[sdiy] Resistor Networks....

Pete Hartman pete.hartman at gmail.com
Sun Aug 30 06:38:10 CEST 2020


#1: ignorance that such a thing even existed, I will go look at that more
seriously, thank you.

#2: the main layout issue is not simply the overall size of the networks
(they're .1" spacing, so a given resistor doesn't take an awful lot more
space than an 0805 resistor) but the forced linear arrangement, and the
occasional "extra" resistor that gets used somewhere nearby, but not
necessarily easily routable nearby.  Individual resistors could be placed
more conveniently to their actual use -- the example of a summer, perhaps
not so much, but there are others in this design that aren't quite so
localized.

I don't know if matching is the reason or not, but Eric's comment about
affordable .5% resistors etc is a further argument that matching in
particular shouldn't be a criterion of concern.

Thanks!

Pete

On Sat, Aug 29, 2020 at 11:17 PM Brian Willoughby <brianw at audiobanshee.com>
wrote:

> Why not use SMD networks?
>
> I've used the following
>
> https://www.mouser.com/ProductDetail/774-746X101103JP
>
> https://www.mouser.com/ProductDetail/774-746X101472JP
>
> … in digital designs without any issues. Granted, these have a common pin,
> but if you check the manufacturer (CTS) data sheets and product family
> you'll see every variation of parallel and network configuration available.
> I've only used them for digital because my analog circuit layout never
> seemed to facilitate a network. I'm sure that an SMD network will work just
> as well as discrete SMD resistors in an analog circuit.
>
> Sounds like you're considering mixing the original through-hole resistor
> networks with modern SMD, and I wouldn't bother with that. Just use SMD
> resistor networks.
>
> Brian Willoughby
>
> p.s. Some digital designers don't like the resistor networks because they
> find them harder to lay out. I did not have that problem. I believe it's
> the folks who actually like using 0102 SMD that find the networks "too big"
> - but I have only used 0102 in one design and was told to never do that
> again for the sake of sanity (at least during prototype stages).
>
>
> On Aug 29, 2020, at 8:32 PM, Pete Hartman <pete.hartman at gmail.com> wrote:
> > I'm working on laying out a classic through hole module design with SMD
> parts.  The original uses a fair number of resistor networks, most of them
> just parallel resistors, not common bus versions.  The resistor networks
> are, well... huge by comparison.
> >
> > Unfortunately the original designer isn't around for me to ask for input.
> >
> > My *impression* based on how the networks are being used (often times
> for things like input resistors and a feedback resistor in a summing op amp
> config, just as one example) is that part of their purpose was to get parts
> that were well matched.  But that's not anything but a gut feeling.
> >
> > So I'm looking for seasoned opinions about whether there is any
> important reason to keep resistor networks, when I can sub in 1% SMD parts
> that will take up less space and be more flexible for placement.  Are the
> networks either 1) better matched even than 1% parts, or 2) have some other
> characteristic which I'm not thinking of that might be important?
> >
> > Thanks
> >
> > Pete
>
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