>I think only the 820 would be usable for LP filtering control voltages
>>(slow waveforms). Of course, LP filtering a flat DC signal would not
>>produce much. :)
Right, I was trying to list all the modules that can process DC.
>Ok, correct me if I'm wrong, but isn't soft sync basically a form of PLL?
Not afaik.
>Hmmm... The 110 produces both sum and diference sidebands, so when one
>>tunes both 300s perfectly at 1000Hz, there will be a resultant 2000Hz
>upper
>sideband signal and a DC output corresponding to the difference in the
>>phase of the two input waveforms.
Right, so if you filter the AC component from a phase comparator using a
four-quadrant multiplier (a linear type I ) the resulting voltage is the
difference in phase. So the cap is a filter. In contrast an edge-detector
(type II) phase comparator outputs either positive or negative pulses when
the two signals are out of phase that charge or discharge the cap. So the
cap holds the VCO control voltage. I don't think that can be done using
MOTM, or at least not yet :)
>Now if they're slightly detuned, say by 1Hz,
>then the 1Hz low band signal could be retrieved from the output by LP
>filtering with the 820. In any case, I would think the PWM settings of the
>two 300s would be critical in this application. If set to anything other
>than precisely 50%, it would add either positive or negative offset to the
>LP filtered control voltage. It could be interesting to try using the PWM
>input to control the offset.
Afaik, they would both have to be square.
>Another issue, when using square waves through a ring mod, there are ∗tons∗
>of side bands due to all of the odd harmonics present. Why not use sine
>waves?
Apparently, Craig got it to work, but I've never seen a type I phase
comparator use sine waves. Then again, I'm not an EE. However, I've spent
a bit of monkey time with a 4046 using pulses.
>It certainly produces a different sound; you don't get the overtones from
>the reset, but you do get some FM-like effects, particularly around the
>attack while the loop vco is still hunting for the right frequency, if you
>set the filter time long enough.
So you are saying that it locks eventually?? Wow!!
>Actually, I am using sine waves from the '300 as the inputs to the ring
>modulator, patching other outputs through a filter for the audio output.
>I'm not using the PWM inputs, I'm using FM. I had the note voltage patched
>to both 1v/oct inputs, with the loop vco detuned so it would have some work
>to do, then I switched the loop vco to another fm input so I could change
>how well it tracks the 1v/oct note. Different amounts of initial detuning
>produce different timbres as well, I suppose because of phase and some
>leftover FM, but the VCO's can't start too far apart or the loop won't find
>the frequency.
That makes sense, but I'm as bit surprised that it finds it locks at all!!
I would like to hear your theory of how this works. What is the phase
relationship between the two 300's when locked?? I'm guessing that when
the two VCO's are at the same frequency the ring mod output is double that
frequency (which is filtered out) and a DC offset that approaches zero as
the two signals approach 90 degrees out of phase.
>I would imagine that a ring modulator and an XOR would produce similar
>results for square waves, since an XOR is multiplying if you call the
>>states +1 and -1. Since the next module after that is a low-pass filter,
>>the extra harmonics might not make much difference.
The output of an XOR will be a frequency equal to the difference in
frequency to its inputs.
>Mostly curiosity after reading about PLLs. I'd seen various 4046-type PLLs
>in the past but then saw a block diagram for a sine vco with a balanced
>modulator and thought "hey, i have all that stuff in my motm..."