[sdiy] Voltage vs current, was Low voltage synthesis?

chris chris at chrismusic.de
Tue Jan 18 11:17:19 CET 2022

Don't forget ground layout.

I have the habit of separating AGND and DGND in the schematic and have a
solder jumper in between, so I can see and control where the two are to
be connected on the actual board. In a multi-board scenario, this may
even be on the PSU board.


On Tue, 18 Jan 2022 10:29:36 +0100 "usenet at teply.info"
<usenet at teply.info> wrote:

> On 17.01.22 18:06, Ingo Debus via Synth-diy wrote:
> > Yes, probably because it’s easier to measure voltages than currents. For 
> > current measurements usually a wire or trace has to be cut. That’s often 
> > difficult or even impossible (think multilayer PCBs).
> > 
> > Thinking in terms of voltage is also reflected in the traditional way 
> > schematics are drawn (i. e. the way we all usually draw them). If three 
> > points (components) A, B and C are to be connected, it’s perfectly legal 
> > to draw either A—B—C or A—C—B, even if it is important that, say, B is 
> > in the middle (think rectifier - filter cap - load in a power supply for 
> > instance). Since both ways to draw these connections are equivalent, PCB 
> > design software cannot tell the difference (at least I don’t know of any 
> > software that does), so doing a good PCB layout is so much more than 
> > just translating the schematics. Maybe it wasn’t if there was a more 
> > appropriate way to draw schematics?
> > 
> In cases where it actually matters (mostly RF/microwave stuff as far as 
> I can see), it is pretty common to place PCB traces explicitly as 
> elements in the schematic and possibly also the layout. This tends to be 
> a bit more work as these extra elements need to have a schematic symbol 
> and a footprint in order to be recognized by the layout software, but 
> can help a lot when it matters.
> In the end it's a tradeoff. You trade flexibility for reproducibility. 
> You can either describe an PCB element as "quarter wavelength at 
> f=12.96GHz, Z=25R" or as "trace, 1.2 mm wide, 14.46 mm long". Both cases 
> have their use, and they can be transformed into the respective other 
> *IF* the PCB stackup and materials are known. But in Audio synths I 
> don't see any benefit in doing that extra effort.
> Even the mentioned arrangement of rectifier, filter cap and load hardly 
> maters at the frequencies in question for reasonable dimensions. Sure, 
> placing the load directly at the rectifier with the filter cap two 
> metres away probably doesn't serve the purpose, but at a few dozen 
> kilohertz it probably wouldn't make a huge difference.
> Florian
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