[sdiy] Polymoog resonator question

[Donald Tillman]

> On Oct 5, 2018, at 10:15 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> 
> So, I've done the Bode plot analysis of the Polymoog Resonator.  The results
> were a bit surprising to me (and I confirmed them with Multisim).
> 
> The surprise is that the LP output has a pretty high gain (about 13dB) at
> low frequencies, while the HP output has pretty low gain (about -7dB) at
> high frequencies.

No, that sounds about right.

> All of this weird behaviour is the direct consequence of that 10% loop gain
> factor.

Yes.  But it's not that weird.

These are integrators.  The only parameter an integrator has is its gain.  Tuning an integrator only changes the gain -- we refer to it as the frequency of unity gain, but nonetheless, it's gain.

In this circuit, with the 10% loop gain factor, it's the same as multiplying the gain of each integrator by sqrt(10), or 10dB.

That said, I have no idea why they did this, and I see no good reason for it.  

And it is somewhat compensated for in those resistor mixdowns before the 4016.

  -- Don
--
Donald Tillman, Palo Alto, California
http://www.till.com