General rules of thumb

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General rules of thumb

Post by crochambeau »

This is, of course, a big topic - probably big enough that no one person has it completely covered.

Inspired by advice on another thread, I figure it's wise to start with replacement parts and saving money: let's begin.

There are numerous value series with passive components:

E3 counts a decade like this: 10, 22, 47, 100
E6 counts like this: 10, 15, 22, 33, 47, 68, 100
E12: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, 100
E24: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91, 100

....and so on. Shift the decimal point as suits your application.

Generally speaking, the closer you can slot your needed part value to E3 the cheaper (more commonplace) it will be.
When in doubt, add resistance.

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Re: General rules of thumb

Post by Indeterminacy »

crochambeau wrote: Sun Nov 15, 2020 3:41 pm
Generally speaking, the closer you can slot your needed part value to E3 the cheaper (more commonplace) it will be.
And woe is you if you end up far out in the weeds with a precision part and explaining why the quote is $xxx.xx to a person that keeps asking "why does this part cost $eleventy.00?"

Or the department manager having to explain why a box of part#xxx xxx costs $many.00 per box and yes we quite actually do need 12 boxes since the engineering dept. specified said part.


Not specific but a very close general approximations:
Somewhere some engineer designed his/her ass into a corner and pulled it out in a clever manner and the part to do it is costly.

Then there are those times that an ultra precision component is necessary.

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Re: General rules of thumb

Post by crochambeau »

Indeterminacy wrote: Mon Nov 16, 2020 10:18 amThen there are those times that an ultra precision component is necessary.
"Why won't this thing work anywhere besides my bench?" Is a benchmark in coming of age.

Exploiting ohms law to add or shave ultimate resistance, or capacitance can come in handy. Thermal cycling; power spikes, troughs, and noise; and a healthy burn in period are encouraged.

I think for the most part, with respect to the sort of person reading *this* thread, we'll be more concerned with the "why won't the car start?" or "how can I make this flat tire round again?" caliber of inquiry, not the trimming of cents off a top octave or other "point the radar THAT way!" types of issues.

As an example, the first generation of Crustacean noise generator was designed on my bench power supply, delivering a dead on balls 9 volts to the circuit for the duration of development. That was a mistake, as I discovered well into it that deviation from 9 volts was not tolerated well AT ALL, typically resulting in a highly diminished or non-output condition (either side of 9 volts plus or minus a stupidly small tolerance).

Since I could not control the power supply these would be used on, and had not yet developed any strengths with respect to PSU development, I spec'd them for a 12 volt supply and brute force regulated with a 9.1 volt zener. Furthermore, since this is a discrete transistor build with gobs of gain and no common mode rejection of power supply noise - and many 12 volt supplies are inherently noisy, I took it upon myself to pair a unit with a supply outgoing - adding expense and time.

I have since revised those issues out of the Crustacean, which involved dialing back/balancing out gain stages, better branch decoupling on the power rail, and reconfiguring the low pass section.
When in doubt, add resistance.

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Re: General rules of thumb

Post by Indeterminacy »

crochambeau wrote: Mon Nov 16, 2020 3:07 pm Thermal cycling; power spikes, troughs, and noise; and a healthy burn in period are encouraged.
Big time flashback to the thrilling days before Eternal September and Bill Gates holding a gun to a big huge company's head.
And a premier product having a holiday tie-in with a major national electronics chain with old style saturation advertisment and said product is having 85-95% fall out in burn in during production. Back when 24 hours burn in was a standard and all those things Curtis mentioned were thrown at the machines. ( Burn in rooms were also invitingly warm on cold Nov-Feb nights.)

It was at around 8,000 units built that someone in de-bug noticed all the power supplies smelled musty.
Cargo hold of a slow boat from Asia equaled corrosion build up on the power supply connectors.

Emery cloth and 91% denatured alcohol to the rescue.

So what Curtis said.
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Re: General rules of thumb

Post by crochambeau »

Indeterminacy wrote: Wed Nov 25, 2020 11:11 amcorrosion build up on the power supply connectors.
That was the failure mode that sent my Eventide H3000 into the deep discount bin, well to my benefit. bounce
When in doubt, add resistance.

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