I agree with Dave on this one. I'll be building the Polymoog resonator
the same as Dave has done. It does use up a few more pots, but it's
the most flexible in terms of being able to set the levels. In fact,
I'm going to be redoing the input and output structures on my 40 band
filter bank to match what Dave has done with the Polymoog resonator:
1. input mixer with level controls to set gain into circuit
2. level controls for each of the individual frequency bands
3. mixer on the output to set the levels of both dry signal and
filtered signal
On the 3U wide big knob panel proposed by Bill & Will, there simply
isn't enough room to fit all this. I'll be using Dave's 2U wide small
knob version.
For those who want to build the big knob 3U version, I'd suggest
simply hooking up the 3 input jacks together (like a multiple) rather
than using a mixer. Assuming you're driving the resonator with modules
that have 1K output resistors, the inputs will still mix together
(passively). But they won't add together they way they would with a
mixer, and you'll have a better chance of avoiding clipping.
> Just a couple of thoughts on the multiple inputs. The resonator has
> a lot of gain and it it easy to drive this into clipping - which
> isn't necessarily bad, just something I wanted to be able to control
> and monitor. Having three inputs which sum is just going to produce
> a +/- 15 volt pk-pk input which will clip so the input to the
> resonator and the dry mix signals will be clipped. The resonator
> gain controls and output attenuators can reduce the output to +/-5
> volts pk-pk but with the input clipping still present.
>
> The circuitry of the resonator uses +5 volts as the reference so you
> only have about +/-9 volts of usable signal range which is lower
> than most modules. That's why my clipping indicator is at +/- 7.5
> volts.
>
> I added the individual input controls to be able to adjust the sum
> of the input levels to a reasonable range for the resonator and to
> avoid input clipping. I also wanted to not have to adjust the
> individual resonator gain controls every time I added or removed an
> input signal.
>
> I'm not sure that three inputs with no attenuation controls will be
> that useful so this is something to ponder.
>
> I'm able to fully follow the thread on the Link Out function. The
> link connector on the PCB is for three additional inputs to the
> output mixer, presumably to link together multiple resonators.
> Since the output mixer is an inverter with level restoration, these
> need to be fed with inverted outputs referenced to + 5 volts from
> other resonators, so perhaps an inverted output referenced to +5
> volts would be useful for cascading. I have only one module and
> plenty of mixers so I wasn't too interested in adding this
> functionality. Or, maybe I'm missing it's function and usefulness.
>
> I don't understand what the Link Out jack is for, unless it is the
> output of the input mixer. In that case, I would label it Dry Out.
> If so, remember the reference for the internal signals is +5 volts,
> so Dry out has to be restored to a ground reference.
>
> Just some thoughts to consider. - Dave
>
