[sdiy] SSM2164 Phaser - another way?

[Mattias Rickardsson]

On 19 February 2014 17:16, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> Mattias Rickardsson wrote:
>
>> When connecting a 2164 according to the datasheet, to the
>> virtual-ground summing node of an OP-amp, the 2164 *output* will look
>> like a voltage-controlled resistor *from the OP-amp's point of view*.
>
> Umm, from the op-amp's point of the view the output of the 2164, being
> a current source, has an incredibly *high* internal impedance
> (theoretically it is infinite).

Well, that might be true in a sense... but the ideal OP-amp *circuit*
behaves like if there were a VC resistor.

>> But the 2164 *input* looks like the virtual ground summing node
>
> The 2164 input *is* a virtual ground node, the same as for an
> inverting op-amp's negative input.  So it will be close to GND only
> while the internal feedback loop is operating in its linear region.
> You can get a rough idea of where that limit is from the datasheet.

Could the input easily be Spice modeled in some other and better way,
or is ground potential "good enough"?

>> Speaking of the SSM2164 datasheet, did you notice the error in Figure
>> 6? It's supposed to show THD+N vs. amplitude - which would be a very
>> useful graph! - but it has a 20-20k frequency scale on the X axis, so
>> it's impossible to know what amplitudes the curves show.
>
> Yes it is a bit of a disaster.  The performance table suggests a
> couple of points of interest, and we can kind of guess that the bottom
> of the Class A curve is around the 0dBu level (0.775Vrms).

Yes, and that the 1% THD top is around the max-speced +22dB.

>> Funnily
>> enough, Coolaudio just copied it to their V2164 datasheet... :-)
>
> Copy-paste the product, copy-paste the datasheet.  At least they're consistent.

But some parts of the datasheet are left out. What did they leave out
in the chip?  :-S

/mr