if you don't have the ability to come up with unique but capable schematics, either study your butt off (always a good idea), or enlist the aid of a good schematic designer who can cover up for your inadequcies. If you can't design high-performance pcb layouts, again study, study, study. OTOH, book knowledge is no substitute for hands-on experience, nor can it replace clever insight and imagination.

Never forget that the schematic is an abstract and simplified version of the "real" schematic, which is determined by the board layout, componentry choice and overall physical construction. In other words, the schematic, board layout and physical construction should be revised flexibly so that what is on the board and the physical construction is as close to what is in the schematic as possible.

And if you can only make single-layer pcbs, start searching for a professional board house who is willing to make multi-layer boards in small quantities.

Regarding componentry, although a good range of high-quality active devices is important, I don't think that the choice of passive componentry is nearly as important as many audiophiles appear to believe. Using only standard electrolytics, motor-grade film caps, industrial SMD caps and metal-film resistors, as long as the schematic, board layout and physical construction are designed really well (which I admit is partly a personal evaluation), you should be able to make a design which beats the pants off 75% of all commercial designs. Componentry can be a bonus, but it can never be a replacement for good basic design.

Everyone - commercial manufacturer or amateur designer - has to start from somewhere. I know that the designs that we were doing some 16 years ago were very much less ambitious and capable than our present products.

I think that the main points are to have a general idea of what direction _you_ want to go in, understand where you are weak - the areas that hamper your progress in the direction that you wish to go in - and then set about resolving those weaknesses. No need to hurry or make haste - steady, consistent progress over time will do the trick nicely, IME.

hth, jonathan carr
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Old 18th June 2003, 01:46 AM   #15
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Jonathan,

Excellent suggestions and comments.

You do actually also touch one thing I have intended to ask
about on the forum sooner or later, so why not now? Could
you, or somebody else, point to some good resources
(preferrably on the web) about rules/guidelines for how to
do good PCB layouts? I could come up with a few things that
seem intuitively reasonable to me, but they may be wrong
and are by no means sufficient. I have tried to search the
web but everything I found seemed to be about how to
use various layout software, which is not what I want.
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Old 18th June 2003, 01:51 AM   #16
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Quote:
Originally posted by jcarr
And if you can only make single-layer pcbs, start searching for a professional board house who is willing to make multi-layer boards in small quantities.
Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.
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Old 18th June 2003, 01:59 AM   #17
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Quote:
Originally posted by EC8010


Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.
Speaking of layers, people very often seem to favour the use
of ground planes, which may be sensible for digital designs,
but is is generally a good idea for analogue considering the
extra parasitic capacitance we get?
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Old 18th June 2003, 02:04 AM   #18
EC8010 is offline EC8010  United Kingdom
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Hello Christer,

oh yes. Ground planes are a super idea. Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise.
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Old 18th June 2003, 03:52 AM   #19
jcarr is offline jcarr  United States
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Christer:

>Could you, or somebody else, point to some good resources (preferably on the web) about rules/guidelines for how to do good PCB layouts?<

Whatever you do, don't study the board layouts used in the vast majority of audio designs (including most commercial products), because as a general rule, they aren't very good. IMO, IC designers and IC applications engineers have a much better handle on good pcb layout practice.

Most of my library is in printed form (and a great deal of it is in Japanese ), but here are some starters on the web.

http://www-s.ti.com/sc/psheets/sloa089/sloa089.pdf

http://www.analog.com/UploadedFiles/...8865AN-202.pdf

http://www.linear.com/pdf/an47fa.pdf

http://www.old555.com/LPE/DaEtiCsuiPitdcrut.html

Burr-Brown also used to have some _very_ nice papers on system board design, (they looked like PowerPoint slide presentations), but after the merger with TI, I haven't been able to locate any URL. I may have them in some form somewhere, but I won't make any promises.

But any paper that you read is only a starting point. It is up to you to study it, digest the contents, mull over the implications, and come up with your own design approaches. Things that I now automatically consider include, total surface area and the sensitivity of the circuit as an RF antenna, trace inductances and capacitances and their effect on circuit performance and stability, common-impedance errors, noise coupling, ground and power planes, ground currents, node impedances, leakage currents and the desireability of guard rings and isolated stand-offs, and on and on.

hth, jonathan carr
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Old 18th June 2003, 03:57 AM   #20
SY is offline SY  United States
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Quote:
oh yes. Ground planes are a super idea. Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise.
What do you think the tradeoffs are between ground planes and putting some bandwidth limiting at the input to keep the RF out in the first place?
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