[sdiy] Resistor Networks....

Pete Hartman pete.hartman at gmail.com
Sun Aug 30 07:10:57 CEST 2020


I haven't done an exhaustive search, but a randomly selected 4 resistor,
not bussed network, by bourns, is about 2x the size of an  0805 resistor.
Yikes :-D.  I was thinking "hand soldering" here, so ...  We'll see.

On Sat, Aug 29, 2020 at 11:38 PM Pete Hartman <pete.hartman at gmail.com>
wrote:

> #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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