[sdiy] SSM2164 Phaser - another way?

[Donald Tillman]

On Feb 20, 2014, at 5:29 AM, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> David G Dixon  wrote:
>> The 2164 does develop a measureable voltage on its input terminals when the
>> gain is increased (I've measured it).  It is not large, but will create some
>> error if the design absolutely depends on that voltage being exactly zero.
> 
> Which is probably most designs using a fixed resistor for the V-to-I
> conversion.  This voltage will cause distortion since the simple
> linear relationship between Vin and Iin no longer holds.

I don't understand what you're saying here.


> Looking at
> the shape of the THD_N vs Amplitude curve (irrespective of the
> horizontal axis *doh*) you can see the very definite break-point at
> the far right at which point distortion shoots up at an alarming rate.

(Perhaps the horizontal axis should have been labeled "mVrms".  That would be close to consistent with the clipping spec on page 2.)

This curve looks very much like a typical example of simple clipping.  I wouldn't call it "alarming".


> I suspect that for many synthesizer modules, where signal levels are
> higher than the nominal 775mV used in the datasheet, few designs
> attenuate the input to keep the input current within the sweetspot.

Really?  Why would a piece of musical equipment would *not* be designed for the sweet spot?

  -- Don
--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com
650 888-9632