[sdiy] Compensating output level for Q

[cheater00 .]

On Sat, Jun 1, 2013 at 11:40 AM, Andrew Simper <andy at cytomic.com> wrote:
> On 1 June 2013 16:18, cheater00 . <cheater00 at gmail.com> wrote:
>>
>> Hi Andy,
>> as an alternative, couldn't putting an inverter in the feedback,
>> rather than between stages, work as well?
>>
>> D.
>
> There is already an inverting op-amp in the feedback. If you put
> another inverter in the feedback path then you fix the bandpass and
> high pass resonance, but break the low pass.

Right, the signal gets inverted quite a few times actually. It seems
to me that with a fully open filter the signal comes out inverted.
The existing inverter in the feedback loop (IC40B) can't just be
switched out, switching it to non-inverting mode isn't good either (on
some modes you'd invert unfiltered signal, on some not). So you can
use an extra inverter.
In fact would it be a good idea to just switch whether the feedback
from IC40B / SP19 goes to the inverting or non-inverting input of
IC41A? It looks like the right way to do the mod to me, correct me if
I'm wrong.

Cheers,
D.