[sdiy] 90-degree phase displacement network calculations

[Tom Bugs]

While I'm definitely keen to hear & check the more precise & wider range 
phase network, I know that you can get amazingly rich phasing feedback 
with just a 15-15kHz network.
Probably a case of engineering vs ears - where I'd describe as 
characterful to sidestep the less deep engineering approach ;)

As I mentioned on your MW thread, feedback is really important for 
phasing at sub-audio rates.

On 24/01/2021 01:57, David G Dixon wrote:
>   
> Hello SDIYers,
>
> I'm just about to commit to a layout for a new frequency shifter, and I have
> to decide whether to build a 16-stage PDN or an 18-stage PDN for shifting
> frequencies from 0.1 to 10000 Hz.  If I build 16 stages, the maximum phase
> error is about 0.5 degrees.  If I build 18 stages, the maximum phase error
> is about 0.3 degrees.
>
> My question is this: Does that extra 0.2 degrees have any impact whatsoever
> on the performance of the shifter?
>
> Of course, these calculations assume perfect tolerance of all caps and
> resistors.  In real life, I will hand-select the caps, but the resistors
> will be subject to 1% tolerances, so the actual phase errors could be as
> high as about 0.9 degrees for 16 stages, and about 0.7 degrees for 18
> stages.
>
> I have formerly built 12-stage PDNs for 15 to 15000 Hz.  The calculated
> maximum phase error for those is about 0.2 degrees, but with 1% tolerances
> these could be as high as 0.5 or 0.6 degrees.  They have worked perfectly
> well.  Hence, I'm tempted to go with the 16-stage version.
>
> Thoughts?  Does anyone have any experience with this particular problem?
>
> Also, one other question: is 0.1 Hz low enough for general phaser duties?
> That's one cycle every 10 seconds, and it seems to me that this would be at
> or beyond the limit of being able to perceive the phasing effect.  Does
> anyone have any thoughts about that?
>
> Cheers,
> Dave Dixon
>
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